Build Your Own Clone Message Board

I'm looking for a little more clean headroom from the champlifier. Would swapping the 12ax7 to a 12ay7 be a good idea?

Yep, it will work for that purpose exactly. As i recall, the 12AY7 has less than half of the gain of the 12AX7 so you will be hard pressed to get any dirt out of it with single coils even at 12. Also, it will probably be a little less dynamic feeling - great if you want your dirt from pedals.

Yeah I'm planning on pushing it with the output from a distortion pedal for overdrive and the distortion from the pedal.

Should be nice, since you'll get all the power tube crunch goodness too

5751 would be a better choice imo.

Yes? Which one? Do you have a favorite?

How would that be better? I've only used 12ax7s.

Well, the 5751 has (I think) about 30% less gain than the 12AX7 while the 12AY7 has less than half, so you would get more preamp distortion from the 5751 but still be able to crank the volume pretty high for power tube distortion. I won't put words in ChrisM's mouth but he might feel that the 5751 is a good middle ground between the AX7 and the AY7.

BTW, the 5751 was SRV's favorite preamp tube, and he had some good tone. I have one kicking around somewhere - if I find it, I will try it out and report back. I don't have an AY7, though...

*EDIT* I've also heard, but cannot confirm, that new 5751s are relabeled poor-performing 12AX7s. Not a worry, since you can get good NOS JAN USA 5751 for about 30 bux still.

Would this tube just drop in?

Yes.

No, you have to push it into the little holes.

(I'm sorry, couldn't resist....)

Har har

5751s are my personal favorite replacement for 12AX7s when I feel like I'm not getting enough clean preamp headroom. Of those, GEs (NOS or slightly used) have been my personal favorites, but I haven't tried dozens of different ones - just Sylvanias, RCAs, and GEs that I recall.

None of this has been in a Champ so take that for what it's worth

The design of the amp is based around the double mu triode that is the 12AX7. The load lines are bias were calculated and setup the 12AX7 in mind.

With a 12AY7 or 12AT7 the stage is biased completely different, gain and frequency response change drastically.

The 5751 is no 12AX7 but it is closer than the 12AY7 or 12AT7. It will take the "edge off" while still maintaining the stages characteristics. As noted you should be able to pick up a NOS 5751 for around $20.


SE amps like the Champ are great cause they don't run many tubes so you can experiment with NOS glass and not break the bank. Also you don't have to worry about many output tubes (usually the costly tube(s)) and if you need matched pairs or quads.

This is exactly what I've used my Valve Jr for - one 12AX7 (or 5751), one EL84. No need for anything to be matched. Well, except potentially the two 'halves' of the preamp tube but I haven't noticed a difference with that in the VJr.

Yup, an NOS Phillips JAN 5751 in the preamplifier section of my Champlifier is spectacular! It won't be everybody's cuppa but it's perfect for me. Where the 12ax7 is edgy-spikey and aggressive, the 5751 is round, full and bluesy. Much more clean headroom before the preamplifier distorts allowing the power tube saturation to come through. Absolutely gorgeous with pedals in front!

I don't know if it can work for this type of amp, but in my Mesa Mark 4, I use a 12AU7 in V2, wich is for the clean, it gives me way more headroom and sound more mellow...less sparkly especially when bright switch is engaged.

I did the same thing in my TraceEllitot 1210 bass combo for the Tube Drive, it's a 12aX7 with a 12AU7, it sounds more organic and less loss in natural bottom end.

got an extra 5751?

I do not Tube Depot (not the cheapest but very trustworthy) has NOS 5751s for smallish money.,.

Meant to make that a PM. apologies.

I'm seeing a JAN Phillips for $29.99 which I would pay for that tube. Any more and I would have to think hard....that's at TubeDepot, BTW.