tube in mark III´s v5

[es335]

Hello,

is it necessary to put in V5 of my Mark III a balanced 12AX7 tube.
Does a balanced 12AX7 give a better sound?
Thanks!

 

[Boogiebabies]

I've never believed that a gain matched twin triode in the phase inverter does much. Both plates are running different voltages, so the gain is not uniform. So, why does the tube have to be balanced.

 

[stokes]

The matched PI is a lot of hype.Even if your power tubes are perfectly matched when you install them they will likely drift a bit and be off a couple of ma's when they burn in.All the components in the PI circuit,like in the rest of the amp are +/- 10% tolerance as well.So there goes the matched PI theory.

 

[edward]

Since you're playing with the PI, try a 12AT7. I put in a NOS Mullard at7 andlove it in my MKIII green simul! Give it a try ...I'll never go back

Edward

 

[Buddy]

Asymmetrical clipping is where is where it's at , cool cat's 8)

 

[es335]

@Edward

can you describe the difference in sound between a AX7 and a AT7 in V5?
I have there a simple chinese AX7, do you recommend to put in a better one.

 

[CoG]

The best way I can describe it is that with a 12AX7 in the PI, if you engage R2 while you're in lead, things get stiff and harsh, and with the 12AT7, the tone gets thicker and a bit fuzzier.

here's a link on PI tubes:

http://www.guitaramplifierblueprinting.com/files/Phaseinverter.pdf

edit: an 12AT7 costs like eleven bucks, just try it.

 

[edward]

Hi es,

Try a good NOS 12AT7 in the PI, V2, or V3 positions (though try the PI slot first). What this accomplishes is "gaining down" the preamp incrementally, whether you use one or all three AT7s in the positions I mentioned.

So as for the resultant tone, it's kind of like "softening" the upper edges/frequencies a bit, as well as blunting the edges of the attack ...think rounding the corners of a slab of stone or countertop. FWIW, I have AT7s in V2,V3, and the PI. The R1 cleans are a bit less stiff, and with an upper-mid voice that's sweeter, and a top end that's less sharp, taking away that brittle upper end. As nice as this is, the Lead and R2 are even more significantly improved. The OD is niticibly smoother/creamier, much less grainy, and same goes with attenuating that upper-mids and high-end sharpness. Of course, ultimate gain is decreased, but there is much there on tap so that's not a problem for me. The bottom line is you must try it in each slot, and let your ears decide.

BTW, I like NOS Mullard CV4024, which are 12AT7s. I've tried NOS RCAs and like them, but the Mullards really seem smoother to my ears. Hope this helps you a bit.

Edward

 

[es335]

Hello,

your descriptions sound very interesting. I will try AT7 in V5/V2 and V3
one after another and let my ears decide.
Thank you very much.

 

[stokes]

I never liked the AT7 anywhere but the PI.It tends to sound too dull and flat in other positions,a better choice,in my opinion to cut a little gain but keep the clarity is a NOS 5751.If you look at various schematics the only place you see the AT7 is in the PI position,it is selected for this in many amps because the lower plate impedance interacts better with the power tube grids it feeds.

 

[ianvomsaal]

Asymmetrical clipping is where is where it's at , cool cat's 8)

+1