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Old 18th June 2005, 05:07 PM   #21
kevinkr is offline kevinkr  United States
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I noticed a big mistake in the design of the output bias circuit. At the minimum you really, really need some high quality capacitors from the bias pot wipers to ground. Better still do what I suggest a couple of lines further along in this post. The transformer secondaries are floating off the 22K pots and the source impedance as well as ac signal level seen at the grids will differ depending on the position of the wiper. This is meant to be a dc adjustment only as well. I would recommend inserting a 50K resistor between the bias pot wiper and the secondary of the interstage transformer, in addition I would recommend installing about a > 0.33uF film cap from the cold end of each winding to the cathode return of the output tubes. This will provide a very well defined ac ground at the cold end of the driver transformer. Should sound a lot better too as the non-linearity of the wiper will not be an issue.. Your measured phase shift is related to the current configuration as well.

Kevin

Edited to improve clarity
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Old 19th June 2005, 01:22 PM   #22
day is offline day  Thailand
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thank youb Kevin
i will do it
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Old 21st June 2005, 06:55 AM   #23
day is offline day  Thailand
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I have new bad thing . ITS get very hot just 50 ma bias same the circuit on the top.
the old once has no ITS work very good.
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Old 5th July 2005, 03:11 PM   #24
day is offline day  Thailand
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the final
thay are work very good
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Old 3rd January 2006, 02:20 PM   #25
day is offline day  Thailand
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this is my new PP-GM70 drive by vv302b with int ll1677
OPT LL1688.
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Old 3rd January 2006, 02:22 PM   #26
day is offline day  Thailand
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this is copper plate
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Old 3rd January 2006, 03:53 PM   #27
Giaime is offline Giaime  Italy
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Whoa, some beautiful BIG work on those beautiful tubes...

yes, I like them BIG

the pictures with the lights off are AWESOME IMHO. I wish one day to build an amp like that...
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Old 3rd January 2006, 04:34 PM   #28
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Whoa! Look at those puppies glow!
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Old 4th January 2006, 02:31 AM   #29
kevinkr is offline kevinkr  United States
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Cool
Nice work, obviously a lot of thought and effort went into these.

Kevin
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Old 4th January 2006, 08:12 AM   #30
day is offline day  Thailand
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yes it very big and very hot but it very good sound.
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