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VOX AC30C2 blowing 500mA HT fuse
Old 4 weeks ago
Here for the gear

VOX AC30C2 blowing 500mA HT fuse

Had a VOX amp in the other day and report is its blowing 500mA HT fuse.I powered it up with NO ht and three of the EL84 vales were glowing heaters as normal but one did not glow but it was SOO hot it could take the skin off fingers(see photo)

Any idea why a valve gets hot without VISIBLE heater?

Have ordered a new valve and i hope this sorts the prolem but i have never seen a valve get hot without visible heater glow???

Photo taken by mate with infrared camera.
Attached Thumbnails
VOX AC30C2 blowing 500mA HT fuse-valve1.jpg  
Old 4 weeks ago

Maybe the heater is shorted to the Cathode?

Either way, it's time to put a new quartet in the amp....


Old 4 weeks ago
Here for the gear

replaced the nuclear valve and all's back up and running-i know a full set would have been best but when i used to work at an electronics shop we used to sell the EL84 for about 30 bob now you need to take a loan out
Old 3 weeks ago
Lives for gear

"Any idea why a valve gets hot without VISIBLE heater? "

A bad connection on the grid pin can cause the tube to run away, glow cherry red, take out the tube, take out the B+ fuse (hopefully) and generally Do Bad Things. I suppose it might even take out the heater.

Check your sockets. The metal on most is "C" shaped, and with time they get a little loose. You might be able use tweezers or jewelers screwdrivers to coax the metal back so it makes good contact, though on EL84's it all might be too tiny to mess with. In that case, maybe it's time for new sockets, or at least a shot of Deoxit.

Old 3 weeks ago
Here for the gear

in the end it was just a faulty valve-unfortunately i was not able to aquire the faulty valve and examine it-pity but on to the next
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