What tubes for the PI on a Marshall amp?

[STRATDELUXER97]

Re: What tubes for the PI on a Marshall amp?

Ok thanks people. I think I've heard enough

:smack:

 

[shredaholic]

Re: What tubes for the PI on a Marshall amp?

Trying to get a balanced phase inverter tube on a Marshall is pointless - Marshalls use a 82k/100k plate resistor combination in the phase inverter, which does not perfectly balance a tube. To perfectly balance the tube, to obtain symmetrical driving of the power tubes, the plate resistors would have to be either 82K/94.1K or 87.1K/100K.

A perfectly balanced PI would sound clean and sterile, you want some degree of imbalance to generate second order harmonics which sounds great. And even if you did want a clean and sterile sounding PI, balanced tubes would drift out of balance with use anyway.

 

[marvar]

Re: What tubes for the PI on a Marshall amp?

A perfectly balanced PI would sound clean and sterile, you want some degree of imbalance to generate second order harmonics which sounds great. And even if you did want a clean and sterile sounding PI, balanced tubes would drift out of balance with use anyway.

I have found this to be true- I've tried just about every 12A_7 tube I could get my hands on, AT,AU,AY GT12ax7M MPI, Ecc83-and the one I keep going back to it a GT12ax7R2- a long plate -btw DrZ uses these in alot of his amps. It seems to give a better sounding bottom end. At least in my Marshall.

 

[STRATDELUXER97]

Re: What tubes for the PI on a Marshall amp?

Trying to get a balanced phase inverter tube on a Marshall is pointless - Marshalls use a 82k/100k plate resistor combination in the phase inverter, which does not perfectly balance a tube. To perfectly balance the tube, to obtain symmetrical driving of the power tubes, the plate resistors would have to be either 82K/94.1K or 87.1K/100K.

A perfectly balanced PI would sound clean and sterile, you want some degree of imbalance to generate second order harmonics which sounds great. And even if you did want a clean and sterile sounding PI, balanced tubes would drift out of balance with use anyway.

Guess what I was trying to say was that you want a good,strong,balanced inverter tube....I know all about the 82k and 100k inverter plate resistors at pins 1 and 6 also....

Not to sound like a smart a$$,but I've been modding old Marshalls and Fender amps for alot of years! LOL I know what I'm talking about....Maybe can't explain it,but I do walk the walk! ;o)

Just finished converting my 73 PCB 50 watter over to PTP......

Before Photo....

NOW!