I put a 12AT7 in the PI spot of my amp and...

[leadfootdriver]

It sounded like a 50's flying saucer spaceship movie.

Wats' doin' with that?

[rooster]

Bad tube prolly. Try another one?

[Paul86]

Talk about coincidences! I had some free time today and did just this with my amp. While my amp isn't exactly a 'Wreck (it's an Alessandro Bloodhound), it's close enough for government work.
Well, I didn't like the results. I was looking for a bit more headroom, and I found it, but along with a muffled sound I didn't care much for (think of a wet blanket thrown over the speakers). While I had the chassis out of the cab, I finally tried out some of nos stash in the V1 position, and ended up with a Hitachi 12XA.

[RevD]

I wonder if the 5751 might be a bit better, its gain is more like 70 compared to 60 on the at7? I'm curious about it, I'm starting a 6v6 wreck'ish sort of build and on my budget nos is probably not happening, although a nos 5751 would surely sound better than the new ones... Anyway just a thought.

Regards,

Don

[Shai`tan]

I thought the Gain factor of a tube doesn`t really come into play in the PI.

[Firestorm]

I thought the Gain factor of a tube doesn`t really come into play in the PI.

You can't really estimate the gain of a long-tailed pair based solely upon the tube's mu. The difference between a 12AX7 and a 12AT7 is almost nil in the LTP, but a 5751 should have noticeably lower gain. Tubes like 12AY7 or 12AU7 are much lower (like 30%-40%).

[zambo]

i run a at7 in my 6v6 amp and it sounds cleaner. less white noise and hash in the sound. Clean to mean is better to and i run it pretty hot. I like the tone of a ax7 better but its way less stable.