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Old 21st September 2013, 08:22 PM   #1
ryuji is offline ryuji  United States
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Default SE GU-50/6CB6 Pentode Design

Ripped up my old 5 channel 807/6cb6 based amplifier because I need to rebuild into a new rack mountable chassis. Decided to go with a completely new design.

Still havent ordered any parts yet. PSU design was inspired by Peter Millett's DCPP.

This will still be 5 channels just like the old one. About 40 mA per GU-50, probably around 8 mA per 6CB6 to match old amp. Of course ill be playing with bias as i made it adjustable

Just wanted some potential commentary before i ordered the psu parts.

Ill be using different mosfets and of course better choice/fewer zeners to get the required voltage. i ran with the stock parts in the program
Attached Images
File Type: png psu.png (112.7 KB, 437 views)
File Type: png gu-50.png (58.4 KB, 444 views)
File Type: png psu2.png (22.1 KB, 444 views)
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File Type: asc PSU.asc (5.4 KB, 8 views)

Last edited by ryuji; 21st September 2013 at 08:39 PM. Reason: typo
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Old 21st September 2013, 08:27 PM   #2
davorin is offline davorin  Croatia
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GU50 screen need more voltage, better 300V than 150V!
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Old 21st September 2013, 08:33 PM   #3
ryuji is offline ryuji  United States
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Hmm, worth a try. But i have doubts that -48v is enough to keep the anode current down. might need to order another/series two 48v supplies together.

Im guessing 300v would be sought after to obtain a flatter curve?

just realized i typo'd out the intended plate current for gu-50's (40 mA)

Last edited by ryuji; 21st September 2013 at 08:39 PM.
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Old 22nd September 2013, 06:58 PM   #4
ryuji is offline ryuji  United States
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Found a cheap single module dc-dc converter at digikey that offers -72v. I think that should be plenty of negative to run 300v screen on the gu-50. Runs off 12v too
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Old 8th October 2013, 10:34 AM   #5
ryuji is offline ryuji  United States
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heres the fully assembled and tested psu board:
12.6v DC and 400v AC input,
500v 300v,150v DC output, no current limit or constraints. full regulation even at open circuit.
6.3v 3A output for operating the small signal pentodes
5x -0v-72v bias pots
5x -0v-5v bias pots
bias supply powered by this guy:
http://www.murata-ps.com/data/power/ncl/kdc_nmt.pdf
Click the image to open in full size.
Click the image to open in full size.
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Old 29th October 2013, 04:05 PM   #6
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Very nice my friend, any updates?
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Old 29th October 2013, 05:04 PM   #7
ryuji is offline ryuji  United States
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I am just about done with the chassis wiring. all the major components are in place but its taking a bit of time to carefully solder to the tabs on the plug i chose for inputs/outputs. Slow progress as i have been distracted and busy with work lately and have been working on it in sessions. also need to resolve a issue i had with a resistor.
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Old 30th October 2013, 01:05 AM   #8
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Move to resistors rated for 750+v in that problem area, R12?
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Old 11th November 2013, 11:25 PM   #9
ryuji is offline ryuji  United States
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Amp is completed, but i need a new mosfet for main b+ ripple filter. the one i have there failed due to a failed zener diode

otherwise works exactly as intended. the fixed bias on the preamp works wonderfully.

i went with 500v and 6au6a's in the preamp positions
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Old 13th November 2013, 04:45 AM   #10
ryuji is offline ryuji  United States
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for anyone that cares. this reflects current state of the design:
sorry for a little bit of messiness in diagram showing lowish voltage design

the lm338 is only running one of the 6AU6A's, the other 4 are running in pairs of two off the 12.6v supply. a bit more power efficient that way anyways.
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File Type: png psu.png (111.2 KB, 37 views)
File Type: png gu-50.png (83.9 KB, 44 views)

Last edited by ryuji; 13th November 2013 at 04:49 AM.
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