B+ voltage

tfrost33 · Post by **tfrost33** » Mon Sep 17, 2007 10:11 pm

OK... hmmmm

So I followed the trouble shooting instructions to the letter. I can find absolutely no problems with either the Output Transformer nor the Power Transformer. All the tests come out fine. Neither of the transformers gets hot or hums or smokes. Maybe the smell is just my imagination since Bob came over and couldn't smell anything.

So here is the deal... I decided to re-test the whole unit as if I had just finished with the assembly. I pulled all the tubes and began the testing phase from square one. All was fine with my readings clocking in around 10% or less (higher and lower) than the chart provided in the instruction cd. All up until the point where I have to measure DC Volts at pin 5 off V4 & V5. I should be getting around a -45 VDC correct!?!? But I get nothing, Zero, Ziltch! I am testing pin 5 to ground on this step correct? It says to check the bias circuit? How? Also I had installed swamp resistors in series with pins 5 to help calm the standby switch squeal. Could that be an issue, I used green blue red, which I think is 56K resistor.

This is gettin crazy

Thanks guys

ScottW · Post by **ScottW** » Mon Sep 17, 2007 10:19 pm

Green, blue, red is 5.6K which is what you want.

OK, you're on to something. Having no bias voltage at pin 5 will cause the tubes to red-plate and die, so continuing to use those tubes will probably cause fuses to pop like crazy.

Yeah, you test stuff in the bias circuit with your meter set to DC volts and with one lead connected to ground. Here's where a good photo would help!

tfrost33 · Post by **tfrost33** » Mon Sep 17, 2007 10:20 pm

Oh yes, one more thing. The amp was on for about 20 minutes or so while did all the testing... And not one fuse blew the entire time. The only tubes not in it at this point are the KT66's. But I still do not have the negative 45 VDC needed on pin 5 of V4 and V5.

Just thought I should add that just in case.

ScottW · Post by **ScottW** » Mon Sep 17, 2007 10:23 pm

Sounds like the tubes have blown for lack of bias voltage. So even when you get the bias circuit fixed, a bad tube could pop your fuse right away.

tfrost33 · Post by **tfrost33** » Mon Sep 17, 2007 10:42 pm

10-4 Thanks a bunch Scott, you have been a great help. I will keep on it and figure out whats going on with the bias circuit and post on it Wednesday or Thursday. Starting to get late now and I should have been doing things other than this all day, but you know how it can get

I have a lot of work I need to take care of the next couple of days but at least I, well... WE narrowed it down to this. I will try and get Bob to come over and take some photo's too.

Thanks again!

uiovbged332 · Post by **uiovbged332** » Wed Jul 06, 2022 12:29 pm

Metropoulos Forum

B+ voltage

Re: B+ voltage