6EU7 tube in a guitar amp?

[AmberB]

I'm curious, does anyone use the 6EU7 tube in the preamp of their amp builds?
I have several of them now that I took out of Bogan amps as part of the conversion to a guitar amp.  The person I converted them for wanted the more common 12AX7 in the preamp.

[Stuff4bikes]

Mid 60's epiphones I believe....

[Latole]

Mid 60's epiphones I believe....

Right
GA-50 RVT, EA-50T

[thetragichero]

i think those of us who have converted old amps for guitar use reached that same conclusion: why limit the end user to an oddball pinout when you can use the exponentially more common 12ax7? (i'm also pretty certain i'd end up with the socket wired half 6eu7, half 12ax7 just out of habit anyway)

[bmccowan]

Many of the Gibson and Epiphone amps from the 60s used them. I have kept them in a few that I have repaired/rebuilt. I bought some spares when they were cheap. Given the disappearing tube market, I would not get rid of them. preamp tubes tend to last a long time and they sound just like their 12V counterparts. If I was selling or giving away a 6EU7 amp, I would include a spare or two.

[shooter]

I changed out a few in Gibson's for AU's or AX.  They were all in the "V1" position, they were all microphonic.  The spares I had were the same.  If you have a bunch, and an amp, wire up the 1st tube position for the EU, then "roll 'em" through and evaluate. 
The bad one's work good as targets dialing in a .22 for squirrel huntin 

[AmberB]

I have seen the 6EU7 recommended for a microphone preamp input tube, so there is that...

[66Strat]

I changed out a few in Gibson's for AU's or AX.  They were all in the "V1" position, they were all microphonic.  The spares I had were the same.  If you have a bunch, and an amp, wire up the 1st tube position for the EU, then "roll 'em" through and evaluate. 
The bad one's work good as targets dialing in a .22 for squirrel huntin 

Are all 6EU7s inherently microphonic or isolated to specific tube manufacturers?

[shooter]

never evaluated that far.  I simply rolled 'em through my breadboard setup and scoped.  Most of the ones I had were from a 5-gallon bucket I bought at a flea market.  guessing 50's/60's for most.  I did buy a couple for a customer that didn't want his Gibson altered.  they seemed to work ok

[Sonny ReVerb]

I wonder why some amps (e.g. Magnatone) use both 6EU7's and 12AX7's? I did see some interesting comments on TDPRI:

The 6EU7 competed directly with the original 7025 tube, which was a low-hum, low-noise variant of the 12AX7...but the 7025 could be used in existing devices, and the 12AX7/7025 had far greater support in the commercial sector because it was the military standard.
 
 I have heard that the 6EU7 was invented so RCA could patent it and charge licensing fees to other manufacturers. It seems unlikely RCA would get a patent on a new twin triode by then, but I don't know. I'm sure it was an attempt at RCA to increase market base...once you bought a new device with 6EU7, then you were caught buying new 6EU7 tubes and maybe new 6EU7 equipment since you had stock on hand.

[HotBluePlates]

... I did see some interesting comments on TDPRI:

... I have heard that the 6EU7 was invented so RCA could patent it and charge licensing fees to other manufacturers. ...once you bought a new device with 6EU7, then you were [stuck] buying new 6EU7 tubes ...

I don't see it as a "patent" thing.

I don't use 6EU7 because it's a different basing & heater-wiring arrangement.  Once you go to 6EU7, you're stuck not-using 12AX7/7025, etc.

Several manufacturers made "special audio types" late in the tube era, that seemed intended to capture an OEM market for replacement tubes once equipment manufacturers incorporated the tube in a product.