Tram D201 VFO mod problem

[9fb177]

Greetings! Name is Kevin. New to the forum. Long time CB collector.

I've always wanted a Tram D201. Years ago I found one at a fleamarket
and bought it. I quickly learned that purchasing a Tram is not something
you should do without a good understanding of what to look for. My radio
had serious burning, lifted traces, etc, and after I spent a lot of time
carefully fixing many of the trace failures, I found a spot where a HV
wire had burned a hole in the board until it open circuited. I decided
this was not the radio likely to be usable on the air.

This year at Dayton I found a very nice D201. Printed Circuit board
23 channel version similar to the one I already have. This time I knew
exactly where to look, and this one clearly has very few hours of use on
it. Some tubes were missing, but most tubes present were original Tram
tubes, and signs of heat damage to the boards are very light.
I'm very pleased!

I've tested the tubes, replaced the missing tubes, removed power mods,
and replaced all electrolytic capacitors. The radio is now working quite
well! My next steps are to go trough an alignment and upgrade key power
resistors, increasing space from the PCB where appropriate.

This forum has been extremely helpful! Many discussion threads here have
really helped me along the way!

Now that I've been through all this the VFO mod has me perplexed. Clearly
a VFO mod has been done on this radio. The VFO functions on TX as desired,
and switching the banks of 16Mhz crystals has the desired effect on VFO
frequency in 50khz steps. My concern is the clarifier. The clarifier
fuctions on RX/TX while on Xtal, but on Manual the clarifier functions only
on TX. To me this is the reverse of what's desirable, and likely to cause
frequency splits in use.

I found the text instructions posted by Nomad on how to correctly do the
VFO mod, and it all makes sense including using R143 to match up the TX
frequency to the 12 oclock clarifier position. This is what I want.

What's driving me crazy is how to get from my current modified condition to
the mod Nomad describes. It's difficult to follow exactly what has been
done in the existing mod. Any advice for me?

Thank you,
73,
Kevin

[2600]

There are three versions of that procedure, one for the original open-chassis built (hand-wire) radio with point-to-point wiring.

Another for the circuit-board 23-channel D201.

And another for both versions of the 40-channel D201A radio.

It does point out things to check that may have been changed in error, and where to put them back for the purpose of making my setup work as desired.

But those only contemplate the stuff I would routinely see that has to be "put back" where it was originally to make my setup function like it should.

Never have shot any pics of this setup. The quarters are a bit tight, and using the pin numbers on the Xtal-Man switch as shown on the factory schemo tends to avoid errors in following the setup.

There are enough different ways to skin a cat that the stuff someone may have taken loose in your radio might or might not be included in my procedure.

And that's where I reach my limits, predicting how many things someone might take loose that should have been left alone.


73

[9fb177]

I'm studying the circuits related to the xtal/manual switch and drawing them out.   It's challenging mapping the schematic back to the physical wiring when you know the circuit has been changed and don't know how it was wired previously.  If I had a photo of the switch prior to mods it might help.  I assume that the 2 diodes on the buss bar on the underside are two of the diodes in the routing around the switch.  I see that one of the white/red wires on the switch has been snipped which effectively removes D125, for example.  There are clues, like I can see places where the solder has been retouched.

With the help of your instructions, I'll work it out.  
Thank you for your help!
73,
Kevin

[9fb177]

I traced the wiring, and found that the mod done was very simple.    
I could only find 2 changes from the schematic.  I carefully did the mod as per your instructions Nomad, and it worked like a charm!
Thank you very much!  Very well documented.
Attachment is the xtal/manual switch in close to stock state.   One white/red wire had been removed leading to D125.
73,
Kevin

Attachments:

[2600]

Rock on!

Congratulations on getting it unraveled.

Gotta love it when a plan comes together!

73