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Post subject: '65 Custom Twin Amp RI - Tube problem
Posted: Fri Aug 22, 2008 7:57 am
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Since my previous post on 8/20, I was able to determine that the only time I have a problem is if the Output switch is in the "Low" (25w) position. Within 30 seconds, the screen grids on all 4 6L6 tubes start glowing bright red, and you can tell the fuse is going to blow any second. If I switch it back to "High" (100w) position, everything settles down and works fine.
Anyone with tips on what to troubleshoot in the Low power position?

Nick


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Post subject: Bad Output Switch!
Posted: Thu Aug 28, 2008 3:27 pm
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The problem was actually the Output switch itself. It is a Double-Pole Single Throw switch. Only one of the poles was switching when the switch changed positions. Instead of dropping the screen grid voltage on the 6L6's from 460VDC down to 250 VDC, the voltage was staying at 460, causing the tubes to draw too much current after about a minute or so, and blowing the fuse.
I changed out the switch, and everything is working fine again!


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Post subject:
Posted: Fri Aug 29, 2008 7:36 am
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WoW 460v, sounds dangerous!
How did you figure out it was the switch?

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