Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => EZ Board postings => Topic started by: Geezer on June 17, 2005, 09:16:09 pm
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Hoffman Amplifiers
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> Output transformer troubleshooting
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klarsen01
Junior tube assistant
Posts: 5
(2/15/04 4:24 pm)
Output transformer troubleshooting
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Hi guys,
I have a 1977 Marshall 100w head that has low volume and ugly distortion. I suspect the output tranformer. The resistance on one side is 13.5 ohms but the other side is only 3.8 ohms. Does this sound like a problem to you guys? Do you have any other suggestions for throubleshooting output tranformers?
Thanks,
Kirk
ganzonimx
Hey get your own solder
Posts: 384
(2/16/04 11:04 am)
Re: Output transformer troubleshooting
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I think there ar a lot of reason for low volume and ugly distortion... go once over the Tube Amp Debug pages, (click on the link in the upper left corner) that may help you to track down the problem ... if you get stuck ask again of course.
Cris
klarsen01
Junior tube assistant
Posts: 6
(2/16/04 12:41 pm)
Re: Output transformer troubleshooting
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Thanks, I've already done that. That's why I suspect the tranny. Everything else seems to check OK. I'm still a bit new at this so I want to make sure I'm right before I buy a new transformer.
What do you guys consider the best way to check a transformer anyway?
Thanks,
Kirk
ganzonimx
Hey get your own solder
Posts: 385
(2/16/04 1:39 pm)
Re: Output transformer troubleshooting
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You find here a simple method to check the impedance ratio of a OT.
I have used this method to check OT's, but I'm not sure if you can consistently detect a gone OT. Check both half's of the primary with this method. If you get the same reading on both half's of the OT it should be fine.
You can even do that without taking the OT out of the chassis, but pull the power tubes. You can solder the AC source to a plug and plug it into the Output jack of the amplifier. I use a 10V transformer from a old cell phone. Then measure between pin 3 of the power tubes (plates) and the point were the center tap of the OT connects to b .
Be careful because you will find a voltage 10x to 30x higher as the AC source.
Cris
Cris
klarsen01
Junior tube assistant
Posts: 8
(2/16/04 8:19 pm)
Re: Output transformer troubleshooting
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Sorry ganzonimx, that link didn't work.
Can you try to post it again?
Thanks,
Kirk
ganzonimx
Hey get your own solder
Posts: 388
(2/16/04 8:26 pm)
Re: Output transformer troubleshooting
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briefcase.yahoo.com/casey4s ore briefcase.yahoo.com/casey4s
click on the "Output Transfomer Impedance" folder
Cris
klarsen01
Junior tube assistant
Posts: 9
(2/17/04 8:32 pm)
Re: Output transformer troubleshooting
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Thanks, I'll give that a try.
Kirk
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