Paging Juans Ampz...

capnjuan

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Hi Dan ...I thank you ... and Coastie thanks you ... :wink: Gibson ... changing amps design and cosmetics the way most of us change socks. According to Wally Marx, the eBay amp is a '54-'56 and he goes on the say the early models ... like this one ... had 8" speakers and the later ones had 10". The auction text doesn't say but it'd be useful to know. Like that juan guy's post said, it's a Class A / single-ended design with twin 6V6s running in parallel; blue is signal in and red is signal out just like a GA8.

The two differences between the GA8 and GA9 are the preamp tubes and the field coil speaker (green box on right). The GA8 had a 12AX7 preamp like the tubes in the GA18 but the GA9 has a 6SJ7 pentode. Both the early GA8s and 9s had field coil speakers and both models later went with more modern speakers. The other difference between the early and late GA9s (and GA8s) is this early model doesn't have a tone control.

GA9B.jpg



These amps do the hot, rich, thick thing to perfection. Many Gibson models used pentodes in the preamp including the GA40, GA83, and GA90 although they dropped the 6SJ7 in favor of the 5879 somewhere along the line. The knock on all preamp pentodes is that they can become microphonic. The 6SJ7s are around as either NOS or used and don't cost very much. There's no such thing as a 'premium' 6SJ7 so it'd be worth going through a few to get the quietest ones. Also, the parallel design means that the 6V6s, unlike push/pull amps, do not have to be closely matched ... although if somebody had a pair of ... say ... matched Brimars ... this amp would sing .. :wink:
 

capnjuan

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A clever man could make the amp ... iffin he had a layout, no?
 

BluesDan

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Thanks again Cap......good stuff.
Lately it seems the GA-5's have been bringing a premium, or at least more than I was used to seeing, in the range of 650+. Maybe folks are starting to catch on......
 

capnjuan

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BluesDan said:
Thanks again Cap......good stuff. Lately it seems the GA-5's have been bringing a premium, or at least more than I was used to seeing, in the range of 650+. Maybe folks are starting to catch on......
Agree that the GA5 is getting its props although I think we're beginning to see some softening of values. The flagship GA40s have retreated and the weaker GA18s aren't doing very well either compared to last year when nasty ones were $600.
 

BluesDan

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capnjuan said:
BluesDan said:
Thanks again Cap......good stuff. Lately it seems the GA-5's have been bringing a premium, or at least more than I was used to seeing, in the range of 650+. Maybe folks are starting to catch on......
Agree that the GA5 is getting its props although I think we're beginning to see some softening of values. The flagship GA40s have retreated and the weaker GA18s aren't doing very well either compared to last year when nasty ones were $600.

Yeah, can't figure the recent trend with the Gibbys, some up, some down. Haven't seen many GA18's pop up, seem a little more rare than the 20's. I have seen a few more of the 77 Vanguard monsters popping up.
Why do think this one is so cheap? (GA8T)
http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... K:MEWAX:IT
 

capnjuan

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I don't think it has any soul. 6BQ5s/EL84s but a smallish power transformer and even smaller output transformer. My guess would be more of an itchy, nasal sound. The more desirable version is the earlier twin 6BM8 in tweed. Seller didn't mention whether speaker is original or not but if so, it's a Gibson 'Ultrasonic' believed to have been made by CTS ... the Ultrasonics are not keepers.
 

capnjuan

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valcotone

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capnjuan said:
I don't think it has any soul. 6BQ5s/EL84s but a smallish power transformer and even smaller output transformer. My guess would be more of an itchy, nasal sound. The more desirable version is the earlier twin 6BM8 in tweed. Seller didn't mention whether speaker is original or not but if so, it's a Gibson 'Ultrasonic' believed to have been made by CTS ... the Ultrasonics are not keepers.


Bingo!!! We have a winner!!

I had a "Gibson GA-8T Discover Tremolo Amp" just like that one and it was a wimpy and lame sounding amp. Sold it as fast as I could.... :lol:
 

capnjuan

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valcotone said:
capnjuan said:
I don't think it has any soul. 6BQ5s/EL84s but a smallish power transformer and even smaller output transformer. My guess would be more of an itchy, nasal sound. The more desirable version is the earlier twin 6BM8 in tweed. Seller didn't mention whether speaker is original or not but if so, it's a Gibson 'Ultrasonic' believed to have been made by CTS ... the Ultrasonics are not keepers.
Bingo!!! We have a winner!! I had a "Gibson GA-8T Discover Tremolo Amp" just like that one and it was a wimpy and lame sounding amp. Sold it as fast as I could.... :lol:
Hi Sean: I had a GA5T 'Crest' Skylark with 6AQ5s and 10" Ultrasonic; fresh caps, tubes, and speakers ... didn't matter what you did to it, just couldn't soften up that nasty tone. :( :wink:
 
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