Johnson introduced the Pacemaker at the tail end of the AM era, to fill a blank in their product line. Please do not take any of my observations as totally derogatory of this finely crafted radio. It was a first generation heterodyne rig. There was a very steep learning curve with the devices available (6BE6) at the time. In fact, many of its contemporaries were far worse. Take this as a cautionary tale for any of the other similar rigs of this era.

     The Pacemaker was meant as a multimode Ranger, but was a short lived disaster. If you are looking for an AM exciter, skip this one, as there are better ways to do it, such as the DX-60. This was a single 6146 SSB rig that heterodyned to the 80 thru 10 ham bands. At that power level, it was suitable for an exciter for a linear. However, the Pacemaker had a fatal flaw: spurious mixer outputs due to the use of a VFO frequency of 3.0 to 3.5 MC for everything but 10 meters. At 21 MC, the harmonics of the VFO generated in the mixer coupled through to the output since they were in the tuning range of the driver stages. The Pacemaker was developed to replace the AM/CW only Ranger, to drive the Johnson Desk KW amplifier in the emerging SSB mode. Wholesale replacement and redesign of the mixer circuit might be a solution if you have a spectrum analyzer. It might be possible to employ a modern double balanced active mixer and get some improvement. This might be why Johnson only produced this rig from only 1956 to 1958. Running such a radio through a linear in any mode only compounded the problem.

     I have radios to operate them. I no longer have the space for a radio museum, nor the interest in radios with such glaring deficiencies. The effort to redesign such a radio is not worth the expenditure. The Heathkit Marauder had a spur on 20 Meters, but included a trap that works if you pay attention to the manual alignment instructions. Much better legacy SSB radio, for less money. SB401 was even better, but a quite a project to redo with non compactron tubes. (it is doable, if you are crazy enough!) If you want to experience a Johnson SSB rig that was a fresh design, not a rehash of an AM rig, check out the Johnson Invader. But be aware that this is a SSB only rig and a lot of work to get it working on AM. On the AM window, there is a big project to make the Invader work right. This is a legacy rig with a lot of problems. Swan pioneered filter rigs at a very affordable price using a 9 MC crystal filter, which became the industry standard even to our time, because it worked out to not have unwanted mixer products that fell within at least the legacy ham bands. They did not use a complicated crystal mixing system, but ran the VFO at rather high frequencies to mix with the 9 MC IF. The higher VFO frequency resulted in unavoidable drift using the components available at the time. Still, they got a lot of first time SSB operators on the air for a very affordable price. Collins and even Heathkit, after they hired some Collins people, reduced the spurious output problems of early SSB mixing schemes and introduced the Permeability Tuned Oscillator with exceptionally accurate dial readout and stability. If you want a good legacy SSB radio, the Collins offerings, the Heathkit SB100 and Ten Tec OMNI and Corsair are much better choices than anything else out there. For the real vintage buff, Central Electronics has some interesting phasing rigs with great sounding audio, but be prepared to get along without operating amenities that you may not be willing to give up. Plug in coils for band change anyone?

     If you wish to verify my assessment of the Pacemaker, set it to transmit on 21.0 MHz and listen to the awful birdie that comes out along with the desired signal. Rock the VFO back and forth to be sure you are listening to both of the signals. There are lots of decent fun legacy SSB radios to play with that will not get you an OO report or a QSL card from the FCC. Avoid this one.

     Here is some of the basic math to substantiate my claim (although the FCC citation should be sufficient). First, the Pacemaker instruction manual itself on page 29 warns about incorrect adjustment for the ends of the 80 meter band. When desired operation on SSB or AM at the top end of the band is set on the VFO dial, it is possible to misadjust the exciter tuning to the 3.5 MC mixer signal of the VFO and get incorrect output at 3.5 MC instead of 4.0 MC. This is in fact true of 40, 20, and 15 MC with the harmonics of 3.5 MC (i.e,: 7.0, 14.0, 21.0). It is true that the VFO has a very effective low pass filter to reduce its harmonics. Where do the harmonics come from then? The 6BE6 mixer is inherently a non-linear device. That property is what makes it work as a frequency converter. However, some of the 3.0 MC fundamental from the VFO when the dial is set to 21.0 MC generates 5th harmonic energy at 21.0 MC in addition to the desired mixer product. The mixer is not a modern balanced mixer which cancels the feed through from the input ports. Since the signal is within the correctly functioning exciter tuning, it passes through the amplifier chain to the antenna. The 15 meter birdie problem occurs when operation is desired in the CW and lowest phone portions of the band, and the circuit Q of the exciter tuning is insufficient to discriminate between the desired signal and the birdie.

     A second problem can occur on 10 meters. Lets say you set the frequency dial to approximately 28.57 MC, a commonly used SSB frequency. The VFO internally is running at about 3.57 MC to mix with the 25 MC crystal oscillator and SSB generation chain. It correctly mixes 25 plus 3.57 resulting in an output of 28.57 MC. However, the 3.57 MC clean VFO output also is corrupted in the 6BE6 mixer when its 8th harmonic, 28.56 MC is generated. This is only 10 KC away from the desired signal, so it passes through the amplifier chain and goes on to the antenna. Since the VFO signal varies as you change the transmitter frequency, there is no way to trap it out, as in the 15 meter example. This web discussion is not meant to be an exhaustive analysis of all the possible birdies. I wanted to point out two really obvious ones. If this radio is operated per the manufacturer's instructions, it should be relatively safe on 80 and 40 meters. Even on 20, you might find it acceptable. Just realize that it is an early heterodyne rig, and exercise due diligence to avoid collecting any unwanted QSL cards from the FCC or an OO.

     There is an excellent photo essay by a real craftsman who restores these Pacemakers and other fine E.F Johnson transmitters. I highly recommend you look his work over before starting your restoration. There are valuable tips, such as the tendency of one of the tube sockets to short out the B plus. His page is here.

     The real fallacy in the Valiant design choice was the lack of a competitively priced E F Johnson SSB exciter. It is a very nice filter exciter, rare and very expensive. Rather than the expensive Johnson SSB generator, many turned to the affordable Heathkit SB10, the Central Electronics 10 or 20, or they home brewed one. I do not plan to use the Valiant on SSB, so any design changes may eliminate that mode. But the Valiant survives till today as an AM legacy rig that is a clear cut above the DX100 and Apache. Considering the price difference (even in Johnson Kit form), many still spent the extra money, and got good value for their dollar.