5150 stopped working - help please

[murraymurray]

Hi Guys,
So yeah, went to play through my 5150 last night and it appeared to turn on so started playing and nothing came out.
Had a look round and noticed that no powertubes were glowing, so thought thats not good.
Im guessing its a bad tube or bad all tubes, it has been about 2 years since i last replaced them. But was wondering if there was anything else it may be so i can perhaps get it going with a  quick fix for a couple of practices before i get tubes shipped in and installed?
I checked the main fuse, it looked sweet, i havent checked any of the internal fuses, but last time one of them blew it acted differemt - i could turn on the mains switch but flicking the standby switch didnt do anything, currently both front lights come on but all the important lights around back are out.

Hopefully its just my amp being a bit behind the game on that earth hour thing the other week of turning all your lights off for an hour.

[Twinfan]

Sounds like the HT fuse to me, popped by dodgy valve.......

[Dmoney]

check the internal fuses anyway.

if the heater was broken, would the amp still make a sound even though the tubes weren't anywhere near a good temperature? just out of interest. like, a terrible sound. Ive had O/P transformers fail, and ive had an amp weirdly, for seemingly no reason blow mains fuses. not had this one yet!

[hamfist]

Sounds like the HT fuse to me, popped by dodgy valve.......

+1

there's a small chance that it's just the HT fuse thats blown for some unexplained reason. But, almost always, it seems that it blows for a REASON, which will almost certainly be a dodgy power tube.

[martinw]

.....noticed that no powertubes were glowing, so thought thats not good.
...
.. currently both front lights come on but all the important lights around back are out.

Doesn't sound like an HT fuse to me, sounds like heaters if there's no glow from any of the output valves.

[Twinfan]

Ah - good point!

[hamfist]

Yup, Martin's almost certainly right here.

No glow in the power tubes means no (or not enough) current is going to the tube heater filaments.

Could be that there is a fuse specifically for those circuits which has blown. If it has blown, though, it's highly likely to be due to a fault in one of your power tubes.

[jpfamps]

Yup, Martin's almost certainly right here.

No glow in the power tubes means no (or not enough) current is going to the tube heater filaments.

Could be that there is a fuse specifically for those circuits which has blown. If it has blown, though, it's highly likely to be due to a fault in one of your power tubes.

Yes, no glow in the power tubes in standby mode indicate no heater current.

It is very rare that the heater circuit in an amp is fused (although the regs actually require that all transformer secondaries are fused...).

Assuming there is a fuse, when they fail valve heaters, like light bulbs, go open circuit, which wouldn't blow the fuse.

However if a valve has shorted plate/ screen to cathode this might blow the heater fuse, although you would also expect the HT fuse to blow too.

Although if not familiar with the inards of a 5150, if the constuction is the same as most other Peaveys then the heater filament wiring to the power valves is likely to be attached to the PCB containing the power valves via a Molex connector, and this can have worked loose.

Regardless this should be a very easy fault for a tech to diagnose.