Glowing plate section on El-34

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Glowing plate section on El-34

Postby Clik2media » Tue Jan 27, 2009 3:59 pm

On my St-70 V2 tube plate seems to glow on one corner of vertical plate. After shut off the "burn" then looks like a water stain...if I am describing it right. i.e a small stain on the corner of the plate.
Kinda weird. My resistor is reading very much in range of 15.6 -15.8 ohms. The other is reading well within 1000 ohm range.

any thoughts

thnx
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Postby Sal Brisindi » Wed Jan 28, 2009 9:03 pm

Move that tube to another position, if the same tube glows, then its the tube, if the other tube glows I would make sure your coupling capacitors are good.

Sal
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Postby Clik2media » Wed Jan 28, 2009 9:07 pm

I did something similar, I replaced the tube, in the same position and it showed the same plate glow. I put in new Solen's on the old original board, with the other original parts still in place.
I may be answering my own question here but could that mix / match be a problem. Should everything be replaced if you replace anything.

thanx

Mike
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Postby Sal Brisindi » Thu Jan 29, 2009 10:28 pm

Can you bias the amp to 1.56 volts per channel?

The Dynaco printed circuit board was not the best quality, make sure you have no broken traces, check carefully with a magnify glass, sometimes the cracks are hard to see.

Did you replace all 6 of the larger capacitors on the board, the 4 .1uf and the 2 .05uf caps?

Also, clean the tube sockets and tighten the socket connectors with a sharp thin pin or mini screwdriver.

You can also measure the primary resistance of the output transformer, the plate to center tap (B+ connection) to plate should be close.

Let us know what the outcome is.

Sal
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Postby Clik2media » Sun Feb 01, 2009 5:10 pm

It holds 1.56v biased, all six capacitors were replaced [Solen], tube sockets cleaned. Still a slight glow on the plate corner. I tried a few times to upload a pic I took of it, but no luck. I am waiting for parts to replace the old board with a new one [ old layout]

Will keep checking stiuff till the board is replaced.

thnx
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