Tube synth modules / amps

[moordenaar]

Hello people.

I love tubes. I really do. And that's why I need to build something with my stuff. I've already decided I need atleast 1 VCO. I found this one on Ken Stone's site http://www.cgs.synth.net/tube/vco.html Which I do have the tubes to build. As it requires 12AT7, OB2 and 2D21.

I would also like to build a small amp. Or 2 for stereo. Maybe reverb.

Also effects, filter and so on would be interesting.

Maybe you can have a quick look on the tubes I got and give me some hints ? Also could someone point me in direction of a good tutorial on the back to back transformers trick ?

I also have some different neons that i would like to build an oscillator of. Some are rated 220 V. and are greenish with a halo on top, and a "rod" on the bottom.

Here's my tubes. BTW if anyones interested in buying the 2 "GEC TT22" you can write me.


EF95 (6AK5) x 5

6AK6 x 2

12AT7

6AU6

EB91 (6AL5)

6AL5

OB2

OA2

GZ34

EBF89 (6DC8)

UM80

EM80

EM87

EZ80 (6V4)

12GN7A

ECH81 (6AJ8) x 3

EF81

EF89 (6DA6)

EF184 (6EJ7) x 2

UL41 (45A5)

ECC85 (6AQ8) x 3

ECC83 (12AX7)

EL86 (6CW5)

ECL82 (6BM8) x 3

UCC85 (26AQ8)

85A2

UF89 (12DA6)

EABC80 (6AK8) x 2

EL84 (6BQ5)

2D21

TT22 x 2

I also have a tube that says

Marconi
Q0.1655C
333.33 KC/s
200/A/30

What is that ? Oscillator ?

[moordenaar]

Also would I be correct assuming that I can just replace the 6064 tube with my EF91 tube in this schema ?

http://www.cgs.synth.net/modules/cgs27_tube.html

[moordenaar]

Also a cute little preamp would be nice.

[EdisonRex]

FWIW, the Wretch from Metasonix uses thyratrons (2D21,5727,PL21) and a regulator (5651) for the VCOs.

Your 12AX7 would make a fine preamp. That's what I've always seen them in since I was a kid. The 12AT7 if I recall is a higher impedance one, makes a punchier preamp (totally from anecdotal memory, so i might be wrong). I have used 12AT7 in place of 12AX7 and it is indeed punchier.

The 6AK5 is used in the filter section of the Wretch, apparently a 6AU6 can be used in that sort of circuit.

Your marconi tube is probably something for a radio transmitter; the 333.33KC/s would be 333.33KHz...

If I can find my tube books I could look up some of those odder looking ones. But yeah you could make stuff out of a lot of those.

[rosch]

the Eric Barbour article you link to also contains a psu circuit that shows how the transformers are connected back to back. actually the voltage is transformed down, there the filaments are powered from. then it is transformed up again for the anode voltages. that way you have high voltages but separated from the mains power, which is important.

i've spent a lot of time searching the web for tube synth circuits and found some that use many of the tubes youve mentioned. there are also designs that use ECH, ECF.

however i decided to start learning in the 12V domain and later also build some tube designs. so, i'm still just at the beginning of learning and honestly it might take me some time until i try to mess with high voltages.

but i can look in some documents (that i printed out at times i didn't have my own pc), there should be a lot of links, most of which you'll be able to find on google or at websites of people who have built tube synths.

one good place with a lot of info is www.electronicpeasant.com

[Boogdish]

Not directly synth related, but a great resource for learning about tubes is www.thermionic.info It's full of old articles from back when tubes were still technologies top dog.

Another good site for understanding amplifier design specifically is valvewizard.co.uk It's geared towards guitar amps, but a great resource. His first book is fantastic as well (haven't read the second yet).

[andrewF]

this thread
has heaps of links & info on tube modules

[rosch]

wow, thank you for this link!

[piedwagtail]

[moordenaar]

Also I'm in europe so we got 220 - 240VAC in the walls.

Is there a schema for PSU at this voltage somewhere ?

And thansk for the help and links guys..

[andrewF]

A power supply is easy to make, just follow the standard design and safety precautions (ie - fuses, earth connections, no exposed wires, clamp down wires so nothing gets loose).
Tube synth circuits don't require much high voltage current, seeing you are on 220-240VAC go out and buy a transformer that converts 240 -> 110VAC. These are for running US or Japanese appliances in 240VAC regions. Here in Australia a 1.5A version costs around $40. 110VAC rectified and regulated should result in around 160-170VDC.

The tube heaters typically require 6.3V at 300mA per tube. If you build a few modules this adds up quickly to a few amps. Two of my tube synths use computer power supplies with some resistors changed to increase the 5V output to 6.3V. These supplies typically can supply up to 20A.....enough for over 60 tubes.
My latest tube synth just uses an 8A transformer and the tube heaters are fed 6.3VAC, no caps, regulator, rectifier.....just wired straight off the transformer.

Finally Eric Barbour has said that you can run the heaters in tube synth circuits at 5V with no ill effect. So if you use a computer PSU, don't bother trying to adjust the 5V output, just use it as is.

[moordenaar]

Andrew so are you saying I should

240vac to 110vac --> 110vac to 6vac ->6vac - 110vac -> rectifier ?

or just 240vac to 110vac --> rectifier ?

What about filtering hum ? Is a load of big caps enough ?

[andrewF]

[moordenaar]

Ok so I got one. It provides me with 128 v. But after the rectifier it's only 113,5 v. What is going on here ? Should it not be multiplied by 1.414 ?

[phdinfunk]

You know what I always thought would rock my synths rig?

A little Discrete FET mixer with a power tube output. Maybe use those miniature 12V power tubes I've seen 'round and about.... I think the power stage is more important than pre-amplification, having played a lot with tube guitar stuff. Of course, you COULD make something like that with all tubes if you wanted to.

Just what I think would be awesome.

If you really wanted to be badass, and play your synths through tube amps, I think two small 15 watt tube amps, like Champs, but with speakers for fuller freq. response. Then put them in some kind of effective sound-baffling cabinet where they're isolated from each other and don't get too loud on the outside so you can CRANK them....

That would be very cool for recording synths, methinks. I've considered trying to build something like this.... maybe I will someday.

[andrewF]

[moordenaar]

Well I'm using a "dedicated" rectifier. Should I use diodes instead ?

Also where do you find schematics for the Wretch from Metasonix ?

[moordenaar]

I just changed it with some big ass diodes.. Works like a charm now. 135 v. DC.