vibrating PT - help...

[HTH]

ok, I've finally got round to wiring up the PT in my '76 Marshall Superbass head. it's the correct part# bought directly from Marshall.

I've checked the wiring many times and planned it all out carefully routing the wires correctly using chassis pictures from another '76 Superbass.

The problem is that I'm getting a vibration on the PT when I touch it. Any ideas what this might be????

btw, I replaced all of the filter caps and the whole bias circuit since it had been bothched in the past. I've ran the amp at bedroom volumes for a hour or so and the PT never got warm so I'm just wondering if I'm being overly cautious.

anyone?

[Amp Kat]

I had a Fender Bassman tranny that did that to me and it actually had a little hum to it that was Audible. Ran fine and voltages were all correct it just vibrated and didn't get hot either. I'm sure maybe theres an explanation for it I'm just not smart enough to know why ?

[Tom Phillips]

Loose laminiations, loose windings or a loose core assembly can cause power transformer hum. Some transformers last a very long time in that condition.
A good quality transformer should not hum. (Sorry, that's just the way it is) If I had the option, I would ask for a replacement but that's just me.
Regards,
Tom

[HTH]

thanks for the replies, a replacement would be no problem I'm sure but it's a right hassle to take the PT out again and wire another in (making a neat job too).

the hum is only margainly worse than any other amp and the vibration on the PT is only when I touch the PT cover.

if it blows I'll just have to go the custom route (like I was going to in the first place anyway, doh!!!)

[Tom Phillips]

OK. Per your description the vibration doesn't seem too serious.
It's common to feel the vidration when you put your hand on the PT cover.
Cheers,
Tom

[HTH]

thanks for that Tom, I hope you're right and I'm just paranoid - I think it's natural to be that way when you're replacing a blown PT, all of the caps, the bias circuit and all the diodes in the bridge recto circuit.