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Power Supply - 6SN7 KT88 PP Amp 50W
Power Supply - 6SN7 KT88 PP Amp 50W
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Old 5th March 2017, 02:41 PM   #1
Mission720 is offline Mission720  United Kingdom
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Default Power Supply - 6SN7 KT88 PP Amp 50W

Hello,

I'm embarking on an 6SN7 / KT88 ~50W PP amp. There's a lot of fantastic designs so for power side the one I've settled on requires ~500/520v B+, 480v, -80v, plus supplies of 320v and 230v for driver and phase-splitter/re-amp stages.

There is a PSU design with it, but no choke in the circuit. I would have thought a choke is very desirable to help minimise ripple. If I don't have to use a choke it will help on cost saving of course! I plan to use a torroidal transformer type: "Toroidal: Shielded, Supreme Series // 230V sec.: 400V at 250mA, 80V at 250mA and 6.3V at 6A" from Dom Audio. This is the suggested by Dom Audio.

For diodes, I plan to use STMicroelectronics STTH1210D Switching Diode, 1000V 12A, 48ns.


I have re-posted the circuits - there's no copyright and they're already posted here.

Can anyone advise please...
Attached Images
File Type: jpg PSU KT88 PP.jpg (108.1 KB, 408 views)
File Type: jpg 6SN7 KT88 PP 50W.jpg (102.2 KB, 404 views)
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Old 5th March 2017, 02:48 PM   #2
analog_sa is offline analog_sa  Europe
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Power Supply - 6SN7 KT88 PP Amp 50W
Quote:
Originally Posted by Mission720 View Post
I would have thought a choke is very desirable to help minimise ripple.
A choke is very desirable to help obtain good sound.

It is trivial to reach acceptable ripple without a choke, just look at 90% of commercial tube amps.
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Old 5th March 2017, 02:58 PM   #3
Mission720 is offline Mission720  United Kingdom
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Thanks for your comment... I understood that would be the case, so was surprised to see there wasn't one in the design I uploaded.

I'm presuming ideally a choke in both outputs then (not heater)?

Hammond seem a logical choice of quality and cost from what I have read/seen.

Next question is what values!! Maximum of 250mA output suggests 250mA choke or should I add some headroom to 300mA?
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Old 5th March 2017, 03:20 PM   #4
petertub is offline petertub  Sweden
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Power Supply - 6SN7 KT88 PP Amp 50W
Quote:
Originally Posted by Mission720 View Post
Hello,

I'm embarking on an 6SN7 / KT88 ~50W PP amp. There's a lot of fantastic designs so for power side the one I've settled on requires ~500/520v B+, 480v, -80v, plus supplies of 320v and 230v for driver and phase-splitter/re-amp stages.

There is a PSU design with it, but no choke in the circuit. I would have thought a choke is very desirable to help minimise ripple. If I don't have to use a choke it will help on cost saving of course! I plan to use a torroidal transformer type: "Toroidal: Shielded, Supreme Series // 230V sec.: 400V at 250mA, 80V at 250mA and 6.3V at 6A" from Dom Audio. This is the suggested by Dom Audio.

For diodes, I plan to use STMicroelectronics STTH1210D Switching Diode, 1000V 12A, 48ns.


I have re-posted the circuits - there's no copyright and they're already posted here.

Can anyone advise please...
V1B should have it's filament elevated to B+/4
If it's a stereo amp then V1B should be shared with the other channel and
it's filament (only) could be raised, the other cathodes would be
close to ground anyway, thus the filament should have a ground reference,
a "hum-dinger" might be the best way.

I also agree that a chokewould be a much better way to smoothen the B+
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Last edited by petertub; 5th March 2017 at 03:22 PM.
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Old 5th March 2017, 03:22 PM   #5
famousmockingbird is offline famousmockingbird  United States
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Reminds me of the Heathkit W5m. I think Heathkit used 1uF coupling caps for low frequency stability.

Click the image to open in full size.
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Old 5th March 2017, 03:31 PM   #6
Mission720 is offline Mission720  United Kingdom
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Wow - a 7H choke in that power supply....

I've read a little about elevated heater supplies. Curious that it wasn't used (and no choke) in the design I posted above. I wonder if he had problems due to that?
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Old 5th March 2017, 03:51 PM   #7
famousmockingbird is offline famousmockingbird  United States
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200mA might be enough for your needs.

$15 is a great deal.

C-14X Triad Magnetics | Inductors, Coils, Chokes | DigiKey

I do understand you on the other side of the pond.
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Old 5th March 2017, 05:34 PM   #8
Mission720 is offline Mission720  United Kingdom
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Thanks for the heads-up about Triad... I can get in UK at 20.15 plus 20%VAT but there's a shipping cost from US of 15 on top....

The narrative says it's made in China (...Triad... lol) so maybe Alibaba is a good place to try...

150 ohms resistance though...!
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Old 5th March 2017, 06:18 PM   #9
petertub is offline petertub  Sweden
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Power Supply - 6SN7 KT88 PP Amp 50W
Quote:
Originally Posted by Mission720 View Post
Thanks for the heads-up about Triad... I can get in UK at 20.15 plus 20%VAT but there's a shipping cost from US of 15 on top....

The narrative says it's made in China (...Triad... lol) so maybe Alibaba is a good place to try...

150 ohms resistance though...!
150 ohms is half of the resistor ( 300 ohm) it replaces. Go for it, but by all means
try to find one in UK first!

Or, try tubetown.de :
https://www.tube-town.net/ttstore/Tr...59R::7101.html
6H 200mA 18 euros including VAT excl shipping from germany
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Last edited by petertub; 5th March 2017 at 06:29 PM.
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Old 5th March 2017, 06:22 PM   #10
famousmockingbird is offline famousmockingbird  United States
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DCR is half but reactance @ 120Hz is 4.5k so you get much better filtering for less.
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