Adjusting tape bias or recording pre emphasis by cathode temperature

At your risk.


For some reason again (see also Pleiades V6, V4 amplifier experiments) when disconnecting the heaters, the sound improves for 1 or 2 seconds and then getting progressively worse as cathode temperature goes further down.


Today's experiments are again in connecting the anode of EF183 operating at low voltage directly to a cassette tape recording head.


The sound becomes much brighter when cathodes are underheated.


Possible reasons:


Bias decreasing.


Internal electron tube plate resistance increasing.





Possibly both.


See also next post.