Guild Beginner said:
... doesn't seem like it would produce that awesome of a sound. It would be like hearing an amp from an adjacent room. I was guessing (I'm not sure about this thing either), that this one can switch from the right to the left independently, or solely use the middle 12" for mono. Maybe you can get them all going at once, but I'm not sure. Man, it's really clean though.
Hi Caleb: the GA79 shown above and below has a stereo input jack that will send L and R signals down each amp 1/2 and to the bridging switch. Left open, the amp produces L and R stereo. If a mono guitar were plugged into either channel, throwing the switch would put the signal out of both L and R ... dual mono.
By contrast, the GA83 doesn't have a stereo input jack. To get true stereo, must have a L signal in one side and an R signal in the other ... the signals are separately amplified until they reach a selector switch on the output side of the output transformers; switch as shown in the schematic at the left. In the middle, the switch is in the 'stereo' position; each amp 1/2 supplying signal to its pair of 8" - sideways facing - speakers. On the right, the switch is thrown tying in the 12" speaker which is being fed L and R. The amp is functioning as a stereo system while the 12" speaker provides mono output.
Wally Marx'
Gibson Amplifiers 1933 - 2008 talks about Ted McCarty's and Seth Lover's interest in 'hi-fi' as it was known back in the day. If you look at the GA78 and GA79, even their cosmetics look better-suited to a drawing room with people sipping wine while listening to some jazz than to almost any gigging environment you can think of ... like I said, maybe i missed something but sending signals off side walls ... I don't know what they were trying to do.
However, while McCarty/Lover were messing with this stuff, they weren't messing with either high-power, R&R-oriented gigging amps like Fender's 4X6L6 100 watt models or exploiting the EL84 designs they were working with towards to the same purpose. Wouldn't have taken a whole lot to re-arrange the speakers on the GA83, get rid of the two output transformers and replace them with one ... the result would have been an early 4XEL84 Marshall ... but that wasn't what Gibson wanted to produce.