1959 Gibson GA8 Gibsonette: Rare Class A Design

Walter Broes

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I don't have the experience you have with the smaller 6V6 amps - I've recorded with a tweed Deluxe a couple of times, and I certainly loved the Alnico's in those, and I'd agree they "belong in there", and I absolutely loved the (6L6) tweed Super I've recorded with recently, and that had its original P10R's in great shape.

I think it's probably as simple as me preferring ceramics on stage for the extra headroom and tighter bass, later breakup - the X175 with the Franzes have pretty healthy output, and lots of bass and mids, and it's easy for things just get a little too compressed and distorted.
Power and volume don't matter at all in the studio though, and I always love Alnicos for recording.
 

capnjuan

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teleharmonium said:
... but I figure I'll try a closely matched pair - and I know I have a real nice pair of NOS Hytrons that fit the bill, so that will be on the menu for tonight.
Hi TH; speaking of Hytrons, a month or so ago I found these matched-used CBS/Hytrons on eBay:

cbshytrons02.jpg


In addition to swapping out the Sylvania JANs, I changed the 12AX7 to a new JJ 12AT7 to damp down some of the gain ... the amp was hot to the point of being touchy ... and I found a pair of used 6087s, militarized / ruggedized versions of the 5Y3 one of which went in the GA8. The result is a lush, harmonically complex, golden crunchy brown tone; chimey, compressed and with an easy, soft distortion. Couldn't be happier with the Hytrons.

To test the parallel 6V6s as a true single-ended amp, I've experimented with this Bendix 5992 and get pretty much the same thing except with a little less presence - the single tube cuts the output by about a third.

bendix5992.jpg


In for a dime, in for a dollar; I was so taken with the warm and complex CBS/Hytrons, I found/bought this matched quad of 1953 NOS/NIB pre-CBS Hytrons on eBay recently:

4Xhytron6v6s.jpg


And for those of you who aren't sure how long ago 1953 was? This is how long ago it was ...

53chevy.jpg
 

teleharmonium

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Glad those worked out for you cap'n. The pictured quad is the same type that I have been using in my Ampeg. Before that I had a pair of French RT 6V6Gs (I'm a sucker for the G envelope 6V6 or 6L6 tubes) which were way mismatched but sounded even better than the Hytrons; unfortunately those are hard to find and very pricey when you do (I think they are the same tubes as the Mazda 6V6Gs, not to be confused with the Mazda 6V6GTs which I have tried and found to be ho-hum).
 

capnjuan

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Still waiting on the Hytron quad ... when you say 'G' style, is that the 'fat bottle' or more bulbous tube shape? A pair of the Bendix 5992 tubes went for $300 in crazy money a month ago ... I tried my single Bendix but don't have anything to compare the GA8 to except itself; it sounded very fine with the Bendix 5992 but sounded finer with the twin CBS/Hytrons ... more signal, more soundstage. If the 6V6s in the GA8 are wired in parallel, I'm not sure they have to be matched like conventional cathode-biased 6V6s ... got any idea?
 

teleharmonium

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capnjuan said:
Still waiting on the Hytron quad ... when you say 'G' style, is that the 'fat bottle' or more bulbous tube shape? A pair of the Bendix 5992 tubes went for $300 in crazy money a month ago ... I tried my single Bendix but don't have anything to compare the GA8 to except itself; it sounded very fine with the Bendix 5992 but sounded finer with the twin CBS/Hytrons ... more signal, more soundstage. If the 6V6s in the GA8 are wired in parallel, I'm not sure they have to be matched like conventional cathode-biased 6V6s ... got any idea?

The G envelope is the sexy one... the term bulbous seems a bit crude to describe these lovelies, but it's not wrong
MZD6v6gwb.jpg
6v6g.jpg


Re matching, I didn't even think that was much of a factor for push pull cathode biased circuits, so long as the they aren't real far apart. I don't think I'm qualified to answer re: parallel single ended amps, but if I were to guess, I would guess that you'd almost be better off using tubes of different makes and construction styles in each slot to maximize the sonic differences (if not the current draw and amplification factor) , along the lines of the THD Bivalve (which is a very nice sounding amp, and I very seldom have any praise for amps made in the last 20 years).
 

capnjuan

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teleharmonium said:
... along the lines of the THD Bivalve (which is a very nice sounding amp, and I very seldom have any praise for amps made in the last 20 years).
Thanks for the pics; never say never but I don't think matched tubes matter in the GA8 ... they aren't each processing half the signal ... 'balance' sort of irrelevant and agree re/ non-matching tubes; like having alnico and ceramic speakers in the same cabinet ...

Coastie: don't you have a THD bi-valve?

CJ
 

capnjuan

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A friend suggested I poke around here at Southbay Amp Works home of the Scumback Speakers AJ if you're looking to bone up on the subject. I got to reading the description of one of Southbay's models the Capt Crunch Combo a twin 12AX7 preamp but with parallel, not push/pull 6V6 output tubes. According to the text:

"The Capt. Crunch is a Class A, 10W dual channel amplifier featuring two 6V6 tubes in the output stage. The amp is a single ended design with the power tubes running in parallel (like the GA8; CJ). The nature of the single ended design allows for the reproduction of both even and odd harmonics, resulting in a fatter, sweeter tone than push/pull style amps which cancel the even harmonics. This results in a harmonically complex, rich tone, and doesn't sound "thin" when turned up into higher volume and gain levels."

I've never messed with a Capt Crunch but the remarks are generally true of every single-(or parallel) ended amp; Champs, GA5s/GA8s, Silvertone 1471s/1481s, and several other makes. It's the lush onset of distortion that separates them from everything else and makes them ideal for recording, practice, and informal settings.
 

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Heh, I have a couple of 6K6's on my bench that I was saving, in case I ended up with a Fender Reverb tank. I'm waiting for a repairman's chest to show up, so I can put all my gear in one place. :roll: Then I'll have a better idea of what I do have. :roll:
 

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I recently got my GA-8 back from being serviced. Wow ! That thing sounds great, I love the distortion. I also like the overall amount of low end, and the relatively low volume considering the kind of natural crunch you can get out of this amp. Great for recording. It's a little noisy if you're playing totally clean, as single ended amps tend to be.

My Noble Super combo also came back the same day, that one sounds great too but is somewhat cleaner (less noisy, too) and has a 12" instead of a 10". I was just playing my blonde '60 T100 through the Noble, quietly, using fingernails only and the neck pickup with the tone all the way up; I thought it was a beautiful sound, kind of a vintage jazz tone but with a pronounced and varied, percussive attack and a little brightness on top.

It's a regular single ended amp festival around here. My girlfriend is out of town, so the living room is full of amps and guitars and I've got the Hammond still miked up from the other day with cables running everywhere.
 

capnjuan

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Hi TH: I chased noise in my GA8 including a temporary 100 ohm pot across the heater circuit that, when spun full to one side, knocked out considerable amount of noise. I substituted a 100 ohm resistor to ground from the indicator light and now only have a little background zzzz. You probably already know that there's enough power there to drive a 12" speaker if you choose. CJ
 

teleharmonium

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capnjuan said:
Hi TH: I chased noise in my GA8 including a temporary 100 ohm pot across the heater circuit that, when spun full to one side, knocked out considerable amount of noise. I substituted a 100 ohm resistor to ground from the indicator light and now only have a little background zzzz. You probably already know that there's enough power there to drive a 12" speaker if you choose. CJ

Excellent information, thanks. I have a buddy that works on amps who's going to come over for a visit, so I'll see if I can get some assistance in doing the same thing on mine.

My amp tech was raving about the sound of the GA8 through his old straight front Marshall 4 x 12.
 

capnjuan

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teleharmonium said:
... My amp tech was raving about the sound of the GA8 through his old straight front Marshall 4 x 12.
Remarkable ... would not have thought they could move that much air.
 

capnjuan

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The GA8 is gone; traded to a friend for this '03 MIM Telecaster and some foot-candy; Digitech Bad (Hey Hey we're the) Monkey(s), Digitech Digiverb, and (Hugo) Boss DD-3 Digital D....e....l....a....y. Plywood body and nacho cheese pickups but in very good condition.

With parallel 6V6s and a 12" speaker, the GA8 Gibsonette is - bar none - the finest low-power commerical or boutique design ever on the market ... but the GA30 was getting all the playing time ... so ... :( I have a call into Keef ... see if he wants to do lunch :wink: J

tele03.jpg


tele01.jpg


tele02.jpg
 

capnjuan

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Hi JP; yes they are! My friend who is very fine player was crazy about the GA8 which was just sitting there ... and he had the tele as trade bait. :D J
 

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Good score, CJ. I'm sure you found it tough to say adios to the GA8, but that Telecaster will be a lot of fun, along with all the new pedals. And, if you found a great and appreciative home for your beloved Gibsonette, the thrill of spreading the faith is its own reward.
 

capnjuan

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Hi 'Zil; the new owner is a former local semi-pro musician who is also an RN. He had a stroke three years ago more or less paralyzing the right side of his body. Since then, he's had to re-learn everything he did with his right hand from holding a fork to picking his ............................ guitar. He has a custom shop Les Paul that is the most beautiful guitar of any kind I've ever seen in real time; he has as much money in the pickups as GAD owners have in their guitars ... and he can play ... getting tones out of the GA8 that I just dream about. Anyway, the stroke left him with slurred speech but, like Tommy, when he picks up a guitar ........ it couldn't have found a better home.

"...well you better pick yourself up off the ground, yes before they bring that curtain down...."

Paul gets my Badge. John
 
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New to me Gibson GA8 Gibsonette:

Slide2.jpg


Not rare in total produced; but a rare Class A, 'student'-grade commercial amplifier. Without wearing anyone out, Class A amps are typically single-ended amps; like a Fender Champ, Silvertone 1471, early Kalamazoos, and others. Single preamp tube and single output tube which means that the output tube handles the positive and negative halves of the signal - it never cuts off. But the distinguishing feature of Class A operation is that when it's overloaded to the point of distortion, it generates even-order harmonics as opposed to odd-order from transistors and, to a lesser extent, cathode-biased, Class A/B push/pull amplifiers which is nearly every twin output, non-Fender amp made before 1965.

Schematic below; most unusual parallel 6V6 output sections; essentially each tube sees and amplifies the same signal; for reasons of physics that it would take Neils Bohr to explain, the output of parallel 6V6s is closer to 8 watts while in A/B-Push-pull, twin 6V6s are good for closer to 15 watts. The amp is widely recognized for its lush, warm sound. It needs some work but already has the sweet, crunchy distortion thing going very well!

Pardon the late arrival, just saw this thread.

I've quite the 40's thru 70's Gibson Amp "nut", I have about 20 of them, including a 1948 BR-6 Lap Steel amp.

I too have a (1959) GA-8 "Gibsonette", but I wanted to point out that this model was also called the Les Paul model, as Les used one for decades even after they were discontinued in 1962. 8 Watts is correct.

I also have a (1959) GA-9T "Discoverer" which included Tremolo, and runs at 10 watts, although with pain staking adjustment to the biases I've chocked out 11.5W with NOS Tung-Sol 6V6's.

Both of these are far smoother and a flatter breakup curve than a 50's or early 60's Fender Princeton (which I have 5 of)

1959 GA-8
1959 GA-9T
1948 Gibson BR-6 Lap Steel amp.
Fender Princeton's (none are reissues) 1964, 1961, 1957 Tweed for comparisons
1959 GA-8 Gibsonette front sml.jpg

1959 GA-9T Gibson Discoverer frt sml.jpg

Gibson 1948 BR-6 Front half.jpg

Princeton Trio - 1965 1960 1957.jpg
 
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Yes, its an old thread but you guys are the ones to talk to re a 59 GA-8 id like to rebuild. Anyone still around?1000013784.jpg
 
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