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Post subject: Help!!! (non-Fender) amp question.
Posted: Mon Oct 29, 2012 6:02 pm
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Hey guys long time no see! What brings me online to day is that I'm having a very strange issue with my Jet City amp after swapping power tubes. During my troubleshooting, I tested bias voltage at each power tube. One (v5) is at ~20mA and the other (v6) is at ~29mA. Based on what I've read, a small discrepancy between the readings is no biggie, but almost 10mA seems a lot to me. This amp is fixed bias, with a 50k variable resistor (trim pot) for fine tuning bias settings. I may have to re-install the original tubes and see if the issue goes away.
The problem I'm having (if it helps) is that there seems to be a weird resonance/crackling as a sustained note fades out. Having never changed tubes before, I at first thought that maybe it was normal and just part of the amp 'adjusting' to the new tubes, but after checking the bias I'm concerned that there may be even more of an issue.
So...hopefully one of you geniuses will be able to help me figure this out.
Thanks in advance!

Tim

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Post subject: Re: Help!!! (non-Fender) amp question.
Posted: Mon Oct 29, 2012 6:41 pm
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It sounds like the new output tubes weren't very well matched.

Arjay

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Post subject: Re: Help!!! (non-Fender) amp question.
Posted: Mon Oct 29, 2012 7:04 pm
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TimDrakeMusic wrote:
... I may have to re-install the original tubes and see if the issue goes away...

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Post subject: Re: Help!!! (non-Fender) amp question.
Posted: Tue Oct 30, 2012 2:27 am
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20 and 29 ma do not mean anything without knowing Plate voltage and output tube !


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Post subject: Re: Help!!! (non-Fender) amp question.
Posted: Tue Oct 30, 2012 6:35 am
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And Class of amp. Is it a fixed-bias AB1 type push-pull? Or a Class "A." ? :?:



Thanks!


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Post subject: Re: Help!!! (non-Fender) amp question.
Posted: Tue Oct 30, 2012 12:31 pm
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BMW2002Ti wrote:
And Class of amp. Is it a fixed-bias AB1 type push-pull? Or a Class "A." ? :?:



Thanks!

TimDrakeMusic write it is a fix bias.

So it is AB , push pull or not , it's same bias


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