Any thoughts on using 6136 vs 6AU6 or 6186 vs 6AG5 tubes ? From the RCA datasheet: (http://www.google.com/url?sa=t&source=web&ct=res&cd=10&ved=0CDAQFjAJ&url=http%3A%2F%2Fwww.shinjo.info%2Ffrank%2Fsheets% 2F079%2F6%2F6136.pdf&ei=M2GQS8a-O430M5PojMYN&usg=AFQjCNHEMQYAxID0H87dwZ3dV2DVr3VqVg&sig2=JDWFJFMQtxtnlj1L8zT74Q)

"Featured in the design of the 6136 is a structure utilizing tube parts which are precisely made and accurately fitted to minimize variations in electrical characteristics due to mechanical movement and to minimize microphonic effects. In addition, the design incorporates a pure-tungsten heater having high mechanical strength to give long life under conditions of frequent "on-off" switching...The 6136 is manufactured under rigid control and undergoes rigorous tests to ensure its "premium" quality as follows...."

Sounds pretty good to me :yes:
I've found a few so far in my stash. Time to look for more...

Sounds good to me as well. Might be fun to compare a 6136 or '86 to their "lesser" cousins and see if the mica supports are thicker, or if the tube structure was noticeably changed to eliminate microphonics. I suppose the long-life heaters that could withstand lots of on/off switching was an outgrowth of the tubes that were developed for underwater communications cables. You definitely did not want one of those tubes to fail.

Looking through my stash, I don't have any of these, just a pair of 6146s. But, looking at the AES price list, they want twenty bucks each for them, so I'll take some measure in comfort there.