Power trans question

[drewl]

So I have this old Marshall 100 power trans that I thought was bad, the filament center tap was shorted to the the mounting bells.
All the other taps are fine and it seems it would work in an amp with the filament center tap grounded, but I was trying to use in an old Ampeg that tied the output tube cathodes to a hum pot connected to the filaments.
When I opened the trans up, the filament center tap was connected to the trans ground
Was that normal?
I isolated that ground so the trans should work with this circuit, it did before I isolated the center tap with the output tubes removed, because in this circuit it was basically shorting the cathode bias circuit through the hum balance.
Sorry for the odd rambling, but I don't think I've ever seen the filament grounded to the bells/ground of an output trans before.
Pretty sure it's a 100 plexi power trans, so I'll probably want to save it for something else.

Thanks.

[J M Fahey]

In my view , it is "normal", since :

* grounding filament center tap has been done since the dinosaurs roamed the earth, and in fact is NEEDED.
That it can be replaced by a couple 100 ohm resistors does not change the main idea.

* elevating center tap is fine, but is a modern-ish idea, done by almost nobody (statistically speaking)
Not saying itb doesn´t work, quite the contrary, but more the province of YT , Gurus and Forumites.

* I would use separate wire for each but joining them is not BAD per se, both would have been grounded to chassis anyway.
Modern trends aside, not sure they weighed much (hint, not yet invented) in 1970

[drewl]

Great, thanks.
Here's the amp I was testing it in, an old Ampeg 625 Bassman, too bad they didn't keep or trademark the name, eh?
I was wondering why I the output tube cathode circuit was measuring a few ohms to ground.

[mhuss]

That's an odd one, not even a volume control.

[Helmholtz]

It's just the power amp.

[drewl]

The preamp is under the power amp in the file, along with the parts list.

[Helmholtz]

The preamp is under the power amp in the file, along with the parts list.

Sorry, missed that.
The preamp has volume controls.