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.
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:
Use 6N7 for curves. http://www.mif.pg.gda.pl/homepages/frank/sheets/093/6/6N7.pdf
VERY little power in class A - it WAS designed for class B zero-bias, after all.
VERY little power in class A - it WAS designed for class B zero-bias, after all.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.