December 28th, 2009, 07:16 PM
i was playing earlier today and the volume of my guitar dropped suddenly, then was completely overwhelmed by a loud humming noise. i got up to check the amp and noticed that there was a very visible orange glow coming from the back of the cabinet; one of the tubes must have been lit up like a light bulb. before i could even shut it off, the amp went off on it's own.
if i try to turn it back on using either the standby or on switches, nothing happens- the indicator light doesn't come on, nor do any of the tubes glow. i've had my tubes for over 3 years at this point and it seems about time for them to go. is this what happens when a tube goes out, or did my amp just die on me?
December 28th, 2009, 07:25 PM
December 28th, 2009, 07:39 PM
Tube's dead and you blew a fuse.
December 28th, 2009, 07:42 PM
You generally hear some screaming followed by some gasping breaths.
Seriously, the scenario you describe sounds like an interelectrode short in a tube. If the plate or screen grid short out to the suppressor grid (which is grounded), the tube will light up like a Christmas tree. This will cause excessive current draw, which will reduce the ability of the power supply filter caps to do their job, resulting in a lot of hum. At some point the fuse will blow.
The problem with troubleshooting this issue is that a tube tested may not show the tube as shorted. Tube testers test tubes at voltages lower than the voltages in an amp. If you are lucky, you should be able to visually detect which tube lit up by seeing signs on the envelope. It could be as easy as replacing the shorted tube and the fuse. Chances are it did further damage like overstressing the plate or screen grid resistor. Good luck.
December 28th, 2009, 08:12 PM
what kind of amp do you have and what tubes? if the amp has a rectifier tube, those can just quit working w/o any warning at all. They usually last a very long time though.
December 29th, 2009, 03:05 AM
it's a fender deville 2x12, which i think has solid state rectification. i had some winged C 6L6's for power tubes and i think some jan-sylvania 5751's for the preamp. not exactly an amp that i'd be too sad to part with; it does a fine job but there are better ones out there.
December 29th, 2009, 04:49 AM
so... what exactly does a dying tube sound like anyway?
See the opening scene of "The Party" /w Peter Sellers.
December 29th, 2009, 10:04 AM
There are also other problems that can cause a tube to red plate besides the tube itself.
Losing the negative bias voltage to the power tube grid on a fixed biased amp will result in red plating. A few possible causes include bias circuit failure, PCB solder connection to tube socket and tube socket not making good connection to the tube pins. Cathode follower circuits can also have problems.
It is wise to do come checking before popping a new tube in.
December 29th, 2009, 10:52 AM
Here's a link to the service manual for the Fender Hot Rod Deville. It is a fixed bias amp.
December 29th, 2009, 11:23 AM
Like this? :lol::razz:
December 29th, 2009, 11:41 AM
"Tube's dead and you blew a fuse."
+1 you also might want to pop in a new phase inverter if it's been in there for 3 years...those typically burn up on a similar cycle as the power tubes.
December 29th, 2009, 12:12 PM
i've only had power tubes go out on me once ... they went nova or something. for about five seconds, i had the most divine tone i've ever heard! then, nothing. didn't seem to hurt the amp, though; replaced the tubes and it behaved from then on. (it was a HRD, now long gone.)
December 29th, 2009, 06:17 PM
the fuse is most definitely blown but i can't see anything visibly wrong with the tubes. i'll take it into the shop to have it checked before putting in new tubes, thanks for the help