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Old 30th May 2009, 11:48 PM   #11
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Default in keeping with the "educational opportunity"

approach, this site is also well worth having a look at. Like Aitken but without so much esoterics. And I'm with Sorenj - could be fun design exercise for the next 24 hours.
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Old 31st May 2009, 12:34 AM   #12
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As a way to not add many additional parts, not add a negative supply, and drive the outputs a little better, how about a grounded cathode to cathodyne splitter?
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Old 31st May 2009, 01:11 AM   #13
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Gotta love the old chalkboard
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Old 31st May 2009, 01:12 AM   #14
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Default ...or even...

ditch the phase splitting completely from the driver stage, and leave it to the outputs as per .Simple EL84 from Yeo... This would allow paralleling of the sl7 to provide better drive
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Old 31st May 2009, 03:26 AM   #15
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Here's my current PS : http://img14.imageshack.us/img14/981...rsupplyfor.png

It is currently powering this :

http://img198.imageshack.us/img198/4...c169aarevi.png

If you look in the lower left hand corner of the PS link you can see the Sams "hard numbers" .
Primary is 117VAC @.62A ,

Secondary is 612 VCT @ .082A ,

5V @ 2A

and 6.3V @ 1.2A

I am running these for rectifiers : http://store.triodestore.com/ssr.html

I am willing to try the simple EL84 circuit. I've looked at it a few times.

I'm not stuck on using the 6SL7GT's, but I DO have a matched pair staring at me.




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Old 31st May 2009, 05:20 AM   #16
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Quote:
Originally posted by zigzagflux
Gotta love the old chalkboard

For all the progress of the digital age, there is nothing like a chalkboard for quickly sketching out ideas -- it was the essential tool for my dissertation.
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Old 31st May 2009, 06:31 AM   #17
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Nihilist,

Some obervations on your amp design:

1.You cannot bypass the cathodes of the 6SL7, because you're using it as a cathode-coupled (A.K.A. LTP A.K.A. Schmitt) phase splitter. If you bypass the cathodes, where's the signal for the lower triode going to come from?

2, It shouldn't make any difference whether or not you bypass the cathodes of the triode-connected 6V6s if they're well matched, but you can try it to see if it sounds better. It won't affect the gain because the cathodes are strapped together,

3. A plate load of 510k for each 6SL7 is about 4 times what it should be. In any case, it is shunted (at signal frequencies) by a 1M OP stage grid resistor.

4. As said, a 6SL7 should not be used to drive 6V6 in triode mode. It's able to drive the 6V6 in pentode mode, but not triode.

5. The 6SL7 LTP as designed will work very poorly, because there is too low a voltage between cathodes and ground. The simplest way to overcome this problem would be to elevate the cathodes by either adding a bias resistor (as in Aiken's example) or using a potential divider from B+ to the grid of the lower 6SL7 to ground. Either way, you'll need to use an extra cap on the IP grid (of the upper 6SL7). With the cathodes elevated, you will need to use a higher value of common cathode resistor or, far better, a CCS using a BJT cascode, ring of 2, or other SS device(s), for proper balance.
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Old 31st May 2009, 06:54 AM   #18
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I'm amazed that the power supply is putting out 405V if the transformer is only rated for 88mA. Are these monoblocks then?

I drew up a schem but it's a little late, I can post it tomorrow.

Are you OK with buying a couple chokes to help drop your B+ a little, blacken the sonic background, and stiffen your supply?

I designed for one of these per monoblock. Just bolt 'em in..

http://angela.com/hammondchoke159p.aspx
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Old 31st May 2009, 07:56 AM   #19
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Default open to comment...

ok, I hope the numbers work... designed to reduce part count to the minimum, stick with the specified major parts without expensive extras, and acheive the output desired.

Issues - will require an elevated or floating heater supply. Easy technically I know, but simpicity rules...

Requires a fixed bias supply - same caveat as above.

Grid stoppers may be a good idea on the output tubes. Dunno. A cheap insurance policy anyway.

Power supply coming...

EDIT!!!! - wahahahahahahahaha... supply voltage ot the voltage amp and splitter should read 250V not 300V. Mea Culpa
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Old 31st May 2009, 08:20 AM   #20
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Wouldn't it be easier to leave out C1, R4, and R5 (see my post above)?
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