Good to hear from you Garey ! As I said to Richard, I'm going to put the schematic under my pillow tonite and meditate on it. Your clues will be a term in the equation.
Again, signal strengths seem PLENTY strong, I can hear plenty loud CW sigs, BFO just quite not breaking into oscillation, at least in the right neighborhood, and those voltages seem a mystery. Also, to eliminate my DVM as a suspect, I checked some voltages in my (happy) R4B, and they seem spot on, so I'm really pretty confident in the DVM, at least for the "high' voltages. Will keep y'all posted ! Chuck, K1OM On Mon, Dec 20, 2010 at 8:49 PM, Garey Barrell <[email protected]> wrote: > 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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