Need a 12V DC power supply for mystery amp

[newey]

Guys-

I bought this thing cheap off Ebay a couple of years ago, "as is"- but I didn't really care as I was just going to use the cabinet for an amp project. The project got shelved, and this amp has just sat.

It is an "Exterminator GA 15R" and is 12 VDC powered. Problem is, it didn't come with a power supply- just had a car cigarette lighter cord which didn't fit the plug on the back of the amp correctly. So I've never had this powered up, don't know if it's dead or not.

The 12V input on the back of the amp is a weird shape, not round like most of these are. It's U-shaped, with a flat portion across the bottom. I've looked at Radio Shack for one of those "universal" 12V wall dimples with the various adapters but haven't seen one that looked like it would fit this. I did a web search and all I found was a Harmony Central review:

reviews.harmony-central.com/reviews/Guitar+Amp/product/Gretsch/Exterminator+15R+Combo/10/1

The guy who wrote it raved about the amp so now I'm really curious as to whether this thing works or not. He said he thought it was imported by Gretsch, but I 'm dubious. I emailed the reviewer for more info on the power supply but no response- the review was from 2004 so who knows.

The rear panel of the amp just says "DC 12 V" under the plug, no amperage or other info listed. Above the plug is a little schematic showing that the center tip of the plug is (-) while the outer shaft is (+), which seems bass-ackwards to me.

Here it is:





Any ideas on how to power this up without frying it in the process? If it works, seems like a pretty cool little amp, has OD, 3-band EQ, and an actual spring reverb.

[sumgai]

newey,

I've seen that amp under half a dozen different name badges. My personal feelings aside, it is worth messing with, at least for a cheap/nearly free practice amp.

What I do when the power cord is lost is simply remove the oddball connector, and replace it with a standard jobbie. These can be had from Radio Shack (advantage: quick gratification..... disadvantage: not cheap price for cheap quality ), or from other outlets, online and off.

The positive shell/negative center is a common scheme, it would seem that probably half of all the doohickies I've ever seen in the music world are wired up this way, instead of being done properly. If you elect to replace the connector, you are free of course to wire it whichever way you wish. But if you do choose to go against the markings on the chassis, then make sure you somehow erase/cover the old notes, and put the new scheme in some kind of permanent marking. The goal is to prevent confusion, both for you and for potential future users.

Or you could, if you're of a mind, insert some steering diodes between the connector and the rest of the power supply circuit. That way, it wouldn't make any difference which way the wall wart was wired - positive on the shell or on the center pin, either way will work with no problems. Then you could leave the current markings alone, and just use whatever DC adapter you had to hand (so long as it was 12 volts).

HTH


sumgai

[newey]

SG-

Good suggestions but I was hoping for something that didn't involve opening the chassis. If that's the only way, then it's going to the end of a long line of projects (which is basically where it's been sitting all this time, anyway, come to think . . .)

No, what I need here is more along the lines of, as Johnny Cash sang, "an A-dapter kit".

[newey]

sumgai said:

newey, My personal feelings aside,

SG- No, I want your personal feelings. If it's such a piece of (insert favorite expletive), then I won't waste my time. I was mostly curious after reading the guy on Harmony Central, but you know, caveat emptor. and all that other latin stuff.

[JohnH]

I think that the common convention of +ve outer barrel on powered guitar gear is crazy, in a universe where grounds are mostly -ve , and yet just about every effects box is like that. I have three or four pedals running, some bought and some home built, and I’ve wired my builds the same bad conventional way, so I can use them from a common supply with the shop-bought ones. But I have to wrap up all the unused power plugs on my daisy chain power connector with tape, so +ve barrels don’t zap against grounded boxes and jack plug cases, mit uber spitzen-sparken.

Back on this amp – to give it a whirl without spending much, some alligator clips and a car battery, or stack of flashlight batteries might be OK to test it. It could take a fair current however, maybe an amp or more? – depending on its power. – so a small wall-wart might not do it.

John

[newey]

JohnH- Yeah, I thought of the car battery idea- at least test it, see if it works before buying some sort of power supply. I was afraid that all those "cold crankin' amps" they advertise in my car battery might be too much for this puppy.

[sumgai]

newey,

No, a power source will provide only as much current as needed, it doesn't jam or force more current than what the device will take (what it requires). A car battery will more than do the job, and it would probably last a goodly number of days before running down.

These amps have small and cheap speakers, so the sound isn't all that attractive. The amp circuitry is OK, and with a bigger/better quality speaker, the thing does OK. I wouldn't take it home to meet my parents, but for a cheap thrill........


John,

Nice call on that alternate power supply. I was more concerned with the fact that newey has an oddball connector, and no matter what the power supply might be, getting it hooked up is the real trick. Thus the idea to replace it in its entirety.

And this thing puts out something on the order of 15 watts at max volume, which would translate to about a half-watt to a full watt at normal volume levels. From that, we can see that it'll draw, perhaps, 1.25 to 1.5 amps at full volume, and only a few hundred milliamps at nominal levels. I should think that a string of D cells would be sufficient for testing purposes.

Indeed, one customer of mine hooked up a pair of 6 volt lantern batteries for his every-week-end-during-the-summer beach forays. He said they lasted a couple of weeks, even under some long nights of playing. I suspect that this was an intentional feature, and that the unit was offered (by some outlets) with alternative power adapters. But I admit to having never seen one. At least not knowingly......

HTH



sumgai

[newey]

Ok, car battery test it is, altho I'll need to score some of those micro-micro clips from the local Shack first. If that works, hey, portability's a plus. Got a couple of 6 volt lantern batteries around here somewhere. And there's an old Fender 8" speaker with a decent cone on it aound here too, and . . Hmmmm

Gawd, where is this going???

[newey]

So I used the car battery test and it's dead. Double checked all the connections, still nothing. Thanks for the help guys but this one is going in the parts bin and I'll use the cabinet if I ever get to that amp project I mentioned . . .