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Thread: Electromuse Model 10 A

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    Electromuse Model 10 A

    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

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    Quote Originally Posted by RitzRed View Post
    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?

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    Supporting Member The Dude's Avatar
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    Click image for larger version. 

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    Thanks!

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

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    Don't forget the joker g1's Avatar
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    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.

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    Last edited by g1; 01-25-2019 at 02:00 AM.
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    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.

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    Quote Originally Posted by g1 View Post
    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

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    Quote Originally Posted by Dave H View Post
    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.

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    Don't forget the joker g1's Avatar
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    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?

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    Quote Originally Posted by g1 View Post
    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.

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