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Old 2nd January 2008, 05:15 PM   #1
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Default Compactron characteristic curves?

Hi,

2 questions:

- Where can I find a characteristic curve for a 6MV8? Google has not been helpful here.
- Are there other triode/pentode compactrons that are rated higher than 6LU8 (14 watts)?
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Old 2nd January 2008, 06:42 PM   #2
mwiebe is offline mwiebe  United States
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I've wished for that sort of tube data base where you could search across all triode pentodes for different parameters, but I haven't found anything like that.
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Old 2nd January 2008, 06:51 PM   #3
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6MY8 seems to be an uprated 6LU8 (16 watts vs. 14). Never seen one though...
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Old 2nd January 2008, 07:07 PM   #4
Jeb-D. is offline Jeb-D.  United States
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I was looking into doing a Compactron amplifier.

The 6LU8 was the highest power one I could find. However, it has a max current of 75mA. Check out 75mA on the curves, it's in a very non-linear region. So I came to the conclusion it was only suitable for a push-pull amp. Don't know how the curves look for triode strapped though, maybe better.

If you want to go sigle-ended I found the dual triode 6GF7A is the only one that may work well. It's rated at 11W and i'm not sure if it's actually a compactron as it only has 9 pins, but it has the compactron look. It's equivalent to one of those popular octal's that are used for single tube, single ended amps. The number escapes me 6em7, I think
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Old 2nd January 2008, 07:07 PM   #5
mwiebe is offline mwiebe  United States
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My above post got posted before I had added that the 6MY8 is rated at 16W, as mentioned above.

14W pentode section tubes are 6LR8, 6LU8.
12W 6MF8, 6T9
and a variety of 10W tubes, 6AG9, 6AH9, 6AK9, 6AL9, 6HC8 (11w).

I've used 6LR8s and over driven them to about 18Ws for a few days so I can't say anthing about tube life.
Matt
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Old 2nd January 2008, 09:25 PM   #6
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Thanks for your help, guys.
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Old 3rd January 2008, 11:24 AM   #7
engels is offline engels  Israel
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Default compactrons

I wonder why do you need triode-pentodes? There are many more higher rated compactrons which are output tubes only and you have those triple triodes as well to compliment them.

As I'm planning to do something monstrous with a quad of 21GY5 (18W pentodes) I'm interested in your developments.
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Old 3rd January 2008, 02:35 PM   #8
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Default Re: compactrons

Quote:
Originally posted by engels
I wonder why do you need triode-pentodes? There are many more higher rated compactrons which are output tubes only and you have those triple triodes as well to compliment them.

As I'm planning to do something monstrous with a quad of 21GY5 (18W pentodes) I'm interested in your developments.
Plan is to build something like a Crowhurst twin-coupled, as revisited by John Stewart. The purpose of this query was to investigate any higher powered tubes that might work -- Stewart successfully used 6LU8's. A prior article by the same author mentions a 6MV8 @ 16W, but I can't find any substantial data, like a real curve. Stewart liked the 6LU8 for a couple of reasons - inexpensive, performed well, and he uses the triode to avoid a "blocking" condition as described by Crowhurst.

One change I'm pondering on Stewart's effort is to substitute the Hammond 125E for a 1620 -- wider bandwidth for $20 more. But I need to analyze the operating point he selected, as I suspect that the impedance of this transformer won't work.

There, it's all out in the open now.
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Old 3rd January 2008, 05:47 PM   #9
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I'm thinking of building something similar myself - the fact that I have about 50 NIB 6LU8s might have something to do with it... I am thinking of using Antek power toroids (at $12 each) as outputs. They should go down to 30 Hz at 15W or better in this circuit.

You want transformers with about 1/4 the "usual" impedance - i.e 2 - 2.5K CT for EL84s, 1 - 1.6K CT for 6L6s. The "universal" transformers are at their best in this circuit, as it's a low impedance and you use all of the secondary.
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Old 3rd January 2008, 07:54 PM   #10
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I used 24JZ8 and 8AL9 tubes, they are decent to drive high power FET+BJT output stages.
''
8AL9 is nice to power filaments: 6.3V rectified by Shottkies is exactly what it needs for a quiet stable operations.
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