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Old 14th February 2011, 08:24 AM   #471
G.Cesar is offline G.Cesar  France
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Very clever, Dave.
Could you please confirm that the 6EM7 are biased at 52 V ? This seems very high .
Cheers,
Ari
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Old 14th February 2011, 10:30 PM   #472
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Congratulation nuvistordave, good looking amp. (THX; and the sound stage on this thing is really to die for. lots of effort and cost over $600 but well worth it.)
If you use another tube amps please share us your experience, and sound differences between 6C33C and the others amp. (That amp behind the 6S33S unit is a KT120 P-P driving Mesa Strategy 400 OPT's in UL configuration)
Can you tell us the name of the speakers that you use? 2 sets; the good ones are home brew 3-way rigs; bought the drivers and crossover components from Madisound. Also have a pair of Klipsch 8" bookshelf units; might have warmed over the crossovers.

The 52V bias on the low mu sections is what I measured and should be about right. The mu is only 5 on those units, so they are going to take a lot of bias with over 300V on the plates.

Oh and BTW on those chassis, which are still available from EBAY seller; the caps are hanging in large holes which the brackets straddle. So they stay cool calm and collected. This was not the first 6S33S amp that I built; the first one I had for 5 years.

Last edited by nuvistordave; 14th February 2011 at 10:33 PM.
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Old 21st January 2013, 12:31 PM   #473
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Location: Hengelo
Default Ari Polisois DCMB amplifier

Hi Midlife,

I'm very interested in the DCMB amplifier and I'm considering to build one. I never heard an Ari Polisois amp and I'm curious what the quality of sound is compared to my Audiomat 6550 Push Pull power-amplifier.
Have you ever compared your amp to a fine commercial amp?
And can you describe the benefits of the DCMB amp in sonic terms?

Looking forward to your answer.
kind regards,
Cambridgedac3, The Netherlands.
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Old 3rd June 2013, 04:47 PM   #474
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Hey!

I want to be a SE-30-50W 6c33c b parallel.
There are quite a schematic anyone? (power supply is included)
Thank you very much!
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Old 3rd June 2013, 05:23 PM   #475
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I think it's not the tube that has the drift but the main voltage. I used for 10 years a se 6c33 with fixed bias at 200v/250ma without any problems. Maybe every month or 3 month checking the bias was enough.

Do not use a stabilised fixed bias or use an all stabilised power suply.

Quote:
Originally Posted by korneluk View Post
Consider going single ended, and most important of all, choose cathode bias. The 6C33 has a tendency to drift when operated in fixed bias and run away with cherry-red plates.

Another recommendation is the operating point: 200V @ 200mA is conservative, but sounds good and provides trouble free operation.

Here some reference cathode bias designs:

BorbelyAudio.com: The Leading Borbely Audio Site on the Net

http://www.metaleater.narod.ru/6c33c.gif

Enjoy,

-- jose k.

Last edited by esltransformer; 3rd June 2013 at 05:26 PM.
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Old 4th June 2013, 06:06 AM   #476
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Had to look up that 'DCMB' That is basically what my amp is; it uses 2 stacked supplies and the drive stage is direct coupled to the output stage. BUT since 'Nuvistor Dave' dreamed the circuit up without consulting any references it has a few twists on it.
1) the output stage is being run as a Cathode Follower
2) BOTH supplies are ground referenced; one positive to ground and the other negative to ground.
3) The amp uses fixed bias and it is very stable because it is a Cathode Follower output.
4) NO 40W power resistors and...
5) no regulators; just tubes and iron, which is as thing should be.
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