I know most 40 channel radios are PLL, but are there any non-PLL radios (crystal synthesis) out there? If there is I want to try retro the switch into my Tram D201A. TIA.
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Non-PLL 40 channel switch
- Thread starter Gman
- Start date
40ch and PLL happened about the same time, 1977, so the odds of finding one will be slim. Nobody wanted to put that many crystals in a radio. And as rare as one would be if you found it, I doubt the channel dial would be what you need.
Unlike most 23 channel radios with 11 or 12 mixing crystals, that radio has a separate 16MHz crystal for each channel that all mix with a single 4.4MHz signal to produce 20.8MHz (which is later mixed with 6MHz to get the final frequency).
I don't think it will be as simple as swapping switches. You will need to add 17 crystals to a board that has no room for more, each with their own trimmer. Most switches choose an A crystal and a B crystal for each channel, this radio selects a single crystal for every channel. So even if there were a 40ch crystal radio out there, it was probably of the A+B design and not directly switching 40 individual crystals.
I'm sure 40-position switches exist, but to use it, you would need to re-design the entire crystal board to make room for the 17 missing crystals. And finding those crystals will be next to impossible.
From the block diagram, I would say the best approach is to add a switch that swaps the 4.4MHz crystal with a higher frequency one to shift the entire dial up in frequency. Not what you asked for, but far easier IMO. That way you are only trying to find a single crystal and not 17 unique ones.
edit: It does do a A+B thing. 23 crystals on a single board does not necessarily mean thats one for each of 23 channels. My bad. I saw the crystal board in the manual, counted 23 crystals and assumed they were for 23 channels because the block diagram make it look that way as well. So my post here is trash, please ignore..
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Appreciate the response. The Tram D201A had this setup. was hoping it wasn't the only radio like this. We all know how the channel switch fails in these radios.
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Gman,
For us non-tube folks, is the 201A a non-pll 40 channel radio? Also, is the issue you are trying to address a problem with the 40 channel switch/dial or are you looking to tinker some?
Yes, the D201A is a non-PLL radio. The channel switch is known to fail. Not IF but WHEN. It mixes 5 crystals with 10 other crystals to get the total 40. So the channel switch has a very different switching matrix then a 40 channel PLL radio. Was hoping there was maybe a few other radios like this before all newer 40 channel radios went PLL and no more crystal switching. My D201A channel switch is still ok, hasn't gone bad YET. But if we could figure out a way to do this, besides using the VFO (manual tune) side, we could help a lot of people. And I just love the vintage gear so I just can't help but tinker with the gear in hopes for a cure or make it better or more reliable. Us tube guys are dinosaurs. I can just see Nomad shaking his head thinking........Gman......again?
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Before I start, bear in mind that I've never worked on a D201A, and so may be talking out of my ass here.
From what I can see looking at a schematic of the radio, the oscillators that make up the crystal synthesis circuits appear to be bipolar transistors and FETs which means low(ish) voltage. So It should be possible to substitute a different channel selector from some other radio. However, it would have to use custom circuitry to translate between the selector and the crystal matrix. Might as well use a rotary encoder and microcontroller of some kind if you're going to have to do that much work anyways. Or just go full bore DDS.
From what I can see looking at a schematic of the radio, the oscillators that make up the crystal synthesis circuits appear to be bipolar transistors and FETs which means low(ish) voltage. So It should be possible to substitute a different channel selector from some other radio. However, it would have to use custom circuitry to translate between the selector and the crystal matrix. Might as well use a rotary encoder and microcontroller of some kind if you're going to have to do that much work anyways. Or just go full bore DDS.