Preamp valves (paging knowledgeable types)

LooseMoose

Hi all,

So, it's often heard that for 'taming' the gain of an amp with too much of the stuff, a preamp valve swap is a good idea.

I have a Fender Deluxe VM and love it but I find that with hot pickups, even 2/3 on the gain control on the drive channel is a little too much.

I'd like to calm it down, so a 12AT7 or 12AU7 seems to be the general plan - is there any way that in doing this, I could harm the amp?  Are there other side effects that I should be aware of?

Thanks in advance,

James

ICBM

Yes, you could harm the amp - not very likely but theoretically possible. It depends on the components chosen and what happens to the voltages with a different valve type, so without access to the spec sheet and an amp to measure the changes on you won't know for sure.

I would say there's at least a 95% chance it will be fine but if that last 5% worries you, stick to a 5751 which is the only definitely safe substitution for a 12AX7.

LooseMoose

Thanks mate - 5751 seems the safe option. Worth changing ALL of the 12ax7s do you think? Or just the first...

strtdv

Just change V1

I actually have one amp that I use an old military spec 1960s 12AT7 in V1, have done for years.

It shouldn't sound good, but it does.

12AU7 is much less gain, you'll reduce the volume/gain of your amp hugely if you use one of those.

ICBM

LooseMoose said:

Thanks mate - 5751 seems the safe option. Worth changing ALL of the 12ax7s do you think? Or just the first…

It depends which valve(s) affect the overdrive channel and/or if you want to alter the clean sound as well. I'm not familiar with the valve layout in that amp though.

pintspiller

i use a mkii mv lead for bass and my amp guy suggested i tame v1 and use the low input. i used ecc82 and ecc83, but he suggested 5751 as it is a lower-gain ecc83 and the circuit was designed to suit the ecc83 valve

marantz1300

The wrong valve will cause a lot of hiss/buzz.