I'm having problems with my Randall RH300 G3 guitar head.

When I turn the amp past 5 (because we play that loud...) the amp eventually (from what I can ascertain) drops after about 30mins to half my volume...and I'm left turning way way up and getting mushy...

I was running my Zoom G7.1ut (at the -10db setting) into the FX loop and into a oversized Mesa 4x12 recto cab in the 4ohms input (still drops out at 8ohms, I think quicker than 4ohms cuz I'm cranking it louder). I read somewhere that once you run two cabs it engages the full 300watts and was previously only pumping 200 watts, not sure if that's the case or not but I did add a Peavey XXL 4x12 (which I think is 16ohms) and started running my pedal through the front (+4 db switch engaged) which has made my sound greatly improve. The added volume of the other cab (or the extra wattage) has allowed me to keep my master volume below 5 without issue.

I would still like to figure out the problem since other bands will be using my amp onstage and it would seriously suck to see it happen to them.

Other information that might be relevant:

-It has the same symptom when I use the amp distortion and the Zoom FX is not connected.
-I have kept watch on the temperature, the internal fan works fine and have cleaned it of dust, have placed a house fan focused on it; air conditioned room.
-The sound is great but has an abrupt volume drop, still loud and the same quality of tone but not as impressively loud as when I first turned it on.

I've read that this series of amps have been problematic...

Hello all!

This is my first post, not sure if I'm in the right spot...
I'm trying to find info on a little practice amp (8 or maybe 10 inch speaker) called a Vintage 30 (probably named to capitalize on the popularity of the celestion speaker of the same name). I doubt it had a celestion, didn't sound like it was 30 watts and had a modern tone, not vintage. This is why I want to find it, 15 years ago I played through this little amp and liked the tone. I would like to find one or preamp info on it. It sounded somewhat similar to a Peavey Ultra Plus high gain channel but was a little solid state combo.
All I remember was the model name, which was on the cloth, it was two channel with one eq, separate channel volumes, gain, a channel toggle (maybe button) and perhaps a headphone out.

Maybe after so many years I have over hyped it in my mind and its actual junk but it'd be nice to find one and tinker with it. Any help would be greatly appreciated.