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OTL Asylum OTL, Output Transformerless Amplifier User Group. |
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In Reply to: The sound of using less 6AS7s posted by jim on February 24, 2002 at 18:02:31:
Jim,Probably do to both, unless your loss of "muscle" is also apparent at low volume levels. Then it is probably do to just the rise in output impedance.
Another thing to keep in mind is that half the output tubes will give you considerably less than half the power when driving the same impedance load. This is because the "maximum power band" of the amplifier shifts from 14-16 ohms up to 28-32 ohms when removing half the output tubes. One would need to remove half the output tubes AND double the speaker impedance for the power loss to remain linear (drop only in half as well). For example I believe that 4ea 6AS7 are only capable of driving 22 watts into 8 ohms, a far cry from the +60 watts 8ea 6AS7 tubes will drive into 8 ohms.
I seems to me you should set the bias so that 275mA is displayed on the meter with the speakers connected when running 4ea 6AS7 output tubes.
FYI: 4ea 6AS7 output tube should do 40 watts into 28-32 ohms and sound quite powerful. In the Summer months I run only 2ea 6336B tubes (equal to 4ea 6AS7) and use the ZEROs autoformers to make my speakers look like about 20 ohms. I get great sound this way. Now that it is Winter, I am running 6ea 6336B tubes (equal to 12ea 6AS7) driving about a 10 ohm speaker load which simply gives me the ability to play the music louder than necessary even with my low efficiency speakers. The extra power is fun to have once in a while.Hope this helps!
Paul Speltz
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- Re: The sound of using less 6AS7s - Paul Speltz 07:58:24 02/26/02 (0)
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