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Old 25th June 2013, 02:02 PM   #21
Renioo is offline Renioo  Poland
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Join Date: Dec 2012
I got the reply and there is propably something with Us being too low. It is taken from half of Ua = 280V. There is something wrong I think with diode you can see on board. The Ua is made OK but after the diode for Us there is only 115V. I attach the photo.

The diode I think is russian D226
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Old 25th June 2013, 03:17 PM   #22
Renioo is offline Renioo  Poland
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It was the diode... I found out what is D226 and replaced it with 1n4007... voltage back to 420 on screen and works perfectly... I have a set of new tubes then... good

Last edited by Renioo; 25th June 2013 at 03:30 PM.
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Old 25th June 2013, 04:29 PM   #23
Struth is offline Struth  Canada
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Hi Guys

Vs sets the range for Vg1, so now that Vs=420V, you will need about -42V on the control grid as a minimum to keep the tubes under control. Before plugging in output tubes, assure that the bias range encompasses this value, and preferably can sweep to about -50 or -60 to assure full control over the tube.

Have fun
Kevin O'Connor
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Old 25th June 2013, 04:57 PM   #24
Renioo is offline Renioo  Poland
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So everything is set nearly allright. I can adjust it up to -40V with this pot (somehow strange). I will measure mV going from pin 8 with 1R.

Last edited by Renioo; 25th June 2013 at 05:05 PM.
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Old 25th June 2013, 05:07 PM   #25
Struth is offline Struth  Canada
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Hi Guys

Modify the bias supply to provide greater negative sweep BEFORE plugging power tubes in.

Otherwise, it is your choice to waste your tubes.

Have fun
Kevin O'Connor
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Old 25th June 2013, 05:17 PM   #26
Renioo is offline Renioo  Poland
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Will do.
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