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Old 10th June 2011, 05:25 AM   #1
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Default 1 Tube 1 Watt Guitar Amp

I am interested in building a small 1 tube low power guitar amp, less than a watt is fine. I know there are numerous options, but I wanted to try an ECL82. OTs are easy to find and cheap but power trannies are not.

So here is what I want to try and need some advice. There are interesting options for outputting around 190V, one of which is the NeonNixie High voltage module (have a kit which takes 1/2 watt 12-14V and puts out 22ma @ 190V), which should do the trick. Has anyone used a small split output transformaer such as the MagneTek FS12-1000 (1watt 12.6 2watt 6.3) and build a power curcuit to drive that (or a similar) tube? Maybe another option is running it off a wall wart, but those are not usually too clean.

Once I have the power worked out I will get to the amp specs, but I think this would make for a small footprint practice amp (stomp box size) that would sound reasonable.

Thanks
Tom
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Old 10th June 2011, 07:10 AM   #2
Doz is offline Doz  United Kingdom
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I doubt your nixie-tube supply will put out enough current to drive the output stage.
I built an amplifier with an identical tube, and used two back to back mains transformers to obtain the HT. Not so easy in the USA, because you have 110V mains, but you could get two transformers : 110 to 6V then 6V to 110-0 110-0 (Universal "Primary"). You can then use the 6V winding for your heater, and wire the 110-0 110-0 for 220V and your HT. Done and dusted and change out of 20

I think you are thinking along similar lines with the magnetek transformer.

I used a Hammond "Universal" SE O/P transformer. The thing had to be cheap, and mine was made entirely from junque box parts.
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Old 10th June 2011, 12:19 PM   #3
Cassiel is offline Cassiel  Libya
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ECL82 is fine but you need more gain, one triode to drive the pentode won't be enough. Here are some ideas for the power supply:

JJS.at : Electronic Projects : Class A Subminiature Amp

freestompboxes.org • View topic - "Superfly" - submini tube version of Doug H's Firefly
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Old 10th June 2011, 12:38 PM   #4
Doz is offline Doz  United Kingdom
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Quote:
Originally Posted by Cassiel View Post
ECL82 is fine but you need more gain, one triode to drive the pentode won't be enough.
Very true, although running the first triode in "starvation" helps, and produces some "colourful" distortion
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Old 10th June 2011, 12:42 PM   #5
SY is offline SY  United States
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Have you considered using a three section compactron? I'm putting together a small practice/studio amp using a 6AF11, which has a nice 5W pentode, a high mu triode, and a medium mu triode in the same envelope (thanks to rsumperl who pointed me toward that tube).
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Old 10th June 2011, 01:44 PM   #6
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The 6AF11 and its equivalents (6BD11, 6AS11) had occurred to me as well - they have 15V versions too, but you'd probably want DC for heaters to avoid hum. A dual-primary 6V / 30+ VA transformer with ISOLATED primaries (not bi-filar wound, like some Signal parts) could be used, with one primary used as 120V secondary. Use a doubler to get 280VDC.
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Old 10th June 2011, 07:40 PM   #7
Fuling is offline Fuling  Sweden
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I made a just-for-fun guitar amp for my brother in law a few years ago: A single ECC81 mated with a 180V power supply, a tiny 7k:4R OPT and a 4" 8ohm speaker. One ECC81 section is good for 0,3W or so, loud enough for bedroom use. A switchable diode clipper after the gain stage increased the rock `n roll factor quite a bit.
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Old 10th June 2011, 08:29 PM   #8
M Gregg is offline M Gregg  United Kingdom
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I still find this interesting.

OK its not one tube the use of the EF86 I find interesting.

http://www.ampbooks.com/home/amp-tec...bench-test.gif

I have never seen an EF86 in SE mode though!

Regards
M. Gregg
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Old 11th June 2011, 12:41 AM   #9
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What's all the fuss and muss about? An inexpensive Triad N-68X isolation trafo feeding a Greinacher doubler takes care of the B+. A 117Z6 is perfect for this job, as it will provide the "sag" guitar pickers favor.
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Old 11th June 2011, 02:10 AM   #10
ChrisA is offline ChrisA  United States
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You can run a micro-power guitar amp off a wall wwort power cube. The trick is to use an AC power cube. Get one that puts out at least an amp at 12VAC. Then inside the amp you have a 12V filament transformer wire "backwards" THat gives you 120VAC and when you rectify it the filtered DC comes out to maybe 160V. You might also use a 6.3V filament transformer and get a higher B+ voltage. This sytem will only give you single digial milliamps but for a 0.25W amp that is all you need.


One other very good power source for micro-power amps is batteries. It is good to not have to plug in to mains power but then you need a switch mode power supply
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