DeserTBoB wrote:

By '61, there was a newer RCA industrial numbered tube (I forget the
number) that was in favor for tape head preamps. *It had more voltage
gain than the 12AX7 used in cascode and was thus effectively quieter


that would be a 7025. that, & the 12AX7 are in big demand & command obsene
prices, especially N.O.S tubes. i have seen them bring as much as $75 on
Ebay & other sites. they were also used in guitar amp front ends as well.

Some
cheaper stereo models also used a 6DJ8 twin triode for tape head
preamps, with space saving and cost economy and little in the way of
performance improvement.

the 6DJ8 was used mainly in MATV distribution amplifiers & general purpose
RF amplifiers . they were not used in the vintage audio equipment (at least
not in the audio signal path). if (& when) they were used, it would be in
the front end of the FM receiver.

however
the current production hifi tube amps use them as well as those CD players
with a tube audio circuit. that because they are much cheaper than the good
NOS 12AX7s