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Post by narfedwards2 on Dec 25, 2020 11:28:01 GMT -5
In regard to the shift from receive to transmit on the 201A.I have even wired in a dedicated 6V transformer for the Osc. filaments only but can only achieve a 1 cycle difference.Does anyone out there have the solution to this anomily as the shift is just not right.I read Nomads attempts and I think I have tried the same.Only thing that makes the 201A a pain if ya use SSB on VFO side.A remote VFO I have not tried but really dont want to go there.Want it to work right.Radio was done over by Greg Barkett 2017 and is flawless otherwise.Its a tough problem but hell we have a whole year of thinkin ahead of us...be safe all
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Sandbagger
Administrator/The Boss
Posts: 6,245
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Post by Sandbagger on Dec 28, 2020 16:39:38 GMT -5
In regard to the shift from receive to transmit on the 201A.I have even wired in a dedicated 6V transformer for the Osc. filaments only but can only achieve a 1 cycle difference.Does anyone out there have the solution to this anomily as the shift is just not right.I read Nomads attempts and I think I have tried the same.Only thing that makes the 201A a pain if ya use SSB on VFO side.A remote VFO I have not tried but really dont want to go there.Want it to work right.Radio was done over by Greg Barkett 2017 and is flawless otherwise.Its a tough problem but hell we have a whole year of thinkin ahead of us...be safe all You have to understand that Tram never really designed the built-in VFO for a TX/RX operation. It was meant for receive only. The difference in voltage loading between TX and RX is responsible for the oscillator drift. The problem can be solved with enough effort and creative engineering, but it won't be anywhere near original anymore.
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Post by narfedwards2 on Dec 29, 2020 10:22:16 GMT -5
Well I'm creative and experienced in vacuum tube repair...would you offer an overview of what would be required?Any suggestions are much appreciated Tx
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Post by 2600 on Dec 30, 2020 1:52:04 GMT -5
Sure... The VFO's stability depends on voltage regulation. Strangely enough, small changes to the B+ voltage that feeds the VFO half of V302 won't cause much drift. Adding a Zener diode there doesn't help. But the voltage to the tube's heater will cause a slow drift if it changes. As a rule this is not a critical voltage that needs to be regulated. But in this case, keying the mike causes the heater voltage to all the tubes in the radio to fall just ever so slightly. V302 is not affected in a big way, but the drift is just enough to be annoying in sideband mode. The effort to regulate the heater voltage for just that one tube is apparently over the top for most anyone who has the wherewithal to try it.
Would probably fix the problem.
I'd rather devote the time to devising a replacement for the original 40-channel crystal board altogether. Tweaking the factory VFO circuit is someone else's job.
73
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Post by narfedwards2 on Dec 30, 2020 6:50:04 GMT -5
Thank You...and agreed..am looking at Ardunio DDS Vfo as viable option..also for the Mk.IV...when discrete stuff starts going sideways
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Post by trashytram on Jan 8, 2021 4:15:34 GMT -5
In all honesty I don't believe Trams were very good on Sideband. Best AM talkers around though. Uniden & Cobra radios are where it's at for SSB use. Totally my opinion here. Some things just weren't designed to be perfect.
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Post by narfedwards2 on Jan 9, 2021 19:18:05 GMT -5
Gotta say the 201A with hot 6gh8a's in the mic preamps has top of the line audio..no complaint there solid as a rock on the crystals
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