Electromuse Model 10 A

[RitzRed]

I am looking for a schematic for an old electromuse model 10 A amp. I have one I am rebuilding as I replace parts I think I put the tubes back in the wrong places because once I replaced the multi can cap and plugged it in the rectifier tube seemed to be shorting out it had blue flames or shorts going on. I found a few schemo,s that look about the same but they have different tubes so if anyone knows where I can find one or maybe what I did wrong.Any Ideas or help will be appriceated thanks

[bobloblaws]

I am looking for a schematic for an old electromuse model 10 A amp. I have one I am rebuilding as I replace parts I think I put the tubes back in the wrong places because once I replaced the multi can cap and plugged it in the rectifier tube seemed to be shorting out it had blue flames or shorts going on. I found a few schemo,s that look about the same but they have different tubes so if anyone knows where I can find one or maybe what I did wrong.Any Ideas or help will be appriceated thanks

I could use the schematic for this amp. Did you ever find one? Or what were the similar ones you mentioned?

[The Dude]

[bobloblaws]

Thanks!

Interesting design, I don't think I've seen phase inversion done quite like that like that before.

[g1]

I don't see a working circuit there at all. I mean, it might work, but makes no sense.
One power tube just has input grounded, so it would act like a single ended amp, I would think. That would be pointless.
Edit: never mind, had not seen this circuit before, my mistake.

[Enzo]

No, the input isn't grounded, the grid is grounded. That leaves the stage cathode driven. The cathode is the input. The signal varying voltage through the cathode of the other side varies the voltage across the cathode resistor, which in turn varies the voltage at the cathode of the mystery side. That works against the grounded grid to put signal through the tube. Think Music Man.

[Dave H]

I don't see a working circuit there at all. I mean, it might work, but makes no sense.
One power tube just has input grounded, so it would act like a single ended amp, I would think. That would be pointless.

It's not single ended. It's a "self split" push pull output stage. One grid is grounded and the common cathode resistor isn't bypassed making it work like a long tail pair PI

[musictronics]

It's not single ended. It's a "self split" push pull output stage. One grid is grounded and the common cathode resistor isn't bypassed making it work like a long tail pair PI

Absolutely...! Think old Magnatone amps (Model 109 if my memory serves me). In the Magnatone amp the signal from the screen grid of one of the output tubes is fed back to the control grid of the other one, creating phase inversion. This technique was used in older radios in the interests of tube economy.

[g1]

Oops.
Thanks for the correction and explanations. I was looking for an 'input' elsewhere and had not seen this type of 'self-split' push-pull before. I saw the cathode but did not pay attention to the lack of bypass cap. It did not occur to me that it would serve as an input unbypassed like that.
So why bother with PI circuits then? There must be some major drawback to this design?

[Dave H]

So why bother with PI circuits then? There must be some major drawback to this design?

I think it's low output power.

I wonder how well it would work as a low power option on a cathode biased amp?
Use a double pole switch to ground one grid and disconnect the cathode bypass cap.