Tube Amp Archive

M Fowler wrote: ↑Thu Mar 01, 2018 7:58 pm So you came over to this forum to stir up some shit is what I got out of your ramblings.

Chances are a lot of us most likely belong to this other forum your so proud of.

Mark

.... you're not helping the cause, dude........ Not helping at all.

I've been on forums that focused on firmware for canon cameras, where you have to be a coder to debug assembly language stuff etc. I volunteered to help but don't know the deep assembly language level stuff, (but I am a software engineer) but the experts didn't deem me worth their while because I c...

M Fowler wrote: ↑Thu Mar 01, 2018 2:29 pm

I rarely read the threads because the posters don't try to solve their own issues or learn about tube amps on their own.

LOL, awesome. Thank you for this.


Also, if you are that grumpy old guy who lived over on Calhoun St when I was growing up, I want my baseballs back.

joeboo88 wrote: ↑Wed Feb 28, 2018 6:01 pm also if someone is helping you, we might not want to chime in and muddy the waters and maybe add confusion, if you are getting sound advice

Not sure I'm following. Muddy the waters? Like suggest scrapping the plan and going with some other approach or component?

I agree that it came across negative and really kinda ungrateful for the input I did receive. I think it was just a personality clash with me and the thread in general. I have to say that I've haunted forums like this long enough to collect some pet peeves, and I think a few of the boxes were checke...

I think everybody here knows their way around a fixed-bias amp. That is probably why it just didn't occur to anyone that you would be trying to measure the idle voltage without resetting the idle operating point ;^) Huh, ok. Let me take a run at it: Q. Well if the zeners aren't zenning, what's your...

...There must be sufficient current flowing through the zener for predictable results. ooo bam sluckey for the win again :) So yeah you did have your answer here. Thanks again for rocking sluckey! ~Phil Well I'm not interested in getting in a bickering match here about who was the most helpful and ...

Thanks mate, I got help on another forum. And ultimately it was a process problem. I needed to get my initial cathode bias, add zeners to get expected B+ drop, then rebias back to the original cathode bias to get the actual B+ drop. I was missing the last step and at a dead end. I needed to essentia...

Fixed.

I gotta say, the level of support here was pretty underwhelming. I would have thought more people were familiar with a fixed bias circuit. But that's ok, no one is obligated to help anyone.

Hmm. Not what I was expecting, but interesting. And the voltage drop looks pretty consistent, so that's something to work with. I didn't take current readings across the diodes. JJ 5Y3-S. Here's some data: B+ 382v 1x15v...............374v...........8v drop..........53.3% of zener voltage 1x20v.........

-

sluckey wrote: ↑Tue Feb 20, 2018 1:11 am Did you get the desired results? Or did you just quit?

My 5y3 is dead. I suspect it was something I did being careless with the multimeter.

But voltages through the current limiter with no tubes in tells me the OT CT swap will be fine.

sluckey wrote: ↑Tue Feb 20, 2018 12:08 am

(btw, pin 8 is also the OT Center tap)

Well, you simply move the OT lead to the original 16µF cap. This may be a factor for why you did not get the desired voltage drop to begin with. There must be sufficient current flowing through the zener for predictable results.

Yep. Done

What's the mathematical formula for that bias string combo? I'm using a 10k pot. Using a smaller tail resistor would give the pot a greater voltage swing, right? You never mentioned you had a non stock bias circuit. The only math I used was just "off the top of my head" reasoning... The stock circu...

Another idea... Replace that 56K resistor across the bias cap with a 50K pot in series with a 22K resistor so you can adjust the bias. Then you can run the 6V6s a bit hotter and this will bring the B+ down. I personally don't use zeners for this purpose. I believe in using the correct PT to get the...