ShortScale.org

Alright so I have been playing through my Epiphone Valve Senior since about March 2009. I never really take it anywhere, but whenever I move it, something breaks. On the whole, it's usually the tubes. However, I've been getting a really weird buzzing sound and I decided to check the fuses. I don't have the schematics but I think I've found the problem. However, I don't know what I'm looking at - I just know that there's an issue. It's in slot R-23 of the big old board thing, and I've got some pictures to look at. I'm thinking this is the root of the problem, because I smelled burning something while playing and there is a strange hum coming from the amp. There's also some rattling, but not as bad as when I broke my preamp tube. (Always sounds like SOMETHINGS broken.)

Here's the problem piece:

Underneath this is some burnt black stuff. It's kinda hard to see, but it's a little below halfway down on the board and it's more on the right than the left. It's labeled R-23, but without schematics I've got no clue what R-23 means.


Here's a shot of the board, not sure if it's too clear:


And a couple random maybe this will help pictures:










And a terrible video demonstrating the sounds I'm hearing and how little I know about amps, guitar tech, and anything else remotely musical.




whomp wah.

Here's a schematic. Unverified, but it says R23 is 1k, 2W.
http://forum.gibson.com/index.php?/topi ... ge__st__80

..and if that schematic's OK, then R21 should be the same. So my guess: if R21 looks perfectly OK, either there's something up with the valve (tube) V4 making it draw too much current, or I'd take a look the other side of the board and see whether you have a bad solder joint. My bet's on a bad valve.
I'm sure you don't need to be reminded, high voltages can kill so make sure your caps are discharged - etc etc - I see there's a 470K EHT bleed resistor in play when the standy switch is in the ON position that will discharge it slowly.

R23 is a resistor. Generally components are labeled R for RESISTOR (also includes potentiometers as they are variable resistors), C for CAPACITOR, D for DIODE, J for JUMPER (piece of wire), V for VALVE, etc...

R23 is a 1k 2w screen grid resistor for the V4 output tube. If you have had an output tube fail before, it could have damaged that resistor enough for it to go out of specification. If you know anyone that can use a multimeter and check that resistor you can tell if it's still good or not. It should measure close to 1000 ohms (1 kilohms).

The hum/buzz is really bad. Tubes are always the #1 suspect. Try powering up without the preamp tubes and see if you still get the hum. That would indicate that it's got something to do with the power section. If there is no hum then you might want to mess with swapping around the preamp tubes to find a bad one. V2 is the most important on this amp. V1 is for your reverb, V3 is the phase inverter. It shouldn't need V2 to operate.

You guys are amazing, thank you so much. Saving me like $150 here at least.