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Old 2nd January 2007, 04:01 AM   #1
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Default Punchy 813 Poweramp

I am looking to build a tube amp for bass in a biamp system. The 813 looks extreemly interesting. I would like between 70-140wpc. I would like strong bass that is punchy. I found these links:

http://www.pmillett.com/813_se_triode_amps.htm
http://members.aol.com/analogengineer/813mat.htm
http://homepages.ihug.co.nz/%7Erwillis/alex/
http://home.zonnet.nl/horneman/813.htm
http://www.izzy-wizzy.com/audio/powamp813.html

When can i add a second 813 in parallel to double the output (only pushpull?)? Assuming PSU can handel it.

What do you think?


thanks
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Old 2nd January 2007, 05:36 AM   #2
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any time you parallel tubes, you double the output and halve the plate resistance.
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Old 2nd January 2007, 05:40 AM   #3
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Plate resistance would change alot?
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Old 2nd January 2007, 07:43 PM   #4
ReidK is offline ReidK  United States
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"Halve" means "divide by two" (just like paralleling any two equal resistances.) In this context, yes that's a lot. If you double the number of output tubes, your output transformer would have to present half the load impedance of the single-tube design, in addition to handling twice the power . Many transformers allow the use of a different tap to acheive the correct impedance; the power handling will probably be the chief issue, especially for low frequencies.

Reid
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Old 3rd January 2007, 10:08 PM   #5
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I did not realy say that right, when i said "plate resistance would change alot?" i was talking about all the values of resistors and capacitors changeing. Can i parrellel on SE? Say i wanted to parallel this scematic: http://homepages.ihug.co.nz/%7Erwill..._schematic.jpg
I would use a 3K transformer?
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Old 3rd January 2007, 10:54 PM   #6
kevinkr is offline kevinkr  United States
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I don't think using a beam power tetrode in SE parallel or not is going to net you the bass you are looking for. The output impedance even in the UL connection is going to be at least a couple of ohms relative to an 8 ohm tap, frankly I suspect higher than that. You would need of feedback to get a reasonable damping factor (say 10) This tube requires a lot of voltage drive as well and plate voltages of around 1KV for good performance.

Why not try something with a couple of parallel 6C33? Low Rp with a properly chosen transformer would allow for low/no feedback operation in SE.
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Old 4th January 2007, 12:27 AM   #7
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Quote:
Originally posted by kevinkr
I don't think using a beam power tetrode in SE parallel or not is going to net you the bass you are looking for. The output impedance even in the UL connection is going to be at least a couple of ohms relative to an 8 ohm tap, frankly I suspect higher than that. You would need of feedback to get a reasonable damping factor (say 10) This tube requires a lot of voltage drive as well and plate voltages of around 1KV for good performance.

Why not try something with a couple of parallel 6C33? Low Rp with a properly chosen transformer would allow for low/no feedback operation in SE.
I was kind of aiming for a pushpull. What type do you think is better suited to clean powerfull and punchy bass? I am open to al options.
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Old 4th January 2007, 12:32 AM   #8
Sheldon is offline Sheldon  United States
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My initial thought too, that PP would be the choice for your application, but the references you cited are SE amps. Bet Kevin would have a good PP example in your power range.

Sheldon
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Old 4th January 2007, 04:20 AM   #9
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That would e great if i could get a pp scematic. The only one i could find on the net was 1KW. Thats to big..
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Old 4th January 2007, 01:28 PM   #10
kevinkr is offline kevinkr  United States
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How much power do you need? I've got a couple of possibilities, not available for general consumption, but I'd be willing to share.
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