Peavey Windsor Studio The output tube el 34 burned out

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Peavey Windsor Studio The output tube el 34 burned out

Postby debuc1234 » Sat Feb 19, 2011 4:48 pm

I tjeck the plate voltage et is 470V maby too heigh for SE Class A Pentode singel tube. Hmm.
http://dl.dropbox.com/u/19526767/Pea...tudio/scan.pdf

Is ther enybobby who has tjekt the plate voltage. is et around 270V ????

I think the reason et burned, was because the bias was wrong:
power anode (Wa) Ua 465- Uc 28 * Ia 72mA= 31W = burne out. and max is 25W

should I only re adjust bias or should I also lower Ua befor adjust bias.
some suggestions ................






Br
Thomas
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Postby Geek » Sat Feb 19, 2011 7:09 pm

Hi, welcome!

A good link would help ;)

Cheers!
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Postby EWBrown » Sat Feb 19, 2011 8:43 pm

Without having an actual circuit description or diagram, I'll just try a guess here:

470 Volts on the anode (UA) is quite high for this tube in Single Ended operation, I would normally use about 420VDC and 60 mA which would give you 25 Watts anode dissipation (WA)

With 470VDC, the current should be reduced to about 53 mA, with a somewhat more negative g1 bias voltage (try about -32V to -34V for the grid bias)

HTH

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Dropbox atatment

Postby debuc1234 » Sun Feb 20, 2011 2:50 am

Hi EW

Thanks for the reply, here is a Diagram with the measured voltages

http://dl.dropbox.com/u/19526767/Peavy% ... o/scan.pdf

Et is catode biased
If you/enybuddy have any suggestions or tips for the output stage et would be super.

Br

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Postby Geek » Sun Feb 20, 2011 4:02 am

Hmmm, seriously over spec. and cathode bias to boot.

My guess is you have high line voltage compared to what it's made for (I worked on a 5150 that was quite over on the B+. I wonder if they just like to run them hot?

My best answer is to up that cathode resistor. I'd start with 560R @ 10W, but you may want to have values up to 820R at your side.

Cheers!
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Hi Geek

Postby debuc1234 » Thu Feb 24, 2011 3:14 pm

Yes those guys at Peavey is not very smart ?
I will lower the Plate voltage and and re biaes it
and continue working with the clean / drive switch

And thanke for the answers

Br

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