High power P-P EL34/6550/KT88 amp suggestions - diyAudio
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Old 13th September 2006, 03:07 PM   #1
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Default High power P-P EL34/6550/KT88 amp suggestions

I've got this big hunk of Power transformer (360-0-50-360-500mA, 6.3-0-6.3- 6A, 6.3-0-6.3-3A) and a monster choke sitting here that is perfect for a 50-60w per channel stereo amp.

Anyone got any good suggestions for a good amp design? I perused the forum but did not really come up with much that wasn't a low power triode or triode connected amp. I normally only do Guitar amps, and have done a ton of them so complexity is not too much of an issue.
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Old 13th September 2006, 04:05 PM   #2
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I think the voltage on your B+ might be a bit low for a 50W PP KT88 Amplifier, but here goes:

http://www.livinginthepast.demon.co.uk/homepage.html

and also:

http://www.plitron.com/pages/Products/Audio/vtvkt88.htm

and even:

http://www.amplimo.nl/download/pubs/hqpp-50/hqpp50.pdf

the S/S Stereo versin of the PSU can be found here:
http://www.amplimo.nl/download/pubs/...0/hqpp50ps.pdf

and the tube Mono PSU will be found here:
http://www.amplimo.nl/download/pubs/hqpp-50/hqpp50p.pdf

Good luck, keep us informed
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Old 13th September 2006, 07:02 PM   #3
cerrem is offline cerrem  United States
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To get the most out of those KT88 valves..you might want to run the plates a bit higher....But if you need to make due with what you have and need a quick circuit....Than you can use what you have on a pair of JJ KT88 valves... Use something like a 1.7K to 2K plate load.. You will wind up with roughly 460V on the plates...with your transformer... You will make roughly 50W..
The big thing you need to keep under control for Hi-Fi amps as opposed to guitar amps, is to keep the screen supply well regulate...In most guitar amps, the chokes are too small and they usually saturate when the amp is fully cranked...this leaves the screen voltage flopping all over the place making enormous distortions mostly intermods... You can make a simple regulator that will do an OK job with a small power FET wired as a follower with a referenced voltage at the gate....

Chris
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Old 13th September 2006, 08:04 PM   #4
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Note that it doesn't have to be KT88s I don't have the Power tubes on hand, I'd actually prefer to stay with El34s.

The choke I've got is a Hammond 193D which is a pretty hefty choke for the most part. Not one of the little piddly Fender replacement chokes.

I'm sort of after a minimalist amp too.
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Old 13th September 2006, 09:11 PM   #5
cerrem is offline cerrem  United States
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If you want to make a small stereo power amp with a single power supply..Then i suggest you isolate each stereo side to some reasonable degree... The plate supply can tolerate more since they sort of act like a constant current source, ideally speaking of course...
The feed for the screens need good isolation from cross-coupling... This can also be used to feed the drivers for each stereo side... Figure the plate could run at 460V and the screens regulated at 400V.. Use whatever tubes you want...personally I would use KT88/6550 for the best clean headroom fro that voltage range...

Chris
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Old 14th September 2006, 10:28 AM   #6
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Then you might consider this project, which is very well explained and will suit your existing transformer as well:

http://www.lundahl.se/pdfs/claus_byr...us%20byrith%22


The circuit is based upon the well-proven Mullard 5-20 approach.


-Eric
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