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6a6 tube as power output in headphone amp
6a6 tube as power output in headphone amp
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Old 4th July 2015, 08:23 AM   #1
Glass_painter is offline Glass_painter  Israel
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Default 6a6 tube as power output in headphone amp

Hello All,

why cant I use this tube as output stage for a tube headphone amp?

The manual indicates this tube as being a class B only OR class A paralleled.

What do you think?

Thanks

Glass_painter
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Old 4th July 2015, 09:26 AM   #2
Glass_painter is offline Glass_painter  Israel
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Hello All,

Just for clearification, I would like to run the tube push pull output stage for a headphones amp without an inter stage transformer or anything of this nature.

Thanks,

Glass_painter
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Old 4th July 2015, 02:04 PM   #3
Keit is offline Keit  Australia
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The 6A6 is a type of twin tube designed for class B zero bias operation. It requires a centre tapped transformer drive.

Since it is operated without bias, it draws grid current. So unless it is operated in push pull, and fed from a low impedance driver, preferably both, distortion will be quite bad.

If you try and operate it in a conventional single ended or push pull Class A circuit, with a grid leak resistor and a coupling capacitor from a tube driver, with zero bias the distortion will probably be intolerable, and becuse it will overload a normal tube driver, you'll get not much power output.

If you apply cathode bias in the normal way, it may operate in Class A without too much distortion, but power output will be very much curtailed. The drastically reduced power output might be adequate for driving headphones. Bear in mind the grid is constructed in such a way as the tube is close to cut off without any bias.


These zero bias Class B tubes are quite rare - they were mainly intended for use where high efficiency in converting HT power into audio was required, and distortion didn't matter so much, such as small PA amplifiers used by spruikers - "Roll up! Roll up! One small dime! See the bearded lady!" Or "Ladies! Bras and knickers 50% off this morning only! Come inside and get some while they last!"

Its power output in zero bias Class B push pull was 10 watts, twice that of a 6V6 for about half or less the DC input under speech conditions.

Last edited by Keit; 4th July 2015 at 02:17 PM.
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Old 4th July 2015, 05:48 PM   #4
Glass_painter is offline Glass_painter  Israel
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Thanks for the reply,

Some folks have used this tube as a single ended driver with both halves paralleled and reported good results. do you think this tube can be used as single ended output as well?

Thanks again.

Glass_painter
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Old 5th July 2015, 01:27 AM   #5
Keit is offline Keit  Australia
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It's hard to give a confident opinion, because the data books I have do not give data for SE driver (that is, as a driver for another tube used as the output tube) operation. Nor can I find grid curves for it.

It would seem quite possible. There may not be much gain.
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Old 7th July 2015, 08:26 PM   #6
Tom Bavis is offline Tom Bavis
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Use 6N7 for curves. http://www.mif.pg.gda.pl/homepages/f.../093/6/6N7.pdf

VERY little power in class A - it WAS designed for class B zero-bias, after all.
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