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 Post subject: Gibson GA45-RVT
PostPosted: Aug Fri 09, 2019 10:30 am 
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Joined: Jan Sat 12, 2013 7:14 pm
Posts: 1151
Location: Plymouth, Michigan
Well, what an experience! This amp sat around for three years, getting dirty in my shop because I’d heard nothing positive about these, tone wise. D-Lab even went so far as to completely gut one and turn it into a Fender clone because of frustration with the design and documentation that’s available for it. I decided to fix mine! Full cap replacement and getting rid of the preamp t filters really improved the overall sound, and the final touch was adding a PPIMV to the circuit and mounting it in place of the power on selector switch, which I replaced with a standard pair of toggle switches for power and standby. Anybody know where I can find Gibson hardware, like handles and amp corners?

Pete

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 Post subject: Re: Gibson GA45-RVT
PostPosted: Aug Sun 18, 2019 6:38 pm 
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Joined: Dec Sat 24, 2011 9:17 pm
Posts: 4585
Location: Vancouver Island, Canada
Hi, try Antique Electronic Supply in Tempe, Az.

Congrats on repairs to your Gibson amp. This is a radio site primarily, but when you do discuss amps here, there is no mysterious mojo, just real world knowledge of antique circuitry.

P PI MV - post phase inverter master volume. :mrgreen:

I found a schematic and maybe someone has insights as to why there was a need to modify the original circuit.


Attachments:
Gibson GA45-RVT schematic.jpg
Gibson GA45-RVT schematic.jpg [ 287.39 KiB | Viewed 218 times ]

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 Post subject: Re: Gibson GA45-RVT
PostPosted: Sep Wed 04, 2019 1:24 am 
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Joined: Jan Sat 12, 2013 7:14 pm
Posts: 1151
Location: Plymouth, Michigan
To get the best overall sound. The preamp stages had a band pass filter network that was just death to any gain at all....by getting rid of those in a standard straightforward manner the gain isn’t so lost, with the exception of the tone stack loss.
And yeah, I realize it’s a radio site, hence my screen name :mrgreen:

Pete

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 Post subject: Re: Gibson GA45-RVT
PostPosted: Sep Fri 06, 2019 1:47 pm 
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Joined: Nov Wed 30, 2016 7:35 pm
Posts: 4807
Location: Sunbury, Ohio 43074
Why just not add a gain stage to compensate for the loss in the input stages? I'd think this would be less of a modification than what was suggested. You could even use a solid state preamp or gain block of some kind .....

I can't be more specific because the posted schematic is blurry enough for these old eyes as to be painful, but you get the idea ....

And sometimes "the experts" aren't entirely correct with these sorts of pronouncements. Many guitar players would likely find this a perfectly good amp today ... perhaps just not the "upper crust". ??

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