What would happen if you changed a Phase Inverter valve?

ChuckManual

Say; swapped a 12AX7 for an AT7 or an AU7?

Blue smoke?

Blue flames?!   

Subtle, almost imperceivable, tonal shift...?

ecc83

ICBM will give chap&verse on those amps that might be damaged. The almost universal Long Tailed Pair PI is a stage that is very hard to overdrive so the actual valve type probably won't change the tone very much (but the cork sniffers will have a say no doubt!)

Then, many of the bigger, 50W+ put negative feedback around the PI stage which makes it all the more immune to valve type.

BTW. The bigger Blackstar amps use a 12AU7 (ECC82) as a driver from the PI. DO NOT use anything else! A 12AX7 will sound horrible and might only just last the night but you are very unlikely to damage the amp itself. Other brands..Not so sure.

Dave.

ICBM

Usually a slightly cleaner, clearer and more open sound.

What amp is it? There are a few where it might not be a good idea because the plate resistor ratings may be exceeded.

ChuckManual

It's a Two Rock Exo 15.

Actually, they are Two Rock Exo 15's. I have two, I use them in tandem, and I've been toying with the idea of changing the valve compliment in one of them for some subtle tonal variation in the stereo picture. I've already put a 12AU7 in the preamp of one, but it's a pretty low gain amp to start with, so it hasn't changed the sound much. So I though, "Next step; Phase Inverter and then Rectifier."

Perhaps it's not worth it...?

ICBM

I'm not familiar with those so I have no idea really!

ChuckManual

Thanks anyway! 

ChuckManual

I'll e-mail Two Rock. I think the new (old) management are a bit sniffy about the stuff that was produced in their absence, but I'll give it a shot. You never know... 

olafgarten

You would be better off using something like a Yellow Jackets YJ20 to convert the output tube to an EL84. I'm not 100% sure if it would work, but it should.