Question for the amp guys

[LPCustom]

Some of you guys seem to be pretty up on the guts of your amps. I usually try to stay away from the inside of high power equipment. But I have an old Marshall Lead 12 (12 watt combo with an 8 inch Celestion speaker) I've had since 1984 that I need some advice on.

 

I dragged it out of the closet yesterday to play with it and discovered that the gain control doesn't work unless you crank it all the way up. It scratches a little but doesn't work at all until it's maxed out. The clean circuit sounds terrific.

 

Does anyone here know where I can get a gain pot for this? I haven't tried tuner cleaner on it, yet. And I guess I will before I try to change it out.

 

I really want to fix this old amp. The sound on it beats the crap out of all the new Marshall low power amps so I want to resurrect it. The guy that works on my amps is too expensive for an old (cheap) amp like this.

[Caevan O’Shite]

Hmmn, try the tuner-cleaner first (the "black and white" is fine, you don't need the more expensive "color" tuner-cleaner). Do NOT get excess inside the amp-chassis, on any other electrical components, etc.

 

Sounds weird, though, like maybe something else is awry, could be a few things.

 

Try (carefully) swapping some of the preamp-tubes around (not the "phase-inverter"/driver-tube, the little-one closest to the output-tubes, though), taking note of which-is-which (use a Sharpy marker on 'em, number 'em). Then power-up, letting it warm up on standby for a while, and see how it acts. Could simply be a tube!

 

If neither of those things change the problem, it might be a small capacitor or even a bad soldering/wiring connection. Hard to tell from my computer! If you're not well-versed in electronic-repair safety, procedures, and soldering/de-soldering, pay your tech to make it right. There may well be other issues at hand that'll get addressed along the way, so you might get your amp back breathing fire with a new lease on life!

 

It couldn't hurt to "ask Myles" what he thinks, either!

[LPCustom]

Thanks for the advice. I'm a dab hand with a soldering iron and I've done a lot of work on my own guitar electronics. I'm just a bit leery of anything that plugs into mains power. The potential for a nasty shock makes me nervous.

 

I haven't opened the top of the amp up, yet. I don't know if it has tubes or not. But I guess I'll find that out when I open it up. Oddly, I can't find any information about his amp on the Internet. I know Marshall made thousands of them. The model number is the 5005.

 

There's just no comparison between the sound of this amp and something like the Marshall MG15CD. The tone from this is nice and warm sweet while the MG15 sounds cold and harsh.

 

I also forgot I have two of these. The other was in the original box up in the attic. I'm thinking of putting it up on eBay as a NOS item. Or perhaps I'll keep the "new" one and put the old one on eBay. But I think I'll try to fix it first. With a Mini-Z on the way, I might not use it anyway.

 

Thanks for the help.

[myles_rose]

www.tubesandmore.com

[LPCustom]

Thanks Myles. I've been there (tubesandmore.com) before. I managed to find a schematic for the amp section in this 5005 (somewhere, can't remember where, now -- wasn't at the blue prints site). It's actually a 5003 (EDIT: 3005 from the Marshall Micro Stack) head amp grafted onto a 1x10 cabinet to make a combo.

 

I haven't pulled it apart, yet. (I'm nervous about opening things that hook to wall power) But I guess Tubes And More will have what I need if find that the pots (all the pots are scratchy) aren't salvageable.

 

I played with it a bit yesterday (cranked up) while my wife was out. My son that it was _way_ too loud. That amp has a nice raunchy crunch to it that even my AVT50 can't seem to match. (now, the JCM800 is another story, but it's far too loud to play at home [100W 2003 head with full stack of 4x12 flat and 4x12 angled] cabs).

[LPCustom]

I found a schematic for this 3005 head. But I'm not sure where to get the new pots (the tuner cleaner didn't work ).

 

Can anyone recommend someplace on the web that sells Marshall amp parts? (knobs, tolex, pots, jacknuts, corner covers, switches, etc.) I did find a place called ampcrazy.com. But they don't appear to have all I might want.

 

The Marshall company website just seems to be a marketing tool.

 

(UPDATE: I found what I needed on one of the sites Myles mention (tubesandmore.com). They have all the pots as well as the knobs, the nuts, even the tolex and grill covering. I ordered everything I needed from them. I should have it next week and I rejuvenate this old amplifier. Great site.)