Failing EL34 tube in push-pull blowing fuses?

[exlabs]

Oh just found a faulty diode on EL34 screen, this has a resistance of 6 Ohms in either direction… but does not explain the path to ground (fuse blowing) when no tubes are inserted. I have some components arriving this week. Will start to investigate…

 

[6A3sUMMER]

What diode is connected to an EL34 Screen?

Post # 1 schematic does not show any diode, it shows a 1k screen resistor.

Please post a real schematic.
Without that, we are like a blindfolded archer shooting at the target (after having been spun around an unknown fractional number of turns).

Having an accurate schematic will help with todays problems.
And it will help prevent future problems, and help if there are any in the future.

 

[exlabs]

Hi

Post #1 also says that this is not amplifier I am have, but the reissue version 😉

I am trying to get a schematic... silence so far from Carlsbro. I am tracing it will post when I have something useful.

 

[chriskim]

tc 60 re issue amp

hi there
ive just come acros this post regarding this amp - i have the same !! 2 x el34 and 2 x 12ax7 - ive got red plating going on and found a pretty charcoal'd resistor - i really need a schematic for this bloomin thing -- did you ever have any luck ??? theres nothing i can find anywhere
Chris 😡

 

[exlabs]

Hi,

Yeah I got some things from Carlosbro, not too sure they were identical to the version I have. Post some pictures. What’s is your PCB version?

I will re-look at what they gave me a bit later.

Dan

 

[chriskim]

Hi Dan
thanks so much for replying
my pcb is v:1.2 -- TC60XXD01 - You got further with carlsbro than i ever managed , also if you have the amp still - would you know the resistor on pcb edge around the p10 and p9 supplies - thats whats frazzled and i cant begin to measure it - this thing could end up in the bin !! Chris

 

[exlabs]

Here is the version 2 PCB from my amp when I had it on my bench.

These are the only files that they had. It’s the version 1 PCB as far as I can tell.

I’m not too sure what you mean P9 and P10, maybe because I have a different version.

 

[chriskim]

Thank you so much but unfortunately totally differant from what i have - my amp has only 4 tubes in total - el34 2 off and 12ax7 2 off - total headache this thing !

 

[exlabs]

The version 1 PCB schematic has two 12AX7 and two EL34. Might give you the value of the BBQ resistor.

 

[chriskim]

yes it does make some sense - but with variations - the pcb was burnt and i cant even read what resistor it is - we'll get there
im very grateful of this help
chris

 

[chriskim]

Actually ive just looked this over again and i think its correct - your a bloody star my friend - yes version 1 , the amp is at my workshop so looking at a pic i have on phone and it makes sense -- happy days
Chris😱

 

[sarcastic1]

what happens when one tube in push-pull configuration is 50% below specification value

1. The second tube is the poor tube. Even g1=0 is below 200mA which is really rather low for an EL34. This is operating at around 40% of specification transconductance.

With EL34 it blows up and melts down!
This is called LIFE.
You are already half way there. 😀