Steve -
This has been 'one of those' problems! Just a quick question.... I've forgotten if you said the PTO
was stable outside the radio? IF so have you subbed the PreMixer tube? Possible load change on the
PTO due to a tube anomaly?
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com>
Steve Wedge wrote:
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 <mailto:[email protected]>
*To:* Steve Wedge <mailto:[email protected]>
*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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