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
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
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
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.
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.
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.
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.
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)
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
)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
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
another thing you can try if your curious is grab some of the old 12v tubes
12k5 and 12al8 come to mind there.
they are tubes used back in the day designed for use in car radios if I remember right and most are designed to be run on 12v for everything from the heater to plate voltage and most also are able to handle a max of around 30v.
try going to www.sopht.ca tog et some more information or check in the internet for "space charge" tubes
12k5 and 12al8 come to mind there.
they are tubes used back in the day designed for use in car radios if I remember right and most are designed to be run on 12v for everything from the heater to plate voltage and most also are able to handle a max of around 30v.
try going to www.sopht.ca tog et some more information or check in the internet for "space charge" tubes
so with the 12DW7 you use the medium mu section as your preamp and the high mu for your output? or I guess it could be used both ways..
If I Can get ahold of one of those I'll try it!
I used my 12at7 and got the desired effect by changing the plate resistors and bias resistors. I used the schematic from a fender amp for the preamp section, it used a 12ax7 but it worked fine with the 12at7. I used a 220k resistor on the pre section and a 100k on the post section. Bias resistors were 1k for the first section and 1.5k for the second, with different capacitors. I didn't get as much gain as I would with a 12ax7 because the 12at7 doesnt have as much, but it worked fine for me and was more than capable of driving the 50c5 to clipping. One thing remains, I still have a little bit of power hum ( no buzz, its a hum)
What could be causing this? I have a rather large filter cap (330uf 200v)
If I Can get ahold of one of those I'll try it!
I used my 12at7 and got the desired effect by changing the plate resistors and bias resistors. I used the schematic from a fender amp for the preamp section, it used a 12ax7 but it worked fine with the 12at7. I used a 220k resistor on the pre section and a 100k on the post section. Bias resistors were 1k for the first section and 1.5k for the second, with different capacitors. I didn't get as much gain as I would with a 12ax7 because the 12at7 doesnt have as much, but it worked fine for me and was more than capable of driving the 50c5 to clipping. One thing remains, I still have a little bit of power hum ( no buzz, its a hum)
What could be causing this?
I have a rather large filter cap (330uf 200v)
You can clone the Supro Bantam. It uses a 12AX7A and a 50L6. The original schematic shows the filaments wired in series and the plates operate with the line voltage directly rectified(no transformer!). I would recommend that you put a 1:1 transformer on the power input.
If you want, you can use a 12L6 and put in a small filament transformer. The beauty of this amp is that the output tubes are really cheap, 2 to 3 bucks a piece. If you go to a hamfest you can probably get them even cheaper than that.
A schematic can be found in the Aspen Pittman guitar amp book.
If you want, you can use a 12L6 and put in a small filament transformer. The beauty of this amp is that the output tubes are really cheap, 2 to 3 bucks a piece. If you go to a hamfest you can probably get them even cheaper than that.
A schematic can be found in the Aspen Pittman guitar amp book.
I think Im going to try a 12c5 instead, I wont need an isolation transformer because Im using a voltage multiplier to turn 24vac @ 2 amp into 180vdc @ 200ma. I also created a schematic for using an EL86/6cw5 instead for slightly more power. You can see it here : http://www.diyaudio.com/forums/showthread.php?s=&threadid=67999&perpage=10&pagenumber=7 , and mockup pics are on the next page.
I said I'm going to use a 24 volt 2 amp transformer and use a 6 stage voltage multiplier to get it to around 180v at only 200 ma or so (rounding up). I have already shocked myself a few times while working on it, theres not enough current to do anything its mostly just an uncomfortable zap. I purposly designed the power supply this way for one so I wasn't wasting power and for two so I don't melt the plates on the tube during testing if something goes wrong.
I plan on using a 24vac wall wart to power my finished project
I plan on using a 24vac wall wart to power my finished project
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