'75 Ampeg SVT high voltages between chassis (!)

[boroman]

Can anyone point me where I should address this weird problem: as on the pic, preamp and power amp on the workbench. I'm testing it because something is wrong - very weak signal - but never mind......

.... I have whoah.... 500VDC betwen main chassis and preamp chassis - measured chassis-to-chassis!
This is deafinitely not good. Onlu when in operating mode.e.g. with standby off (silent) position, there is no DC voltage at all.
It's strange also because plate voltage is over 600V.

Amp, in general, is dead-quiet in terms of noise, hiss, hum etc.
Any ideas?...

[g1]

There is a ground wire in the multi-pin connector/cable between the 2 units that sometimes breaks.

[Jon Snell]

The chassis MUST be connected together with a test lead, (shorting link with crocodile clips for ease of use) if separated.

The ground is connected normally by the chassis screws. Separating will allow the 'ground' of the preamp side to float up to almost HT level.

[g1]

As far as I know, the old SVT's preamp chassis screwed into the wooden cabinet, no chassis connection.

[Jon Snell]

As far as I know, the old SVT's preamp chassis screwed into the wooden cabinet, no chassis connection.

In that case, I agree with you that the ground wire is missing/not connected.
Judging by the neutral wire from the mains lead, (I highlited in my earlier post)I wouldn't like to hazard any guesses.

[boroman]

The chassis MUST be connected together with a test lead, (shorting link with crocodile clips for ease of use) if separated.

The ground is connected normally by the chassis screws. Separating will allow the 'ground' of the preamp side to float up to almost HT level.

And that exactly what have happened. Thank you. The ground between those two was lost. And it seems ground is only a tiny wire on the top connector that can break easily when disconnecting... They designed that part so bad and it so risky to leave it as is!