# Cheap 3-5w tube guitar amp design



## pabbi1

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.


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## FrankCooter

How about a Fender "Princeton"? Simple 12ax7 and 6v6. Schematic over at Angela Instruments. PM me if your looking for parts.


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## Volkum

How cheap, is cheap? You can pick up an AX84 P1 kit with a CNC punched 16x8x2 chassis for ~$300 shipped from Doberman.

AX84


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## nikongod

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


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## dsavitsk

Quote:


  Originally Posted by *FrankCooter* /img/forum/go_quote.gif 
_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* /img/forum/go_quote.gif 
_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.


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## pabbi1

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".


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## jamesbobo007

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 !!!!


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## pabbi1

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.


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## dsavitsk

I typed "5 inch guitar speaker" into google and found a 5 inch guitar speaker.

http://www.jensentone.com/mod5-30.php


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## forsakenrider

what about this? http://ax84.com/media/ax84_m276.gif
 Im thinking of building one.


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## ovrclkd

Did you look at Ted Weber's offerings? 

https://taweber.powweb.com/weber/


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## jamesbobo007

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.


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## pabbi1

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.


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## nikongod

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.


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## pabbi1

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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## Zigis

for output you can use EL84, 6BQ4 or Russian 6P14P without changing schematic.
 I think trans is enough for guitar amp too.


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## FrankCooter

Change the 6v6 and you'll change the whole tone of the amp. There's a reason guitarists love this tube. Best small power tube ever made.


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## pabbi1

OK, laid this out on perf board (well the parts that I have onhand) just to have a look. This is the version with the "scrap parts'. I have about $30 total with a cheap 5" test speaker (4 ohm).

 Now, should I lay this out on a steel or aluminum base, or will perf 'work'? I actually need to trim about an inch of width to fit it in the case but it lays out pretty well.


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## pabbi1

Well, I got quite an assist with some vintage parts, so I just have to move the passive components to the strip board, solder them up, then wire the connections.


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## Zigis

Hi pabbi,
  I think with so simple schematic you don't need pref board at all.
  You have both tube sockets installed, add input jack and pots to your chassis, then secure 3 power caps somehow and choice one screw for star ground. Than simple go with other parts point to point by schematic.


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## pabbi1

Leo Fender thought the strip terminals were a good idea, especially since we are talking 330v, so hard to argue with. If it was 30v, maybe, but safety first. Besides, this is more old school, in keeping with a 62 year old design. It is rare we build circuits older than we are, which is way harder for some of us than we would care to admit.
   
  Besides, I have always been facinated about building something on a terminal strip with the turrets.


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## m0b1liz3

Hey Pabbi1,
   
  I was wondering how this turned out?  I am wanting to build a super small Champ clone myself.  Any advice on how to source the parts cheaply?  There is also a Micro Champ out there I thought of as well.
   
  -Mark


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## pabbi1

Funny you should mention this - having to get some assistance, as I am out of my depth... but, here is where I am, though I did pick up a 1950's Jenson alnico speaker to swap out once I get 'er working.
   
   
   
   
   
   
  Note: This amp is NOT UL listed...


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## TimJo

I may be building a Champ as well for a friend of mine.  
	

	
	
		
		

		
			




   
  Looks great Al!


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