Reasons for 3A fuse blowing

[jasperok]

Last night was giving the dr103 a good bass shakedown when i lost souund - only after 10 mins of playing.
Anyway
it turned out a burnt out 3A fuse the other 1A fuse is fine -
Maybe just maybe the power chord could have ben loose and kinda wiggling half in and half out i'm not sure - would that cause it?
If not what are common causes for blown 3A fuse?
thanks

[mhuss]

Where are you? 3A is only appropriate for 240v mains, for 120v you should be using 5A.

--mark

[jasperok]

ireland

240v it is!

didnt hae time to probe around last night

really hoping it was just a loose connection of the power cord (kettle plug connection 3pin)

any idea what else causes that one to go?

[mhuss]

It could be one or more of your power tubes is red-plating when you are really pushing the amp. Also, on rare occasions fuses sometimes just fail from age and vibration -- have you tried replacing the fuse at least once to see what happened?

--mark

[jasperok]

Ok so got a new fuse at last!

unfortunately its redplating - I tried a different tube just incase but she still sizzles.

Where to start troubleshooting?

[OldSchoolDave]

Ok so got a new fuse at last!

unfortunately its redplating - I tried a different tube just incase but she still sizzles.

Where to start troubleshooting?

Redplating can be resolved by proper bias. If your DR103 hasn't had the bias adjustment mod, now might be the time.

Dave

[jasperok]

maybe so
but i dont know- one second i was playing - the next - gone
i tried running it in 50watt mode with only the centre two tubes but the same position tube lit up well started to light up about 8 seconds after switching it out of standby.
i'll check the bias though

[mhuss]

Could be a leaky coupling cap (one of the 47nF on the preamp board), but in that case I would expect both tubes on the one side to red plate.

Check the 22k connecting to the grid of the problem tube. Make sure the bias voltage on that grid (pin 5) is the same as that of the other three tubes.

--mark