Chassis tubes on M4

[Resonant Alien]

Pardon my stupidity, but what are the 12AX7 and 12AT7 tubes in the M4 chassis for? Phase inverter and buffer?

Also, any recommendations for replacement tubes for these locations?

Thanks
RA

 

[guitarslinger]

Phase inverters are only present in power amps and heads with power sections.

preamps don't need them.

One of the chassis tubes is the initial gain stage after the guitar, and it's shared by all channels.

The other chassis tube is PROBABLY some kind of buffer to achieve a desired signal level.

I'm not looking at a schematic though.

I've tried a few tubes in there.

On the board, the 12At7 is supposed to be V1, and I'm loving an early 90's 12AX7 Chinese tube in there, and a new Chinese tube in the other "12AX7" position.

I tried a NOS RCA 12AT7, and it just didn't do it for me. I've also tried JJ ECC83s in both positions, and those kind of muddied it all up.

However, I'm using some JJ's in my modules, along with a few CHinese tubes.

 

[RockManiac]

The upper right tube, labelled "12AX7", is the input tube. For the tube labelled "12AT7" you can also use a 12AX7 tube.
I use a JAN GE 5751 in input tube position and a JJ 803 in the other position.

 

[guitarslinger]

The upper right tube, labelled "12AX7", is the input tube. For the tube labelled "12AT7" you can also use a 12AX7 tube.
I use a JAN GE 5751 in input tube position and a JJ 803 in the other position.

Hmm, I need to check mine again.

I think Somebody at the amp lounge put the 12AT7 sticker on the V1 spot.

 

[Resonant Alien]

The upper right tube, labelled "12AX7", is the input tube. For the tube labelled "12AT7" you can also use a 12AX7 tube.
I use a JAN GE 5751 in input tube position and a JJ 803 in the other position.

Hmm, I need to check mine again.

I think Somebody at the amp lounge put the 12AT7 sticker on the V1 spot.

Hmmm. me too. When looking at the back of the M4, the tube in the upper right corner is labeled 12AT7 and the lower left one is labeled 12AX7. Both tubes are actually Sovtek 12AX7-WA though.

 

[RockManiac]

I'm sorry guys, I was wrong. The upper right tube is labelled "12AT7" also on my amp, I just checked it. The lower left tube "12AX7" is the input tube.

 

[Jeff Hilligan]

It really doesn't matter we shipped the last run with 12ax7wa's in both slots. Not a big deal.

 

[Resonant Alien]

So the tube labeled "12AX7" is the input tube for initial gain. Is the other tube (labeled 12AT7) a buffer, as GS suggested, or what does it do?

Tx