hey Capn.... Look what I got

tele4tone

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I love pawn shops.

b85ff31d.jpg


0518a443.jpg


79128c15.jpg


79128c15.jpg


Now I'm going to go play it

Cheers, Jeff
 

capnjuan

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Caramba Jeff :shock: :shock: A GA40 Les Paul!! According to Wally Marx' book (page 86), it's looks like a 1956:

GA4056.jpg



In the '50s, a number of Gibson designs used pentodes ... built like a power tube ... as preamp tubes. Sometimes the 6SJ7 that had an octal base and sometimes the 5879 that's found in both preamp channels of your amp. Both Snake River Amplifiers and Divided by 13 Amplifiers make amps based on the 5879 as did Victoria Amps in their 're-issue' of the GA40 a couple of years ago.

That's a Jensen Alnico 5 field coil speaker .... that chunky thing hanging on the side is more than an output transformer. At some point, it became cheaper for speaker manufacturers to produce speakers with permanent magnets; the magnet in your amp probably has very little magnetic properties when it's turned off. When turned on, the power supply sends power out to that coil and, like a jHS science fair project, magnetizes the U-shaped chunk of iron under the bell. Unlike permanent magnet speakers that can be changed out like underwear, you either replace with another field coil speaker or re-engineer the power supply but the cone and voice coil are no different than any other speaker.

If you have trouble with the trem, chances are it will be that one or more of the caps in the trem circuit are shot. The trem function is 'on' whenever the amp is turned on but it's just grounded out when switched off. Those (probably) original caps in there have been capping away since the amp was built and, annoyingly, they are under that circuit board. Even at its slowest settings, you may find you'd like it to be slower. It can be slowed by changing the value of the caps however if you do it, it will never reach its original fastest speed; the speed would be cut at all pot settings.

Our member mad dog has a GA40 that's a couple of years newer than yours. The Tonequest article and Victoria re-issue pushed interest and prices for these up although the bloom may be off the GA40 rose ... with prices falling noticeably. Anyway, there are several back-in-the-day amps that stand out with their very distinct, signature tones; Fender 5E3 Deluxe, Vox AC15, Marshall 100W Super lead ... and I think the GA40 goes in that group too.

Congratulations!
 

tele4tone

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AHHH It is a GA20T

I meant to put that up.... Sounds great..... Are those caps original? I noticed the power cord is three prong. Trem works fantastic! Where do I get Repro knobs at? The speaker seems strong, but it was kinda late to test it last night (I did notice the field coil tho). This is going to be a fantastic amp for me to use in a worship setting at church and the tone is WOW!!!! I love 6V6's.

I got this for a good price I think. What is market value for this? Low side because of the dirt and grime..... I am going to start cleaning tonight. I want to keep this forever. It is a great partner for the '65 Starfire and Echoplex EP1.... No effects pedals needed ;)

Jeff
 

capnjuan

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tele4tone said:
AHHH It is a GA20T ... Are those caps original? I noticed the power cord is three prong. Trem works fantastic! Where do I get Repro knobs at? The seems strong, but it was kinda late to test it last night. This is going to be a fantastic amp for me to use in a worship setting at church and the tone is WOW!!!! I love 6V6's.
Hi Jeff; in the earlier models, the GA20 and GA40s both had the same field coil speakers leaving the most significant difference the 12AY7 in channel 1 instead of a 5879; otherwise the circuits are the same GA20 schematic matching your and my GA20s (default's runs on 6EU7s).

The power cord was probably updated when those big blue power supply filter caps were put it ... and they look newish. Knobs? eh ... get in line :( There are no accurate reproductions out there; Weber and maybe Hoffman sell an 'oxblood' chicken head but they aren't the same shape or color. Default and I checked with the Chicago company who owns the old Daka-Ware molds and they won't make any dupes without paying for 100 of them in advance.

This is what you'd be looking for; see the swirly marbled quality? They only show up rarely on eBay and usually as onesy-twoseys ... very hard to find loose and dead early Gibson chassis with or without knobs are just as rare. The one in the pic below has been cleaned in alcohol and detergent and had its pointer slot refilled with paint.

knobs02.jpg



Maybe when the amp was serviced, somebody went to the trouble to update the trem caps but, in any event, be happy it's running well. Congratulations; I'm crazy about 6V6s too!
 

coastie99

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capnjuan said:
Knobs? eh ... get in line :( There are no accurate reproductions out there; Weber and maybe Hoffman sell an 'oxblood' chicken head but they aren't the same shape or color. Default and I checked with the Chicago company who owns the old Daka-Ware molds and they won't make any dupes without paying for 100 of them in advance.

This is what you'd be looking for; see the swirly marbled quality? They only show up rarely on eBay and usually as onesy-twoseys ... very hard to find loose and dead early Gibson chassis with or without knobs are just as rare. The one in the pic below has been cleaned in alcohol and detergent and had its pointer slot refilled with paint.

knobs02.jpg

John, were you actually quoted a price ?

Seems like a hundred wouldn't be too hard to get rid of, assuming the price wasn't too great. I'd take some for a start.
 

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coastie99 said:
capnjuan said:
Knobs? eh ... get in line :( There are no accurate reproductions out there; Weber and maybe Hoffman sell an 'oxblood' chicken head but they aren't the same shape or color. Default and I checked with the Chicago company who owns the old Daka-Ware molds and they won't make any dupes without paying for 100 of them in advance.

This is what you'd be looking for; see the swirly marbled quality? They only show up rarely on eBay and usually as onesy-twoseys ... very hard to find loose and dead early Gibson chassis with or without knobs are just as rare. The one in the pic below has been cleaned in alcohol and detergent and had its pointer slot refilled with paint.

knobs02.jpg

John, were you actually quoted a price ?

Seems like a hundred wouldn't be too hard to get rid of, assuming the price wasn't too great. I'd take some for a start.

We were, but when push came to shove, the only people that were interested were us. I might revisit that topic, as I found out I'm not quite as poor as I thought, but the problem is getting it to have the swirly choco-chip texture. We can get the oldstyle solid color brown-sh red w/yellow stripe made pretty easily. The major problem is I'm going to be sitting on a vast quantity of knobs that most amp purists won't want and, and the biggest producer of repo Gibson amps, isn't doing it any more.
Also, the Gibbie knobs are push-on, so you can't use strict repos on any other amp...
I don't have the paper in front of my, but IIRC, we were quoted about 3 bucks a part. I could be wrong, like I said, it was a while back.
 

tele4tone

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I obviously would buy some at a profit to the seller of course... and a extra set in case I found another amp. I think you could probably sell the rest on Fleabay even if they weren't completely correct. So... I would buy 10......
Actually, I have another japanese no name head that needs knobs as well. I might as well buy 15... Look that is 1/6 already gone. :)

Jeff
 

capnjuan

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coastie99 said:
... John, were you actually quoted a price ? Seems like a hundred wouldn't be too hard to get rid of, assuming the price wasn't too great. I'd take some for a start.
Hi Gary, Steve, and Jeff; my recollection was that the quote was $467/100 units and a one-time setup charge. Steve and I posted on several BBs including Buffalo Rob's Vintage Gibson Amps BB where guys had posted there before in search of vintage Gibson knobs. We got nothing except a couple of lectures on the makeup of old v. new plastic and the chemistry of industrial dyes .... we didn't get a peep :shock: It began to look like it would take 10 years to get rid of them. We could guarantee a color match in the deep, reddish brown but in the smooth, not marbly mid-'50s plastic and in the later/shorter, not the earlier slightly elongated, chicken head.

We'd have been offering them at $5.XX but any interest would have been one here ... two there ... If they'd been spot-on replicas, I don't think the cost would have been an objection because they'd have been sold one or two at a time but the lack of interest was surprising .... (sort of like mobilizing LTGers to get a manufacturer to come up with a case for small-bodied Guilds ... nudge nudge wink wink :wink: )

Anyway, Steve still has the paperwork and color swatches (or do I :? :oops: ??)
 

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I think I do. I'll dig them up, but I'm looking at an appalling amount of unforeseen home repair....
Right before going on the most expensive vacation of my life....
Knobs are not what I'm focusing on in the near term. :(

Yeah, over 4 bucks seemed to be a pain point for most of the people I talked to.
"Hey, if you could get exact reproductions for under a buck, I'd be interested."
 

mad dog

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Jeff:

Wonderful score. These things are in a tone zone all their own. I can tell you from messing with my '58 GA40, these are very responsive to speaker and power tube swaps. Running an Emi Crex in mine now. Not exactly expected, but it's a perfect match. I suspect the Emi swamp thang would be just as good. On the tube side, I've tried several. JJs are excellent, especially for the price, take it a bit more to the 6L6 side. Best yet is a set of RCA oldies ... blackplates I guess. Once they went in, it was point, set, match.

IMO, the coolest thing about this type of sound is what it lets you do with the tone knob. Certain guitars with my amp - like teles, the Dearmond M-75T - you roll tone partly or mostly off and it turns the sound inside out. Very gainy, scooped and dense yet defined at the same time.

MD
 

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I have to admit this particular amp sounds a lot better than the Crest Falcon I sold a while back. It is warmer than my other amps, but it sounds great cranked and still has definition. Dead quiet cranked unless you set the tremolo a certain setting. I have been searching for a lower wattage amp to use at church. I am required to play those cutesy little lead lines and then disappear into the mix and finding an amp that does that is difficult. I had bought a Fender Vibro champ xd.....they are so cheesy and the modeling is crap

Tubes are mostly rca preamps and sovtek 6v6's. The rectifier is old.. can't remember the brand. I have some older tungsol 6v6's I think laying around. Does this amp require the bias reset for different power tubes? Which tube is the driver for the power tubes?

I have heard some of you guys raving about these Gibbies and Maggies and am glad to have found one that confirms your claims.

Thanks for the info guys!

Jeff
 

mad dog

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No bias needed on the 6v6. The rest of the tubes, I defer to capn juan.

MD
 

capnjuan

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Hi Gents: I just got a memo from Gibson's Nothing's Easy With Us department. Pic on the left is from this mid-'50s GA55 auction. Likely to match what was on Jeff's amp; note the 'flat' top. The middle pic from a GA8 and all the other amps in the thin, blonde tolex. On the right, the last style used in the tweeds before switching to skirted knobs; smooth plastic about the color of dark chocolate; the last two having the raised or ridged top.

knobGA5550s09.jpg



Davies Molding. Most likely commercial source for everything in the market now. Own the rights to the old 'Daka-Ware' name.

Davis Molding part # #2300-E, set screw chicken head

This is what they make:

2300.JPG



So ... knob-wise ... (................) :?
 

capnjuan

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mad dog said:
No bias needed on the 6v6.
Hi Jeff: Michael's right; no need to concern yourself with biasing your amp. The bias in your amp ... setting the idle current and forcing the DC voltage on the cathode to be more positive/higher than the DC voltage on the grid ... is done with a cathode resistor and a bypass capacitor as shown below:

Bias03.jpg



Tube lineup with the phase inverter/driver ID'd. The tubes that will have the most influence on the amp's tone are the 12AY7, 5879, and the 6V6s:

tubelineup.jpg



Schematic here. Subject to checking what's under those tubes shields, matches i every way except for the field coil; schematic shows a standard permanent magnet speaker.
 

capnjuan

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On eBay: '59-'62 GA20T About as clean as they come. In the last couple years, the mintish tweeds have been running in the low $1,000s.

ebayGA20.jpg
 

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capnjuan said:
On eBay: '59-'62 GA20T About as clean as they come. In the last couple years, the mintish tweeds have been running in the low $1,000s.

ebayGA20.jpg

So......$180 was a good deal? haha

I finally got to crank this thing. Channel 1 is Link Wray awesome! Channel 2 is more refined and the tremolo still works fine at higher volumes.

The speaker seems strong, but I wonder where I can get a new one for a back up. When the original goes I will need time to get it reconed.

I didn't expect to get all of this awesome info from a Guild Forum, but Guilds do play nice with Gibson amps....

Thanks everyone!

Jeff
 
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