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Double Bass GK 200mb repair

#21
MR PC said:
Close, but no banana. The old 200 series GK has a much warmer and present sound, ime, imho. Maybe because GK opted for more power with the MBS? Kind of silly because adding 40 more watts to that little box didn't really equate to any usable volume past the point were the rig sounds good. The power amp in the 200 series was perfectly matched to the cabinet........



Rick, it's true about the old B-15, not only are the parts available, but the sound is unparalleled. Mated with a more efficient and upright friendly box, it could be the ultimate in amplified tone coming from a production line amp.

Can't wait for the rant here about how wrong I am... :) :) :)
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Mr.PC
You'll get no rants from me. I gigged with a pair of JBL loaded orphaned B-15N cabinets, and a Walter Woods MI-100-8. It sounded great with my 1966 Fender Jazz. GK took a mistep when they re designed the MB series. I traded my 200MB for a MBE and sold it in less than a month. The MBE & MBS pre amps midrange voicing changed the amps timbre and warmth. Just my take.

Ric
 
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#22
MR PC said:
Close, but no banana. The old 200 series GK has a much warmer and present sound, ime, imho. Maybe because GK opted for more power with the MBS? Kind of silly because adding 40 more watts to that little box didn't really equate to any usable volume past the point were the rig sounds good. The power amp in the 200 series was perfectly matched to the cabinet.
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Here's two beauty passes of a 200MB recently sold on ebay. This particular amp was in pretty good condition, but what you'll see is that unless you had the matching GK case, the amp was very succeptable to cosmetic dammage. Also, I think it's important to note that the power supply was bolted onto the underside of the amp below the speaker, so if the amp fell from even a few feet, it took out the power transformer. I own a GK 200RB, which was the head only version of the 200MB, and it's a incredibly complicated amplifier. I think that's why GK redesigned it, so the assembly and production was less labor intensive. What you can clearly see is the EQ sections frequency points and there are no "semi parametric" midrange controls. IMHO along with the power section, that's the magic of this particular amp. Nothing's quite like it.

GK 200 MB #1.png
GK 200MB ebay #2.png
 
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#24
Ric Vice said:
Here's two beauty passes of a 200MB recently sold on ebay. This particular amp was in pretty good condition, but what you'll see is that unless you had the matching GK case, the amp was very succeptable to cosmetic dammage. Also, I think it's important to note that the power supply was bolted onto the underside of the amp below the speaker, so if the amp fell from even a few feet, it took out the power transformer. I own a GK 200RB, which was the head only version of the 200MB, and it's a incredibly complicated amplifier. I think that's why GK redesigned it, so the assembly and production was less labor intensive. What you can clearly see is the EQ sections frequency points and there are no "semi parametric" midrange controls. IMHO along with the power section, that's the magic of this particular amp. Nothing's quite like it.

View attachment 700460 View attachment 700461
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My amp is clean, too. I sprung for the padded zippered case when I bought it. I did have the speaker replaced a few years ago. The cone had gotten brittle from old age, Kinda like me :) I think I am going to take another shot at getting 200MB fixed. Like a poster above said, I, too, often used it with one of my old B-15 speakers that I saved when the transformers went and Ampeg went out of business. I foolishly gave the amps (I had two ) away to a music shop for "parts." I still have the speaker cabinets.
 
#25
Yes, Ric, I've owned 2 of the combos, as well as a 200 head. I wish I'd kept one. Really great sounding for upright without lots of knob twisting. For electric bass, it could be pretty cranky sounding sometimes. I think maybe the redesign was to make it more bass guitar friendly. Parts are hard to source now, not much different than the old WW's. Biggest problem is that people would toss these combos around like they were indestructible. The 200 head that I sold to a friend for 90 bucks...he came back to me after 3 years complaining, because it didn't work after he'd dropped it down a flight of stairs.
 
#26
One more thing to try: Plug in directly to the effects return. If the problem goes away then you have either a dirty/bad main input jack, or maybe something else wrong in the preamp section. I once bought one of these as defect hoping I might repair it myself. It turned out that a screw holding the top handle was too long and was pushing into one of the large filter caps. It was easy enough to replace the cap and grind down the screw and the amp worked for years afterward. It could indeed be a rotted surround or loose screws. Both things could be diagnosed at home with little time invested. Although I don't like these amps personally, it seems silly to just bin one when it might easily be repaired.
 
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#28
robobass said:
Anyone know why the EQ was arranged the way it was? Every other EQ device in the world has bass on the left and treble on the right.
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Robo Bass,
You know I'd totally forgotten about that. It never bothered me when I owned one, but that layout is counterintuitive. Repairing one is almost a lost art these days. Just look at how labor intensive a repair could possibly based on the schematic is for the amp.

A wise man on TB once told me that there just aren't that many tech's out there anymore that could attempt a major repair on one of these amps, even if they could find
a source for replacement components.

Screen shot 2015-10-02 at 9.12.26 AM.png


Ric
 
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#29
Ric Vice said:
A wise man on TB once told me that there just aren't that many tech's out there anymore that could attempt a major repair on one of these amps, even if they could find
a source for replacement components.
Ric
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Sad but true. Thing is that I bet a lot of failures don't involve proprietary parts, as was my case. It's just the type of training modern techs have, in which they know how to swap out components, but not look at the bigger picture. If I may throw in a bicycle example. I had an old Peugeot road bike. I broke a spoke on the rear wheel. I took it to a bike shop just to remove the freewheel so that I could replace the spoke. The guy told me that the tool needed to remove it no longer existed, and the only option was to scrap the bike. It wasn't even a consideration to replace the wheel entirely, just throw the bike away, period. With a bit of Google I found the tool quite easily and quickly put the bike back into service. Well, this is just another of my rants against waste. Hope I didn't offend anyone too much, 'cause I don't plan for this to be my last one:)
 
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#30
Yes, very complex circuit, look at that schematic! If a company like Aguilar came up with a small lightweight combo, with a tiny sealed cabinet like the GK...they would sell piles and piles of them to upright players and school bands. The preamp voicing of the DB amps is very warm and upright friendly, much like the old GK.
 
#31
MR PC said:
Yes, very complex circuit, look at that schematic! If a company like Aguilar came up with a small lightweight combo, with a tiny sealed cabinet like the GK...they would sell piles and piles of them to upright players and school bands. The preamp voicing of the DB amps is very warm and upright friendly, much like the old GK.
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Mr. PC,
That would be amazing, I've heard good things about the Aguillar Tone Hammer 500, from players who owned both a Walter Woods and a Tone Hammer 500. Apparently, the EQ of the Aguillar has similaraties to the Electroacoustic Amps
Walter built/builds?
 
#32
robobass said:
Sad but true. Thing is that I bet a lot of failures don't involve proprietary parts, as was my case. It's just the type of training modern techs have, in which they know how to swap out components, but not look at the bigger picture. If I may throw in a bicycle example. I had an old Peugeot road bike. I broke a spoke on the rear wheel. I took it to a bike shop just to remove the freewheel so that I could replace the spoke. The guy told me that the tool needed to remove it no longer existed, and the only option was to scrap the bike. It wasn't even a consideration to replace the wheel entirely, just throw the bike away, period. With a bit of Google I found the tool quite easily and quickly put the bike back into service. Well, this is just another of my rants against waste. Hope I didn't offend anyone too much, 'cause I don't plan for this to be my last one:)
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robo,
I had a similar bike experience - the only tech at the bike shop that had the freewheel tool for my 1981 Raleigh Super Course, was the only tech that had grey hair.
I'm grateful that he was not willing to "let go of the past" so easily.
You kids get your fancy "Carbon Graphite" frames off my lawn!
 
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#35
MR PC said:
Seems that for the most part, we are stuck with Class D amps for upright bass combos...and yeah, they are all over the lawn, too. :)
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Since I've been using a Class D amplifer since I purchased my first Walter Woods MI-100-8 in 1980, I'm very comfortable with the sound and feel of a well designed Class D amp.
I currently own two Woods amps, that are magnificently built and sound great. Nothing lasts forever though. My biggest concern with the current crop of B&O Ice powered amps, is their throw away design. I'm personally not a fan of planned obsolescence. It's bad for the Evironment. That said, among the current offerings
of Class D bass amps there are a few standouts. Tecamp and Aguilar come to mind. Just my take.

Ric
 
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#36
Ric Vice said:
Since I've been using a Class D amplifer since I purchased my first Walter Woods MI-100-8 in 1980, I'm very comfortable with the sound and feel of a well designed Class D amp.
I currently own two Woods amps, that are magnificently built and sound great. Nothing lasts forever though. My biggest concern with the current crop of B&O Ice powered amps, is their throw away design. I'm personally not a fan of planned obsolescence. It's bad for the Evironment. That said, among the current offerings
of Class D bass amps there are a few standouts. Tecamp and Aguilar come to mind. Just my take.

Ric
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I bought a 200mb and put the Paragon 12 from my MB150 that was vibrating and rattling after 15 years of gigging. The foam surround was disintegrating on the 200mb. I put new weather stripping around where the grill meets the cab and it has been quiet ever since. I am not sure if they used a different driver on the original 200mbs but I wish I would have thought about having it reconed.
 
#37
dylanjohnson said:
I bought a 200mb and put the Paragon 12 from my MB150 that was vibrating and rattling after 15 years of gigging. The foam surround was disintegrating on the 200mb. I put new weather stripping around where the grill meets the cab and it has been quiet ever since. I am not sure if they used a different driver on the original 200mbs but I wish I would have thought about having it reconed.
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Dylan,
If memory serves me the original speaker was manufactured by Pyle, who were known for building car stereo speakers that would work in small enclosures. The speaker from your MBE/S is what GK would send out to you if you had ordered it directly from them. That speaker is designed specifically for the MB series combos, so you made the right choice.

Ric
 
#38
Ric Vice said:
Robo Bass,
You know I'd totally forgotten about that. It never bothered me when I owned one, but that layout is counterintuitive. Repairing one is almost a lost art these days. Just look at how labor intensive a repair could possibly based on the schematic is for the amp.

A wise man on TB once told me that there just aren't that many tech's out there anymore that could attempt a major repair on one of these amps, even if they could find
a source for replacement components.

View attachment 700958

Ric
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Your "wise old man" is indeed a wise old man.
I recently had my (above mentioned) GK 200MB returned to me by my go-to technician-- unrepaired (with no charge!). He had had it for nearly a year and simply could not find the problem. In his defense, he has a stellar reputation for being the guy who can fix anything. I know he spent hours with it, but finally gave up and told me to try to find someone who specializes in repairing GKs. If I am unable find a knowledgeable tech, I will rip out the amp innards and use the relatively new speaker as an extension as I did with my two B-15s.
 
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#39
Earl said:
Thanks everyone! I haven't been able to try an external speaker, and it's not a dirty jack. Someone pm'ed me the name of a repairman who re-foamed his GK speaker but he never returned my call. I guess I'll just try taking it to a different repair place.

Oh, and I did have another amp recently that was vibrating loudly on a certain note, and it turned out to be a loose screw. I wish the fix on the GK was as easy!
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