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Post subject: '65 drri transformer problem?
Posted: Sun Jul 02, 2017 4:40 pm
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Hi folks, looking for a bit of advice here - I've got a '65 drri as a main gigging amp, and it's started behaving a bit iffy. It's fine for the first hour or so of a gig, but later starts to get more distorted and thinner sounding, and sometimes feels 'stiffer' to play, if that makes sense? I've also noticed the power transformer gets very hot after a while of playing, has anybody else had this problem? Could there be a link between the two? How hot would you expect the pt to get after, say 2 hours or so of playing?


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Post subject: Re: '65 drri transformer problem?
Posted: Fri Jul 07, 2017 1:20 am
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Location: Province de Québec, Canada
Transformer hot ; normal

Distortion after 2 hours ; output tubes ? Bias is wrong = more heat on transformer
Resistors burn or / and solder in the amp.
!2XX7 tubes ?

New power tubes need always a bias check and adjust

Second hand amp ; Check if fuse is the right one to protect the amp ; A must


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Post subject: Re: '65 drri transformer problem?
Posted: Sat Jul 08, 2017 11:52 am
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Output tubes are fresh, biased to about 22/23ma, 12AU7 in reverb send spot to tame reverb, 12AT7 in PI. Just how hot is 'normal' hot port the PT on these amps?


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Post subject: Re: '65 drri transformer problem?
Posted: Sat Jul 08, 2017 12:29 pm
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Coleye71 wrote:
Just how hot is 'normal' hot port the PT on these amps?


Too hot to comfortably touch with unprotected fingers -- same as the tubes.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: '65 drri transformer problem?
Posted: Sat Jul 08, 2017 12:57 pm
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Coleye71 wrote:
Output tubes are fresh, biased to about 22/23ma, 12AU7 in reverb send spot to tame reverb, 12AT7 in PI. Just how hot is 'normal' hot port the PT on these amps?


Look good, if amp sound is good, forget the transformer heat.

Poor sound could mean a short output transformer wich need more current = more heat

What about the fuse ?


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Post subject: Re: '65 drri transformer problem?
Posted: Mon Jul 10, 2017 10:26 am
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I would check the electrolytics and resistors in the doghouse. What year is the amp? They ship w/ the least expensive parts which are likely to wear out more quickly than there ancestors. You may have developed a leaking cap or a resistor value has strayed. Also possible, you're rectifier tube is becoming less efficient.


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Post subject: Re: '65 drri transformer problem?
Posted: Mon Jul 10, 2017 11:07 am
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sfceric64 wrote:
I would check the electrolytics and resistors in the doghouse. What year is the amp? They ship w/ the least expensive parts which are likely to wear out more quickly than there ancestors. You may have developed a leaking cap or a resistor value has strayed. Also possible, you're rectifier tube is becoming less efficient.


I desagree.


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