Quote from: saturated on April 09, 2024, 08:49:16 PMThese two ceramics are still hot enough to cook steaks on....

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At least small steaks...well done...

So I'm going out on a limb here and proposing that the 8k ohm 10w resistor is shorted to ground.  It measures 170v on one end and zero on the other.
A quick look at the schematic (a forensically enhanced version kindly provided by the Mighty Mick) to me places cross hairs directly on the zener diode.

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So I'm guessing that the zener diode is shorted...idk.

Or perhaps I'm unfairly blaming it. 

 


To be continued...the story of the zener diode that was (possibly) framed

Welcome to the forum Valleyslad

 

And I'm ready to put forth another conclusion:

If I measure xxx volts on one end of a resistor.....and ZERO volts on the other end

Guess what


 

It's time to go ISO

 

What it does mean is:

The circuit is open.

 

Today I learned:

Just because a resistor has no voltage drop across it and measures the same voltage at each end with respect to ground

Doesn't mean the resistor is shorted

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Quote from: joecool85 on April 11, 2024, 03:53:39 PMI recommend making sure that the input jack is clean and connected well to both line and ground.  If not, it could be only letting some signal through causing these issues.

I will, thanks.

Hi. Did you manage to make much of an improvement to the amp? I've just picked one up for £20 on marketplace. I'm looking to tinker a little too!

Quote from: saturated on April 09, 2024, 05:20:43 AMThank you sir I am glad I did not have to touch any power tubes...in the back of my mind I had heard about tube biasing and was dreading having to do something like that.  But I looked it up and evidently preamp tubes are just plug and play...?

The two 12ax7 I switched positions were in there really tight.  To avoid broken glass and blood I put on a leather work glove.

I really appreciate everyone's help with this idk what we did but it's sounding really crazy nice it still has a little hum at low volume but I ain't touching it right now.

A little hum at low volume may well be normal for this amp.  It certainly is for others.

I recommend making sure that the input jack is clean and connected well to both line and ground.  If not, it could be only letting some signal through causing these issues.

Quote from: g1 on April 11, 2024, 12:24:42 PM

Quote from: RookieRecurve on April 11, 2024, 10:09:19 AMMy main concern is with the ground.  I am unsure if sharing a ground with an external amp and an internal amp would cause any issues? 

It can cause issues with ground loops or worse.  Some amps require their output (-) terminal to be isolated from ground for things like current feedback schemes.
If you want it to be safe as possible, use a Cliff S2 style jack, which will be insulated from chassis, and also will allow switching of both the positive and negative wires.

Thank you!  This is what I had suspected, but your answer confirms this.  Much appreciated.