diy tubes

Well, first you take off the back cover of any old effects pedal, and then, to quote tplyons:...

 

The circuits aren't all that complicated, but the trick is that you need to get hold of the the right DC voltages to run the tube - a low-voltage filament supply, and a high-voltage plate supply. The low-voltage is 12V, and the high is something like 200V, if I remember correctly. The high voltage supply must be very pure, with no 'ripple' or other noise.

When it comes to how many tubes; the 12AX7 is a twin triode, so you're getting two class-A stages per tube, or you could go push-pull or differential. The latter two amp types are very low in even harmonics - the evens cancel. I think the more 'musical'-sounding amps are class-A; they have both even and odd harmonics. A single tube should be plenty, I'd think. You're not really looking for lots of gain - for a bass preamp it'd be running more like a buffer amp or current amp or impedance converter or whatever. If you're thinking of having tone controls on it, then that gets more complicated, and probably involves more tubes - especially if you want cut/boost or some kind of parametric control. Just straight high-cut or low-cut is simple, but I think you'd still need an extra buffer stage - with just a simple high-cut, I think one dual triode would do it; one buffer amp between the input and the lowpass filter, and one between the filter and the output.

I haven't been into electronics for a while. That does sound fun to mess with valve preamps! Hm.

Joe

 

Here's a resource you may find helpful: www.firebottle.com . Spend some serious time following the links and reading the articles there. By serious time, I mean like months, really.

I'd personally start with either a Fender knockoff, or an Ampeg one. Schematics are easy to come by, and you'll have no trouble getting troubleshooting help if needed. If you don't use scrounged parts (which is what I do), or maybe a kit, expect to pay at least as much as buying a nice used preamp would cost. This depends a lot on how much you value your time though, and whether you are willing to buy specialized tools and can amortize them eventually. OTOH, you can find old PA heads and make something funky looking that sounds great for pretty cheap, and I'd recommend that as a good starting approach.

2-3 tubes will do nicely, especially if you're only looking to build a one channel preamp with a standard tone stack of some sort. Don't limit yourself to 12AX7s necessarily, there are some other nice choices out there as well.

Feel free to PM me for more specifics if you like.

 

It's still well worth doing though. The amp pictured below was used by a friend at many gigs as a guitar head after I modified it, then I got it back, and currently it sounds a lot like an Ampeg B15. The price on the tag is what I paid for it originally.

 

I am very intrested aswell, ive thought but have never tried
check out theses schematics
http://www.drtube.com/guitamp.htm#

 

Ummm - OK.

Metal film resistors have less noise than carbon.

Use good-quality film caps in the signal path.

Use a real quiet, noiseless power supply for the plate. There's this method of using a regular filtered voltage source that's a little high, and then using a couple stages of series-R, shunt-C, series-R, shunt-C to really smooth it good.

Get tube sockets that will take the bayonet-mount noise shields, and use shields for absolute mnimum induced noise (but often builders don't, just because the metal shield covers-up that beautiful, glowing tube!).

Make sure the output terminal is DC-isolated with a good film cap. Let that 200V plate potential get at your amp head, and sumthin'll toast!

You'll go mad trying to use one of those super-crappy Radio Shack soldering irons. It makes a huge difference to use a $30 Unger or somthing - 30-45W is good. The main trick is to make it one with the iron-plated copper tip. Also, What really makes soldering a dream is to get some liquid flux to brush on the metals before you solder; I usually water it way down with pure alcohol or laquer thinner til it's thin and barely yellow (I've even watered-down the brown Radio Shlock paste-flux for this). Between the weak flux and an iron-plated tip, soldering is a breeze.

Uhh... have I missed anything?

Probably plenty.

Joe

 

I have a first generation B.K. Butler Blue Tube, ca. 1991.

I recently gutted the three passive tone pots, which were nothing more than 250K ohm resistors. I just hardly use it much anymore. Built like a tank.

Maybe I can post the schematic if anyone is interested. I don't have a scanner but I am sure somebody does.

I would like to use something besides a 12AX7A. The chassis is steel and there is no power switch. Ostensibly, it can be totally reconfigured into anything. AC operation only.

 

great thread! i'm actually wanting to make an overdrive pedal with a 12au7 JJ and some eq before the tube stage. i want to try to make if the old fashion way withouth OP AMPS and see how difficult, noisy it gets. i wanna have all the dynamic an overdriven tube has ..you know from really clean but fat sound when softly playing to really dirty sounds when plucking hard on the strings. I got a couple of books from the 60's and 70's with all the tube stuff in them and an iron solder, osciloscope and tubes!!

now i just need time!

 

Cool. An old thread back from the dead! Interesting stuff. My room mate and I where recently discussing building a tube preamp. Thanks for the link Passinwind!!

 

The current version of the Ampage forum is now here: http://music-electronics-forum.com/

Have fun!

 

Nice!! Thanks

 

One thing I would look into for modeling as far as tube operation goes would be my rocktron silver dragon pedal. It uses 16.6 volts to run a 12at7 tube (lower gain tubes would work as well) so that means no lethal voltage, but the tube operates just fine. This also means less cost for the power supply.

 

The Rocktron Silver Dragon looks to be pretty good! Seems to be reasonably priced too.

 

I even have a schematic for it on PDF if that would help you

 

Trevorus - I would be really interested in getting a copy of that Silver Dragon schematic, too.

Here's what I'm working on...
http://moosapotamus.net/IDEAS/F2B/alembic.htm
I need to update my web page, tho, because I'm actually well into the process of building this alembic F2-B clone.

I've built, wired and tested everything (audio & power circuits) and it really sounds great. Now I'm in the process of stuffing it all into a 1U rack enclosure with a second audio section feeding a transformer balanced DI output.

I'm not installing the brite switch (SW2 in the scheme) because it doesn't work nearly as nicely as the hi cutoff swich (SW1), which I am installing.

I'm also putting in a switch to disconnect the mid eq control (VR3) from ground which acts as a bypass for the whole 3-band eq section.

And, I ended up having to make a different PCB using axial lead caps for the power supply because I couldn't find 47uF/350V radial lead caps that were short enough to fit in a 1U rack box.

Anyway, if your up to the DIY challenge, this is definately a nice sounding single tube preamp for bass. Oh, and I think I'll be using a groove tubes 5751.

~ Charlie