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Old 11th November 2005, 05:15 PM   #1
gianis is offline gianis  Greece
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Default 6550 tubes

I found from military stock 20 [and maybe more ] 6550 Tung sol USA NOS in original JAN boxes. I want to build something powerfull with these tubes.. Any idea ? schematics? Thanks...
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Old 11th November 2005, 05:55 PM   #2
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Drool!! Those are some NICE beam tetrodes and they are VALUBLE.

Somthing powerful, you say. Is 55 WPC or thereabouts powerful enough? A single PP pair in each channel will do that for you. You'll have to go PPP to get more power.

Selling some of the stock to raise cash that would go towards "iron" is an option open to you. You definitely want to use high quality O/P trafos.

If you can get O/P trafos of sufficient quality (not at all easy), "cloning" the H/K Citation 2 is something to consider. FWIW, I own a Cit. 2 and it's EXCELLENT.
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Old 11th November 2005, 05:57 PM   #3
SY is offline SY  United States
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These are terrific tubes, easily the best 6550s ever made. In pentode mode with a 2000-2500 ohm plate to plate load, you can get 100 watts out of a single pair.
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Old 12th November 2005, 09:02 AM   #4
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Default Some guys have all the luck!

@ gianis

Send me about 10 of them and I'll send you all the schematics you can handle, hehe!

Push-Pull pentode or Ultra-Linear with a nice driver stage and a brute power supply would be the way to go. Search the forum for 6550 and Push Pull, and see what you'll find! I'll search my computer and brain and post a few for you if someone doesn't beat me to it. Will this be for Hi-Fi audio or say a guitar amp?

Good luck!
Wayne
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Old 12th November 2005, 09:10 AM   #5
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@ gianis

Scroll down and look at this thread:
KT88 push pull

A KT88 is similar to a 6550. You may get some ideas from that thread.

Cheers
Wayne
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Old 13th November 2005, 09:23 PM   #6
gianis is offline gianis  Greece
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Smile 6550

Thanks for the responses..i`l try to do something maybe in triode mode.
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Old 7th March 2006, 03:05 PM   #7
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Did you ever build your 6550 amp?

I have one you may want to build based on the Triode Electronics MK3 PC board.

Attached find a photo of the front panel of one Monoblock.
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Old 7th March 2006, 08:05 PM   #8
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Quote:
Originally posted by SY
you can get 100 watts out of a single pair.
Follow schematics suitable for KT88 and one can't go wrong. In fact I regulary swap both tubes so long bias range can accomodate. If you really have the original A version 6550 then 100W per pair is pushing their lives. It would be a pity to slam a near-collectors item.
Watchout screen grid ratings in UL mode......my spec for 6550A g2 shows max 470V and with so many clones about I don't push g2 above 400V in UL.
To be honest, I've got a set of JAn 6550A (green logo) and I get more out of these than MO KT88's.
Parallel pairs in triode mode would sound very nice to my ears and the low Z is attractive. Lower B+ means longer life.

A drawback.... my 6550 spec shows a low grid leak resistance (max 50K) in fixed bias. This places the onus on a low distortion slam driver stage to provide the required swing.

richj
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Old 9th March 2006, 12:43 PM   #9
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I keep seeing references to this article on the internet:
Herbert I. Keroes, "Adapting the 'Ultra-Linear' Williamson to 6550 Operation," Radio & TV News, November 1955, pp.52-54, cont. p.136.
Does anyone here have a copy?
There's another article in Radio & TV News, November 1955, I think it starts at page 60, about a 6550 amplifier.


http://www.google.com/search?hl=en&l...55&btnG=Search

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Old 10th March 2006, 06:28 PM   #10
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I've got both articles in case anyone is interested.
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