12AT7 or 12AU7 in a Fender Hot Rod Deluxe iii - opinions?

Philtre

Just bought a s/h Fender Hot Rod Deluxe iii. Great amp, but frickin' loud at home. At the moment I've put a passive foot volume control in the s/r loop to tame it a bit, but I'm thinking of replacing the main 12AX7 with a 12AT7 or 12AU7. Anyone done this? Good? Bad?

ICBM

The best combination I've found is a 12AY7 in V1, 12AX7 in V2 and a 12AT7 in V3.

The valves won't really make it quieter though, it's more that they will give it a bit less gain and open up the tone. A volume box in the loop is by far the more effective for low volume.

Philtre

@ICBM ; Interesting. How does the amp tone using that valve set compare with the stock 3 x 12AX7?

impmann

I can't remember what the valve was I changed V1 for on the basis of internet wisdom to get less gain/more headroom. It just made it sound bland and have slightly strange overtones on note decay.

I don't think you'll acheive what you want to by changing the valves - the volume control in the s/r loop is the best way I've found for taming my HRD. And it sounds great now, even at home!

Philtre

@impmann OK, that's what I've got at the moment.

impmann

I think the point is, if you like the sound of the amp as it is - don't change the valve types that are in there. I don't think you'll change the volume but you may affect its sound.
Its a bleeding loud amp for its size!

ICBM

impmann said:

I can't remember what the valve was I changed V1 for on the basis of internet wisdom to get less gain/more headroom. It just made it sound bland and have slightly strange overtones on note decay.

Quite likely a 12AT7 - that's often recommended, but I always find they sound like that in a V1 position, I don't like them in a 'gain' stage at all usually - they're great in V3 (phase inverter) though. The right lower-gain valve for V1 is the 12AY7, which was what Fender used in the 1950s. I still prefer a 12AX7 for the drive channels (V2).

Philtre said:

@ICBM ; Interesting. How does the amp tone using that valve set compare with the stock 3 x 12AX7?

Less gain, clearer and with less midrange, and more punchy dynamics. You might get *slightly* more control with the volume knob, on the clean channel - but not that much. It won't make and difference on the drive channel, although it will reduce the effective amount of drive - which is a good thing in my opinion, I don't like it above halfway if you're going to use More Drive.

Philtre

What about a 12AU7 rather than a 12AY7?

ICBM

Philtre said:

What about a 12AU7 rather than a 12AY7?

I find they drop the gain too far and sound a bit odd. They also put significantly more load on the plate resistors even than the 12AY7, which probably isn't a good idea.

I do like them in some amps - they're great in V1 in a Peavey Classic 20 for example, where they reduce the gain to a sensible range instead of the Metal Zone emulation it normally does...

Philtre

OK, thanks for all the advice guys. My decision is to not change the valve, but keep the volume pedal wedged in the s/r loop at home, and it's not a problem when gigging or at practice.

jpfamps

Philtre said:

What about a 12AU7 rather than a 12AY7?

A 12AU7 will cause the anode load resistors in the pre-amp to over dissipate, so don't use this valve.

Also the cathode resistor is optimized for biasing  a 12AX7, so a 12AU7 will not be biased correctly.

You could modify the amp to accept a 12AU7, but that would probably be more trouble than it is worth.

cj73

Philtre said:

Just bought a s/h Fender Hot Rod Deluxe iii. Great amp, but frickin' loud at home. At the moment I've put a passive foot volume control in the s/r loop to tame it a bit, but I'm thinking of replacing the main 12AX7 with a 12AT7 or 12AU7. Anyone done this? Good? Bad?

I've never got this.   I've had a stock hrd3 for the last 3 years and i've never found it to be too loud or hard to dial in a suitable volume, maybe you need a more sensitive finger ( phnarr).  

ICBM

cj73 said:

I've never got this.   I've had a stock hrd3 for the last 3 years and i've never found it to be too loud or hard to dial in a suitable volume, maybe you need a more sensitive finger ( phnarr).  

I never even found the II to be so, despite it being by far the most common complaint about them, and the 'perceived wisdom'. Nor that the Drive channel is unusable. It's just a matter of learning to move the volume controls *very* carefully, which luckily is easy because they're chickenhead knobs. With the Drive channel, I found it best to dial the amp in for the More Drive mode and let the other two take care of themselves, which they do quite well if you approach it that way.

That said, a volume box does make it easier still and I think does improve the tone a bit, just because it lets you get the controls out of that 'only just on' zone.

The other day I was listening to an album by a local band which was recorded with a stock HRD and as far as I know from seeing them live, no pedals - and the guitar tones are fantastic, both clean and overdriven.

Danny1969

I've been selling quite a few of these recently, it's what I use for my own HRD. 

Philtre

@Danny1969 ; Where do you sell these?

Danny1969

I do these on Ebay for £20 plus £2.90 PP but if any forum member wants one then will do one delivered to UK for £20, just PM

normula1

jpfamps said:

Philtre said:

What about a 12AU7 rather than a 12AY7?

A 12AU7 will cause the anode load resistors in the pre-amp to over dissipate, so don't use this valve.

Also the cathode resistor is optimized for biasing  a 12AX7, so a 12AU7 will not be biased correctly.

You could modify the amp to accept a 12AU7, but that would probably be more trouble than it is worth.

I've had a 12AU7 in my Mesa Studio 22+ for quite a while. The gain channel started to make a  horrendous crackling noise the other day and it looks like the anode resistor is the culprit. It's supposed to be 68k but is reading 160k.