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Vintage Asylum Classic gear from yesteryear; vintage audio standing the test of time. |
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In Reply to: True Mullard 5-20 design. posted by jusbe on February 27, 2015 at 12:44:47:
I kind of thought so..The 4Uf cap you are speaking of is a filter cap.As long as the B+ is ok going into the choke which is 465vdc or a bit higher,that cap is fine.The caps that will cause the output tubes to run away are C7 and C8.Old caps like that tend to leak DC voltage on to the grid of the tubes causing the tubes to draw grid current and therefore start glowing cherry red.If you replace the power supply caps other than the 4uf which I'm pretty sure is ok, then change the coupling caps and change any out of tolerance resistors around the tubes,your tube runaway problem will disappear.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Edits: 02/27/15
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Follow Ups
- RE: True Mullard 5-20 design. - Michael Samra 13:04:59 02/27/15 (3)
- RE: True Mullard 5-20 design. - jusbe 02:44:28 02/28/15 (2)
- If the 480vdc and 500vdc are what you were referring to as runaway voltages, - Michael Samra 07:29:08 02/28/15 (1)
- Okay. - jusbe 13:29:00 02/28/15 (0)
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