DX 60B as a "final" for an SB 104A?

[WB2YGF]

OK, so I inherited an SB 104A several years ago and it's just sitting in the attic.  The PA section does not work but it still does 5W of QRP which is basically the same as the driver signal to the PA.  The PA transistors are unobtanium at this point.  I also have a DX 60B that I plan to try to get on the air.  I just got the recap kit.  So I was wondering if I could use the SB104 as the VFO for the DX60 for AM and CW.  (I assume there would be issues pushing an SSB signal through without rebiasing the amplifiers for linear operation.) If I were to be able to parallel T/R relays between the SB104A and the DX60 I think it would effectively turn the SB104A into a 90W hybrid transceiver with a 6146 final. The DX60B would do the AM modulation.  Dumb idea?

I believe the DX60B expects the VFO to be 80M and 40M fundamental, and then the driver picks off the 40M harmonics for the higher bands, so what would be the effect if feeding a 20, 15 or 10M signal into the VFO input?

[Steve - WB3HUZ]

Doubled with the DX-60 bandswitch on 20, 4x on 10, etc. I  don't think you'd want to do that.

I believe the DX60B expects the VFO to be 80M and 40M fundamental, and then the driver picks off the 40M harmonics for the higher bands, so what would be the effect if feeding a 20, 15 or 10M signal into the VFO input?

[WB2YGF]

Doubled with the DX-60 bandswitch on 20, 4x on 10, etc. I  don't think you'd want to do that.

I believe the DX60B expects the VFO to be 80M and 40M fundamental, and then the driver picks off the 40M harmonics for the higher bands, so what would be the effect if feeding a 20, 15 or 10M signal into the VFO input?

Sorry, I don't understand what you mean.

[Steve - WB3HUZ]

If the DX-60 is seeing a 40 meter signal on it's VFO input, when the bandswitch is set to 20 meters, that 40 meter signal has to be doubled to obtain a 20 meter output. If you instead put  a 20 meter signal into the VFO, it will probably be doubled 10 ten meters. But since all the tuned circuits are resonant on 20, not much output will be obtained. It will only be worse when the switch is set to 15 and 10 meters.

If you keep the input to 80 and 40, it will probably work.

[WB2YGF]

I guess I assumed that if the bandswitch was set to 20M it would act like a bandpass filter and pass a 20M signal as well as the second harmonic of a 40M signal.  Clearly my understanding is deficient.

[K1ZJH]

I guess I assumed that if the bandswitch was set to 20M it would act like a bandpass filter and pass a 20M signal as well as the second harmonic of a 40M signal.  Clearly my understanding is deficient.

There are only two tuned stages in the DX-60 from what I recall, the PA tank and the grid circuit after the 6CL6 multiplier. So, if you inject a 20 Meter signal into the grid of the osc. 6CL6, you will essentially  have two 6CL6 buffer stages.  I'd be very leary of applying a five watt signal into two low-level stages, you're going to drive the heck out of them.  The best remedy(IMHO) would be to link couple directly to the PA grid tank circuit. That would involve extensive modifications to the DX-60.  You could try using a power attenuator between the five watt exciter and the input to the oscillator, that will help with the excessive drive and gross impedance mismatches as well. Maybe going back to the pre-driver in the SB-104 might be a consideration? It won't be an easy mating in my opinion.

Pete

[WB2YGF]

I was not planning on driving the VFO input with 5W.  I was assuming I would use some kind of attenuater.  I would not want to drive the PA directly. I would want to take advantage of the driver tuned circuit to attenuate any spurious emssions. 

http://members.cox.net/n4jk/images/dx60b1.jpg