OK, more work done today! I did check and double check all the contacts on the band switch, especially those around the Xtal area. They are all good and tested good for continuity. There's a big contest going on today and I was able to hear some signals on the 28.5 band and the 28.0 band too! BUT they are very distorted, you can tell it's SSB but can't understand a thing (and yes, I tried both LSB and USB). Even the CAL signal is distorted. Not a pure tone, almost a buzz sound. All the other bands are working OK including the 29.1 band, I can hear the CAL signal fine there. Oh yeah,? I swapped another 6EA in there for V1, no change.?

Thanks for everyone's help so far, any other ideas??

73, Dave KD5FX

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Yes, I have tried switching the Xtals all around. I first put the 28.0 Xtal in the 29.1 slot and got nothing, no receive. I then put the 28.5 Xtal in 29.1 and got the same, nothing. Then I put the 29.1 Xtal (which works OK when in the 29.1 slot) in the 28.0 and 28.5 slots and got nothing. So that was strange, the problem didn't move, still no receive on 28.0 and 28.5.?

A friend suggest using my SDR to listen to the V1 oscillator freq and see what I was getting. So I made a sampler probe with a short piece of coax and a small coil of wire and only needed to get it close to V1 to get a strong signal.? I started with 7.0 band which is 21.5 MHz and the 21 band which is 35.5 MHz and got good strong signals on the SDR with both bands. On 29.1 I am getting a strong signal at 43.6 MHz but 28.5 (43.0 MHz) and 28.0 (42.5) had nothing. So I set it to 28.5 band and tweaked the L5 control I was soon able to get a signal near the proper 43.0 MHz but not exactly, it would be just below that and then as I turned it just a bit more it would skip over and be above 43.0 by a few KHz. I could never get it right on 43.0. However, when I hooked the Drake back up to an outside antenna I am now getting SSB signals across that 28.5 band! But the dial is off by about 20 KHz. So that's better than nothing on that band! 29.1 band is still working normally and 28.0 band is not working at all, I could never get it to tune up and oscillate. Perhaps that Xtal is bad.?

I temped to just quit there, it's working except for 28.0 band.?

73, Dave KD5FX

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Well, I tried that, no joy. So I tried a few other things. Using my SDR to receive the Xtal oscillator I find this:

28.0 (42.5 Xtal) oscillates at 42.603 but no proper receive, warbly sound

28.5 (43.0 Xtal) oscillates at 42.975 and receives OK but is off freq on the dial, NO XMIT

29.1 (43.6 Xtal) oscillates at 43.6 and receives and Xmit is OK

When I put the 28.0 (42.5) Xtal in the 28.5 position I get oscillation at 43.359 and distorted audio

with the 28.5 (43.0) Xtal in the 28.0 position I get oscillation at 42.507 and no good audio, distorted.

I've tried tweaking L5 and T1 but that doesn't help and I've turned them many turns both ways.

Looking at the schematic there are 3 pF caps in that circuit. I'll check them next or maybe just replace all 3 if I have spares.

73, Dave KD5FX

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Steve, for the uneducated, please describe the baking process. I assume you are rewetting the solder connections on the sides of the crystal blanks.

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Dave

OK, I'll bake the two tomorrow. I think they'll taste best with chocolate icing! LOL!

Dave

Curious Steve, does baking ever make them worse.? ie if you had a xtal that was marginally off frequency are you taking a risk of making that xtal worse than it already is?? I've got a couple that have drifted but not drastically off.? I would like to get them back on target but don't want to risk ruining them.??

EUREKA! IT WORKED! I baked the 28.0 and 28.5 Xtals for 3 hrs today at 350 then let them cool down for an hour or so. Put them in the radio and now I'm hearing signals on both bands! Xmit isn't working on 21 and above so that's another problem to figure out. It's also getting stuck in Xmit mode any time I key it up or hit tune. I bang on the back righthand corner and it comes back to receive. Where is the relay? Also, I can't get the BIAS to set any more. I checked that when I first got it and set it to 0.1 like the book says. Now, when I put all the controls according to the book to check the BIAS it shows nothing on the meter, bias control on the power supply goes all the way or down but there's no change on the meter. Maybe that's related to the relay sticking in Xmit?
73, Dave?

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Hi Steve et al

Em 22/01/2025 22:35, Steve Wedge, W1ES/4 via groups.io escreveu:

There are two relays. One controls changing over the antenna and mute functions and the other, smaller one changes enabling voltages from receive to transmit.

The schematic will show K1 and K2 relays.?

I read somewhere that there was 2 slightly different diagrams for TR-4C, I mean above and below certain serial number. I never found this "newer" diagram version (mine have serial 38636). On it one relay is a quad one K1 (antenna, T/R cathodes grounding, linear amp key) and K2 at the 9MHz oscillator (insert/short a 68pf cap to generate CW carrier).

Another note:!if this is a TR-4C of any type, and it doesn’t have a new can capacitor, plan on replacing it either with a Hayseed replacement or by discrete parts. The original can cap has a very high failure rate and usually fails shorted — taking R192 with it. It’s a good thing that that resistor is there on the relay board, as it saves the wiring from melting. If that resistor blows, replace with the same value and rating to keep the protection.?

This made me ask about this two diagrams. On the diagram I have the highest resistor value is R183, highest cap C220. The quad one at this schematic is C145. Still the original here, I'll measure-it one of this days but I'll "build" a new can with newer parts ?. But inspecting the diagram R192 seems to be there, near the power supply connector. Image not clear.

73 Marcus PY2PLL

Well, this morning it's behaving normally and I was able to set the BIAS with no problems. Strange! I'm hearing lots of stations on 28.0 and 28.5 bands this morning but nothing yet on 29.1. I can hear my signal generator up there so I know it's working, that part of the band just isn't open yet or there's nobody up there. The can cap (C145?) has been replaced with individual caps by a previous owner.

Current problem is Xmit on 21/28/28.5/29.1 bands. It will tune up but when I key up the mic I don't get an SSB output. It's a strange output, it will send a very brief output on loud voice peaks but nothing on lower volumes. This is with the Xmtr gain all the way up and a hand mic that works just fine on 80/40/20. What output I do get when tuning up is about half of what I get on the lower bands.

73, Dave

Yes, using PTT after a tune. AND I swapped the 12BY7 with a spare I had on hand. I did notice the tube doesn't have a tube shield on it. Would that cause a problem like this?
Dave