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Old 27th November 2010, 02:25 PM   #1
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Smile low wattage valve amps

Hi there. First post and first forum I've joined. I live in south africa and have been building amps
for about ten years now. Early days were all about volume but since wife and two kids came along,
its been about getting tone at a decent soft sound. Decided to join a family of people that
understand what I am talking about since the are few around that understand valveamps, except for
the guy who winds my transformers and he is in a different town.
Well, I have been playing with different output valves that were not intended as output.
The tryed and tested 12at7, 12bh7, E80cc, but
I have had so much fun with a 6an8a pentode output. Very cool crunch at low level!
Designed (on paper only) a full pushpull amp with PI and reverb with 4 tubes.
Has anyone else done something similar?
At the moment it has only been SE, but still loud!!.
1 watts are still loud!!

Thanks.
Benj
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Old 27th November 2010, 04:04 PM   #2
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Old 27th November 2010, 04:39 PM   #3
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Default low wattage

Most of the low wattage work in the past was for portable radios in the early sixties. Obviously saving battery life was the goal. The biggest watt sucker was the thermal vibrator used to create the B+ (plate voltage) in radios up to about 1960. Special 12V b+ tubes(valves in UK-speak) were developed, something about "space charge effect" or something. As soon as transistors got fast enough to do radio frequencies, all this work went down the tube. Most tube hobbiests now are plugged into the wall socket and don't worry about the heat. There have been long threads here about those 12V only tubes, but I can't remember the exact nomenclature to give you a search key.
People doing guitar effects for clipping distortion that are worried about battery life and tube cost (overdriving tubes burns them up) use zener diodes for clipping, or digital computer based effects.
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Last edited by indianajo; 27th November 2010 at 04:44 PM.
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Old 27th November 2010, 06:32 PM   #4
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Been trying to get some low voltage tubes but my supplier here doesn't stock them.
I made a 12v 12au7 pedal that works quite well. I am allergic to solid state.
Won't put diodes in to clip tubes. Clean valve tones are best. The ability to control
The clipping just by the pick attack. The best. Just like small tubes running on
High voltage. The idea of an EF86 and 6an8a pentode output is cool. And I really like
the tone of the little 6an8a pentode.
Thank you for the welcome
Benj
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Old 27th November 2010, 08:16 PM   #5
Gilgy is offline Gilgy  United Kingdom
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Hello Benjamin! From the words about pedals and clipping I take it you're a guitar amp guy rather than a hifi guy?

I'm a lurker here, very much still in the copy-paste school of amp design but diyAudio is full of godlike geniuses of vacuum tube technology and my knowledge is slowly advancing. To quote Isaac Newton, if I have seen further it is only by standing on the shoulders of giants.
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Old 27th November 2010, 11:32 PM   #6
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Hi Benjamin,

Ive been busy thinkin about the same problem for a while now.
A few things to consider:
- most distortion done in the pre stages of the amp sounds "hard".
- The sound I like the most is when the complete amp is overdriven, it sounds way smoother then the above or a pedal.

I think the sound of the power-tube in overdrive, combined with the saturated tranformer, gives the smooth distortion most people look for. (this is the real "tube" sound)

So I was thinking of building a normal SE tubeamp, but with an el 34, on a transformer of an el 84. Should give about 3-5 watts.

Then: after the output transformer connect an L-pad, before going to the speaker. There are L pads who can dissipate up to 100 watts, so the 5 watts shouldnt be a problem.
This way you can put the amp in overdrive, whith the smooth sound you want, but at the same time at a low volume.
I dont know if someone else build something similar...

I think my amp will be a Fender princeton clone, or something similar.
Building starts in a few weeks.
If you want I can update here if there is some progress.

Paul

Last edited by pauldune; 27th November 2010 at 11:36 PM.
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Old 28th November 2010, 03:14 AM   #7
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The forum is excellent. Love getting replies. Yes guitar amps!!:-)
Good to talk to people that don't just nod and smile and go that's nice.
Nothing against attenuators, but been trying to make an amp
that is complete without trying to squash the output.
There is a bit of tone sucking with this concept. Would really like
projects to be posted here. Dropping the voltage over whole amp works quite well
to reduce volume.
Its just that I have an interest in using little pentodes for quarter watt amps.
Pauldune: Remember to use a choke before the plate supply to remove hum.
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Get shocked, make crap amps. That we learn from!!
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Old 28th November 2010, 04:41 AM   #8
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Quote:
Originally Posted by Benjamin Craig View Post
Its just that I have an interest in using little pentodes for quarter watt amps.
This could be far in excess of your target then . . .

Click the image to open in full size.

This is a one watt guitar amplifier, using a 12AX7 preamp valve, with a 6T10 output valve. The power supply uses two low-voltage transformers back-to-back, while the output is a reverb driver transformer.

Construction details are here: The Uniwatt Amplifier Revisited
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Old 28th November 2010, 06:48 PM   #9
M Gregg is offline M Gregg  United Kingdom
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Benjamin,

I have been looking at this web site just for interest.
Using Push-Pull EF86 Pentodes in a Low-Power Guitar Amp

I have been thinking about trying the circuit to see how it sounds. I built a fender champ a while back and used a 6L6 single ended it sounded very good.

It would be interesting to hear what kind of pedals you have made.

Regards
M. Gregg
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Old 30th November 2010, 10:35 AM   #10
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Quote:
Originally Posted by M Gregg View Post
Benjamin,

I have been looking at this web site just for interest.
Using Push-Pull EF86 Pentodes in a Low-Power Guitar Amp

I have been thinking about trying the circuit to see how it sounds. I built a fender champ a while back and used a 6L6 single ended it sounded very good.

It would be interesting to hear what kind of pedals you have made.

Regards
M. Gregg
I've looked at that pentode press website. That is when I started playing with small pentodes.
I haven't hooked up a ef86 yet, but the 6an8a works well. Have some e83f's at home to try.
My voltage is abit high on my test chassis, so scared of frying some valves I've got.
I've built a 200v pedal, two stages. A 50v pedal, one stage with C follower (it was for an accoustic guitar)
And a 9v - 12v pedal.

Benj
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