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In Reply to: Re: Looks like we got a preamp problem... posted by groverg on December 26, 2004 at 17:21:28:
Hang in there, we're making progress. We can probably solve it tonight.
Follow Ups:
Most interesting. It only lasted 5 minutes this time with the CD player going straight into the amp. I did have the volume pot up a bit higher than usual, but not that much. So it seems we only have a problem when we have a signal, yes? Of course I may not have heard it when it went off with no preamp hooked in and the shorting plugs in place because there was no music to stop playing. This is quite a puzzle my friend. Next move?
Vince
Vinnie, why don't you call me at 301-699-8227 and I'll call you back on my dime--don't worry it doesn't cost me anything.
To any who have been following this thread to see how it ends, Grover was kind enough to march me through my whole layout step by step on the phone until we found the problem. It was the bloomin' EL 34! Grover says that most likely it shorted out when the B+ voltage hit the plate before the filaments had a chance to warm things up. It would run for awhile then shut down. Once it cooled down you could start it up again and run it for awhile longer. It about drove us nuts until Grover had me put the DVM on the plate of the EL34 and watch it while it was running. When it quit the voltage on the plate spiked up, indicating that it wasn't drawing current anymore. At his suggestion I have now installed a separate 6.3 supply for the filaments that will be turned on first.
Bottom line is this is one great sounding amp! Once I got it running I just kept trying one CD after another and they all sounded great. I can't wait to hear it in stereo. Now will come the longer process of deciding just how to turn this into a real amp instead of a bread board. Lots of work and fun ahead. Many thanks to Grover for both the design and helping me get it operational. You're a good man Grover!
Thanks for the suggestions Grover. I think it's best if I take a break for tonight and start again tomorrow. I'm tuckered. I will try the these tomorrow and get back to you with the results.
Thanks!
Vince
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