Question about fuses popping in H&K Warp X

[Wes]

I've got one of these amps here, it was made in 2005, and it keeps blowing the fuses that
feed +22 and -22 into what seems like the relays and maybe the heater supply. I don't
grasp the use of -22vdc in the heater supply if in fact that is what it's doing, but.....

Have any of you guys seem something like this? I'm not really experienced with relay circuits
and this one seems entailed...

Could it be possible that a cap in this circuit's supply is bad e.g. C4-C12 as seen in the poweramp schematic listed below?

The weirdness with the -22 and the heater supply can be seen on the preamp schematic, below, in the lower left corner.

http://music-electronics-forum.com/a...itch-board.pdf

http://music-electronics-forum.com/a...a_poweramp.pdf

http://music-electronics-forum.com/a...-1a_preamp.pdf

http://music-electronics-forum.com/a...4_fx-board.pdf

http://music-electronics-forum.com/a..._led-light.pdf

Any help you may have is greatly appreciated!

[nosaj]

Save your fuses and make a dim bulb tester look it up cool tool.

[Enzo]

The tube part is the easy part. The heater of one of the 12AX7s is wired for 12v operation - the two halves in series. This series pair of heaters is across the 22v supply ALONG WITH a pair of parallel resistors. There is a 100 and a 180 ohm in parallel. That results in about a 64 ohm total. So 64 ohms in series with the tube. Now we know that a series connected 12AX7 will use 0.15A of current and that is with 12v across the tube. So with that 0.15A cirrent through that 64 ohm combination of resistors, Ohm's Law tells us that about 9.6v will drop there. 9.6v from 22v leaves about 12.4v for the tube, and that is darn close to the nominal 12.6v it wants.

Now the fuses. Are they blowing instantly? Or do they just blow at some point during the evening?

If they blow right now, while anything is possible, the caps around the bridge are probably OK. Measure all four diodes of the bridge, any shorted? Are either of the 22v rails grounded off?

And you are using the slow blow fuses, I hope?

[Wes]

When I got this amp it had no fuses in it so I had been using T500mA in the amp
for about a month due to not being able to find T630mA in my local Radio Shacks.
After I burned them up I tried FA700mA and those went right away. I may have
gotten a pair to last a bit there at the end.

Anyway I got the T630mA fuses in today from Mouser and the amp fired right up
and I was able to play it for about 45 minutes.

I did also take out the preamp board and I cleaned up well around V1. I checked
the components in there and they looked good and all measured out to spec as
well.

Thanks for the help guys. I've got my fingers crossed that it'll hold out now.....