marshall super lead keeps blowing fuse?

HELLO ALL i have been having trouble with my 1973 marshall super lead 100 blowing the 1 amp fuse what is the best starting place to find the problem tubes-caps etc...thanks in advance james.

You can check the tubes first because you can swap them out without opening the chassis.

You should probably check the power supply next and look for any shorts.

If you don't know how to properly drain the filter caps then have a pro work on it so you don't electrocute yourself. They hold very high voltages even when unplugged.

A 1A fuse doesn't sound the correct size for a 100W amp, even if it were 230V. Is this the value stamped on the chassis plate or are you simply replacing it with whatever was in there when you got the amp? Or are there multiple fuses on a Super Lead?

Also make sure you are using "Slo-Blo" fuses.

I have been using the fast acting fuse not the slow blow type is this the problem?

Hi

A typical Marshall tube amp like this may have a 4 amp fuse for the AC mains and a 1 amp fuse for the HT. It may be marked HT - which is High Tension or called High Voltage and AKA B+.

One of the frequent problems blowing this 1 A fuse is shorted or intermittantly shorted output tubes. It only takes one to be bad to pop the fuse.

If you carefully remove all the outputs from the amp and try a fuse and it does not blow - best guess would be to change outputs.

If you get sound for a period of time and it blows, gain access to the tubes while operating and lightly tap each output. If you see an arc, change the output set.

If the 1 A pops with no outputs installed - now you will be looking at another area pulling excessive current.

During output replace - establish proper biasing along with a good waveform on a O'scope.

I continue to run into bad valves right out of the box, especially Groove Tube. Without going into a long detail - I humbly recommend a matched set of outputs with an origin from Winged C ( Svetlana ) or JJ.

Rebranders ( GT, Ruby and many others ) get their tubes ( other than NOS ) from China, Russia or Europe as a general rule.

From my years of both repair and stage performance with tube amps......

Anything China incl even STR types - no

Sovtec - no

Winged C ( Svetlana ) - yes

Europe - yes

I am not looking to get into a flame war over tubes. My opinions and preferences on ''best chance of a good set'' are from decades of experience.

Your milage may vary........

If you play a lot and or loud or been a long time since replacing outputs..........time for new tires on the car so to speak...

Best of luck

That's at lest part of the problem.