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What tubes for a OTL tube amp?
What tubes for a OTL tube amp?
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Old Yesterday, 10:49 PM   #881
Demonkleaner is offline Demonkleaner  United States
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Luckily I just received 30 6N13S from Russia.

I'm guessing they were already in the US before the current situation occurred.

FWIW I use nos 12SN7GTA's for my input section.

A lot cheaper than the 6SN7's. Could never get the Russian equivalents to sound right.
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Old Today, 03:51 PM   #882
atmasphere is offline atmasphere  United States
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Quote:
Originally Posted by alexanderfa View Post
Power supply voltages:
For 6sn7 B1+- 310VDC, B2+- 300VDC
For 6as7 2x B+ 135VDC

I let the tubes burn for 24 Hours then I set the bias for 480 mA per rail. I didn't use any A-AB switch as per schematic
I set the trim for zero DC offset
I plug my signal generator, with 1kHz sine wave before clipping i measure 17V at 8ohm load about 36W

My first listening test wasn't so impressive because the sound is little harsh
What may couse this harsh sound?

The voltage for 6sn7 is ok or high?
6080 tubes?
Need some feedback?

My speakers are 8ohms, I also tried different speakers but same.
For 6sn7 I used the Russian equivalent

I would certainly give it time to break-in! Also the circuit can be quite revealing; a cheap coupling cap can easily cause issues- one example is the brown Zicon polypropylene. I don't know why; I've heard them do this consistently but not actually measured them to see why.



Your B+ seems a bit low. If your filament voltage is low as well, that can really shut down the transconductance in the output stage!


BTW 24 hours was probably insufficient time to precondition the 6080s; don't be surprised if you find that they arc over quite easily (and I would test them right now to see if they are alright; I've seen up to 60% of them fail within 5 minutes of service when not given enough preconditioning time)!
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Old Today, 04:34 PM   #883
Indigent Audio is online now Indigent Audio
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What kind of outcome do you think you would get if you took the gain stage of the m60, doubled it and made a 8 tube balanced 6sn7 preamp?
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Old Today, 05:38 PM   #884
atmasphere is offline atmasphere  United States
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For a preamp you don't need that much gain! A single 6SN7 provides enough gain if set up as a simple differential amplifier. You do need to buffer it to the outside world (otherwise the output impedance is rather high, and in the bass even higher due to the coupling cap).
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Old Today, 06:39 PM   #885
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You need that much gain and a 20v-20v swing to properly drive balanced F4 monoblocks and I like the gain stage layout. Do you think it would work well? I can imagine 8 6sn7 wont be cheap and might be overkill, sounds like a perfect audio project to me.
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Old Today, 07:14 PM   #886
atmasphere is offline atmasphere  United States
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That kind of swing is easy for a single 6SN7. With the input impedance of the F4 at 47K, it could do the job easily.
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