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]>wrote: > > ----- Original Message ----- From: "Chuck Grandgent" <[email protected]> > To: "drakelist" <[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 (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]> >> 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. > > > > > -- > Richard Knoppow > Los Angeles > WB6KBL > [email protected] > >
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