overcompressed sound in new amp

[TD_Madden]

I recently purchased a highly-hyped "anniversary" amp based on the 5F6A bassman, with a few differences such as three-inputs (clean/lead/both) and reverb on the "clean" channel.

Yeah, I know, I shouldn't have fallen for the hype.

The first preamp tube is a 12AX7 (unlike the original bassman's 12AY7) and seems to be setup to prefer single coil pickups. My guitars being all HB or P90 based, this has caused a problem where the input seems overloaded, notes feeling very compressed or "squashed". Since this is a 45-watt amp, I expect a LOT more volume before getting the compression I'm seeing at 4 or so on the volume knobs.

I sent a note to the builder asking about this and here is his response:

"Regarding the amp question, let me say this: When you play a Mel Bay "cowboy E" chord with a single-coil strat pickup, the guitar's output is 1/8 of a volt. Do the same chord with a humbucking pickup and the output is 1/4 of a volt - about double. But play the same chord on a P-90 pickup and the voltage is 1/2 volt - four times as much as a strat. So, if you are going for clean tones, you can't get it without either: 1. Turning the volume of the guitar WAY down, but when you do, you will lose highs, so a small compensating cap on the volume control of the guitar will help ( use a 500 pf value)
2. Change the first gain stage tube to a lower gain version. Since the P-90, is four times the gain of the strat pickup, a tube with a fourth of the gain of a 12AX7 will work nicely. 12AX7 has an amplification factor of 100, so you need about 25. A 12AU7A is a factor of 20, which will do the best. Or you could try a 12AY7 and then bump the guitar volume down just a "C" -hair"

Does this make sense, or would a change to the circuit be more in order?

Thanks in advance!

[MWJB]

This makes sense to me. Whenever I've had 5F6A owners in for a retube, they usually try a 12AY7/6072A (early/idealistic days I used to suggest it as the "proper" tube before I gave up as no-one liked it, sometimes they're curious & ask)...Strat/Tele players always seem to prefer a 12AX7, 335 player once liked a 12AY7 but ended up with a 12AX because the AY made the amp too thin/clean for his other guitars.

I suspect Fender were looking for better fidelity when they fitted the 12AY7.

I doubt that the builder has strayed too far off the original preamp voltages, I'd be looking for 220-230v-ish at V1 WITH A 12AX7 (two thirds of that with a 12AY and around a third of that with a 12AU)?

Previous models from this builder had a switchable in/out additional gain stage, don't know about the anniversary model, maybe check that this has not been inadvertantly engaged (if fitted)? But what you're describing sounds pretty 'par for the course' with humbuckers and a 5F6A on "4"

[TD_Madden]

thanks for the insight...and good guessing on the builder as well!

The work is very clean and with absence of any schematic/layout diagram I'm hesitant to take it apart. On the other hand, voltage-checking is pretty simple.

I've never played a "real" 5F6A, so maybe that hype was part of the problem as well.

[acorkos]

whatza "C" -hair"?

[DirtyGeorge]

whatza "C" -hair"?

That would be the crude term for the pubic hair of the female of the species.

[TD_Madden]

I ordered one of those cheap Squier "Classic Vibe 50's" telecasters to give it a try with the original tube in-place....maybe it's best just to stick with those kinds of pickups when using this amp....sure seems a waste to be designed that way, though.

I was wanting to try a Tele anyway, and the reports on that model are all pretty positive.

[MattT]

Just curious but why not use the lower gain input when using humbuckers? Or maybe do a tweek to one of those extra inputs to pad it down to the perfect amount?

[TD_Madden]

there's no "lower gain input"...just clean, lead, and both.

[TD_Madden]

changed the PI to a 12AT7...seems to have done the trick.