Want to build single tube amp

Syrus1312 · Post by **Syrus1312** » 31 Jul 2011, 18:39

Hey,

I'm new at this forum, so this my introduction.

I really enjoy this forum and all the posts. Some are really good.

In this experience, I'm hoping to find some help.

I've been amazed by so many mainstream amp's having to much non-sense onboard.
Therefore, I'm looking for something pure.

Something like a singe tube, low watt amp.
With minimum part count. Just a volume, perhaps. Just want to plug my guitar into a simple quiet tube amp.
I have experience with solid state, but I'm most aware of the hazards of getting shocked when playing with Caps.
Death by electrocution isn't funny.

I found this online http://guitar-dreamer.blogspot.com/2011 ... e-amp.html
Maybe, just what I needed.

Is this schematic any good, what are things to be improven?

How do I make a simple layout?

Many thanks in advance!

SirElwood · Post by **SirElwood** » 31 Jul 2011, 19:24

I would not recommend that amp... There are some quite good small 12ax7/12AU7 amps, but if I have to build an amplifier with just one tube I would use a ECL82 (or 6bm8 if you are in US). That is a preamp triode and power pentode in one bottle. Gives about 3 watts. And it can be very very simple.

Here is a draft schematic just to show you how simple it can be (and there is still some parts you can take away). Of course it needs a power supply, but that's not a big deal to come up with on amp like this.

EDIT: Crap, that pentode g1 220k resistor is in a wrong place... Well. There might be some other issues as well, so do not build this. It is just to show you an example.

Syrus1312 · Post by **Syrus1312** » 31 Jul 2011, 19:49

Well thanks anyways

What I'm aiming for is, simple 12ax7 amp. These tubes come in all flavors and are widely available.
Low watts, so sub 1 watt.

What do you recommend?

SirElwood · Post by **SirElwood** » 31 Jul 2011, 20:03

Syrus1312 wrote:Well thanks anyways

What I'm aiming for is, simple 12ax7 amp. These tubes come in all flavors and are widely available.
Low watts, so sub 1 watt.

What do you recommend?

To be honest... Forget it. 12AX7 is a preamp tube. You can build some very nice preamps whit it...

But! There is this thing called firefly: http://fireflyamp.prv.pl/images/scheme.gif That is ok and some people really like it, but I didn't like it as it is. However something like ECC99 instead of 12AU7 in power amp will work better. Or should I say "sound better".

You can also use any common power tube (6V6, 6L6, EL84, EL34 etc.) if you lower the supply voltage. Something like 100-150 volts to 6V6 and you have a 1W amp. It makes power supply more complicated and preamp needs some adjustment, but it can be done.

Scruffie · Post by **Scruffie** » 31 Jul 2011, 20:29

This one always interested me... needs a special tube though - http://www.solorb.com/elect/musiccirc/squirrelmonkey1/

Syrus1312 · Post by **Syrus1312** » 31 Jul 2011, 20:36

SirElwood wrote:
Syrus1312 wrote:Well thanks anyways

What I'm aiming for is, simple 12ax7 amp. These tubes come in all flavors and are widely available.
Low watts, so sub 1 watt.

What do you recommend?
To be honest... Forget it. 12AX7 is a preamp tube. You can build some very nice preamps whit it...

Actually, I own a Killer Ant. Which is just 2 pre-amp tubes, 2 x 12ax7. This amp uses only one half of a 12ax7 as power-amp.
The thing is, I want it more simple. No tone-stack and single tube.

if all else fails, I Will build a PTP version of it. Only those damn transformers are bugging me. It has to be possible to make an amp with just a single 12ax7. Power is no concern. The tone-stack is probably the only reason why there a two tubes and not one.

Syrus1312 · Post by **Syrus1312** » 31 Jul 2011, 21:29

Scruffie wrote:This one always interested me... needs a special tube though - http://www.solorb.com/elect/musiccirc/squirrelmonkey1/

Thanks for the link. That's the spirit.

12dw7 seems like a good option too or 12AT7

Yeah, that is a weird tube

yet very interesting too

ansil · Post by **ansil** » 31 Jul 2011, 21:49

ECL82 i think i have fallen in love with this tube. this is a much better choice than my old 6dx8's thank you thank you thank you

Syrus1312 · Post by **Syrus1312** » 01 Aug 2011, 16:28

In the sense of ECL82

http://niteglow.webs.com/

DrNomis · Post by **DrNomis** » 04 Aug 2011, 13:39

You could also use a Tube like a 6GW8, these are in a 9-pin format and are similar in size to an EL84, but they contain half of a 12AX7, and a Beam-Power Tetrode in the one glass envelope, you could use one to make AX84.com's P1 amp, or maybe a High-Octane if you added an extra 12AX7 Tube.....

If you decide to try using a 6GW8, just bear in mind that the heater (pins 4 and 5) requires 6.3VAC.....

DeanM · Post by **DeanM** » 04 Aug 2011, 22:24

DrNomis wrote:If you decide to try using a 6GW8, just bear in mind that the heater (pins 4 and 5) requires 6.3VAC.....

Datasheet says AC or DC.

btw...the ecl82 mentioned above also contains a triode and a Pentode.

Zipslack · Post by **Zipslack** » 05 Aug 2011, 01:49

Take a look at this...it's not bad. My 12AT7 version is a clean to slightly dirty version for using OD/boost pedals. The original version by Rexindigo uses a 12AX7 and sounds pretty decent from his clips.

*** Warning - it's on that OTHER forum ***

http://music-electronics-forum.com/t4563/

ansil · Post by **ansil** » 05 Aug 2011, 03:43

My biggest question with mini amps is why does everyone serum to want
To use a fender reverb transformer ?i don't get it why not a champ one. better specs higher voltage more wattage same price biggest dif is 4 ohm load but they make 8 ohm replacements now I have two in the shop now.

DeanM · Post by **DeanM** » 05 Aug 2011, 11:29

Zipslack wrote:Take a look at this...it's not bad. My 12AT7 version is a clean to slightly dirty version for using OD/boost pedals. The original version by Rexindigo uses a 12AX7 and sounds pretty decent from his clips.

*** Warning - it's on that OTHER forum ***

http://music-electronics-forum.com/t4563/

The MP3 he posted sounds pretty good!

RnFR · Post by **RnFR** » 05 Aug 2011, 13:05

Zipslack wrote:
*** Warning - it's on that OTHER forum ***

http://music-electronics-forum.com/t4563/

I'm pretty sure you were just being facetious, but if not, please don't hesitate to use the name of any other forum here. we don't have any of those stupid rules. it's printed nice and big in the link, anyway.

Zipslack · Post by **Zipslack** » 05 Aug 2011, 14:29

You caught me...I was being facetious. Some forums are really fussy about cross-posting and linking.

As far as the reverb transformer, it's designed to match-up with 12AX7/12AY7/12AT7. It's got a nice high impedance on the input (11k - 22k, depending on model) with 8 ohm out and is much cheaper to obtain -- about $8 - 10 US.

Syrus1312 · Post by **Syrus1312** » 08 Aug 2011, 14:54

Damn

Been on a holiday for a week, but look at all the posts

Great !

Thanks all, is everybody feeling the single tube mojo already

?

DrNomis · Post by **DrNomis** » 08 Aug 2011, 15:06

Hmmmm....I've had some experience with re-winding transformers, I might have a go at making a small 1 tube amp, and see if I can make my own output and power transformers for it.....

Syrus1312 · Post by **Syrus1312** » 08 Aug 2011, 19:13

DrNomis wrote:Hmmmm....I've had some experience with re-winding transformers, I might have a go at making a small 1 tube amp, and see if I can make my own output and power transformers for it.....

Sounds Cool, is it difficult?

( I Realise that is a relevant question to skill) But in general? It should be more easy then, say pick-ups?

I was wondering about hum, my thoughts are to recitfy the Heater current to DC and twist the cables, use starground, and so on.

Ac -> DC is better right? Hum-be-gone?

I was also thinking about making a sort of faraday cage around the Transformers and grounding this, does this seems logic to you guys?

ppluis0 · Post by **ppluis0** » 09 Aug 2011, 01:04

Hi Syrus,

My recommendation is to use the supply design found in the niteglow example, or better is to use a wallwart to provide 6 Vac (replacing transformer TR1) and an internal transformer of 120 to 6 Vac connected backwards (as TR2 are) to provide the high voltage needed by the tube.

Keep in mind that the ECL82 was commonly used at no more than 200 Vcc, so the supply voltages listed at the diagram seems to be excessive.

Don't worry about use dc for the heaters. If you follow the approach used in that schematic, you see that the heater are elevated some volts from ground. Better than that is to build a voltage divider taken from the plate supply to obtain 40 to 60 Vdc to feed the junction of both 100 ohms resistors.

This way the leakage between cathode and heater is cancelled, and also the hum, so you don´t have to provide regulated supply to heat the bulb. Just twist the filament wires inside the unit.

Regard the transformers, the best is to have one constructed with a shield, like the reverb driver of the Fender amps:

This is also valid for the 120 to 6 volts to be placed inside the chassis (TR2 in the schematic).

Cheers,
Jose