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?

[Jazz P Bass]

Wierd.
Maybe the tube is bad.
What tube should be in the PI?

[leadfootdriver]

12AX7.

Btw, said tube was a Nos GE 6201 from 1986. The pins look a little dull and blued. Do tube pins tarnish over time?

I was afraid to rock the tube in the socket because they're so tite. I killed a Telefunken by messing around with another amp that had tight tube sockets; it ripped the pin right off' the tube.

[pontiacpete]

You could clean the pins with a small wire brush or scrape them with a razor knife.

[J M Fahey]

I put a 12AT7 in the PI spot of my amp and...
It sounded like a 50's flying saucer spaceship movie.

Ahemmmm !! , you didnīt pull it from a Flying Saucer crashed close to Roswell, New Mexico, did you?

[g1]

What is the amp in question? Does it have board mounted tube sockets? If so, (with the sockets being so tight) removing the tube may have broken some of the solder joints at the socket.

[leadfootdriver]

I tried a few others known to work, and they did the same thing. It must be the way they react with the design of the amp, although I can't explain it technically.

[J M Fahey]

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

And what happened before you did that?
What did you use before?

[Steve Conner]

Ahemmmm !! , you didnīt pull it from a Flying Saucer crashed close to Roswell, New Mexico, did you?

Where do you think Ken Fisher got the design?

It is probably some sort of oscillation. You could try adding grid stopper resistors to the PI. Or maybe with a 12AT7 it needs the little capacitor slung between the PI plates.

As far as I know it's OK for tube pins to look dull and bluish, they seem to make contact fine. If there is a contact problem, the amp will crackle violently when the offending tube is wiggled around.