I may take you up on this. First, a few observations that I made tonight:
1. Voltage at the +DC supply terminal on the small board under the PTO was 9.18
V. As the frequency jumped around, this voltage did not change. I am
accustomed to nominal voltages in older tube gear being "not exact", so being
off by 8% didn't seem to be a matter of concern.
2. Waveform on a 100 MHz scope looked good but there was a slight amount of
jitter visible at 50 nS/div.
3. Interesting observation: waveform on the premixer side of L6 had some
modulation on it that looked like the twists you'd see in loose rope. I'm
assuming this is a little bit of cross-mod from the band oscillator.
4. Signals sound less "pure" (almost chirpy) when using the R-4A to control
frequency. This occurs on all bands. Everything sounds great when using the
T-4X to control the frequency. The T-4X has none of the problems with changing
frequency when wiggling the tuning knob. The R-4A is very sensitive to all
mechanical inputs.
I'm also straining my eyes on this schematic and trying to figure out how the
INJ works. I think it's the output from the premixer, V8, which is the
difference between the PTO and the crystal band oscillator. How does the
receiver "know" which signal (transmitter or receiver) to pick? I'm assuming
there's a DC voltage on the INJ line as well as the RF signal (sorry, my eyes
were crossing following the switching in the T-4X schematic).
73,
Steve Wedge, W1ES/4
"I can't complain, but sometimes I still do."
- Joe Walsh
If the above message appears, it came from Steve's Son of Laptop!
----- Original Message -----
From: Gary Poland
To: Steve Wedge
Sent: Sunday, July 17, 2011 7:06 PM
Subject: Re: [Drakelist] R-4A PTO, Act III
Steve,
Except for a few PTO’s that had no output, I have not had the problems you
mention with any Drakes I have owned or serviced over the years. Some that
where heavily oxidized or had rusted frames I installed a piece of solder braid
like the TR-7’s have. Maybe once in a while the shield would be loose and I
would have to “ rework” the spring clips to make them grab better. Except for
cleaning and relubing the bearings and worm shaft they just don’t seem to have
problems. I have quite a few PTO parts here recovered from the Drake plant when
they gave up repair service and a few complete PTO’s that had issues also from
Drake. Anyway I would love the challenge if you want to send it this way and of
course you would get it back. It’s too bad eBay has run the prices up so high
on vintage radio gear and parts.
73, Gary
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