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Old 15th July 2010, 12:38 PM   #1
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Default Triode in Class B or Beam Pentode in Class AB2

Greetings everyone,
Given the tubes that I can use have roughly the same power output and plate voltage requirements, which would be wiser to build, P-P Triode (809) in Class B or P-P Pentode (6146B) in Class AB2? At this point I need to order the output xfmrs and my intention was to go with Edcor.

Thanks,
Ray
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Old 15th July 2010, 01:04 PM   #2
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Pentodes and triodes usually sound somewhat different... that might make a difference to you?

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Old 15th July 2010, 03:56 PM   #3
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how much power are you looking for?
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Old 15th July 2010, 03:58 PM   #4
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Planning 100 watts. Thought of sweep tubes. What are your thoughts? I have many different sweep tubes.
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Old 15th July 2010, 04:38 PM   #5
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I have a few 809's. They are nice looking tubes, and I have a suspicion that they would work well in class A2 or AB2, but not at 100 watts. I have not had the time to play with them, but I did stuff one into a Tubelab SE a few years ago and got 5 or 6 watts. I also think that it will be hard to get a 100 watt class B amp sounding good at the 1 watt level, which is probably the average power level it will see unless you have bricks for speakers. SO...

That leaves sweep tubes or the previously mentioned 6146's. I think that 100 watts from a pair of 6146's is squeezeing them a bit too hard, but again I haven't tried it yet. I have been working on several big power experiments, and there are some 6146's sitting on my workbench, but I have been at work for 12 hour days, 7 days a week lately, so....no tube time.

I have found a few minutes here and there to play. I bought a bunch of NOS 35LR6's a few months ago, and I finally got around to stuffing 4 into the red board and setting the power supply on KILL. The result, 250 WPC. Yes thats 500 watts from Petes big red board, on lab type power supplies. I also found some real cheap power transformers on Ebay, so the obvious experiment is to connect two of them to the red board, stand behind something substantial and hit the switch. It will happen when there is time.

Seriously, sweep tubes make 100 watts relatively easy. Find out which flavors you have several of. You need 4 good ones. With used tubes I have needed as many as 10 to find 2 pairs that are even close enough to make work. I got about 50 NOS 35LR6's and it took 5 of them to find 4 that played nice with each other.

If you have tubes that are compatible with Petes board, that is the easiest way to get there. Some modification of the power supply circuitry is needed. I have been using lab type supplies, but now that I have cheap transformers, I will figure that out too. I still plan to design my own big power amp, but it won't happen soon.

10 pounds of power for $15
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Old 15th July 2010, 09:07 PM   #6
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Quote:
Originally Posted by rsumperl View Post
Greetings everyone,
Given the tubes that I can use have roughly the same power output and plate voltage requirements, which would be wiser to build, P-P Triode (809) in Class B or P-P Pentode (6146B) in Class AB2?
PP 809s are rated at 100W+ for Class B operation. However, that's for AM modulator duty where fidelity is neither necessary nor legal. The cross over distortion that's inherent in Class B sounds really nasty. Also, these AM modulators frequently included an LPF between the modulator output and the AM xmtr for that very reason: to reject those nasty harmonics and to keep the AM signal within legal limits. It won't work at all well for an audio amp if you're looking for sonic performance and not just lotsawatts.

If you go with the 809s, you'd be better off accepting less power out, and improve the sonic performance.

As for 6146s, you have the same problem: intended for modulator useage, lotsawatts, and not fidelity. That means operating deep into Class AB territory, and, yuppers, more X-over distortion. Probably best to try new loadlines that get 'em more towards Class A operation, and accept the reduced power out in exchange for better sonics.
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Old 15th July 2010, 09:23 PM   #7
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Quote:
Originally Posted by bear View Post
Pentodes and triodes usually sound somewhat different... that might make a difference to you?
Sure. Pentodes with local feedback (last Forum fashion, code name Schade) may sound cleaner than triodes.
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Old 15th July 2010, 11:14 PM   #8
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Sure. Pentodes with local feedback (last Forum fashion, code name Schade) may sound cleaner than triodes.
The red board uses Schade feedback and GNFB is optional. I have Schade enabled, but no GNFB. It does sound very nice.
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Old 15th July 2010, 11:30 PM   #9
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Quote:
Originally Posted by tubelab.com View Post
The red board uses Schade feedback and GNFB is optional. I have Schade enabled, but no GNFB. It does sound very nice.
I have both in Pyramid-V (6N6P LTP driver), Pyramid-VII (6P15P LTP driver), Pyramid-8 (6J51P LTP driver), with GU50 outputs, all sound fantasiche, like SE on pianissimo and SS on fortissimo.
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Old 16th July 2010, 12:28 AM   #10
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So what do you think of the 6DQ5's? I got lots of JAN 6DQ5's. I also have
21LG6A's and 6MJ6 in quantity.
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