"Broken" Orange TH30 - where to begin?

scarry67

I've luckily acquired a broken TH30 amp that belongs to the school I work in; a strange purchase by now departed Head of Music. It powers on and I can see 3 valves glowing but there's no sound or electrical "noise" when you connect a lead. I haven't got it home yet to examine and it could simply be one valve gone or even a blown fuse. My grasp of electrics is sub-minimal so where shouId I start in bid to get it going again?

Sassafras

Make sure it's connected to a speaker?
That sounds obvious but I've seen it happen.

jpfamps

Check the HT fuse first.

If this has blown the valves will glow but you'll get no sound.

If the fuse has blown then the most likely cause is a power valve has expired.

When you say 3 valves glowing, is that 3 of the power valves?

scarry67

It’s connected to 1st of 2 8ohm speaker inputs and 3 visible valves are lit but the 4th is dead. Behind these 4 are 1 and then another 4 sealed in metal casing valves. If the 3 are on would that suggest fuse is ok? Obviously I need at least one new valve but I suspect this amp has never been recalled or serviced in 3 years...

rico

The easiest thing would be to take it to an amp tech. It could be all manner of things!

scarry67

Yeah. I’ve got a couple of numbers of local amp techs and it’s probably worth the investment...

Teyeplayer

1) I love your old head of music!
2) Triple check the obvious (standby switch, valves, plugged into a speaker of the correct ohms). 
3) Amp tech if stuck...although you might want to get the school to write it off as damaged/broken and offer them a nominal fee for taking it off their hands to ‘mess with’ (tenner). Then once it’s yours take it to the amp tech (I don’t know an incoming head of music that did this with lots of ‘stock’).

jpfamps

scarry67 said:

It’s connected to 1st of 2 8ohm speaker inputs and 3 visible valves are lit but the 4th is dead. Behind these 4 are 1 and then another 4 sealed in metal casing valves. If the 3 are on would that suggest fuse is ok? Obviously I need at least one new valve but I suspect this amp has never been recalled or serviced in 3 years...

NO.

The HT fuse can blow and the valves will still light up; I'm regularly told "the valves must be fine as they light up". All that tells you is that the filaments are fine and the filament supply is working.

Sounds to me that the valve that isn't lit up has expired and taken the HT fuse out with it.

The HT fuse is accessible from the back of the amp.

Sounds to me you will need some new valves and an HT fuse.

DJH83004

+1 for the suggestions from jpf, there are a couple of small complications on the TH30, if I recall correctly, it has a full / half power standby switch, which reduces the HT voltage, and a two / four tube selector switch on the back, does changing those make any difference to the output (or lack of it!) in any event one EL84 sounds like it Is dead ( and it would be good practise to change all four) and the HT fuse is definitely A suspect.

scarry67

I’m going to buy some fuses & valves and attempt fix. Will report back if successful or contact tech. 

scarry67

Can’t even get the bloody ht fuse out! Turns a bit but won’t pop out. Not a good start...

ICBM

scarry67 said:

Can’t even get the bloody ht fuse out! Turns a bit but won’t pop out. Not a good start...

That’s common with them. You can do it easily if you take the chassis out, you can push it out with a small screwdriver. If you don’t want to do that, the tip of the corkscrew on a Swiss Army knife will hook it and pull it out if you’re careful.

scarry67

And it’s up and running. New fuse & 2 valves. Bloody loud but Dirty channel is quite usable and sounds even better with OD pedal thickening it. Just wondering if a passive volume pedal in fx loop simply reduces loudness or does it allow for “better” sound?