Fender Twin Amp valve help

andy1839

A big daft Twin has always been on the bucket list, and I found a mint PR266 'TwinAmp' last week. 
First impressions are that it's awesome, but the power valves are on their way out, so I thought I'd treat the amp to new valves. 

Theres a mix of 12AX7 and 12AT7 in there so if anyone's got any experience of what valve positions are the most important for the tone of the amp I'd be grateful for any insight, the manual doesn't say much and the valve layout doesn't give anything away to me.

I also have some old 12AD7 valves, anyone got any experience of them, would they go in?

http://i53.photobucket.com/albums/g55/andy1839/IMG_3534_zpsyhubp5ai.jpg

So here's the chart, any ideas what valve does what?

cheers in advance!

http://i53.photobucket.com/albums/g55/andy1839/IMG_3533_zpswtl6dhng.jpg

ICBM

The numbering starts at the lower right of the chart - closest to the input jacks:

V1 - half of this is on all three channels/modes. The other half is for the clean (green) mode.
V2 - pushed clean/crunch (yellow) mode.
V3 - lead (red) channel.
V4 (12AT7) - FX loop send and return.
V5 (12AT7) - reverb drive.
V6 - reverb return and gain stage for all three channels.

Then along the back of the amp in the opposite direction:

V7 - preamp out/power amp in loop.
V8 (12AT7) - phase inverter.

The 12AD7 is a higher-quality lower-noise 12AX7 basically, so you could use them in any position that calls for a 12AX7, but they would be of most benefit in the early preamp stages, so V1-3 - especially V1 since any noise here is amplified by V2 and 3 - and possibly the reverb return/gain stage V6.

Don't mix the other valve types, 12AT7s and 12AX7s aren't always interchangeable in modern Fender amps due to smaller resistors being used than in vintage amps.

andy1839

ICBM said:

The numbering starts at the lower right of the chart - closest to the input jacks:

V1 - half of this is on all three channels/modes. The other half is for the clean (green) mode.
V2 - pushed clean/crunch (yellow) mode.
V3 - lead (red) channel.
V4 (12AT7) - FX loop send and return.
V5 (12AT7) - reverb drive.
V6 - reverb return and gain stage for all three channels.

Then along the back of the amp in the opposite direction:

V7 - preamp out/power amp in loop.
V8 (12AT7) - phase inverter.

The 12AD7 is a higher-quality lower-noise 12AX7 basically, so you could use them in any position that calls for a 12AX7, but they would be of most benefit in the early preamp stages, so V1-3 - especially V1 since any noise here is amplified by V2 and 3 - and possibly the reverb return/gain stage V6.

Don't mix the other valve types, 12AT7s and 12AX7s aren't always interchangeable in modern Fender amps due to smaller resistors being used than in vintage amps.

That's great info mate, cheers!