How do I know if I've cooked my Hot Plate??

Nerine

Just lately, I've been running up my JCM 800 into my Hot Plate. 

I mainy use it less for attenuation, more for the "Deep" switch to thicken it up a bit. (I'm gonna go for an EQ pedal in the loop). 

Anyway, I experienced a pretty severe drop in level just whilst noodling away at home. I was like WTF? 
Had a look in the back of the amp. Appears normal. All 34's are glowing with a faint blue tinge. I did notice when I twotted a chord or something that in one area on one of the power valves there was a focusing of the blue hue a bit. 

Anyway, fast forward. I took it to rehearsal not that long after this happened and left the attenuator at home (I think. Can't really remember. Ha.) and the amp functioned as normal and it has been since. The level hasn't been doing anything weird. I've not really used the Hot Plate since then, just in case, but is there any specific way to tell if it's the THD that's potentially on the fritz?? 

Ive got a new set of EL34's to pop in the amp if needs be, but I haven't really got the skills to bias it. (I do have a multi meter, so if I can bias it properly using just a multi meter, then all cool, I'll give it a stab) but I'd rather not change them if I don't have to. The tech I use has some other gubbins he attaches to the valve sockets. 

I'all do some more dicking about tomorrow, but in the meantime, was wondering, as stated, if random level drops where something to expect from an attenuator that's starting to get a bit iffy?? 

ICBM

Marshalls and Hotplates are a bad combination and put a lot of stress on the valves when you push them hard - although the warning sign is orange glow from the valve screens not blue glow, which is normal. If you’re not driving the amp hard it won’t be that though.

It could also be a fault with the Hotplate, most likely the main level switch, but also possibly some other internal connection.

timmysoft

If you want me to come over and talk you through the biasing, that’s not a problem mate! 

Nerine

Thanks bro. I'm hopefully actually gonna get some time to play it today after cleaning the bloody studio since Monday.