EL84 Guitar amp questions (long, sorry)

[Sherman]

Having just finished a project I'm looking for another one. Since both my sons play guitar and I own several guitars (but the cat runs to the other end of the house when I start playing ) I thought a nice project would be to build some inexpensive SE guitar amps. So of course I have a bunch of questions.

I'm thinking of doing the AX84 P1. It seems pretty simple, I've heard samples which sound good to me and I have some EL84s on the shelf. Also I can use some inexpensive trafos from Uncle Ned (I have one set).

So here are the questions-

1- Would it be possible to "drop in" the overdrive and master volume setup from the P1 Extreme by Phil Rowley? He uses EL34, 6L6 or 6550 type output tubes vs. the EL84 of the P1.

(One son plays almost 100% acoustic and wants very clean sound, the other plays about 100% electric and wants to be able to grunge things up, though he can use a pedal.)

2- If I made the proper value changes for the first two stages which as designed use a 12AX7 would I lose anything by using 12AU7 valves instead? The EL84 is easy to drive so I think the 12AU7 should be OK?

(I have a bunch of 12AU7s on the shelf and no 12AX7s.)

3- I have a couple of 8" PA speakers I'll use initially but I imagine we'll want something better eventually. What similar sized speakers do you recommend for a- acoustic guitar and b- electric guitar?

Thanks for any input!

 

[Trout]

1- Would it be possible to "drop in" the overdrive and master volume setup from the P1 Extreme by Phil Rowley? He uses EL34, 6L6 or 6550 type output tubes vs. the EL84 of the P1.

YES, actually I have done that in a project seeing as it is a rather simple conversion.

2- If I made the proper value changes for the first two stages which as designed use a 12AX7 would I lose anything by using 12AU7 valves instead? The EL84 is easy to drive so I think the 12AU7 should be OK?

I have run 12AU7,12AT7,12AX7,(various brands) without any changes. I think you will be hard pressed to get that crunchy gain unless you run at least a 12AT7. But on the other hand. The 12AU7 had very flat eq type effect. (boring at best)

Even brand to brand swaps of the same tube had a profound effect.
You might want to just build it stock with no value changes and grab a couple cheapies like Electro harmonix EH12AX7's generally they run 6 bucks a pop new on evilbay . I have run those,Not the best, not the worst. But, they work!

Run the 12AU7's until you locate a couple cheap 12AX7's.
trout

 

[Sherman]

YES, actually I have done that in a project seeing as it is a rather simple conversion.

Great to hear. It did look pretty straightforward.

I have run 12AU7,12AT7,12AX7,(various brands) without any changes. I think you will be hard pressed to get that crunchy gain unless you run at least a 12AT7...

Yeah, I ran a couple variations using TubeCAD and it does appear that I really should go with the 12AX7. I'll pick up a couple since I have to run by Uncle Ned's sometime this week anyway.

It wasn't the money so much as the 6 12AU7s sitting on my shelf.
If it works out like I hope it does I'm going to end up building at least three of these!