Magnavox V4 Question - ATTN: Amp Guys

[tombhex]

Hey guys, I'm playing bass right now and my V4 is running much hotter than I remember it running. I haven't played in about a month, but I let the tubes warm up before coming off standby and I don't remember it ever running hot like this. The tubes are in good shape and I've never had any problems, nor had the previous owner (whom I know really well).

I'm playing my bass straight into the V4, into a Marshall 1525 215 cab wired for 8ohms. I've got the amp set on 8ohms and I'm playing at a pretty low bedroom volume level.

The top of the head is hot above the tranny to the touch, as is the back plate by the first two tubes and power cable section. I'm rehearsing with a band I'm filling in for in about 40 minutes, so if anyone has any input I'd really appreciate it. I'd hate to take it to rehearsal and have something bad happen if it can be avoided.



As you can see here, the tubes are glowing but not gleaming more than usual - my initial thought was they were running hot and to have it biased. Any help is appreciated. thanks!

[Pissy]

Have you measured the cab's impedance to verify that it's actually running that way?  Should be just below 8 ohms with a multimeter.

[Hemisaurus]

Depending on the type, trimmers used in biasing can be vibrated out of trim, or something else could have changed in your bias circuit. Biasing is like the idle setting in your car, too high you'll shorten engine (tube) life.

Are any of the tubes glowing red?

[dunwichamps]

too high of a idle power dissipation in the output tubes and u could be redplating which causes excessive heating

[tombhex]

After a while of it performing totally normal, it started getting hot again and one of the tubes is glowing blue. I'm going to have to replace them obviously, but I didn't see redplating. I mean, I've never seen it in person but the dudes I was jamming with have and said I'm just going to need to get a new set of tubes and have the amp biased when I replace them.

[dunwichamps]

blue glow is usually no problem. Your PT getting super hot sounds bad, as those amps have pretty damn solid iron which I would not think to run hot or anything.

[Lumpy]

Take it in for a tune-up. Tell the tech you want to keep the old tubes, if they need to replace them. Try to remember what the old ones looked like

[dunwichamps]

make sure u get 7027a

[tombhex]

thanks guys!