Big time mistake with my 1974x!!! Please help!

[Johansen]

Hello,

During a rehearsal yesterday the mains fuse failed, 315mA/250V. We are in a big hurry since we're going to studio this weekend so i did the worst mistake you can do with a valve amp, i placed another fuse i had in hand, but this one with 1,6A/250V, guess what... Burn smell!!! I quickly disconnected everything and opened the amp, apparently everything is fine except for the mains transformer which i was going to replace with a shinrock i have waiting at home (the PT was already replaced also with a shinrock). Now, the thing is, do you think anything else could have been affected with my idiot attitude? Is there anything i should carefully check when replacing the mains transformer tomorrow?

Kind Regards and thanks for all your help!

[guitarmike2107]

Well you still have to find what blew the fuse in the first place. the stuffed PT may be a result of the fuse you put in or it could have been the primary cause for the fuse blowing.

[Chubsman]

Ya did the PT blow the fuse?? Or something else.... and the new fuse (bigger) did not protect the amp as it was intended...

[Johansen]

Hello,

I'm pretty sure it was the PT that blew the fuse in the 1st place.

I'm asking if i should have a closer look at the caps or something, but everything seems esthetically fine...

Kind Regards

[Chubsman]

If you are pretty sure... I would power up without any tubes in and test as if a new build...

[guitarmike2107]

I am no professional with this sort of thing, but here’s my 0.02c

You seem sure it’s the PT in the first place, so either you were expecting it to go, were abusing it,
or have had problems with it in the past.. me jumping to useless assumptions.

Anyway, you can check the output transformer by measuring the resistance of both sides of the primary,
should be roughly the same on each side. Same for checking resistors and caps (if you have that function
on your DMM) .. etc etc not sure how to check your valves though.

To be safe I would go through the ruby start up guide, checking for shortages were there shouldn’t
be and measuring voltages in stages, if it was not the PT at fault originally the fault will probably reveal
itself through this process, probably as a direct short to ground.
This may be obvious, but make sure you have the right size fuses in this time.

Good luck

[Johansen]

Yup, won't make the same mistake twice...

Those are nice suggestions! I'll take a look at that!

The transformers that come from marshall suck big time, that's why i bought better ones from Shinrock, i mean, the marshall ones keep blowing all the time, they act like 2nd fuses... :p

Kind regards