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Cheap 3-5w tube guitar amp design

post #1 of 24
Thread Starter 
A kit would be ok, as I have been looking at the guts of several Epiphone Valve Junior. I have a vintage (1940's) tweed case, and am tasked (by an insane player) to retrifit it with a tube amp. The operative word (since it is for a musician) is cheap.

Looking at Fostex 4.5" full range drivers, so speaker recommendations are also welcome, anything between 4-5.25". The Jordan JX-92S driver was what I wanted, but over budget.

Anything will help, but I should just walk away from this one... just need an excuse.
post #2 of 24
How about a Fender "Princeton"? Simple 12ax7 and 6v6. Schematic over at Angela Instruments. PM me if your looking for parts.
post #3 of 24
How cheap, is cheap? You can pick up an AX84 P1 kit with a CNC punched 16x8x2 chassis for ~$300 shipped from Doberman.

AX84
post #4 of 24
link
The kit in that thread is out of production, but the new version uses more easily findable tubes and may be more easily tweaked to guitar amp standards

There was a monoblock available.

The original used some funky TV tubes with a triode and pentode in 1 envelope which makes rolling a difficult task. The new one separates the driver/gain tubes from the output tubes. Get creative with the distortion generators. Or build it to run clean and find the distortion elsewhere.

link to store
post #5 of 24
Quote:
Originally Posted by FrankCooter View Post
How about a Fender "Princeton"? Simple 12ax7 and 6v6. Schematic over at Angela Instruments. PM me if your looking for parts.
This is the correct answer. Any of the old Fender schematics are what you are looking for -- you can find a few at Fender Amp Heaven Schematics - Tweed Blackface Brownface Silverface Bassman Champ Deluxe Princeton Super Vibroverb Reissue

The 5F2 is a particularly good and simple design -- I did a version with a 6sl7 instead of the 12ax7 and it is a great little amp.


Quote:
Originally Posted by pabbi1 View Post
Looking at Fostex 4.5" full range drivers, so speaker recommendations are also welcome, anything between 4-5.25". The Jordan JX-92S driver was what I wanted, but over budget.
No, that's not the right answer. Basically, a guitar amp sounds good if you make the worst hi-fi amp possible. You want it to distort, clip, and for the PS to sag. Similarly, the speaker should have a limited frequency range and should break up under signal. Different speakers break up differently, but a good quality full range driver is exactly what you don't want. (Smallest guitar specific speaker I've seen is 6")

I have a Jensen C10R that I will be happy to let go cheap -- I bought it as a tester speaker, and used it for about 2 days until it got replaced with an AlNiCo based Weber. Oh, I also have an OPT I'd like to part with -- the second half of the pair I used in mine. It is a cheapo Hammond something or another -- 125CSE I think.
post #6 of 24
Thread Starter 
The case will only hold something less than a 5.25" speaker, so any suggestions there would help (just really hard to cheap out on the speaker, but I will not go Howlin Wolf and poke holes in the paper... ).

OK, pics included - there is a nice shelf for the guts, and the inside dimensions are roughly 11" x 5".
LL
LL
post #7 of 24
Ok, well I would reiterate or confirm some things posted already,
Any old Fender 6v6, champ, Princeton would fit the bill.
For a more modern approach the AX84 is the place to start and kits are at Doberman.
You'll want a guitar speaker, the 6" or 8" Jensen MOD is a good start.
But you know "cheap" and transformers just dont mix
Good luck, I am jealous !!!!
post #8 of 24
Thread Starter 
Just to set the stage, I have owned a _few_ Fender tweed amps, but, this ain't THAT kind of project.



Not even aspiring to vibro Champ.... think more like Pignose.
post #9 of 24
I typed "5 inch guitar speaker" into google and found a 5 inch guitar speaker.

http://www.jensentone.com/mod5-30.php
post #10 of 24
what about this? http://ax84.com/media/ax84_m276.gif
Im thinking of building one.
post #11 of 24
Did you look at Ted Weber's offerings?

https://taweber.powweb.com/weber/
post #12 of 24
Awesome collection !!!
Maybe something like a powerman then ? Very pig nose like.
Cant find my links right now, but the next one I am going to build will be a 6112/5902 sub-mini amp.
post #13 of 24
Thread Starter 
OK, so I finally got back to this, sort of, now that some other projects decided to start working, so, here is the plan.

I have been looking at Boozhound at both his 6s4a (my strongest preference) and his 6sl7, which is VERY intriguing, but way out of scope for what I want to do here.

Champ is the answer. Further, I want to avoid the rectifier tube, so I found this nuggett - made from scrap parts.

Let's be honest - I struggle with simple things, and, this is a favor to my brother (we won't go into quid pro quo, cause there ain't none), so, quick and cheap.

Now, my real question is: What can I use other than the 12ax7 (6922, 6n23p, and 5963 are all onhand)? THEN, can I use 6s4a or 6h30 instead of the 6v6? I have the mini sockets and tubes, but no octal anything.

Buying an "old" speaker, but, should that fall through, I'll get the Jensen 5" MOD.

Finally, looking at the Antek AN-300 for power/heater, and a Hammond 125H for OPT - again, just curious if that is all reasonable. Hard to imagine I can find anything significantly cheaper, but, I'm certainly open to suggestions, well, and, of course, ridicule.
post #14 of 24
For the output transformer: Im pretty sure the 125ase or bse is the one to get. The 125H is push pull. If you decide on the speaker first the multiple output taps are an unnecessary expense. On that note, the low end Edcor SE transformers here are less expensive, although they have a bit of a lead time.

Edcor makes power transformers too, see if they have something that will work. you can probably find something less expensive than the antek if you go for a lower heater rating. 6A of combined heater current is WAY overkill.

I would stick with the 12ax7 for the gain tube. Changing this tube changes how all of the tone controls work.
post #15 of 24
Thread Starter 
So, would this be enough for the power trans?

EDCOR - XPWR076

Probably a push on cost with (combined) shipping.

Ok, resigned on keeping the 12ax7 (cheap enough), but thoughts about changing out the octal for something 9 pin?
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