Sheepishly, I'm going to admit that the reason I was seeing very different voltages at V607 is that I was not measuring the pins of V607 but was looking at V604! The labeling on the top of the AF deck confused me a bit and I was off by one tube location.
The voltages are still off just a bit for the real V607 but not nearly as much as I thought. I might have spotted a few things with the new measurements so have more work to do. Thanks, Barry - N4BUQ ----- Original Message ----- > From: "n4buq" <[email protected]> > To: "Jacques Fortin" <[email protected]> > Cc: "R-390 Mailing List" <[email protected]> > Sent: Friday, November 18, 2022 1:58:48 PM > Subject: Re: [R-390] R390 B+ Expected Tolerance > Hi Jaques, > > I should've said film caps, not paper. > > Vishay MKT1813422254 > and > Vishay MKT1813410255 > > Honestly, I'm tempted to put the original parts back in. They're probably > still > good and may last even longer than these replacements. > > I'm seeing some very different voltages at V607 and am going to pull the AF > deck > once again to see if I can determine why those are the way they are. I do > note > that I'm not seeing 182V on the cathodes of the regulators and, with the 1.5V > - > 2.0V drop across the load balancing resistors (which, BTW, are running right > around 50-ohms), accounts for a bit more of the "under-voltage". > > As David Wise commented, 175V is probably well within tolerance and I'm > picking > at nothing but, just the same, it bugs me... > > Yes - I have adjusted the HUM BALANCE per the manual. > > Thanks, > Barry - N4BUQ > > Subject: RE: [R-390] R390 B+ Expected Tolerance > >> Hello Barry, >> >> When you mention "new paper caps" did you really mean paper-in-oil caps ? >> I do not trust any paper cap for a long time, except the sealed ones >> (Sprague Vitamin Q, for ex.) >> All "real", not vacuum sealed PIO caps develops leakage with time. >> Better to use Mylar (polyethylene) or polypropylene ones, especially for >> C608. >> >> There are other causes that can make the output a little low in this >> circuit: >> R623 can be of an higher value than the tolerance range. >> One of the two voltage divider resistors R616 and R617 can be out of their >> tolerance range, or both. >> V607 can have a higher transconductance than the "mean" value. >> The sum of the voltage drops of V608 and V609 should be 170V: if it is >> lower, the output of the regulator will be lower as well. >> >> Just curious: what is the brand of the 5651 you have there ? >> They vary by few volts from one maker to the other and when they age also >> (they tend to go up when they age). >> >> If nothing wrong can be found in the resistor values and you are still >> unhappy with the 175V (which is not a bad result at all, IMHO), try to lower >> the value of R626. >> A 100K resistor bridged across the actual R626 should raise the output by >> few volts... >> Adjust value in consequence of the measured result. >> >> Last comment: the HUM BAL. adjustment can "move" the output voltage also. >> Be sure to adjust for minimum AC voltage at the test point J601. >> > > 73, Jacques, VE2JFE in Montreal ______________________________________________________________ R-390 mailing list Home: http://mailman.qth.net/mailman/listinfo/r-390 Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
