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Old 21st January 2009, 06:39 AM   #1
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Default 6550 Triode B+

Hello,

This is my fisrt time posting here, but I am currently working on a large triode 6550 amplifier and am a bit confused about B+ voltages. I see many triode 6550 amplifier schematics with B+ around 500v, but the Svetlana (Supposedly one of the better 6550s today) spec sheet says 450v maximum B+ in triode. I'm going for 100w in triode with 6 X 6550 in PPP triode.

I already have most of the parts, and am using an 800vct tranny, so a simple adjustment made previous to the choke can change the B+, but I do not want to damage the tubes by running them too hot. What is the safest B+ to run with this configuration?

Up until now, I have been planning to use 450v B+ which shoudl give me approximately 92w or so into 8 ohms. I'm using 2K primary opts with 330 ohms DCR if anyone needs this information.

Thank you,

Blair
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Old 21st January 2009, 03:22 PM   #2
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Location: Alps:Tube amp designs over 150W, SMPS guru.
Default Re: 6550 Triode B+

Quote:
Originally posted by deicide67
Hello,

I do not want to damage the tubes by running them too hot. What is the safest B+ to run with this configuration?

Up until now, I have been planning to use 450v B+ which shoudl give me approximately 92w or so into 8 ohms. I'm using 2K primary opts with 330 ohms DCR if anyone needs this information.

Thank you,

Blair
Heat shouldn't be an issue so long you manage the chassis mechanics with enough ventilation both top and under as in pic. 2K A-A primary is fine.
I wouldn't go above 450V+; the screen grids are the easiest to destroy. Not all 6550 versions are bomb proof and I'm running new edit TungSols in my amp at 85mA at 450V+ (i.e 38W) without hiccups now 5000hrs. Power for power you will get the same power as KT88's but 6550's are cheaper. BUT:-
As you are using parallel pairs; if you are using fixed bias take note of the maximum value of grid leak resistor for 6550s. A low value can up the thd by a sweating driver stage. A low Z driver stage design is crutial to the sound quality- and with outp stage in triode, a considerable AC driving voltage is required.

richy
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Old 21st January 2009, 03:37 PM   #3
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Thanks Richy,

This is the power stage schematic I'm using. I did swap the screen to plate resistor with a 220ohm. It uses a modified DIYTUBE front end I will be PTP wiring and a 6CG7 for the LTPI stage. When I said "hot" I was referring to the internals breaking down. I have them spaced well with plenty of air curculation around them I think.

It is not showing up in the preview, so I hope it comes up.



Click the image to open in full size.

http://img.villagephotos.com/p/2005-..._schematic.gif


Thank you,

Blair
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Old 21st January 2009, 03:43 PM   #4
Brit01 is offline Brit01  United Kingdom
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http://img.villagephotos.com/p/2005-..._schematic.gif

your link wasn't working. look out for the http:
I've done the same.
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Old 21st January 2009, 03:45 PM   #5
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Thank you!! I was about to introduce my foot to the computer

Thanks,

Blair
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