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Help re-building/modding my bass guitar with an old tube amp i want to salvage parts from? Answered

Right so I have this bass guitar with most of the electrics missing, I'm only left with the jack out and the humbucker pickup. I want to do something a bit different as i have fixed guitars before and as this one is actually mine i want to experiment with it.
I also have 2 old guitar tube amps with a "Speed" effect on them which makes it sound like the speaker is pulsing, one of the amps now doesn't work, I'm presuming and hoping it's the just the tubes or power input and i was wondering if there was any way i could put the "Speed" effect into the bass.
I'd also like to salvage the treble and bass pots too if it's possible.
The speed effect is controlled by a pot that when turned all the way down clicks and turns off, i have opened it up to try already but I've only ever really done basic electrical repairs and this is connected to a proper circuit board. I can send more photos to help.
Thanks in advance
el Ginjo



9 years ago

It seems to me that what you're going to have to do, based on the conversation below, is to go with the stompbox built into the guitar. You will probably have to router out that control panel to add space for a few more switches and other electronics. You could build in either toggle switches or rotary switches depending on how you want it to look; functionally they'd be the same.

Yeah you know it! just wish I had a router, its going to be a hammer and chisel job :-S, I'm glad I enjoy wood work.

Well, so be it! Just make sure that chisel is razor sharp before you start, for best results. Have it professionally sharpened if you can't do it yourself.

hmm, yeah very good point. might have to think about investing in a router then.

Or a Dremel Tool---easy and light and easy to make your own bases for it for specific applications.


9 years ago

The effect you're describing is the "Tremolo" effect (or sometime termed "Vibrato") and usually has a speed knob, and sometimes a depth knob, too. Technically, tremolo varies the volume and vibrato varies the pitch, so most vibratos are really tremolos...

But no, I doubt it. You couldn't re-use a tube-driven circuit on a guitar, because the tubes run at high voltages. That means you also need the transformer--and to plug it into the wall socket. Many tube tremolos work by varying the bias voltages on the output tubes, which doesn't translate into a simple stompbox.

Not that it's impossible to make a battery-operated preamp/tremolo--you could setup a voltage multiplier for the tube's plate voltage. But the filament of a tube uses a lot of current, and batteries would drain very quickly (or be massively heavy.)

You can buy or build one with solid state components. It's basically a oscillator-driven volume control. Here are a couple examples...

thank you for the explanation and link, unfortunately I don't really understand circuit diagrams, everything I've done before has been trial and error. I don't know if it makes any difference but i don't want the valves themselves in the guitar, i was hoping a would be able to just use the speed knob and possibly some capacitors or something. Would something like that work or does a tremolo require them and the high power to work?

Oh, I thought you wanted the Tremolo in the bass (that's not a project for beginners...)

You could use the components themselves to rebuild the wiring. The "Speed" control is a potentiometer; basically the standard building-block for volume and tone controls.

So If money is tight, those POTs could be used for the internal wiring. POTs are pretty cheap--you can find them at RadioShack for 2-4 dollars.

But you might get $60-$80 for a small, non-functioning tube amp on ebay (or much more, depending on the model.) And more $$$ if it works. Or try selling on Craigslist.org. There's a real demand for tube amplifiers.

So I'd advise you NOT to scavenge the components, but to sell one of the amps to fund the rebuild.

RE: the bass wiring, here's a couple wiring diagrams:

Sorry there's been some confusion, yes I want the tremolo effect fitted in the bass i just didn't want to have to use the valves. Thank you for the wiring diagram, that will be really helpful

OK, I gotcha. ;-)

Vintage tube amps use tubes for the tremolo, so there's no getting around it. You'll need the tubes, and the high voltage.

Some of the modern cheaper tube amps use a solid state tremolo circuit. But you don't want to build from scratch, and those circuits probably won't work without the amp.

There are plenty of tremolo stompboxes like this one, if you can stand having it external (or disassemble the pedal, and install the guts in your bass.)

Re: excuse the USD prices, from your use of valve, I recon you're a Brit...

Thank you for all your help, it's really appreciated, and yeah you're right I am English :-)
Pretty sure what I'm going to do with bass now which is to get a tremolo stompbox and install that into the bass. still got a few questions though...
1. Pretty simple one and i'm sure i can do it. I want to use a double tone/volume pot (like this one) for the pickup before it goes to the effects and then to control the speed and depth of the effects itself so i can save space. Is this possible?
2. The Stompboxes I'm looking at, like the Tuna Melt you linked, have a switch to chose the wave form i was wondering if i could set that to a pot and therefore get more choice out of it?
3. And yet another question about pots!!! How would i go about putting in a control to adjust the amount of effect actually goes through? I think i mean the wet/dry mix.

If you're really serious about integrating stompbox guts inside your bass, you should chose the stompbox itself carefully. You couldn't easily add mix, etc. after the fact--but if those features are already present on the fx box, then you're already set. There's just no way to have all those "wants" (as in, "I want it to do this, and this") without having several additional knobs on the bass... Doubling up the POTs doesn't really give you any control, if you cannot separate the two functions.

see i don't know if they're called double or stacked pots but they are two separate controls on one pot, that's what i mean. what i was saying about the mix control is would i be able to swap the switch to a pot to get a fade between the 2

You can use 'em, but you're giving up independent control of each POT.

You should first experiment with the stompbox as-is. You may find you cannot live without the on-board depth and speed controls, for instance. Then plan your wiring schem...

hi i have been playing bass for about 5 years and your solution would probably go with a stompbox than totally ruining the amp (even though it doesn't work ) you could have an easier time with the actual wiring and working than worrying about if it is going to work good luck:) p.s. what part of Britain do you live in?????

Don't get me wrong, I'm well aware that a stompbox would be tones easier but then it's just another bass isn't it?! I'm a drummer primarily i play bass because i can and it makes writing songs easier, i want to do this with my bass also because i can. Surely on this site in particular the easy answer isn't necessarily the right one. I know that using the stompbox as a stompbox would be the easiest thing to do but that's no fun :-) I'm currently living in Norfolk with my misses whom is going to uni here, from Islington, London originally.

Well i was just saying that because i thought it might be harder to screw up the bass but yes i totally agree with what you are saying why ruin the thrill of it all right?? p.s. i have a friend that lives in Norfolk p.s.s. thats really cool that you are drummer do you have a band???