Chuck -
I'm away from home, but a couple of observations. Higher than expected
plate voltages usually mean the stage is not drawing the expected
current. I'm going from memory here, but I believe the plates of the
tubes you reference are run from the +150 unregulated bus, so the VR
tubes really don't enter into the equation. Also, the BFO in that
version is solid state, and DOES run from the VR tube supply, via a
wirewound dropping resistor. V12 is the crystal calibrator, and has no
effect other than the calibrator signal itself. Also, V9 is the Noise
Blanker and has no effect unless the blanker is ON.
73, Garey - K4OAH
St Charles, IL
Drake Service Supplement CDs for
2-B, 2-C/NT, A, B and C-Line,
TR-4 and TR-4C
Chuck Grandgent wrote:
Thanks Richard,
Ya, I've dealt with VR tubes since the early 60s. This one does glow
just fine.
And indeed, all 3 OB2's I've tried in the R4A yield the same
anomalously high voltages, within a volt or so.
Have had this meter for maybe 6 years, it's always been quite
accurate, it was in the $50 price range.
But, not high impedance, so I have seen it read LOW on some lines
where a VTVM would've been called for, but I've never seen it read
this HIGH. Like V12, pins 5 and 6 s/b 55, but are reading 128, V5 and
V9 also, but not by THAT much.
Can't understand the failure mode.
And, don't know whether those anomalous voltages have to do with the
BFO not working.
I checked the voltages back in 2008 and they were fine, and it was
working when I stuck it on the shelf when I got the R4B.
Chuck, K1OM
On Mon, Dec 20, 2010 at 5:14 PM, Richard Knoppow
<[email protected] <mailto:[email protected]>> wrote:
----- Original Message ----- From: "Chuck Grandgent"
<[email protected] <mailto:[email protected]>>
To: "drakelist" <[email protected]
<mailto:[email protected]>>
Sent: Monday, December 20, 2010 11:13 AM
Subject: Re: [Drakelist] R4A no BFO
Well, since I couldn't make out the markings on the VR tube in
both my R4A
and R4B, I just drove over to vacuumtubes.net
<http://vacuumtubes.net> (next town over) and got a
couple 0B2's, these with clear markings.
But, voltages in my R4A are still high, just as described below.
So anyway, they weren't 0A2's in there, they were the correct 0B2.
Chuck, K1OM
On Sat, Dec 18, 2010 at 6:40 PM, Chuck Grandgent
<[email protected] <mailto:[email protected]>> wrote:
I dusted off the R4A that I retired maybe 3 years ago when
i got an R4B, as
I recall it WAS working fine when I put it on the shelf,
but I could be
wrong.
Signals seem plenty strong. but no BFO though signals seem
plenty strong,
sounds like it's ALMOST oscillating.
It's the 11-tube mode, serial 6987G.
Other notes: My DVM is cheapo, so not high impedance. My
scope is on the
fritz.
I run the Drakes off an autotransformer, so 110VAC not 120VAC.
I have Garey's new R4A CD.
Took base voltage readings (see below), plate on V5 and
V12 were quite a
bit higher than they should be,
so I thought to myself, whoa, maybe an OA2 is in there
instead of an OB2.
So, I took the OB2 from my R4B, but this didn't change my
readings, but
actually, can't make out any markings on either of the tubes.
Now I'm worried both receivers had OA2 in there instead of
OB2, but I find
it doubtful that both would be wrong, and the R4B has been
working fine for
several years.
I have the voltage readings from when I worked on the AGC
back in 2008, and
they were fine then.
V5 pin 1 s/b -1, was -18
pin 5 s/b 110, was 146
pin 6 s/b 70was 95
V8 - haven't been able to check that one yet, hard to get
the probes in
there
V9 pin 1 s/b -1 was -21
pin 5 s/b 128 was 144
pin 6 s/b 110 was 120
V11 (OB2) - haven't been able to check that one yet, hard
to get the probes
in there
V12 pin 1 s/b -44 was zero
pin 5 s/b 55 was 128
pin 6 s/b 55 was 128
Besides these voltage anomalies, what else might I check,
maybe D11, D12
for the BFO Q6 2N3394 ?
Chuck, K1OM
You might want to borrow another voltmeter. Its just possible
the meter is out of calibration, if it is you are just chasing
your tail.
Most modern meters, either electronic or passive, have high
enough impedance for DC not to give false readings and, in any
case, if the impedance (or rather resistance) is too low the
voltages will read low, not high.
For the most part gas regulator tubes are pretty close to the
nominal value, within a volt or two. If you read high right at the
tube plate the meter is wrong. The voltage might be high if the
tube is not conducting but that would be very obvious because it
would not be glowing. You can double check by pulling the tube out
and measuring again. If the tube is applied correctly there should
be _no_ voltage on the regulated line when it is removed because
the tube has a built-in jumper for just that purpose (i.e., to
prevent excessively high voltage from being applied to the
regulated stages. If the tube is glowing its working.
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