Re: EL34 self cathode biased amp hum pre volume/gain control
« Reply #60 on: April 22, 2020, 07:27:47 AM »
Exploding speakers doesn't sound fun. I hate when that happens... so does one of my dogs...

abbey mentioned very early in the thread, about your heaters and, I too am curious about how they are grounded. Your description is confusing and, I'm not sure your drawing is 100% right. I make little errors all of the time when trying to trace things out...

There's always something when I go back and look again it seems.....

Anyway, it would be nice to see how the circuit is wired with respect to the heaters at least.  I'm not sure how it affects everything with the way that 1/2 ecc83 is grounded ...  if the other tubes aren't? maybe someone else knows...

I was thinking pin 9 may not need to be grounded but rather complete the circuit since 4&5 are tied....maybe ground the entire heater circuit with a couple caps or resistors...or pot (like the original drawing)..... Guessing it's wired for 6.3v....

Also, I'm not sure what the school of thought is on how to treat the unused triode.... I see the anode is floating... Don't think it matters but, the other pins are sort of wired an after thought.... The grid and cathode resistors etc still there.....

That 60k resistor is confusing too.... I still struggle with load lines so, even if I could figure out what is going on  in the drawing, I wouldn't know if it's optimal.....

Hopefully you'll get some more help....

I know it stinks to have to redo things but, in the end, it really doesn't take too long and you'll feel better about making sure everything is right.  I have some hokey looking stuff too and, although I know it's safe and works, I'd be hesitant to share or sell anything to anyone I didn't know or trust not to hurt themselves......

 :) yeah .. i might start and re wire the heaters... pulled out all the tubes left in only the GZ34 and the EL34s... I hear some zap zaps electrical sparks some where but can not see where this is coming from. Its not a loud spark, a smaller spark... could be the heater wiring somewhere shorting? or touching something ?

Thank you for your help and suggestion... 


Re: EL34 self cathode biased amp hum pre volume/gain control
« Reply #61 on: April 22, 2020, 10:07:45 AM »

Are you hearing this through your speakers or from the actual unit?

If through the speakers, apart from bad joints,sockets, resistors...etc.... could even be a number of other things apart from the interconnect ....a cell phone too close ...etc..

At the end of the day, you'll probably want to rewire this anyway as there's a chance you won't be happy with the hum or noise with it wired up as it is even when you find the main issue atm

. .. The differences are not small even with small differences in layout...

Hopefully someone else can offer some direction in the meantime.... still curious about grounding the one tube heater and not the others though..... Not sure how that works... I've seen it plenty with all tube heaters grounded themselves.....just not one alone like it is in this if I read your description right.... maybe it doesn't affect anything...

« Last Edit: April 22, 2020, 11:08:39 AM by scott2000 »

abbey road d enfer

Re: EL34 self cathode biased amp hum pre volume/gain control
« Reply #62 on: April 22, 2020, 01:06:36 PM »
still curious about grounding the one tube heater and not the others though.....
My understanding is that the 6.3v is wired to the EL34's and then joins the phase-splitter where one side is grounded to the chassis; after that the heater voltage goes to pins 4&5 of the remaining tubes, which have their pins 9 grounded to the chassis. It's not the nicest thing to do IMO, because having AC current circulating through the chassis, where it mingles with the audio ground path is not a clever idea. But it should not result in an unusable product.
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.


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