apparent voltage surge : help with trouble-shooting damage?

[keto]

Hi all, there was a big voltage (and current?) fluctuation in my building while I was listening to a little music. The apartment lights flickered and then the 300B filament went out on one of the Paramounts. I switched the tubes and its not the 300B itself, but something in the amp. All 4 LED's light up and the fuse has not yet blown, so I figure it can't be a shorted secondary winding. Maybe one of the 300B filament diodes got burned in the process, since they would fail "open" (right?)? I'm wondering, would it still be safe to plug in and turn on and do some voltage readings? Any suggestions as to what else to look for? Thanks!!!

[Grainger49]

I would imagine if the lights dimmed you had the old voltage dip.  If they grew brighter there was an upset on the power lines.  That doesn't often happen.  A voltage increase can put things "out of whack" (how's that for technical?) inside the amp.  In particular the 300B heaters float up and down with the incoming voltage. 

PJ has posted some guidelines for the Paramount heater voltages, you can search and find those.

Since it isn't tied to the tube I have great hope that there is something loose that cropped up when this happened.  Give it a good look over.  Then do the voltage checks and get back to the board.

Good luck!

[Doc B.]

I agree with your assessment, check the heater supply rectifiers for shorts before you start it back up. Pull the 300B so you don't get a false reading through the filament.

[Grainger49]

I had thought the heaters in one of my Paramours was not lighting in 3 of 4 points.  Then last night in the dark I verified that everything was fine.  

So, you can't trust the visual confirmation with all heaters.

[keto]

Woohoo! Using both bits of sage advice, I pulled the 300B, turned over the Paramount, checked all kinds of continuity with the big diodes (which I assume are the heater diodes), finding no apparent anomalies, but then looked at the lower right hand solder joint in the photo, thinking that not only did it look a little light/incomplete, but that between the diode lead and the PC trace there seemed to be a complete ring of brown (flux?). Maybe that joint conducted enough for the lower-current multi-meter but not enough for the higher-current heaters? So, for good measure rather than scientific integrity I flowed a little solder onto each of the four diode-lead/PC-trace points and... voila! Back up, and running! Thanks, guys!!!