Relpacing 6EU7s with 12AX7s - Good idea?

[Turbo7MN]

Alright, my Bogen PA head that I'm going to be getting pretty soon to use as a guitar amp uses 6EU7 preamp tubes. I know there's really nothing wrong with them, but there are very few brands/varieties available to play with. From what I've read, these are very similar to the 12AX7. I was just curious if a 12AX7 is a straight drop-in into a 6EU7 socket. I figured I should ask before I try it, I don't want to be celebrating the 4th of july in the garage . Thanks.

-Darren

 

[anatech]

Hi Darren,
The 6EU7 has a completely different pinout than the 12AX7. I'd keep them in there. They sound great. This is kind of a secret great sounding tube. They were designed originally as very low noise, low microphonic, low hum tube. The curves look close to a 12AX7 on a quick glance.

You can buy new 6EU7's from New Sensor for one. I'm sure there are other sources.

-Chris

 

[Turbo7MN]

I know where to buy them, I was just pointing out that there are only one or two different varieties of new ones compared to literally 20 different varieties of 12AX7. Of course, I see NOS GE 6EU7s go pretty cheap on ebay all the time.

 

[DigitalJunkie]

I see NOS GE 6EU7s go pretty cheap on ebay all the time.

Really? They were hard to find a couple years ago,when I was looking for some for a couple SE EL84 amps I have.They were kinda spendy too. (Especialy for used/tested tubes -NOS was outta my price range,at the time!) I should have rewired the amp sockets for 12AX7's,but I was stubborn,and wanted to "keep it original"

As far as I know,the 6EU7 and 12AX7 are basically the same/very similar tube,but with a different pinout.

 

[anatech]

Hi Darren,
You may find the GE's noisy (like some 12AX7's I ran across). But if they're cheap give them a shot.

These were supposed to be a really low noise type tube. That's why you see them in the mic inputs instead of 12AX7's. The specs look the same as 12AX7's otherwise (by 12AX7, I am referring to 12AX7A/7025).

DigitalJunkie,

They were kinda spendy too. (Especialy for used/tested tubes -NOS was outta my price range,at the time!)

Yes, that's what I've seen over the years. These were much more pricey than others similar tubes. Like 7199's were / are.

-Chris

 

[Eli Duttman]

AFAIK, the 6EU7 is supposed to be even more resistant to hum than the 7025 is. I've seen Heath schematics with AC on the phono stage heaters. Frankly, I have my DOUBTS.

JMO, rewire the sockets for 'X7s and use Sovtek 12AXLPSes. The 'LPS has a hum bucking spiral heater, is good sounding, and it's quiet.

 

[amperex]

12AX7 are an ok replacement for 6EU7 with wiring changes at the socket. 12AX7s are much more common as well.

 

[DigitalJunkie]

I like the Sovtek 12AX7LPS tubes.. they're humless in my hifi amp,they sound good,and they're a good value for the price.

 

[anatech]

The new 12AX7 variants are good. I find the 12AX7EH are humless also and seem to sound better. Depends on the circuit and both types are not expensive. The sad thing is that the 6EU7's were there years ago.

-Chris

 

[cerrem]

The 6EU7 was basically a 12AX7 tube BUT with different pin-out...
The pin-out was changed in order to re-route the heater leads...Some clever engineer figured that re-routing the heater configuration of a 12AX7 improved it by reducing hum, thus the 6EU7 was born...

Chris