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Old 17th January 2006, 06:35 PM   #1
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Default 6SL7 driving SE EL34 ?

Hello,

I have a El34 SE UL/Triode with 2x 6SN7 cascade (no bypass caps) amplifier, running at 370V.
To remove one interstage cap and alter the sound I tried one 6SN7 stage only but it had not enough gain without bypass cap. With the bypass cap, there was enough gain, but it sounded worse (more midrangey) than the two sections.

Would it be possible to mod for a one stage only 6SL7 without bypass cap ? - I search the internet but didn't find any schematic. Perhaps there is too much "Miller capacitance" or whatever ? Overall, would it have less distortion than the current setup ? What else low-distortion octal socket tube would drive the EL34 with one stage alone ?

Thanks,

Günther
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Old 17th January 2006, 06:49 PM   #2
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Miller shouldn't be a problem with UL. Schematics using 12AX7 drivers for EL34 are commonl enough (e.g. Mullard 5-20), so a 6SL7 should be able to do the job as well.
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Old 18th January 2006, 02:29 AM   #3
kevinkr is offline kevinkr  United States
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You can use the 6SL7 driver circuit from my 45 se amplifier which you will find on my website at www.kta-hifi.net.. Should work extremely well with the EL34 given the relatively modest voltage drive requirements.

Kevin
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Old 18th January 2006, 05:59 AM   #4
kopite is offline kopite  New Zealand
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Try this circuit: http://www.tubes.mynetcologne.de/roe...el34set_e.html
Phil.
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Old 18th January 2006, 06:00 PM   #5
jsn is offline jsn  United States
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If you want to keep the 6sl7, you need to get more gain out of it. You could try replacing the platr resistor with a current source or a large choke. That would give you a bit more gain. Or you could use some sort of stepup transformer, maybe on the input.

If you want another tube, the 6c45 is a popular input/driver tube for 2 stage amplifiers. It has lots of gain, and very low plate ressistance.

jsn
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Old 19th January 2006, 03:57 AM   #6
kevinkr is offline kevinkr  United States
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Umm, 6SL7 running in SRPP at about 2mA will generally provide more than 30dB of gain with a cathode bypass capacitor.

A single SRPP connected 6SL7 will provide about 100Vpp of drive before running out of steam on a 350V plate supply.

The EL34 can be driven to full output with something like 68 - 76Vpp which would equate to about 750mVrms at the grid of the 6SL7 - more than adequate for use even without a line stage.

Works fine with 45's which require >90Vpp for full output incidentally.

Kevin
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Old 19th January 2006, 09:53 PM   #7
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Default 6SL7

Hello,

Thank you for your replies. I might have a special siutation, as I am only listening to my CD player.

It puts out 1,6V RMS measured, which is about 4,5Vpp I think.
So I think I might get enough gain from one 6SL7 section even without cathode bypassing, as I have a gain of x13 currenlty and I tried just 3db more would be enough which would be about x26 I think. With mu=70 of 6SL7 this should be possible ? I thought of 6SL7 because it is also common, cheap, and fits octal.

I also might try 6SN7 or 6SL7 SRPP and I read very different opinions on SRPP (but it will very easy to rewire and try).

Sorry bringing up so basic things but I am more or less beginner, though I have much fun with the amp as it currently is.

Günther
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Old 20th January 2006, 04:57 PM   #8
kevinkr is offline kevinkr  United States
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IMO the 6SL7 SRPP sounds sweet...
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