turning an old stereo console speaker into a guitar amp?

[scott macdonald]

Folks --

So I've got this tube-amp speaker thingy from an old stereo console. It was given to me and it works. Here's a picture of it:



I'd like to install a 1/4" high-impedence input on the thing and make it a guitar amp or a weird vocal amp for high-z mics. It looks cool and it would be fun to take to shows. Here's a page with more pictures of it, including the insides:

http://www.rumandrebellion.com/tube_amp.html

I have virtually no DIY electronics skills, but I want to learn. Is my idea workable and/or worthwhile, and if so, how should I approach it?

Thanks in advance,

-scott

[nclayton]

My only advice is to attach a 1/4 jack and play the guitar through it.

I'll bet it will sound perfeck.

Ned

[scott macdonald]

This thing has one wire going into it, with an RCA connector on the end. So should I strip that and attach the 1/4 jack there? Or is there something else I should look for?

[A-Barr]

I would suggest getting a standalone mic pre with an unbalanced out and plugging that into the line in on the amp. Maybe a mic pre with a DI so you can plug a guitar in there too. Hopefully that's not a phono input because that will give you some crazy de-equalization and other weird stuff, can you plug a cd player or ipod into it and get a reasonable sound? I would check it out this way first.
This thing is just BEGGING to be converted into a Marshall 1974/18watt. But that would obviously require some electronics experience, check out 18watt.com if you want some more opinions on this... if only I was on the West Coast I would help ya out.

[nclayton]

This thing has one wire going into it, with an RCA connector on the end. So should I strip that and attach the 1/4 jack there? Or is there something else I should look for?

Yeah, I'd just drill a hole in the back panel, install a 1/4" jack and then solder that wire to it.

I think it's pretty likely you'll get useful sounds out of this thing without doing any mods. It might not sound quite like any other specific guitar amp, but it will probably sound cool. It's good that it already has a tone control.

It's true that it might be designed for phono input in which case it will sound weird with guitar, but with just one 6at6 gain stage and a phase inverter, I THINK it's probably can't have enough gain to have phono preamp AND a tone control. Probably it's intended to be a stereo addition to a mono console and would be fed from a preamplifier that would have done the phono stuff.

The 6AT6 seems like it would be a weird tube, but it's actually almost just like a 12ax7 with a single triode. If you want you can put in a 6AV6 which is generally considered to be a single section 12ax7 exactly (but with a couple of probably unused diodes).

Ned

[standup]

Here's a project that's kicking around occasionally in my head:





It came from a record player, and i have two 6" speakers that connect to the "LS" plug. The blue wire is a 1/4 plug that didn't sound good when it worked. I think it needs a preamp stage. The green wire has a bulb attached to it. It's jumpered for 110 mains voltage. The plug with two snipped wires says "GRAM" above and "MAINS" below, I forget what that was for. Mains power comes in on the black wire to the left, above "Cambridge, England".

The big blue cap is loose, and I can't tell where it was originally soldered at one end. No schematic.

It needs a cabinet and a few small repairs, maybe a preamp stage.

One day I'll get around to it

[scott macdonald]

I did plug in the RCA jack and play some music through it and it sounded normal, so I'm pretty positive it's not a phono input. I'll do the 1/4 thing and see how it goes. If it's not a good sound, I'll still be able to plug a standalone preamp into it. I'm thinking my Bellari MP105 would work well for that, as it can work as a DI too.

Thanks for the ideas and feedback. I was hoping to hear that this would probably work without any mods. When I get it running, I'll update with some samples.

-scott

[RustyBrooks]

If it takes input from your cd player fine then I'd suspect you're probably going to need a little something in the way of a preamp stage. I've gotten away with chaining something like a TS-808 and a compressor and upping the volume quite a bit on each of them (with very low or no gain on the TS-808) when using an amp that wanted "line level" sound.

Looks fascinating, makes me want to troll the area for stuff like that.

[lancebug]

Here's a project that's kicking around occasionally in my head:

If all that happened in your head, I'd hate to see what kind of shape your head must be in.

[wenzel.hellgren]

UTFSF!


Schematic :
http://www.angelfire.com/vt/audio/zenith.gif


More info :
http://www.angelfire.com/vt/audio/zen12w12.html