1963 Vox AC-4 with stripped bolt

[christarak]

Can I please thank Jon, Pixel, Chuck, Mick, and Seven for your inspiration and suggestions?
I got the chassis out. I bought a narrow nose set of vice-grips today that enabled me to get either side of the nut. I sprayed the thread on both bolts with a bit of WD40 and just started rocking the nut back'n'forward with the 5/16 spanner. I eventually got to the end of the bolts. I didn't have a strip of copper, Mick, but used a folded-over business card to protect the threads. Once I have the amp working I can face the less daunting exercise of getting the correct nut and securing the bolt to the wood with adhesive. I'll try the superglue suggestion first and maybe reinforce it with epoxy.

[christarak]

Does the chassis have to be removed?
If it trips an earth leakage breaker/trip then it may be something basic, like a silly and dangerous death cap..

You're right Jon. The death cap was still there. I removed it, but the house still went dark. So tomorrow the detective work begins. I am just so happy that the chassis is out. Everything will seem easy compared to that (famous last words).

[Jon Snell]

Do you have a Megger or earth leakage meter?
Hopefully it is not the transformer!
Have you checked inside the mains plug.

[christarak]

Do you have a Megger or earth leakage meter?
Hopefully it is not the transformer!
Have you checked inside the mains plug.

With no valves installed, it trips the cct breaker when I reach around 180V on the primary (I'm in Australia - 240V). I pulled out the Power Transformer now that I have the chassis out The switch, power lead and plug behaved with no short up to 250v on the primary. But, I think the PT may have some shorted winds. With just the PT on the bench plugged into the Variac, I could go up to 240V with no tripping. The HT had 500V across it, but the heater only had 2.5VAC at 240v. Odd that it didn't trip the cct breaker when it was on the bench, but only when installed. I'm taking the PT to my transformer guy in the morning. Of course, I will report back when installed.

[The Dude]

The 2.5VAC on heater windings was outside to outside and not to CT?

[christarak]

The 2.5VAC on heater windings was outside to outside and not to CT?

That's right, Dude. Outside to Outside.

[Helmholtz]

Not clear if it trips the earth leakage breaker or the main circuit breaker.

If it's the earth leakage breaker the problem won't show with the PT out of the amp and not grounded.
Be careful!
The PT could have a primary-to-secondary or primary-to-core short (or at least leakage).
In the latter case the PT core would be live!

[christarak]

Do you have a Megger or earth leakage meter?
Hopefully it is not the transformer!
Have you checked inside the mains plug.

Yep. It was the PT. There were shorted turns in the heater winding. Fortunately there is a great transformer repairer near me (Sydney). That came back and the voltages looked great, and even better, NO SHORT!
Thank you for your support.

[christarak]

Not clear if it trips the earth leakage breaker or the main circuit breaker.

If it's the earth leakage breaker the problem won't show with the PT out of the amp and not grounded.
Be careful!
The PT could have a primary-to-secondary or primary-to-core short (or at least leakage).
In the latter case the PT core would be live!

That's a very good point, Helmholtz. Fortunately for me, the the short was between winds in the heater, and not the frame of the PT.