1/2 watt tube guitar amp

[9am53]

I have a Dream......A dream of a <1 watt tube guitar amplifier...I have looked at AX84 and the like, but I cant find what I'm looking for. I have some spare tubes lying around so I was thinking this: I want a <1 watt guitar amp for bedroom practice...no frills at all, no volume or any other control, just an input and out for the speaker. I would like to possibly make this using 1 tube and I would like to run in from a 9volt battery if possible...as tiny as possible, I intent to have this thing at max volume at all times (hence no volume knob) so I would like to to not fry everytime I use it. I recently bought a Peaveyt CLassic 20 for this reason, and holy it has way too much volume (grreat amp though) just too loud, I want something quiet but still have nice saturation. oh yeah, the tubes I have are 6eu7's and ECL86's

[thomsva]

Sounds like you have almost exactly the same requirements as I had some time ago. I ended up making my own design using affordable parts. It is a single tube amp using the ECL82 and no controls.
The ECL86 could be even better. It would be nice to try if it could be a drop-in replacement.

Here is some more info about my "Niteglow" amp:
http://www.angelfire.com/music6/thomas_s/

-thomas

[DigitalJunkie]

I once made a "pintsize" amp with a 1U4 tube..Little OPT from an old TV,and a camera flash circuit for the power supply!
It worked nicely,and could drive a little 1-inch speaker(similar to whats in headphones) pretty loudly..
The camera flash made a nice little power supply,running from 1 'D' cell,and another for the filament.

[Fuling]

A couple of years ago I made a guitar amp out of one 12AT7 (ECC81) and some parts from old radios.
One triode section as preamp and the other as "power" amp.
The OPT was 7k/4ohms or something, connected to a 4" 16ohm fullrange speaker.
Sounded pretty good, but I had to use clipper diodes to get a decent distortion.

[thomsva]

Fuling,
Have you measured how much power you get from a single ecc81?

[9am53]

Hey Thomasva thanks for the info. This is EXACTLY what I was looking for. Do you mind if I copy your schem? and if I ask you questions while I work on it? thanks a lot

[thomsva]

9am53:

Yes, of course you can copy the schematic! I hope it works well for you. The only thing I'd like to ask is that you share how the project turns out.

If you can find transformers that are close to the ones I use, everything else should be easy to get to get ideas transferable. The transformer is a 10VA with a 6V secondary. Without load the secondary is 7,6V.

My amp is still only a test circuit mounted on a piece of wood. I will still make minor changes but I will not touch the basic structure. Ideas are welcome! (if they aren't about how to make the circuit more complex :-))

[James D.]

I've built a 0.6W guitar amp and found it was still too loud to run flat out all the time... This was into a 12" celestion speaker of 96dB sensitivity... so I eventually found a 12" speaker at 82dB sensitivity and found that this works well as I can overdrive the amp all day long without getting a headache The low sensitivity 12" is a cheap chinese twin cone - I must have tried dozens of different speakers before I found this one - shame I don't know what it is....

James

[aletheian]

Go to ax84.com and check out the "firefly" priject. Self-split 12au7 output stage with lots of onl;ine help at the forum

[Fuling]

Have you measured how much power you get from a single ecc81?

No, I never did any measurements.
I´d guess somewhere between 0,1 and 0,5W