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Old 08-01-2012, 11:04 PM   #1
Culler Amps
Matt Culler
 
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1/2 Watt Tube Amp Build

I'm currently working on a new amp. A 1/2W high gain tube amp, I've named this amp the "Milliwatt"

This one is going to be interesting. I'm using "space charge" tubes, designed in the late 50's for use in automotive applications. Made to run on the 12-14V DC you'd typically see in a car.

The tubes I'll be using are NOS CBS 12EL6 and 12AL8.

I'll be using the 12EL6 and the triode section of the 12AL8 for the pre-amp, and the power tetrode section of the 12AL8 for the output.

Currently in the design phase. I may end up adding a transistor boost stage, or maybe use another 12EL6 for a bit more gain.

Tubes


Ready to get started


Getting the 12AL8 sorted


Added the 12EL6 input stage and now tweaking




Got it pretty close to what I want now, I'll be tweaking a bit more tonight and tomorrow and then get it built into a 1590BB enclosure.

Last edited by Culler Amps : 08-02-2012 at 01:48 AM.
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Old 08-01-2012, 11:09 PM   #2
assparade69
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that's awesome man, i'm stoked to see how it turns out. some audio samples would definitely be awesome
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Old 08-01-2012, 11:21 PM   #3
Viban
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Whats the green box off to the side with the cables in it? load box? This is really cool though , I like the use of these "space charge" tubes
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Old 08-01-2012, 11:41 PM   #4
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Quote:
Originally Posted by Viban
Whats the green box off to the side with the cables in it? load box? This is really cool though , I like the use of these "space charge" tubes



Its a breakout box I built. Easy way of hooking up to the breadboard.....

Signal and power both come in through the box. One of the toggles applies power, and the other is a bypass switch, for the guitar signal. That gives me the option of bypassing the circuit on the breadboard when building effects.

Last edited by Culler Amps : 11-08-2012 at 04:05 AM.
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Old 08-01-2012, 11:49 PM   #5
Viban
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Seems like a pretty handy little thing to have.
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Old 08-02-2012, 12:03 AM   #6
nickdohle
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Stickied! How high gain are you looking for? I figure the more preamp tubes the better for a higher gain amp.
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Old 08-02-2012, 12:43 AM   #7
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Quote:
Originally Posted by nickdohle
Stickied! How high gain are you looking for? I figure the more preamp tubes the better for a higher gain amp.


I'm shooting for something around SLO territory.

Currently with the 2 pre-amp gain stages, I am getting something along the lines of a tame JCM800 dirt wise.

With a MPF102 transistor gain stage in front I am definitely where I want to be.

I may add another tube gain stage instead of the transistor, but current draw is already pretty high.....

And the transistor will only be in the signal path while the boost is engaged, so I haven't made my mind up yet.
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Old 08-02-2012, 12:55 AM   #8
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That's pretty cool!
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Old 08-02-2012, 01:34 AM   #9
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Every time I see one of these kinds of things take shape I want to learn to build amps so badly, then realize that I am nowhere near competent enough in electronics to make it happen . Kudos to you though man, I'd love to have one for practice purposes. Especially if it hit SLO levels of gain.
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Old 08-02-2012, 03:30 PM   #10
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Quote:
Originally Posted by valennic
Every time I see one of these kinds of things take shape I want to learn to build amps so badly, then realize that I am nowhere near competent enough in electronics to make it happen



10 years ago I had no experience in audio electronics. I got started by building a boost pedal. Haven't been able to stop since..........
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Old 08-02-2012, 03:42 PM   #11
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One of these is exactly what I'm after, once you've finalised your design/prototyping I'd definitely be very keen to buy one, even more keen to get a kit version if you'd be willing to supply me the bare parts
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Old 08-02-2012, 07:07 PM   #12
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Okay. Got it close to what I want. I'll probably make a few more changes before the production model.........

Getting the enclosure ready now.

Bare Enclosure


Ready to drill


Drilled, label applied and ready for clear coat...
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Old 08-02-2012, 10:37 PM   #13
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2 coats of clear have been applied, got the tube sockets installed to give an idea of what it will look like.

Cooling down from the baking process, rubber feet added




Tube sockets in place


Now to get the other chassis mount components in. Pots, jacks, etc.

I'll probably do the wiring tomorrow.
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Old 08-02-2012, 10:47 PM   #14
RealGuitarHero
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Dude, I live in GSO and play with some people from King who go to UNCG with me. Nice to know there are people doing this kind of thing so close to home.
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Old 08-03-2012, 10:59 PM   #15
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Well, its been a busy day. I was working on boost pedals and attenuators all day, so literally the only thing I accomplished on the amp was installing the chassis mount components.





Hopefully tomorrow we will have a working amp and some sound-clips..........
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Old 08-04-2012, 04:43 PM   #16
nickdohle
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Looks pretty sweet. Cant wait for clips
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Old 08-05-2012, 02:44 PM   #17
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Holy smokes that is so awesome!! Will you share schematics with us, if we like it (which we do. We love small things with tubes).
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Old 08-06-2012, 05:20 PM   #18
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Seems like you know your way around tube amps. One question: Where do you get those tiny transformers? Online shops? Also, where did you get your tubes?
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Old 08-06-2012, 08:21 PM   #19
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Yes! I've been waiting for this! Can't wait to hear a demo of it once it's complete.

Any plans for adding tone controls? I saw in one of your youtube videos you have one with 6-7 knobs on it and it sounded fantastic. Do you take special orders/requests? I definitely want one of these amps.

Edit: Here it is.

Last edited by ExDementia : 08-06-2012 at 08:41 PM.
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Old 08-07-2012, 03:55 AM   #20
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Quote:
Originally Posted by Supercolio
Seems like you know your way around tube amps. One question: Where do you get those tiny transformers? Online shops? Also, where did you get your tubes?


In the US, the Xicon transformer used here can be ordered from Mouser. Its equivalent to the LT700.

I get all my tubes from Tube Depot. Production and NOS.


Quote:
Originally Posted by ExDementia
Yes! I've been waiting for this! Can't wait to hear a demo of it once it's complete.

Any plans for adding tone controls? I saw in one of your youtube videos you have one with 6-7 knobs on it and it sounded fantastic. Do you take special orders/requests? I definitely want one of these amps.

Edit: Here it is.



I may indeed add a single knob tone control on this amplifier at some point.

The amp in the video you linked was one I built a few years ago. It was a hot rodded JCM800 pre-amp with a single ended EL84 output.

Essentially a 5 Watt JCM800 with a hair more gain.

I will do special orders every now and then when I have the time.

Last edited by Culler Amps : 11-08-2012 at 04:06 AM.
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