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OTL Asylum OTL, Output Transformerless Amplifier User Group. |
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In Reply to: Re: Stay tuned. posted by John Harper on August 1, 2002 at 15:28:16:
John: I remember your telling us that you increased the plate voltage for the B+ supply to 600V. That is not an easy option for me with the humongous MA2 transformers on my chassis'. However, the MA2s do develop +/-400V, so that is some additional headroom vs the M60. I did not know, however, that you are now using the 6SN7 with as much as 7mA current. (I presume you mean 7mA per phase or a total of 14mA through the DDC.) That sounds like a great idea, if one has 600V to play with. Ideally, I would like to be running 10-12mA per phase for the 6900, but the load resistor would have to be much reduced AND a high impedance CCS would be difficult to construct (using a triode) within a -400V envelope. (One could resort to a pentode or solid-state CCS, but at present I am too much of a purist for that.) Right now, I'm running an ECC99 in cascode for my CCS, developing about 10Megohms impedance. That would not work safely if I wanted to draw much more current. Can you report on the sonic differences using the 6SN7 with high current compared to the Atma standard? Anyway, that's what makes this so much fun: there are always new ideas to try in obtaining essentially the same objective. BTW, do you know a formula that relates current to gain in this circuit. If it's a third root relationship, then I was incorrect to have said it was "linear". I did not make careful measurements, but it seemed to me grossly that when current doubled, voltage gain doubled as well.
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Follow Ups
- Re: Stay tuned. - Lew 07:01:29 08/02/02 (0)
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