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Old August 3rd, 2007, 07:12 PM   #1 (permalink)
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Need Help with an old GK 250ML

Howdy all!

I just purchased, mostly unseen, a old (and pretty beat up) GK 250ML. I'm not really much of a solid-state guy anymore, but the first electric amp I ever played through was a GK (wish I still had that little thing), so it was mostly a nostalgia purchase.

Got a good deal on it as the speakers are shot. Need to be replaced. I've e-mailed Ted about some webers, but I don't know if he's gonna have anything because the size is pretty odd. Does anyone know where else I could or should look? I know I could build a cab for it and use it as a head, but I'd like to keep it as a combo unit if possible.

Specs:
50W
2 channels
8 ohms into each channel
and here's the kicker: speakers are 6.5"

Thanks!

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Old August 3rd, 2007, 11:27 PM   #2 (permalink)
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I'll bet that Bob Gallien or Rich Krueger could help you.

http://www.gallien-krueger.com/
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Old August 4th, 2007, 03:35 AM   #3 (permalink)
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Quote:
Originally Posted by trandy16 View Post
I'll bet that Bob Gallien or Rich Krueger could help you.

http://www.gallien-krueger.com/
Hmmm. Maybe. But GK has been into the bass amp thing for a while, and they don't have anything guitar amp related on their site (except the manual, which is Super Cool). Am I missing something?
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Old August 4th, 2007, 09:54 AM   #4 (permalink)
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I'd contact GK directly and see if they can source you some speakers. Pick up the phone and enthuse to them about one of their old amps and see if they can help you out.
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Old August 4th, 2007, 12:20 PM   #5 (permalink)
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Originally Posted by tiktok View Post
I'd contact GK directly and see if they can source you some speakers. Pick up the phone and enthuse to them about one of their old amps and see if they can help you out.
Yep...my point exactly.
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Old August 4th, 2007, 03:08 PM   #6 (permalink)
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Where the heck have all these things gone, anyway? I haven't seen a GK guitar amp in probably six years! I had a 250ML in the late '80s, but it's been rare that I've run across one since then. They're one of those amps that make "that sound" that is instantly recognizable if you've ever played through one, but it's a dated sound that was short-lived. I'm not sure if I'd want to have another one or not. Those active tone controls sure had a lot of swing to 'em.
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Old August 5th, 2007, 10:22 AM   #7 (permalink)
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I used to love them things for just THAT SOUND!!!!
They were cool.
I'd bet they've still got inventory on the speakers in their warehouse.
Now THAT'S a reissue I'd love to own!!!!
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Old August 6th, 2007, 12:12 AM   #8 (permalink)
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Thanks all. I haven't heard it in years myself and am really looking forward to it. I'll give GK a call tomorrow and let you know how it goes.
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Old August 7th, 2007, 12:29 AM   #9 (permalink)
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Well, GK does stock speakers they describe as "drop in" replacements. Eminence speakers. The gal didn't know the model number, so I'll have to see them to figure that out. They're $54 each and I'm ordering them tomorrow. The originals are Pyle speakers.

I did a lot of research trying to find speakers for this thing, and discovered a few interesting things: 1) Nobody makes a 6.5" guitar amp speaker that will handle the watts of the 250ML (that is to say, a speaker designed specifically for the guitar amp). Interestingly, the Vox DA5 also uses an 8ohm 6.5" speaker, but it's nowhere close in terms of RMS (10 watts)
2). 6.5" speakers are incredibly common in the home-surround and car audio applications, and I believe that's what's in the GK 250MLs. So that opens up some opportunities for experimentation down the line.

Salute!
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Old April 25th, 2010, 12:09 AM   #10 (permalink)
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Hi,
Sorry my first post here is to come in and dig up an ancient topic! But I have a question about this amp. I got one from a friend that's very old and well used-- a broken off pot/knob, but you can still use what's left to adjust it... however on top of that kind of damage, the speaker surrounds have rotted away with age, they were full of holes so I opened the amp to disconnect them so I could run an external cab without further damaging the old speakers-- when I brushed by them, the foam surrounds just crumbled away :p ... it does, however, sound beautiful pushing my 2x10 cab.
But, I'd like to get this amp running with the original speakers for compactness and that original sound... I know this may be heresy on a telecaster forum but apparently Chuck Schuldiner played through one of these mic'd up live, a tone I'd love to recreate.
One possibility I'm aware of is refoaming the speakers, I guess popular with old and more valuable hi-fi gear. I could probably get my hands on a kit for 6.5" drivers, and from there it's just a matter of me doing my research and taking my time to do the replacement correctly. But I'm concerned: Since these tiny little speakers handle so much power and presumably can kick out some volume, is the cone going to actually travel too much for a normal refoam kit? Might you need a surround material designed for increased inward/outward travel for such a relatively hard working small speaker?

If that isn't practical or I mess it up, I'd probably buy replacement drivers. Apparently I could go to GK and might as well because $54 (or whatever the cost is now) doesn't seem too expensive for a reasonable quality speaker of that size and power handling. But, I also found these eminence drivers and I'm curious... could these work? They're only rated down to 500 hz-- over 2 octaves higher than a big 12" guitar speaker. On the other hand, it's a 6.5 inch speaker-- the one this amp is designed around can't go tooo much lower than that? The amp probably uses something without too much deep bass either, so I guess my question is: Was the amp designed around something with wider response-- if it was, GK would probably provide me with a specialized speaker with those characteristics-- or does its design and unique sound come from speakers without strong bass? If the speakers in the amp are nothing out of the ordinary I guess I could try a normal (fairly robust) midrange driver like the one I linked to there. Any thoughts?
Thanks in advance!
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Old April 25th, 2010, 03:07 AM   #11 (permalink)
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That mid driver would be out of place in a guitar amp. It might live, but it won't be happy and will tell you about it when you play. The frequency response of a driver is only loosely related to its size.

The refoam kits are inexpensive and the job so likely to succeed I'd try that first. There are a lot of 6.5" home audio woofers out there so the odds of the replacement surround being able to handle the excursion are excellent. The frequency range the home speakers are intended for is not that different from a guitar amp. Small drivers like that are expected to go 100-4K. If it doesn't work you're out less than $20 and a half hour. Worth the experiment.
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Old April 25th, 2010, 11:53 AM   #12 (permalink)
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Thanks for the advice! I'll definitely get a refoam kit and try to restore the speakers when I have a chance. Any thoughts on the snapped off pot shaft? I mean I guess I should just replace the pot, but if I remember correctly these are PCB mounted pots... is the size of some PCB mount pots standardized to some extent? I know I've certainly seen some of greatly varying size and shape (and probably pinout) in various electronics, am I going to be able to find one that will fit this amp or should I make do with the remainder of the pot that's broken?
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Old April 26th, 2010, 12:10 AM   #13 (permalink)
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Did anyone ever actually use the Echo on those amps?

I've had two GK 250ml's... One back around 1989, sold it in about 1994. Then for nostalgic reasons, I got one in about 2000 and sold it 2 months later becaue I had no use for "that sound" anymore.

Did anyone ever pop the top and turn the internal adjustment pots inside to increase the gain? I sure did!

Fun little amp...... and pretty punchy with lots of low end for an amp not much bigger than a toaster. Just no use for "that sound" any more.
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Old April 28th, 2010, 06:44 PM   #14 (permalink)
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I've heard of adjusting the trim pots for more gain... any advice about that? The time I opened it to disconnect the shredded speakers, I did not note the trim pots (wasn't at all thinking about it at the time). Which ones do what... or should I just tweak and reason my way through it with experimentation? I'd love to open it up and mess with those as I've heard the results can be very cool but I don't want to damage it. Are the trim pots basically are linked in the gain (etc) circuits so they basically let you turn the gain further than the knob on the front allows? If so I'm not too concerned, but if there are a bunch in there and some control biases or other "not melting the amp" related stuff I'd be pretty hesitant to touch any of them without knowing what each does.
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Old April 28th, 2010, 11:47 PM   #15 (permalink)
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I don't recall the trim pots, and would definitely not mess without a schematic or some serious amp expertise. At least one is probably bias for the outputs and you do not want to get that wrong. A tube amp will survive a mis-set bias long enough for you to realize you screwed up and recover. A solid state amp will chernobyl in nanoseconds.

As for the pots, I don't recall them being anything but the usual Alps PCB mounted things. Try GK or post a photo and we'll dig up a suitable sub.
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Old August 20th, 2010, 08:51 AM   #16 (permalink)
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Trim Pot Adjustments

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Originally Posted by Ronsonic View Post
I don't recall the trim pots, and would definitely not mess without a schematic or some serious amp expertise. At least one is probably bias for the outputs and you do not want to get that wrong. A tube amp will survive a mis-set bias long enough for you to realize you screwed up and recover. A solid state amp will chernobyl in nanoseconds.

As for the pots, I don't recall them being anything but the usual Alps PCB mounted things. Try GK or post a photo and we'll dig up a suitable sub.
You are SOOOO right. Mis-bias a G-K and it will become a real toaster instead of looking like one.
As for the gain trimpots, I called G-K and asked them for a tech sheet on adjusting them. In return, I received a full schematic, parts list AND the tech bulletin on where they are and how to adjust them. Turns out, the three main ones are for setting up the B channel, (high gain). the first two not only adjust gain, but have a tremendous effect on treble and bass response while the third is an overall gain adjust.

BTW...new speakers can be had from Parts Express. I've replace damaged ones in two of my 250MLs with Pyle Pro PDMW6 6 1/2" Mid-Woofers and they sound great. Plus, these speakers are rated for double what each channel puts out. A great way to get new speakers and an upgrade at the same time.
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Old August 20th, 2010, 11:24 AM   #17 (permalink)
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Originally Posted by tele_jas View Post
Did anyone ever actually use the Echo on those amps?
All the time!
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Old February 6th, 2011, 12:47 PM   #18 (permalink)
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HELP ... I have a GK 250ML , absolutley love this little wonder, but am not sure what to do to connect to a spk. cab. namely 410...I am considering making the cab..son need to know what to do like what ohms should the spks be and where to connect from the amp, so afraid of blowing something...PLEASE
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Old February 6th, 2011, 01:51 PM   #19 (permalink)
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I have a later but not dissimilar GK 206MLE, with which I had the same problem with the foam surrounds for the speaker cones. The UK importers quoted a fairly hefty price for replacement speakers so I had the originals reconed by Wembley Loudspeaker in Acton, West London - an excellent firm.

Regarding speaker outs, the 206MLE, as a stereo amp, has two. Recommended impedance per side is 16 ohms with the internal speakers on and 8 ohms with them switched out. I configured a 4 x 10'' cabinet with 8-ohm drivers wired with two series-wired pairs connectable in parallel and switching sockets, so that if either were used by itself the cabinet impedance was 8 ohms, but if both were in use it became a stereo cabinet, 16 ohms a side. I don't know whether the earlier 250ML's speaker connection layout is similar in this regard.
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