Gibson GA42RVT

[EFK]

Here is a schematic for this amp. I tried to convert from a pdf - if this is viewable, can someone who can actually read this thing tell me anything about it? For ex., which preamp tube is driving what? (5) 12ax7, (2) 6l6gc, (2) speakers, (2) channels w/ 3rd input for mix. What I'd REALLY like to know is, what - if any - old amp might this be based upon? Old Fender? Old Gibson? Something else? Does it look familiar to anyone? Is there any transformer info contained here? Any info MUCH appreciated! Thanks!

[rf7]

Here's your signal flow.:

Input J1 feeds V1a, then into a volume pot, into V2a which feeds the tone controls, then into V5 - the Phase splitter tube, and then into the power tubes V6 and V7 (push pull cathode biased 6L6's).

Inputs J2 and J3 feed into V1b, then into a volume pot, into V2b, which feeds the tone controls, then is mixed in with Ch. 1 signal into V5 and then into the power tubes.

The volume pot of channel 2 feeds the reverb driver stages of V3. The reverb returns via V4a and is mixed in with Ch. 1 and 2 signals into V5 and then into the power tubes.

V4b is the vibrato oscillator, which affects the signals going into the V5 phase splitter.

[Enzo]

Gee, post the pdf, I find those a lot easier to work with.

[EFK]

rf7 - THANK YOU! That is quite helpful.

I'm posting link to pdf.

Does any of this look familiar, i.e. like any other amp? Is there anyone else out there playing with one of these? It is very difficult to find any information. For example, why would Gibson choose to install very colorless 'modeling' speakers in these things? Also: I have repeatedly read that, given enough room, it is possible to use kt66 in place of 6l6gc although there may be issues w/ heater current and transformer. So, how does one determine if the transformer or other pertinent components can handle the kt66?

[EETStudent]

Are you sure thats the schematic for the amp? Ive got the same amp, but my circuit has several differences from the one in the post. Where did you get it from?

[EETStudent]

Actually, this schematic is VASTLY different than mine.

-4.7K grid stoppers and 3K screen grid resistors on the power tubes?

-1uF cathode bypass caps in channel 1, as opposed to 22uF caps in mine

-1M grid stopper on V1B not in mine, 68.1K on V2B not in mine

-Several minor changes in both tone stacks, and different cathode and tail resistors in the phase inverter.

-Tremolo has several major differences.

The GA40 and GA42 are supposed to be the exact same circuit, one being a 1x12 the other being a 2x12. You do have Eminence Legends dont you?

[EFK]

I received this schematic directly from Gibson. Maybe they're making these things up as they go along? Mine does have eminence speakers in it. One interesting note, which now that you mention the schematics being different is even more interesting: does this schematic (above) show reverb and tremolo on both inputs? I don't mean the mix - I mean, on channel one input alone? I have reverb and trem on channel one input also, which I *thought* (at least according to manual) it was not supposed to have.

Do you have a schematic you can post?

[EFK]

Possibly also someone at Gibson is, or was (are they still making them?), modifiying these to rectify issues as they arise. I have heard of some problems with these amps when they first hit the market, but nothing since. I haven't had a single problem with mine at all but then it's only @ 4 months old. Most dealers I think are selling stock that they've had sitting since they obtained them, as I don't think these were ever huge sellers, so maybe it's a crap shoot as to whether you get an early one or a later one? This is all theoretical!

[EETStudent]

Im thinking that Gibson has made several, and I do mean several, changes to these along the way. I believe they are still making them, as most online carriers are waiting for their shipment. And yes, I DO have reverb and tremolo on both inputs, contrary to the manual.

I wish I had a schematic to post. I should install some sort of schematic designer and draw it out. I may just hand draw it and scan it. But yeh, I wish there was just more available info on these amps. From some of the things Ive read, Im afraid to even put the amp back in the hands of Gibson. Who knows when Ill get it back or if itll be fixed or anything