Is v4 or v5 phase inverted in Mark IV type-A models?

[holdsworth]

Is the v4 (12at7) or v5 phase inverted in Mark IV type-A models?

 

[holdsworth]

Anybody? I really need some help on this as I'm about to change my order at dougs tubes.

 

[Platypus]

I believe it's V5 but I'd wait for a more def. response. V4 is responsible for Reverb.

 

[holdsworth]

I believe it's V5 but I'd wait for a more def. response. V4 is responsible for Reverb.

Cheers Platypus, this simple question has eluded me for the past few hours and I've been trying to scour the net for more information.

Could anybody shed some light on the subject?

 

[torquey]

According to the Mark IVb manual, v5 is the phase inverter, and I'm almost certain that's the case with Mark IVa amps as well. V4A is the second lead high gain stage and V4B is the reverb send. So on a MarkIVa, the 12AT7 should be V4 and the low-noise 12AX7 should be V5. The Mark IVa mentions that V4 is a 12AT7 but I couldn't find mention of V5 being the phase inverter. I made the mistake of running a 12AX7 in V4 for a while, and although it functioned, it did not sound up to par. Once I got V4 sorted out, I was much happier with the sound.

 

[holdsworth]

According to the Mark IVb manual, v5 is the phase inverter, and I'm almost certain that's the case with Mark IVa amps as well. V4A is the second lead high gain stage and V4B is the reverb send. So on a MarkIVa, the 12AT7 should be V4 and the low-noise 12AX7 should be V5. The Mark IVa mentions that V4 is a 12AT7 but I couldn't find mention of V5 being the phase inverter. I made the mistake of running a 12AX7 in V4 for a while, and although it functioned, it did not sound up to par. Once I got V4 sorted out, I was much happier with the sound.

Cheers torquey, you're a life saver! I'll let Doug know straight away.

 

[holdsworth]

Here's what I ordered from Doug:

V1 - Tung-Sol reissue 12AX7
V2 - high gain JJ ECC83S
V3 - high gain JJ ECC83S
V4 - Mullard CV4024
V5 - balanced Shuguang 12AX7C9

Can't wait to try them out!

 

[torquey]

In case you want a copy of the original MarkIVa user's manual, you can find it here.

Someone posted a scan to the Boogie Board a while back.

 

[Russ]

The way I understand it is that the V4 is solely reverb on a Mark IVA. I spoke with Mesa about this because I was considering using a 12ax7 in the place of the 12AT7. They said you can use a 12AX7 there but it will just sound different. It will not damage the circuit but it may not be what you are looking for in regards of sound. They said that the tube should remain a 12AT7 as designed.

The V5 tube is the last tube in the chain for the preamp and is in the position that is most often than not the phase inverter. I am going to put big money on the assumption that it is in fact your PI tube. Mesa's ideas about PI's are slightly different than the rest of the world though. They don't believe you must have a balanced tube there. I still hold fast to the old school train of thought and use a balanced 12AX7 there anyway. But you could use a 5751 or a 12AT7 there to experiment.

Realistically you could use most of the 9 pin minis (12AX7, 5751, 12AT7, 12AY7, 12AV7, 12AU7) in any position. Just be prepared for different tone. The amp was designed for V1-3 as 12AX7 with V4 as 12AT7 and V5 as 12AX7. The other tubes mentioned above will have varying degrees of gain.

 

[torquey]

Thanks for the clarification. The 12AX7 certainly wasn't what I was looking for in sonic terms. There was a harshness I could never dial out, particularly in R2.

The way I understand it is that the V4 is solely reverb on a Mark IVA. I spoke with Mesa about this because I was considering using a 12ax7 in the place of the 12AT7. They said you can use a 12AX7 there but it will just sound different. It will not damage the circuit but it may not be what you are looking for in regards of sound. They said that the tube should remain a 12AT7 as designed.