ECC91 / 6J6 in Audio-service

[tri-comp]

I wanted to add this info to the recent thread about the ECC91 / 6J6 double-triode with common cathode and it's performance in audio.
The thread has been closed so here's a new one with the info.
It seems some problems may exist with microphonics and I wont deny that.
I haven't done audio experiments with this valve yet, but I have it planned.
Mainly because I have a handfull of them (GE, Sylvania, Mullard, Miniwatt, Haltron) and it would be nice to actually put some to good use.
It seems that people weren't too concerned about microphonics in the past, or perhaps the 6J6 of the time was built to higher standards.
This early 1953 article shows how to use the 6J6 in audio frontends where microphonics should be avoided at all costs.
They got away with it, perhaps I will ?

[Radio Wrangler]

Note the early remark that these are for "high output magnetic, and crystal types". Running with highish levels of signals and low gain make microphonics and noise less important. Such transducers are now hard to find in working order. Crystal microphones and cartridges have absorbed water and dissolved. High output magnetic pickups were for 78s many have been killed by green-spot corrosion ans almost all have hardened rubbers, though some people on here have repaired the latter.

Probably all the 6J6 to be found nowadays date from that era. There were so many on the surplus market.

David