John -
OK. Well, there is definitely something awry (love that word! :-) ),
on the decoupled (+245V) bus. The FIRST suspect in any electronic
equipment is the electrolytic capacitors, since they are the least
reliable component in any piece of equipment over a couple of years
old. They ain't particularly reliable even in brand new stuff, ref the
"stolen" electrolyte formula from a few years ago!
As you can see from the schematic I sent you, the only two stages on
that bus are V16 and V18. Something is also wrong with your readings of
the two voltages, since if you were REALLY dropping 117 V across that
poor little 3300 ohm, 1/2W resistor, it would be trying to dissipate
over 4W, enough to smoke it pretty quickly. So the first order of
business is to find out why that voltage "appears" to be 137V, which it
clearly cannot be! So.... On the other hand, a low voltage here could
at least potentially be a cause of your audio distortion situation.
A couple of suspects would be the coupling capacitor (C134) to the AF
Output stage, V17, and/or the cathode bypass of this stage, C135. A
check of R92, cathode resistor of V17 would also be indicated. A
problem here is also going to affect your S-Meter, since V17 is one leg
of the S-Meter bridge.
There are only three resistors that come off of that +245V bus, all high
value (220k - 330k). I would start at this point to make voltage
measurements on these three tubes to see if we can get a handle on where
that voltage is really going.
The added 100 ohm resistor in the AF pot / grid circuit is there because
someone suspected an RF oscillation in the AF section. It's called a
"squeal stopper", and while almost certainly not a problem, will do
absolutely no harm. The circuit impedance here is very high, and that
100 ohms look like a piece of wire to the "desired" signals that
"should" be at that point.
Yeah, once you get elbow deep into a troubleshooting problem, it's best
to fight through it. If you leave it for another, you lose your place
and essentially have to start over! I believe your current symptoms are
all related, and indicate a single cause, although that "cause" may be
the result of more than one faulty component.
I consider Al a good friend, although we have only met a few times in
person at Shelby. I used to go every year when I lived in Atlanta, but
haven't been in the last couple of years.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 4-B, C-Line & TR-4/C Service Supplement CDs
<www.k4oah.com>
John King wrote:
Thanks Garey. I installed R 111 as I remembered it was when I removed it and the TR 3 is receiving. The other early TR3s that I was sent sent pictures of
(of the two boards and resistor between then) were wired differently and the incorrect placement of the resistor was causing the smoke.
Voltage measurement shows the voltage on one end of R111 to be 254 bolts and on
the other end volts. Sounds LOW on the volt end. But I am not
sure.
Upon putting the TR 3 on an antenna and comparing it the the TR 4 as far as
sensitivity according to the ear, meter readings, and sound of the audio, I
find the following:
1. The TR 4 S meter, while using the same antenna and same SSB signal
tuned in, shows about 3 S units more on the S meter.
2. The receive audio on the TR3 sounds MUCH hotter and is loud with the AF
gain pot at about 7:30.
3. I notice some distortion when the AF gain pot is raised to provide more
than audio necessary for what I consider comfortable listening.
4 I note that the S meter on the TR3 doesn't appear to react in quite
the same manner as the TR4 in that it doesn't respond as to signal
level changes. (May be my imagination)
5. I also note that someone has added, what appears to be an after
market 100 ohm resistor from the center of the AF pot in series
with the wire that would normally attach to the center of the pot (rear
ganged pot).
I hope to get started on the transmitter section SOON!!
Garey, words cannot express the appreciation I feel for your assistance. You are so very
helpful and assist guys, like me, who don't really enjoy such trouble shooting
challenges. When I get a rig going, I feel pride but I can't say I enjoy the
frustrations. I probably have over 100 receivers and transmitters made by Collins, Drake,
Hallicrafters, National Hammarlund, RME, Heath Elmac, Morrow, WRL Globe, Military and
homebrew and if I don't get on a piece of gear and STAY on it until it is repaired, I
will never get it working. If I walk away from a piece of gear, and move to another, I
will have to start over when I return to it. I have a Hammarlund HX 500 transmitter with
what appears to be a parasitic problem in the low level misers that puts a
"fuzz" (not ac hum) on the signal and have been working on it off and on for
about five years but haven't found the cause. That is because I become frustrated and
walk away and because my son's spectrum
analyzer is on the blink (as if I knew enough to use it HI!! HI!!).
If you ever need an item or part that I might have, don't hesitate to check
with me. I will be glad to share with you. Al, W8UT and I are good friends and
have visited for several years at the Shelby, N.C. Hamfest and we communicate
regularly.
Again, THANKS for helping, you keep me digging in the right direction. 73, John, K5PGW
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