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Post subject: Super Champ XD audio issue
Posted: Sun Jan 22, 2017 2:52 pm
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Hi all!

I bought my SCXD about 1 year and I used it very little and only at home with the sound almost always softly.
After maybe 2 weeks I decided to turn it on and it has no sound in either the clean channel or the drive. Someone who has already gone through this would have some hint of what it can be? The only thing that lights up is the red lamp on the front of the amp and the middle valve (12x7) and both 6v6s tubes are completely dark with no light.

I appreciate any help!


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Post subject: Re: Super Champ XD audio issue
Posted: Sun Jan 22, 2017 5:32 pm
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The amp has three diodes in the output stage. One or more may have gone bad. Need to do some voltage measurements. Maybe, a good amp tech?

http://bmamps.com/Schematics/fender/Sup ... Manual.pdf


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Post subject: Re: Super Champ XD audio issue
Posted: Sun Jan 22, 2017 6:08 pm
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This topic rightfully belongs in the "modern amp" section.

You'll get more useful data there.

Arjay

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Post subject: Re: Super Champ XD audio issue
Posted: Sun Jan 22, 2017 6:38 pm
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Retroverbial wrote:
This topic rightfully belongs in the "modern amp" section.

You'll get more useful data there.

Arjay


I request to mod/admin move this thread to "modern amp" section please.

Thank you for clarify!


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Post subject: Re: Super Champ XD audio issue
Posted: Mon Jan 23, 2017 5:37 am
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BMW2002Ti wrote:
The amp has three diodes in the output stage. One or more may have gone bad. Need to do some voltage measurements. Maybe, a good amp tech?

http://bmamps.com/Schematics/fender/Sup ... Manual.pdf


Yes, what kind of voltage measurements do you need?
Could you please point me where can I find this three diodes in schematics?

Thank you for your attention ;-)


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Post subject: Re: Super Champ XD audio issue
Posted: Mon Jan 23, 2017 7:36 am
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Nominal working voltages are posted on the schematic. The red dots indicate the diodes within the output section:

Image

I believe that D1 and D2 are there to act as flyback diodes. Preventing excessive back voltage onto the 6V6GT anode plates, during amp shutoff. D3 may also be there for that reason. Or could be a "fuse" for excessive current flow due to shorted tube? Anyhow, the voltages within the output section should be checked by tech.

Good luck! :)


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Post subject: Re: Super Champ XD audio issue
Posted: Mon Jan 23, 2017 9:57 am
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BMW2002Ti wrote:
The amp has three diodes in the output stage. One or more may have gone bad. Need to do some voltage measurements. Maybe, a good amp tech?

http://bmamps.com/Schematics/fender/Sup ... Manual.pdf


All three D1, D2 and D3 diodes are ok. What can I do next? thanks.


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Post subject: Re: Super Champ XD audio issue
Posted: Mon Jan 23, 2017 10:27 am
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Pull chassis out of cab. Place on secure work bench. Have all tubes in. A speaker connected. No input. Volume = 0. Check voltages on the anode plate of the 6V6GT. Check idle bias on 6V6GT tubes. Check voltages on phase inverter section.

Be careful! High voltages on the circuit board. If you don't feel comfortable, have tech do the voltage readings.


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Post subject: Re: Super Champ XD audio issue
Posted: Tue Jan 24, 2017 12:13 am
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rmarconcini wrote:
Retroverbial wrote:
This topic rightfully belongs in the "modern amp" section.

You'll get more useful data there.

Arjay


I request to mod/admin move this thread to "modern amp" section please.

Thank you for clarify!


While you are at it, delete your other (duplicate) thread. There is an "X" below your post, click it and delete the thread.

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Post subject: Re: Super Champ XD audio issue
Posted: Wed Jan 25, 2017 1:46 pm
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BMW2002Ti wrote:
Pull chassis out of cab. Place on secure work bench. Have all tubes in. A speaker connected. No input. Volume = 0. Check voltages on the anode plate of the 6V6GT. Check idle bias on 6V6GT tubes. Check voltages on phase inverter section.

Be careful! High voltages on the circuit board. If you don't feel comfortable, have tech do the voltage readings.


I replace 2 6v6GT valves and BINGO! Amplifier is ok again. Two old ones are dead ;(

Thank one more time!


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Post subject: Re: Super Champ XD audio issue
Posted: Thu Jan 26, 2017 7:29 am
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Kinda unusual for both output tube to go out, on their own.

Glad it was a quick and relatively cheap, fix


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