What tubes for the PI on a Marshall amp?

[STRATDELUXER97]

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

Ok, so what specific brabd/type of 12ax7 would you recommend for that position if I want mucho Marshall crunch?

You don't want your PI tube to be the one to get you the crunch....V1 is the tube you need to hone in on and the PI needs a strong,reliable tube,but it doesn't have to be high gain.

[shredaholic]

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

I disagree a bit - I've noticed crunch varies quite a bit when swapping out 12AX7's in V3. The effect is less noticeable in V3 than V1 than you'd expect, but I'd still take tonal properties of a phase inverter tube over strength.

The more upper mid emphasis the tube has, the more crunch you'll get. For crunch, a Mullard or Valvo will probably be the crunchiest, if you like to retain crunch but with a bit more "ballsy" tone an RFT would be great for that.

[STRATDELUXER97]

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

I disagree a bit - I've noticed crunch varies quite a bit when swapping out 12AX7's in V3. The effect is less noticeable in V3 than V1 than you'd expect, but I'd still take tonal properties of a phase inverter tube over strength.

The more upper mid emphasis the tube has, the more crunch you'll get. For crunch, a Mullard or Valvo will probably be the crunchiest, if you like to retain crunch but with a bit more "ballsy" tone an RFT would be great for that.

Remember though that the PI tube is more about function then tone though A strong,balanced from side to side PI tube is really what this position benefits from.
..Most of the overall tonality we hear comes from the preamp and not the PI by itself...V1 is the main tube to tweak.

[Kommerzbassist]

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

Ok thanks people. I think I've heard enough

[Rocker35]

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

A balanced JJ is real nice in the PI position.

[STRATDELUXER97]

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

Ok thanks people. I think I've heard enough

[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......

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