Gibson GA42RVT repair issues

[wildcatstrat]

I haven;t measured the voltages in one for quite a while but real 5881 would not be a safe sub; IIRC, the plate and screen voltages were in the 450V range give or take a little, and even after subtracting the cathode voltage you'd still be too high for a real 5881. 6L6 GC, KT66, and JAN Phillips 6L6WGB all work well in this amp. Also, it is actually set up (the versions I've seen are, anyway) to handle EL34 i.e. the power tube socket wiring, however these draw even more heater current than KT66 and I'm not sure if the PT can handle it. The transformers are IMAG made in Mexico, I contacted the company hq in Arizona and tried to get specs from them but they claim the specs are proprietary to Gibson and they won't hand them out.

Thanks for the info! I've loved this amp since I bought it, and it just keeps getting better and better with each "upgrade." To this point I haven't done anything major (just swapped out all the preamp and power tubes, the original bridge rectifier, and a few of the signal caps in the preamp section for orange drops.) When I placed the order for the bridge rectifier on Mouser, I figured I'd go ahead and order some metal film resistors to help cut down on some hum. Are there any particular spots in the preamp section you'd recommend swapping the original carbon comps for metal film? Sounds like you've done quite a few mods on yours, so I thought you might save me from some pitfalls. My next upgrade will most likely be swapping out the crappy Eminence modeling stock speaker that came with this thing. I figure that if I already really like the amp, I'll be blown away when I put something good in there. Probably gonna try to pick up a Weber Ceramic Blue Dog based on your recommendation. Anyhow...if you have any other tips I'd love to hear them. Have a good one!

[EFK]

I can;t speak to the noise as I have not found them to be overly noisy. I did come across a reference somewhere to someone who was having hum problems or something like that, and it turned out to be crosstalk between a non-shielded wire and a wire in the reverb circuit. Don't remember where I saw that, I think it was on one of the Gibson boards.

IMHO, if you have not swapped the speaker/speakers yet, RUN don't walk to do that before you do anything else. This will single handedly make th biggest change in this amp. I think the best I have heard in these are some kind of G12H clone. I particularly like the WGS Reaper, either 75hz or 55hz. 55hz is VERY nice. Have to go with the 50W rated versions.

[wildcatstrat]

I guess the noise isn't really a big issue in mine either...I just didn't know if I'd benefit from swapping out some of the carbon comps for metal film resistors. The shipping from Mouser was more than the cost of the bridge rectifier, so I just HAD to order something else so I would feel like I was getting my money's worth, hence the Orange Drops (.022 microfarad) and plethora of metal film resistors.

As far as speaker changes go, I actually just sent a Paypal payment last night to a guy on the Gear Page for a 30 watt Weber Blue Dog. I'm more of a hobbyist/tinkerer than a "real" guitarist sadly, and I'll be playing at home more than anywhere, so I'm not so worried about pushing the speaker too hard. I'll be using an attenuator too, so hopefully I'll be in good shape in that regard. Here's an odd tidbit though...I decided that I'd try out the Vintage 30 that came in my Gibson GA-30RV Super Goldtone combo in the GA40, and I actually prefer the sound of the crappy Eminence that came stock in it: go figure? The Eminence in the Super Goldtone is a disaster however...the Vintage 30 seems to really mate well (along with the Vintage 10) with that amp. I'll be putting the V30 back in ASAP. I've been debating on trying something more "American" sounding, maybe a Weber 12F150? On the Weber site, it's cited as a "favorite for the deluxe reverb." The Super Goldtone that I have is very British flavored in its own rite with the V30/V10 combo, and at home I usually play through both amps simultaneously using an Radial Bigshot ABY. I guess I'll see how the Blue Dog works in it and go from there.

[wildcatstrat]

I can;t speak to the noise as I have not found them to be overly noisy. I did come across a reference somewhere to someone who was having hum problems or something like that, and it turned out to be crosstalk between a non-shielded wire and a wire in the reverb circuit. Don't remember where I saw that, I think it was on one of the Gibson boards.

IMHO, if you have not swapped the speaker/speakers yet, RUN don't walk to do that before you do anything else. This will single handedly make th biggest change in this amp. I think the best I have heard in these are some kind of G12H clone. I particularly like the WGS Reaper, either 75hz or 55hz. 55hz is VERY nice. Have to go with the 50W rated versions.

Well I must say EFK...you were 1000% correct in saying that a speaker change would make a huge difference in this amp! I installed the 30 watt ceramic Blue Dog yesterday, and I can honestly say that it's like playing through a completely different amp! Cleans are gorgeous and full of texture for lack of a better word, but the real kicker is when I kick on the OD. Oh so sweet tones! I'm not sure if I'll mess with the guts of this thing too much more or not, because now I'm tickled pink with my tone!

[Slunderfungus]

Greetings, I am reviving this old thread because I recently bought one of these GA20RVTs and it too has generated the rectifier and optoisolator problem. The revtifier is an easy enough fix but can anyone tell me the correct way to install the 5C1 optoisolator?

[seanman]

The rectifier I used was a Fairchild GBPC1210W. It is considerably larger and able to handle a LOT more current. Here's a link:

GBPC1210W Fairchild Semiconductor Bridge Rectifiers

Because each of the 4 legs is soldered down into a turret, and there are also wires wrapped around those same turrets, the best thing to do is to (1) cut the old one out, leaving as much old leg as possible sticking out, then (2) heat each turret one at a time and yank the individual legs out, (3) use a solder sucker to clean out the turrets and (4) stick the new legs down in there. The higher off the board you can leave it the better, as it dissipates a lot of heat and it's good to get it away from the heater filter cap to ground right next to it. This rectifier is technically overkill, but once I stuck it in there, the heater fading issues faded into the sunset permanently.

I have replaced the Rectifier with the above. I am still having issues with the Fuse's. The amp comes on, but pop's the fuses when I turn the amp off standby. I have replaced the 6L6's.
Any idea what could be popping the fuses? Could it be the caps in the power section?
Thanks