Older Pittbull UL 12AX7/12AU7 driver.

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Intimidator333

Member
Hi. I just got an older VHT Pittbull UL. It’s the version with 6 preamp tubes, a 12AX7 as the pi and an option for 12AX7 or 12AU7 as a driver tube before the power tubes. Anybody have experience A/B both types?
I believe the current versions run a 12AT7 in that slot. Any idea if I can safely run one of those?
 
Intimidator333 said:
Hi. I just got an older VHT Pittbull UL. It’s the version with 6 preamp tubes, a 12AX7 as the pi and an option for 12AX7 or 12AU7 as a driver tube before the power tubes. Anybody have experience A/B both types?
I believe the current versions run a 12AT7 in that slot. Any idea if I can safely run one of those?
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A 12AT7 can sub for a 12AX7 without issues, in any amp I’ve owned. It’s something that can be tried to reduce the gain a bit in a modern high gainer. EVH for example. You shouldn’t have a problem running an AT7 there.
 
The driver tube isn’t really about gain, it’s the difference in impedance sent to the power tubes, it changes the response of the power amp. The ULs that are spec‘d for the 12AU7 should have it there, any 12A series tube will “work”, but the amp won’t be “optimized” without the correct tube type.
 
I would stay with a 12au7 or 12at7, that tube is for the driver in the power section because it uses a Cathodyne PI. I thought a 12ax7 should NOT be used.
 
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