ELK Viking Bass 100 help

[diydidi]

Hi.
I have this amp for repair. Someone replaced the OP transformer with a single CT primary instead of the Two primary system as seen in the schematic.
So now it basically as if the two primary windings are in parallel. They removed the feedback resistor. The amp works after replacing a couple filter caps and resistors, but the amp oscillates with a low freq input signal.
Shouldn't there perhaps be a feedback resistor somewhere??

[Enzo]

So, stick one back in.

[olddawg]

Couldn't you just float the center tap and put the circuit back to stock?

[custom_amp_30]

Hi.
I have this amp for repair. Someone replaced the OP transformer with a single CT primary instead of the Two primary system as seen in the schematic.
So now it basically as if the two primary windings are in parallel. They removed the feedback resistor. The amp works after replacing a couple filter caps and resistors, but the amp oscillates with a low freq input signal.
Shouldn't there perhaps be a feedback resistor somewhere??

I sent this inquiry to Joe Fire the american engineer who worked at Elk before the big fire burned the factory down. Hopefully he can offer you some advice on this. Good thing you have the schematic already so that will not be the issue.

Can you please post a "Gut Shot" of that chassis to see what else may have been done to this amp?

[diydidi]

I would need a second identical transformer to do this. This amp just has so much work to do on it before it can operate. Thanx for all the advice. Will fire it up today.

[diydidi]

Awesome!! Thanx man. I will post a gut shot today.
Watch this space

I sent this inquiry to Joe Fire the american engineer who worked at Elk before the big fire burned the factory down. Hopefully he can offer you some advice on this. Good thing you have the schematic already so that will not be the issue.

Can you please post a "Gut Shot" of that chassis to see what else may have been done to this amp?

[custom_amp_30]

Awesome!! Thanx man. I will post a gut shot today.
Watch this space

I believe that if the original OT was available, that Mercury Magnetics offers a special service that could disassemble the original windings and find the problem and upgrade it with thicker plate material, with the proper amount of turns to get that extra tone that was missing as well as get you back up and running. Having done this they could make you a second one for your needs to match that schematic.