Click on links below to jump to topic AUDIO SYSTEMS FOR THE K7DYY SUPER SENIOR TRANSMITTERS MY PERSONAL EXPERIENCE W/THE K7DYY SUPER SENIORS QST REVIEWS THE K7DYY SUPER SENIOR AM TRANSMITTER INTERFACING THE K7DYY SUPER SENIOR W/THE RECEIVER USING A SYMETRIX 528E OR SIMILAR AUDIO PROCESSORS ANTENNAS AND THE K7DYY SUPER SENIOR TRANSMITTER ADJUSTING AN ANTENNA TUNER WITH THE K7DYY SUPER SENIOR OTHER K7DYY SUPER SENIOR INFORMATION FREQUENTLY ASKED QUESTIONS

K7DYY WITH MAX AUDIO PROCESSOR

TOP TO BOTTOM: 1. HOMEBREW TUNER 2. K7DYY 80/40 3. K7DYY 160/80 4. K7DYY MODULATION    MONITOR 5. VU METERS 6. MAX AUDIO PROCESSOR 7. BBE EQA231 EQUALIZER
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K7DYY 80/40 AND 160/80 CONTROLS

Note: if you are looking for the K7DYY home page, here it is: www.k7dyy.com. This page has been updated, reorganized, and new material (specifically audio chain notes and Inovonics 223 setttings) as of 9/8/2020. If you are having problems with your Super Senior or need customer support, write them directly at: k7dyy.com/p/support.html.

NOTE: This is NOT an official K7DYY page; its a "fan" page. I am not an employee of index labs, nor do I receive any compensation. I just enjoy the product, and have documented my experience and solutions here to share it with others.

To connect with other K7DYY Super Senior users, try the Facebook group. It requires an invitation (to minimize spam), but you can find others who enjoy their K7DYY gear.

I know this page is about the K7DYY Super Senior Transmitter. But I am so enthusiastic about the Inovonics 223, I have to say something about it first. If you are having protection trips, especially with the 80/40 Super Senior, you need to know this first. As Bruce Franklin states: "You MUST provide a HARD LIMITER to prevent overmodulation in the negative direction." A Symettrix 528E will NOT cut it for this purpose. The 528E has a compressor stage, but it is not a hard limiter. Use it or a similar device in the audio chain if you want, but it must include a fast acting limiter right before it goes into the audio input of the K7DYY Super Senior transmitter. The Inovonics 223 includes a fast acting 3 band look ahead limiter that will take your signal from average to standout audio. I may put up a separate page, detailing its features and advantages, but for now, download the manual and see its specs at: http://www.inovonicsbroadcast.com/product/223.
NOTE: I do not receive any compensation from Index Labs or the manufacturers of the K7DYY Super Senior, BSW, the MAX processor, or Inovonics. This information is provided free, because I just like their gear. Getting set up can be complicated, and I wanted to save some users the pitfalls I experienced.

I know this page is about the K7DYY Super Senior Transmitter. So many people experience protection trips on audio peaks that I have to say something about this problem first. If you are having protection trips, especially with the 80/40 Super Senior, you need to consider this during initial installation. As Bruce Franklin states: "You MUST provide a HARD LIMITER to prevent overmodulation in the negative direction." A Symettrix 528E will NOT cut it for this purpose. The 528E has a compressor stage, but it is not a hard limiter. While the K7DYY D104 processor does some compression, it is necessary to back off the level control in the base from what you would expect, because it is not a "look ahead" processor and is limited by its attack time constant. Voicing a steady state "aaaaaahhhh" and adjusting for 100% on a scope will result in a setting which is too high, and will result in protection trips. The "first syllable" after a pause will be maximum gain (as with any conventional compressor) and have too high a level. The solution is to back the audio level down until there are no protection trips. On the scope, it looks like you are not getting 100% modulation, and that is partially true in an "average" sense. The D104 processor is a simple one chip circuit using a 2167 (which is used in other brands of processors). The limiter provided is not a true "hard limiter" it has some "slope". It does a reasonable job, if properly adjusted. For denser more effective modulation, you will need more complex circuitry than can fit in the base of a mike.

Many people get started with the K7DYY processor board that fits in the bottom of a D-104 mike. Use ONLY the Mark 2 D104 audio processor board with the 40 meter Super Senior. The first D104 processor versions did not have the proper protection for the 40 meter Super Senior; that is why there is a Mark 2 version. If you had an older 160 Super Senior with the older D104 processor board, that may be why you are getting protection trips using the same D104 processor on your new 40 meter Super Senior. The earlier D104 processor boards still work fine on the 160/80 Super Senior and your vintage equipment. Be aware with the older D104 processor, you signal will be broader. Do not crowd 7295 KHz or you will get a pink QSL card from the FCC, because there is no output filtering.
The DYY MK2 and MK3 processor boards may need modifications to perform better for some critical users. The MK2 added a defeat jumper for the noise gate. Also, as designed, it will mitigate an excessively wide signal. If you take out the high end rolloff capacitors, your signal will be 16 KHz (40 meter) or 20 KHz (160 meter) wide. If you use a smaller capacitor, adjust its value to your preference. My opinion is that eventually you will probably want to upgrade to a better audio system for your DYY transmitter. The cost of the $80 DYY board plus another $50 for a D104 mike (IF you are lucky enough to find one with a good crystal element on the first try) compared to alternatives should be weighed. The DYY mike processor board is unsuitable for any mike element other than a D104. See my page on the K7DYY D104 mike processor for more information.
https://wireless-girl.com/Projects/AMTransmitters/K7DYYaudioboard.html

There is a new more complete audio system now in production. I have replaced my Behringer and Innovonics 223 gear with the MAX audio processor. It is a KIT with conventional thru hole mounting components. The makers are developing a network of kit assemblers, if you feel you cannot assemble a board. Complete assembled boards may become available later. Make inquiry of the MAX people to find the most current status.
The MAX includes everything you need for a complete AM audio processing system. It is available in a variety of enclosures. Most importantly, it includes a "hard limiter" which will prevent modulation peaks exceeding 100% negative, something the K7DYY Super Senior needs to eliminate protection trips and achieve the dense distortion free audio you want.
The MAX Audio Processor also can be mounted in a 1 rack unit height enclosure as shown above. It has a unique compressor circuit that totally eliminates the K7DYY fan noise from the transmitted signal, while still providing robust modulation. The peak limiter can be set for either symmetrical modulation or +120% peaks for more audio punch. It will completely eliminate protection trips from overmodulation.

The MAX audio processor output low pass filters have a very steep slope, and have a wide variety of choices for transmitted bandwidth. Up to 3 filters can be switched from the front panel, and can be internally set to anything you want. I have mine set for 3, 4, and 5 KHz audio (@ -3 dB). The 3 KHz setting is perfect to operate on 7295 or 3705 KHz near the band edges with confidence you will not be out of band. The 5 KHz setting gets good reports when conditions allow a wider signal. I built one of the prototypes for N9PVF to eliminate his K7DYY protection trips, and it corrected the problems he was having. I demonstrated that prototype at the Antique Wireless Association convention in Rochester. (By contrast, the Innovonics 223 has many complex menus and internal levels to set and the only filter suitable for amateur radio is 5 KHz.) As you can see, the MAX audio processor is easy to set up, and is a perfect match for trouble free operation with the K7DYY Super Senior full legal limit transmitters.
https://www.internetwork.com/MAX/

To hear a demonstration of the functions and performance and review of the MAX audio processor from a user, WA3VJB, watch:
https://www.youtube.com/watch?v=R9zsypghPko

The Schlockwood 200 audio processor is designed by the same engineer who made the Inovonics 222 processor. It is primarily targeted at Low Power AM Broadcasters (Part 15). The output low pass filters do not have as sharp a cutoff slope as I would like to see on a high power amateur station such as the K7DYY Super Senior. You could be at risk on the band edges 7295 and 3705 as described above.
https://www.schlockwood.com/products
Specs:
https://1e179e62-3cbc-4b46-b8db-48f96b7b2950.filesusr.com/ugd/aee96f_1b2501b20cbf4755ba4584fc79314172.pdf

You could use an audio chain assembled from Behringer or similar devices and a final peak limiter such as an Inovonics 223 or an Orban Optimod. These have a multitude of setup adjustments you would have to configure. You would also need a bigger 19" rack enclosure. The cost rises quickly with these options. The Inovonics 223 only has one filter suitable for amateur use, 5 KHz audio. I used to use such a system, but have replaced it with a MAX Audio Processor. The MAX can have a selection of up to 3 filters that can be selected by the front panel switch for anything you want, and is foolproof to set up.

Finally, a completely digital approach would be to use a computer and software to do your audio processing. Sharing the computer with other station functions like logging, looking up people on QRZ, etc might not work out. Also "Windows Sounds" must be disabled to prevent "You've Got Mail" from going out over the air. If you like to monitor your audio on headphones, there could be some latency from your spoken words to the audio processing output, which can be very difficult to listen to. Consider the cost of the dedicated computer and the software licenses. Personally, I hate to have to fire up a computer to talk on the radio on AM or SSB, or use CW. It makes sense to have a computer for digital modes like FT8, or logging when contesting or working DX.

I have had this Super Senior AM transmitter for 80/160 since 2013 and the 80/40 version since 2015, and it has delivered everything I expected from it and more. The audio reports are all enthusiastic whether I am using the D104 mike processor that goes in the base of the microphone or my audio chain. I would recommend it for anyone that wants a high quality AM signal at full legal limit. The front and rear panel connections for both rigs are identical. The drive level for them is different though, so be careful when cable swapping to reset the audio level. I made a small box with a pot to insert in the input to lower the level for 40 meters from the higher audio settings of the 160 version without any retweaking of the audio chain. The 40 meter rig exhibits an upward drift in carrier power level. Mine drifted from 375 watts output carrier cold to 420 watts hot. I adjusted the cold output to 300 watts and it stayed within its limits (375 carrier out) just fine, for a safety factor. I also run the 160/80 at 300 watts; the upward drift on that one is significantly less. Be SURE you are using a peak limiter ahead of the K7DYY input connector. Be SURE the SWR is 1.00 to 1. I experience NO safety trips when running this way into a coax fed dipole.
WHICH MODEL TO BUY: If you are wondering which model to buy and only expect to use it on 75 meters, I recommend you buy the 160/80 model. The finals are more robust, and therefore the protection circuit is less aggressive, leading to fewer trips. However, the 80/40 works well for those who have small lots. You should consider the improving propagation and the opportunities it presents on 40 meters. From New York state, in just one afternoon, I enjoyed QSOs with TX, AR, and SD on 40 meter AM. I bought both models.

This positive review of the K7DYY Super Senior AM Transmitter should authoritatively answer any remaining questions about the technical performance of this equipment. Lab tests show that the K7DYY Super Senior met all FCC specifications. It also reports the results of the use of this rig in the AM Rally at W1AW. In fact, if you want to hear a K7DYY rig on the air, listen to the AM bulletin from W1AW on 7.290 MHz at 0145Z or 9:45 PM Eastern Time. There is a link in the QST review of the K7DYY Super Senior on youtube, as well as a link to ARRL multimedia for a recording of the audio of the K7DYY Super Senior. The author notes that using window line feeders to an 80 meter doublet antenna during rainy conditions, you can get SWR safety shutdowns. He did not state the transmatch used during the tests. Reducing carrier to 250 watts output avoided shut down under these conditions. Under normal conditions, the reviewer, W1ZR, found that setting the carrier to 325 watts output and limiting the modulation peaks properly caused no safety trips. He notes as I do that the carrier output drifts upward slightly during operation, and the level should be set a few minutes into a transmission for best results. After initial setting, it is stable. There are variations between 80 and 40 meter output that may require readjustment when changing bands. There is now a mod for the 80/40 that puts a knob on the front panel for carrier adjust instead of a screwdriver adjustment. The screwdriver adjust is a 10 turn pot. The knob is only one turn. I wish I had stuck with the screwdriver adjustment and 10 turns, because the one turn pot is a bit touchy. ARRL used the following audio chain for a first rate station setup:

• Shure SCM268 five channel mixer ($315)
• BBE EQA231 dual channel 31 band, 1/3 octave graphic equalizer ($145)
• Behringer Pro-XL MDX2600 Composer compressor/limiter ($130)
• Orban Optimod 9300 AM Audio Processor ($4,950)
• Radio Engineering Associates AMM-SD1 Series AMplitude Modulation Monitor ($210)

Click picture to enlarge it. I use the circuit above to make connections to the rest of the station. It provides more attenuation to the receiver antenna port when in transmit mode. My own signal is S9, and I can monitor off air with headphones without overload. It includes a fuse lamp and protective diodes also. The high voltage from a vintage receiver is switched in my external box, not the K7DYY Super Senior. This keeps all high voltage OUT of the K7DYY rig. The relay coil is protected by a spike catcher diode which supresses voltages generated when the current collapes in the relay coil. It also has an LED htat lights in transmit mode, if you want. The relay and wall wart power supply were just what I had laying around in the shop. Use what you have on hand or order something new. DO NOT USE 115 VAC RELAYS!

Another point on the rear connector: Some of these pins go directly to the embedded microprocessor. For protection, I removed all wires except ground and the two pins needed to drive the external relay or the receiver. If you have power on, static, or even some stored charge in the device you are connecting, you can blow out the microprocessor. While it may allow some clever antenna switching lashup, I don't use these pins, and don't think its worth the risk of having them exposed.

I added a switch to this circuit to select either the 160/80 or the 80/40, to avoid cable swapping to the rear connector.

DO NOT USE A SYMETRIX 528E WITH A K7DYY SUPER SENIOR, UNLESS YOU FOLLOW IT WITH A PEAK LIMITER. An example of a popular compressor that does NOT have a peak limiter, the Symetrix 528E has compression and parametric equalization, but does NOT have a "hard limiter" to prevent the audio drive from exceeding 100% downward modulation (on the scope it hits the base line at 0%). I get inquiries on this from time to time. If you have a 528E, you MUST follow it with a peak limiter, and it will be OK. The Behringer Ultra Voice Digital VX2496 is also a nice processor but it has NO peak limiter. You would be better off to get the Behringer Pro-XL MDX2600 and use an external multiband EQ. Please note the MDX2600 has a hard limiter, but it is not a look-ahead type of limiter; its a good start, and it will improve modulation and reduce trips. If you use either the 528E or the VX2496, you MUST use an external hard limiter of some kind. The Innovonics 223 provides the best performance possible, unless you want to spend for an ORBAN optimod. The Inovonics 223 also includes a "brick wall filter" that limits the high frequency response to some choices in the menu. I use 5 KHz audio, because it allows me to operate safely on 7295, and it absolutely protects the 80/40 model K7DYY transmitter from excessive high frequency transients that can provoke a safety trip. The protection circuit in the 80/40 is very aggressive, and it is what ended the early prototype failures in this model. You must carefully adjust the audio chain into a dummy load while watching the scope and gently raising the drive to the transmitter. Otherwise, you will be one of the people complaining about protection trips. If you exceed 100% modulation, the K7DYY trips on protection; its doing its job correctly.
The 528E has been around for a while. Newer gear of the same type is less available, with computers taking over a lot of these tasks for podcasts. You might consider the DBX 286S, if you want current production with a warranty (but you still need a LIMITER.) The DBX 286s also gives you more control over the compression characteristics.
In my opinion, you can achieve better results at less cost and complexity, by using a MAX audio processor for your K7DYY Super Senior transmitter.

Be sure there is no arcing at the antenna tuner or on the open wire line, if you are using that equipment. I prefer to use high quality coax feed; the losses at these frequencies are so low, there is not enough advantage to open wire to justify its quirkiness. If you are using Alpha Delta antenna switches, the lightning protector arc plug will fire if the SWR at the point of the switch exceeds 2:1. The newer switches have a label on the bottom that states that. If you have this problem, simply unscrew the brass screw that holds the arc plug and remove it; put it in a plastic bag stapled to the manual and put it in your manual drawer. Screw the brass arc plug access screw back in just flush with the surface of the Alpha Delta switch enclosure. Be sure you adjust the antenna tuner to exactly 1:1 SWR using an MFJ-212 noise bridge. Or you can homebrew a noise bridge from a Ten Tec 1051 board as described at Ten Tec 1051 noise bridge

This is a full legal limit, all solid state AM transmitter producing 1500 Watts PEP. Think about it. If your 4-400 AM rig had repeated Screen Current protection trips, you would check it out before continuing to operate it. Just because this rig does not have spectacular arcs inside the cabinet, do not ignore an improper operating environment. The protection circuits are doing their job. Investigate.

If you observe these precautions, operating this radio will be a pleasure to both you and the listener. You may not be able to get a perfect 1.00:1 match with a Johnson KW matchbox. Having only two knobs, it has only that many variables to change the equation to obtain a match. That is why I built my own transmatch, which is a Murch style design with 3 adjustments..

The rig comes with an operating instruction sheet that is one page. Probably that is all you really need once you get it set up. After all, the front panel has only a power switch, a VFO knob, and two toggle switches. There is a status panel (Frequency, HIGH SWR, Transmit indicator) and an audio input jack. The rest of the panel is covered with fans. I am elaborating a bit here to share my experience with others to shorten the learning curve if you have never encountered one of these before or you are a newcomer to AM. Or maybe you are reading this as you consider whether you want to acquire one for yourself. The manual also includes a complete parts list and other information which will be useful during installation. You can download a manual from the K7DYY website referenced at the end of this article.

Observe RF safety rules for antenna location. This is a full legal limit rig.

Provide a low SWR to the K7DYY rig. I use a tuner with a coax fed dipole antenna. The only load this rig sees direct is the Bird 1 KW dummy load. The homebrew tuner is shown in a separate article. I recommend the larger Palstar tuners if you want a commercial one. The big MFJ-9982 for open wire or the MFJ-989D for coax feed might also do it. If the antenna SWR is less than 4:1, the Dentron 2000 might do the job. The Ten Tec 238C is not a "high power" tuner and probably will not cut it on 160 and possibly 75 meters, due to the small disc ceramic capacitors failure and drift in value from heating (see my repair article on the 238B).

The K7DYY AM transmitter provides a 60 to 70 Watt low level (about 20 watts on the 40 meter model) signal for adjustment purposes. My power meter had some crazy readings due to waveforms resulting from high SWR when the tuner was way off resonance. I found a better way and it protects the K7DYY from bad load conditions. The only time I ever use this low power feature is to do a tuning check on the power meter, right before going to high power.

I use an MFJ212 noise bridge or a clone I built based on a Ten Tec kit board. (See my review and construction article on noise bridges.) These are not your average noise bridge. The old Palomar Engineers noise bridge of another decade had a constant noise output that was hard to distinguish from band noise. Both of the newer styles I mentioned pulse key the noise so that it is easily distinguished from the band noise. It makes a choo-choo train sound. Insert the MFJ212 or the clone between the receiver and the antenna T/R switch. That way no expensive high power switching is necessary to protect the noise bridge. Once I have the antenna matched, I test the match with the 60 watt low level signal from the K7DYY observing the wattmeter. If it shows a good match, I go to high power. This also greatly reduces QRM from tuning up on a QSO. NOTE: Do NOT modulate the low power signal used for tune up. He warns you about this. Not sure what happens if you do this. The production run 40 meter models incorporate a mute function to prevent modulation in tune mode. The newer 160/80 units also mute in low power mode.

If you are using open wire line to a Johnson KW matchbox, I strongly advise you obtain an MFJ212 or build a Ten Tec 1051 noise bridge kit to avoid possible damage to any of your rigs. NOTE: The smaller Johnson matchbox is not big enough to use with this rig. The KW matchbox is rated for 4 KW peaks. If you run open wire, you have become used to the drifting SWR from rain or ice on the feedline. Your 4-400 screen current protection relay may trip, but the tube will forgive you probably, if you have no zorches. This is a solid state rig (with no output tuning circuit) which depends on a nearly perfect SWR on its output. If you get any protection circuit trips, take it as a warning to correct the problem; do not subject the rig to repetitive abuse. I abandoned open wire feeders in favor of multiple coax fed resonant dipoles. In my estimation, the only good reason for using open wire line is that you can only put up one antenna, and you want to operate it on every band from 160 to 10 meters. The consequence is that the transmatch needs to be built with much wider spaced capacitors and much heavier wire in the inductors than you would use for a comparable tuner for coax feedline. I do not recommend any sort of balun on an AM transmitter of this power level, unless it is an actual coil of coax or a simple "choke" balun with beads over the coax. Check for heating, if you try one. Furthermore, a transmatch that operates well on 160 probably will not work efficiently on 15 or 10 meters, negating any possible gain you might think you have in some random direction from the malaria germ antenna pattern on those bands. You would be better off with an elevated ground plane, an AV-620 vertical, or a separate dipole system for 15 meters and up. My dipole was rubbing against a tree at one point, and the Valiant plate current constantly jumped between 300 mA to 340 mA and the reflected power meter was showing intermittent visible levels. I did not let this problem persist. I got out there with a long handled tree saw and amputated the offending limb. Before I trimmed the tree, I did not use the K7DYY rig as a precaution. While we are on the subject of antennas, do not use inferior center insulators or cheap plastic end insulators. The PVC spreaders I use in my broadband antenna are very long, are not at the end sections (where higher voltages live), and have end caps and drain holes in the bottom to deal with moisture. See my antennas page for the construction details.

The transmitter comes set for full 375 wattts carrier; theoretically the modulation takes this to 4 times that or 1500 watts on peaks. Most voices do not cause theoretically ideal lab waveforms. I reduced the power to 300 watts carrier when hot, to allow for non symmetrical voice characteristics and a slight upward carrier level drift, just to provide some headroom. Some people run them at 250 watts carrier, if they are getting modulation safety overload trips due to inadequate peak limiting in their audio chain. The K7DYY AM transmitters WILL make 1500 watts full peak legal power under normal operating conditions, and still run cold. PEAK power MUST be limited at 1500 watts or you will get a protection trip. NEVER exceed 375 watts carrier, warm or cold. NEVER overmodulate in the negative direction so that the scope shows the envelope going to zero (hits the baseline) or you will get protection trips. You MUST use a negative peak limiter in the audio chain. If you operate properly, you will not get protection trips, unless there is a flaw in the antenna system.

If you use an external audio chain limit the high frequency in the output. The K7DYY AM transmitters go 20 Hz to 10 KHz at the 3 dB points on the 160/80 rig. The 40 meter rig is -3 dB at 8 KHz. A low pass filter is advised somewhere in the audio chain. This is especially true for 40 meters, where the band edge is adjacent to the AM window. If you operate on 7295 and have an 8 KHz audio bandwidth, your upper frequency sideband edge is at 7303. The response drops off smoothly from the -3 dB point and can still stretch out quite a way. I used to use a Heathkit brickwall filter set to 3.5 KHz max audio bandwidth when near the band edge. Now I use the Inovonics 223 set to 5 KHz brickwall maximum audio frequency. Most legacy receivers are 6 to 8 KHz wide and will not benefit from much more than 4 KHz audio anyway. A software defined radio can be set to 20 KHz wide or more and the brickwall filter and Equalizer on the transmitter turned off, and music sounds great played through the K7DYY rigs. (Please do not do this into an antenna! Use a dummy load for this test!)

One more important point about the Q of antennas and tuners: You may show a perfect 1:1 match at the carrier frequency. But what is the SWR at +/- 10 KHz from the carrier?
Perform a test with just a carrier signal at the center frequency. Then change frequency to 10 KC above, and then 10 KC below the carrier frequency. If the SWR does not remain below 1.2:1, you may get protection trips due to your modulation bandwidth edges.
Some antennas or tuners may present a high SWR at the frequencies in the modulated envelope some distance from the carrier. If so, the K7DYY Super Senior will do a safety trip on modulation peaks, even when it works fine in a dummy load! Its just doing its job. This is one reason I do not recommend open wire line or Johnson Matchboxes and the like for solid state gear. This is true even for linears in SSB service. A coax fed resonant dipole and a standard Murch or L or Pi match tuner generally will not show this problem. A multiband dipole can be constructed for most bands ("FAN DIPOLE"). It works best if configured for 80/40/20. Put up separate antennas for the other bands to avoid interactions. I use a separate coax fed 160 loop.

The best method is to log all the antenna tuner settings so you start out close to the correct setting; I have had no protection trips when I follow that procedure.

Obviously when setting up a new antenna or antenna tuner, the best way is to use an antenna analyzer or another radio to determine the approximate antenna tuner settings at frequencies you use. Only then, you could use your regular SWR/Power meter and the K7DYY "tune" mode to dial it in exactly.

I use an MFJ-212 ($100) pulsed noise bridge, and in my setup I can get to 1.2:1 or better, often good enough that I can just go ahead and transmit, but I always check in "tune" mode first to make sure I did it right. I first flip up the spot switch, then the "tune" mode transmit switch with both switches ON; check if SWR is OK. Then just turn OFF the "spot" switch and you are at regular operating power. This method allows you to check into a roundtable or net without QRMing them for tuneup.

If these precautions are not followed, it is possible to get protection trips even in "tune" mode, with highly reactive loads common when using open wire line. Solid state gear requires a readjustment of operating procedures compared to classic tube transmitters. Actually, in a well designed 4-400 transmitter, you probably would have gotten a screen current trip under these conditions.

Nominal power drain is only 5 Amps at unmodulated carrier, slightly more on peaks. I have a separate 10 Amp fused filtered AC supply. I have provided an exact measurement. See FAQ below.

The K7DYY AM transmitter is easy to interface with a classic receiver. But I plan to use a solid state receiver in the future. I included a second relay to short the receiver antenna to ground during transmit for better isolation. I also provided a lamp fuse and a pair of signal diodes to protect the receiver front end as is commonly found in communication monitors of a bygone era. Probably not necessary for tube radios. But the relay system did make headphone monitoring while transmitting a snap by reducing the signal enough so that there is no distortion. I was nervous putting tube receiver plate voltages on the muting contacts of the K7DYY AM transmitter. This also is included in my external relay box. It may be over thinking the design, but better safe than sorry. It also saves wear and tear on the relay inside the K7DYY switching receiver B+. I will provide a schematic of the T/R external box later.

All connectors required for installation of the K7DYY AM transmitter are included with the transmitter as shipped from Bruce. The receiver antenna output is a BNC. The original DIN connector on the oldest 160/80 models for T/R switching and other control connections is updated with an 8 pin mike connector you can get from Radio Shack. The front panel 4 pin audio jack is also a common Radio Shack part, if you want to provide for more than one mike or an audio chain. NOTE: VERY IMPORTANT! NEVER PLUG OR UNPLUG CONNECTORS WITH THE POWER ON!!! If you do not align the connector properly and make the wrong connection it is possible to damage things. This is just common sense, but even experienced operators can get rushed.

Fan noise is minimal. I have installed the K7DYY AM transmitter high up in a rack away from the mike. One of the photos circulating on the net and on the front cover of Electric Radio shows the mike right in front of the fans. Also, I have adjusted the compression of my K7DYY D104 boards to reduce fan noise by changing one resistor value from 100 K with a 22K parallel resistor; see the article on this page. Remember, if you set a dead carrier at 375 watts, and the background noise with audio is resting at 420 watts, you are going to heat up the K7DYY. Either reduce the background noise or back off the compression level; otherwise, reduce the carrier level until the "resting" output is less than 375 watts. You should not see much audio on the scope when you are not talking, or you will be generating your own QRM pile up, with the kids or dog or washing machine in the background.

The K7DYY AM rig runs stone cold when connected to a proper low SWR load. Old buzzard transmissions of 10 minutes leave the whole case and exit air cool to the touch. He has done a great job of ensuring excellent device protection from heat. Keep SWR very low. Class D rigs do not like high SWR and you will get the rig hot if you are careless about this operating necessity.

I provided for a large red transmit LED and an old buzzardly VU meter with a level control (to compensate for the difference in input audio levels for the 160 and 40 meter rigs) on a separate panel. This kept all the wiring tidy between the audio chain and provided an obvious ON THE AIR indicator. I will provide a schematic for the hookup if you want to do this. I also need to provide a switch to change between the 160 and 40 meter versions of the K7DYY so that I can share the audio chain and receiver. I run the audio EQ in cascade for extra attenuation above 4 KHz, if needed.

Bruce, K7DYY answers questions about the "Super Senior" AM transmitters: http://www.k7dyy.com/p/f-q.html

Here are some other questions I have been asked about the K7DYY rigs:

I GET A LOT OF PROTECTION TRIPS ON VOICE PEAKS. I AM USING A SYMETRIX 528E IN THE AUDIO CHAIN.

DO NOT USE A SYMETRIX 528E UNLESS YOU FOLLOW IT WITH A PEAK LIMITER. An example of a popular old school compressor that does NOT have a peak limiter, the Symetrix 528E has compression and parametric equalization, but does NOT have a "hard limiter" to prevent the audio drive from exceeding 100% downward modulation (on the scope it hits the base line at 0%). I get inquiries on this from time to time. If you have a 528E, you MUST follow it with a peak limiter, and it will be OK. The Behringer Ultra Voice Digital VX2496 is also a nice processor but it has NO peak limiter. You would be better off to get the Behringer Pro-XL MDX2600 and use an external multiband EQ. If you use either the 528E or the VX2496, you MUST use an external limiter, such as the Innovonics 223. These processors were for use in the studio or announcer booth; the limiter circuit was included in the feed to the transmitter for all inputs. If you neglect this essential component, you will be one of the people complaining about protection trips. If you exceed 100% modulation, the K7DYY trips on protection; its doing its job correctly. Fix the problem before you break something expensive.
The 528E has been around for a while. Newer gear of the same type is less available, with computers taking over a lot of these tasks for podcasts. You might consider the DBX 286S, if you want current production with a warranty (but you still need a LIMITER.)

I GET RANDOM NUISANCE SWR PROTECTION TRIPS ON VOICE PEAKS ON MY K7DYY TRANSMITTER. I AM USING ALPHA DELTA ANTENNA SWITCHES WITH AN ARC PLUG LIGHTNING PROTECTOR.

If you are using Alpha Delta Switches with an Arc Protector, and have some SWR on your antenna, remove the Arc Plug. This is not to say the Alpha Delta Switches are not good switches. The Arc Protector is doing its job correctly. When high SWR causes voltage spikes on modulation peaks, the protector fires. Then the K7DYY AM transmitter SWR protection trips. That also is doing its job correctly. Nothing defective in either, they are working as designed. Simply unscrew the brass plug, hold the antenna switch so that the Arc Protector falls out into your hand. Then put the arc protector in a plastic bag stapled to the manual for your Alpha Delta Switch. Put the manual in your filing cabinet for future use. The Arc Protectors will be there for future use, or if you choose to sell the Alpha Delta Switch. For lightning protection, disconnect all antennas when not in use, or whenever you hear thunder or anticipate a storm. This is much better lightning protection than optimism and an Arc Protector. When screwing the brass plug back into the Alpha Delta Switch, just screw it in far enough that the top is flush with the top of the switch case. All of my coax fed antennas have bulkhead style coax adapters attached to ground rods far away from the house, before they attach to the feedline which goes into the radio shack. I can disconnect them there, and roll up the house side of the feedline to keep all the arcs and sparks far away from the house.

If you are getting protection trips from arcing in your antenna tuner or SWR variations from wet open wire line, STOP! Repeated arcing can damage the Super Senior. Diagnose the cause of the protection trips. Just because the failure modes of solid state rigs are not as spectacular as those of a 4-400 with a few kilovolts on the plate, it is not reason to ignore protection trips. Diagnose your problem before you break something.

DO I NEED AN ISOLATION TRANSFORMER?

Absolutely not. This urban legend relates to much older K7DYY Senior and K7DYY Junior models. In certain cases, people encountered problems with connecting PTT and other lines directly to earth ground. This is NOT a problem with the Super Senior. Any modern equipment which employs switch mode power supplies can provide good isolation from the AC line without an isolation transformer. All modern consumer gear uses switchmode power supply techniques which fully comply with UL and VDE safety guidelines. Moreover, you would need a rather large transformer, probably 10 Amp or more to do this, and the expense is not justified. You do not need one for your modern transformerless TV or stereo equipment; you do not need one here either. This comment is also the case with the mike input line; a high quality 600 ohm line transformer can be used, but I directly connect the output of my Behringer equipment or Inovonics 223 to the audio input. NOTE: do not plug or unplug anything, particularly the rear accessory connector, with the AC power on; you may accidentally short pins to the wrong connection as you are mating the connectors. This is just careful operating practice.

I HEARD THERE WERE CAPACITOR FAILURES IN THE OUTPUT RF FILTER; IS THIS A PROBLEM?

No. Again, this applies to the prototype and earliest production runs of the K7DYY 160/80 Super Senior quite a few years back. A heavy duty part was done as a design upgrade to all recent units. This was never a problem with the later 80/40 production run model. Use very low SWR and make sure there are no intermittent connections in your antenna system or transmatch. No solid state equipment enjoys high SWR. There was a brief run of output FETs that had some QC problems from the original manufacturer, but this was not a fault in the K7DYY design. All of this was taken care of under warranty.

I HEARD THERE WERE PROBLEMS WITH THE 80/40 MODEL; IS THIS STILL A PROBLEM?

The prototype and Beta test units did have a problem that was partially caused by feeding too much high frequency audio energy into the mike jack. The internal peak limiter was not fast enough to deal with the problem and had to be improved. I experienced this as an early adopter of this technology, but Bruce corrected the problem. The K7DYY D104 mike processor has been reissued as a Mark 2 model, with a phase rotator, improved noise gate (which could be turned OFF), and most importantly, high frequency roll off necessary to address that problem. The current production K7DYY Super Senior 80/40 model design has also been changed to eliminate that problem when using an external audio chain. See my separate article for data and frequency response curves of the K7DYY D104 mike processor.

Use very low SWR and make sure there are no intermittent connections in your antenna system, switching, or transmatch. I replaced all my cheaper antenna switches with Alpha Delta switches. I did remove the "arc plug" by unscrewing the brass plug and saving the device inside (just in case I wanted it later). If the antenna has significant SWR (for connections after the transmatch), the arc plug will fire on voice peaks with a full legal limit AM or SSB transmitter. This is not a flaw in the Alpha Delta switch or the radio equipment; it is just doing its job protecting against voltage peaks. SWR will increase the voltage above normally expected levels, firing the "arc plug" even on a legal power level. No solid state equipment enjoys high SWR. It may cause trips of the K7DYY protection circuitry if the arc plug fires. Do not allow this to be a common occurance. Fix the problem with the antenna or switching circuitry.

Avoid pushing too much "presence rise" above 4 KHz into the K7DYY Super Senior audio input, particularly the 40 meter model. It defeats the protection circuitry that limits the peaks inside the transmitter. See the photo of my EQ settings; it has a peak at 4 KHz, but the 8 KHz is set to full attenuate (20 dB). This protects the transmitter and avoids an excessively wide signal. The Inovonics 223 should be set for a brickwall filter of 5 KHz when connected to the 80/40 K7DYY transmitter. DO NOT use the wider than 5 KHz audio settings offered in the Inovonics 223 menu. When operating on 40 meters at the top of the band, excessive high frequency energy will cause splatter outside the band and invite an FCC QSL card. Most vintage receivers will not hear anything above 5 KHz audio anyway; the commercial AM band uses 10 KHz spacing, which implies a similar upper frequency response. Early production K7DYY D104 processors had no upper frequency limit. They can be very broad, especially with a replacement electret condenser element. New Mark 2 versions limit the highs to prevent damage to the 40 meter model and avoid splatter. You can watch this on the scope when saying "SSSSS". Early Mark 2 processor boards had a sluggish response on the noise gate; a capacitor change eliminated that, and response is flawless when the mike is keyed. I have provided data on the separate page I have for the mike processor, along with my adjustment of the 100K compression resistor with a 22K parallel resistor, to reduce fan noise, while still providing adequate compression.

See my article on splatter: HIGHLEVELsplatter.html

See W8JI article on splatter and its causes (equally applicable to wide band SSB and AM): http://www.w8ji.com/transmitter_splatter.htm

WHAT ABOUT UPWARD MODULATION? CAN I RUN 120% PEAKS?

If you reduce the carrier, you can run higher upward peaks. Usually vintage receivers will tolerate some upward overmodulation, but if you get above 120%, receiver generated distortion increases. Wasn't the whole point to have good clean low distortion audio? Of course, with a Software Defined Radio or a Synchronous Detector, it will work fine. I do not favor that much technology. If you are in a net with mixed vintage and modern AM checkins, the Synchronous Detector goes nuts when someone with a drifty DX-100 transmits off frequency a bit. The K7DYY limit is 1500 watts PEAK. You get that when set to 375 Watts carrier and symettrical modulation, which is about what I use (300 W carrier). I set my carrier to 300 watts (at operating temperature). I run up to +120% peaks, which is 1500 watts PEP, now that I have the Inovonics 223. It gets good reports, and it has more punch without sacrifice of audio quality due to clipping. I favor the KISS principal. Some people report they get as good or better compliments on their audio using a D104 with the K7DYY processor in the base compared to a whole rack full of technology. The new K7DYY D104 Mark 2 processor even has a phase rotator in it.

It is important to realize that the whole concept of 120% upward modulation is a practice deriving from TUBE AM broadcast transmitters. The positive overmodulation allowed you to overcome the power limitations of your plate modulated RF final by stacking on some extra power from your modulator upward peaks. In those days, it worked to provide a marginal added level of punch. The K7DYY is a modern solid state AM transmitter; its PEAK specification limits it to 1500 Watts PEAK, regardless of audio modulation percentage. I suggest that you use a symettrical modulation waveform, and skip the complexities, unless you install an Inovonics 223. The K7DYY D-104 audio processor provides a symettrical output, and employs a distortionless phase rotator to reduce the non-symettry in the audio waveform ahead of the compressor. Just use a good monitor scope to set up the D-104 processor and forget it.

MY K7DYY HAS NOT BEEN USED FOR A WHILE. NOW WHEN I TURNED IT ON, THERE IS NO RF OUTPUT

The contacts in the T/R relay have built up some oxide. No damage results from this, the protective circuitry takes care of that. While the transmitter is powered on but in standby mode (both switches DOWN), tune the VFO to the band edge. Cross the band edge, causing the output band filter relays to cycle several times, thereby cleaning the oxide off the contacts. The K7DYY Super Senior switches automatically between the two bands when the VFO display shows the lower or upper band, for instance, 80 or 40 meters. Tune back to your favorite frequency and you will see full output when you go to transmit. I have had this occur in my Yaesu FT-950 antenna tuner relays. Just cycle them a few times, and all will be OK again.

HOW MUCH CURRENT DOES THE K7DYY SUPER SENIOR DRAW?

Well that is not a frequently asked question any more. People are used to a full legal limit AM station requiring 240 VAC at 30 or 40 amps, maybe 3 phase. Not this one. Being the anal retentive detail freak, I did a test, just to get the data. I used the popular modern digital "kill a watt" device. It measures line voltage, current draw, wattage, power factor (related to phase of voltage and current), and other things, all in one convenient box. No, you do not need to get your slide rule out and chase a phase vector down a rathole. This data is for a Super Senior 160/80 running on 120 VAC (exactly) at 300 Watts carrier and 100% modulation at 3870 KHz. Standby (receive): 0.23 A. Carrier, no modulation: 5 A. Full modulation: 6 to 6.5 A. You probably do not care much other than you can run this rig from a standard 15 amp outlet, along with a receiver all your accessories. But I like hard data, so there ya go.

The 80/40 version is a fresh design and production models have been shipping for some time. Some hams may not have the real estate for a 160 antenna or may live in the south or west where 160 is too noisy to be of real use. I hope Bruce is able to reach that market with this new 80/40 meter addition to his lineup.

OK so here is the question: is this a good value for the money? Compare the cost of a fully refurbished Johnson Desk KW or Johnson 500. There is one ham who advertises in Electric Radio that does a beautiful job restoring them to like mint in box condition. Compare the cost of a KW-1, if you are lucky enough to find one. Compare the cost of even a WRL Globe King rig. This is a brand new, basically plug and play that delivers better audio than any of those options. I simply had to reduce the amount of parts and racks in my house to make room for some lifestyle changes. I moved three large truck loads of glass tubes, modulation transformers, condensers, power transformers and chokes to a new owner and made some reasonably good swaps including a nearly new treadmill for exercise. I think it was a good move.

AM is a special mode that many of us first fell in love with as shortwave listeners when we were kids half a century ago. Maybe you came into the hobby from CB and were frustrated with the stuff that went on at 27 MHz, but became accustomed to the sound of AM and studied for your ham license. Or possibly you stumbled across an AM QSO and someone helped you adjust your ricebox. You met new friends that you actually had a QSO with, not just swapped signal reports. I still love my Johnson AM equipment and working on it; but to own a legal limit AM rig for this price, I think it all turned out great.

There is another consideration to deal with: Is this still real AM? Many AMrs have adopted highly modified Yaesu FT101s, flex radios or homebrew Class E or other solid state rigs. For our SSB and CW, there are Japanese alternatives to hollow state. The availability of large glass tubes is getting problematic; recently RF parts has been shipping 572Bs from a Chinese manufacturer that actually work, according to rumor. Don and I discussed this in context of fitting two packrats in the same 900 square foot house and the K7DYY AM transmitter was the only real solution that did not result in unacceptable limitations on HF operating style. We made the same decision when we obtained an ALS-1300 solid state linear.

If you are concerned about the cost of a set of finals, consider this. You will need some FETs and 2 gate drivers to replace everything in the final compartment PC board. Both parts are stocked by mouser.com. The FET is Mouser P/N 512-FQPF11N40C and the gate driver is P/N 849-IXDD614CI. Mouser has no minimum order and they charge about $8.00 for Priority Mail shipping. Compare this to the cost of a single 4-400 from a reputable manufacturer. Large glass tubes will be harder to find. The availability of smaller ceramic external anode tubes suitable for amateur power levels will shrink as production focuses on the larger broadcast sizes that are still in demand. This is what the future looks like. Modern AM broadcasters have already made the switch to solid state; get with the program.

It helps if you think of the output FETs as vacuum tubes without an internal pilot light to tell you they are working. For the truly classic (old buzzardly) AM crowd, I offer this: This is an AMERICAN MADE product. It is being sold by the actual engineer entrepreneur who created it. When is the last time you were able to support such a concept? Frankly, whenever I can, I use American made gear. The Ameritron amplifier for my SSB station is an example. I have a Ten Tec original brown front Corsair and OMNI with a Heathkit SB200. My station includes classic Johnson and Hammarlund and other Heathkit equipment, as well as American made test equipment whenever possible, even some classic Techtronix and Hewlett Packard gear.

For other information on purchasing or setting up the K7DYY AM rig, see the following links:

• Bruce K7DYY's homepage: www.k7dyy.com
• Dan W1DAN's review of the transmitter: http://amfone.net/Amforum/index.php?topic=33537.0
• I also recommend the yahoo group for Index Labs. Craig is a great moderator for this list, and you will find lots of info for getting the most out of your K7DYY Super Senior. Here is a posting I made to a problem some one was having.
• NOTE: I am not employed by, nor do I receive any compensation from, either Index Labs, the manufacturer of the K7DYY transmitters, or Inovonics or BSW. I just know good American made products when I see them, and recommend them for others.

On 2018-04-09 17:19, 'Bob Donahue' [IndexLabsAMXmtrs] wrote:

Operating on 3.880 the other day, there was a whiff of smoke and my power meter dropped from 300W carrier to 150W. At the same time the REA modulation meter on my computer jumped up quite a bit. I turned down my modulation and continued my QSO. My contact reported good sounding audio. I'm still getting full power on 160M.

A cursory inpection inside did not reveal any burnt looking parts.

Any ideas on what to check?

Bob Donahue ND9B

Subject: Re: [IndexLabsAMXmtrs] 80M suddenly at half power on Super Senior

From IndexLabsAMXmtrs@yahoogroups.com Message Body

Dear Bob Donahue ND9B,

Depending on the production run of the transmitter or its user history, you probably have a bad capacitor in the 80 meter output filter.

The PA is OK and the 160 meter output network is OK. The problem is in the 80 meter output filter. You will also notice that the exit air is hotter than normal in the back, and maybe a hot smell on long transmissions. This is a testament to the ruggedness of the K7DYY AM rigs. Fix the real problem before it causes more serious problems.

EARLY 160/80 transmitters have been beefed up with huskier capacitors. Contact Bruce Franklin for further info on the better rated capacitors. This is NOT a big deal failure. If you are comfortable working on PC boards, you can fix this, or send it back for repair. You already took the case off to look.

Be sure to maintain a very low SWR. Use of Ladder Line in wet weather, loose connections in the antenna, mistakes in setting of antenna switches, anything that can cause spikes in SWR can also contribute to this problem. I use a MFJ-212 to adjust the antenna tuner, off air. NO tune up QRM. That way, the transmitter never sees anything but a perfect SWR. You can place the MFJ-212 between the receiver and T/R switch so that it does not have to switch max legal limit energy. /Projects/Antennas/MFJ212.html

Many people use an antenna switch AFTER the tuner. If you are using an Alpha Delta switch or any other that includes a spark gap, REMOVE THE SPARK GAP. The link below shows how to do that properly. At more than 2:1 SWR with legal limit, the spark gap fires; they tell you that on the sticker on the back of the switch. 160 and 80 meter dipole antennas typically have much more than 2:1 at the band edges. href=/Projects/Antennas/ADswitchRepair.html

Be sure you have no arcing of the capacitors in the antenna tuner on peaks. Be sure there are no burnt turns on the roller inductor, which can also cause SWR spikes. A wimpy antenna tuner will eventually make you wish you had obtained the right tool for the job, such as: https://www.palstar.com/en/at5k-hp

I built my own from surplus parts: /Projects/Transmatches/HomebrewKW.html

Be sure to use a good modulation monitor like a scope to set modulation levels. The REA or the telepost monitors are even better, and well worth the expense. You have already provided that.

Be sure to use a modulation limiter in the audio chain. Lots of people like the Symmetrix 528E, but it does not have a hard limiter. This means lowering the average modulation to prevent any modulation peaks from hitting the base line on the scope. The last device in the audio chain before it goes into ANY AM transmitter must be a hard peak limiter. Otherwise, loss of audio punch will result if you lower the audio drive to the K7DYY AM transmitter. If you do not lower the drive to prevent overmodulation, you WILL get protection trips and have to reset frequently. If your transmitter has protection trips, investigate the cause, or you could cause damage. The protection works very well, but do not abuse it.

NOTE: I have ZERO protection trips - ever - by observing these simple precautions. Be aware that the 80/40 K7DYY protection is more aggressive than the 160/80, so you may have to dial the audio back a little more on that one. But do not ignore protection trips. If you had a rig with a 4-400, and the screen current relay kept tripping, you would fix the cause, right? Most of the big boat anchor rigs had spark gaps on the modulation transformer terminals. Nobody ignores the zapping; mod iron is unobtainum today. You will still have plenty of great sounding audio without setting all the dials to "11".

I use an Inovonics 223 multiband processor-limiter between the audio chain and the input jack of the K7DYY. It has been the single best upgrade to increase modulation density and overall audio quality I have installed. It is a poor man's Orban Optimod. The limiter is a "look ahead" system that anticipates modulation peaks and adjusts system gain BEFORE the overmodulation occurs. Analog compressors like the 528E or even the K7DYY D104 mike compressor cannot anticipate the incoming peak, and may let some through, because analog systems cannot act fast enough. A standard clipper can be used to catch the overmodulation peaks, but will cause noticeable distortion if you work it too hard. The Inovonics 223 works around all these problems. Best prices at: https://www.bswusa.com/Broadcast-On-Air-Processing-Inovonics-223-P11684.aspx

I set my carrier level to 250 W cold. It drifts on warm up to 275 W. The Inovonics can be set to +120% positive peaks, which is about 1500 W positive peaks. This results in dense audio that cuts through QRM without distorting in older receivers, which cannot tolerate modulation above 120%. It gives a slight edge over a bigger carrier with less audio. The Inovonics 223 also has a broadcast grade brickwall 5 KHz filter that keeps you in band when operating near the 40 meter upper band edge. You can set the filter to other band widths in the menu. Your K7DYY transmitter is capable of 8 - 10 KHz audio response without a band width limiter in the chain, resulting in a 20 KHz wide AM signal. I recommend you set the pre-emphasis (high boost) to OFF to avoid splatter or a wide signal. It is preferable to take care of contouring of frequency response in the EQ section. The pre-emphasis feature is to get better sounding audio in a crappy receiver for commercial broadcasting.

The 223 is so effective, you could possibly get by with a mike, a preamp, and go right into the 223 as a beginning professional broadcast audio set up. Since the 223 is a 3 band processor, some adjustment of frequency response is available. A one piece device like the 528E or a similar Behringer would put all those items in one box, and they add an adjustable analog compressor and a parametric EQ. BTW, BSW has great mikes cheap too!

For more info on the K7DYY Super Senior 160/80 or 80/40, see: /Projects/AMTransmitters/K7DYYtransmitter.html

You only have a minor repair. Fix the problem that caused the failure to prevent it from recurring. Hope this helps.