Marshall TSL100 Humming....until I clipped C46...?

[acorkos]

What is the purpose of C46? This amp was humming, even without any tubes installed. I read the recent thread about the humming DSL100, and someone mentioned C46 being shorted. I checked this amp's C46 and it is shorted, too. i clipped on leg...hum is gone. I'm not sure of the purpose of C46....is it necessary to replace it, or can i leave it off?

thanks for your help.

[Enzo]

It is there for stability. If you snip it out, you might get away with it, or you might wind up with parasitic oscillations at times.

I'd replace it with a 1000 volt cap.

Even without ppower tubes, when it shorts, it shorts plate and screen together, and that then makes the OT primary winding on that side in parallel with the B+ dropping resustor between those two nodes. So now any supply ripple current through the B+ string will also now be flowing through the OT primary, and thus making that hum.

[drewl]

Is that a common problem on those?
I had a DSL with that cap shorted.
I put in a 2kv ceramic, problem solved.
One of the bias pots on the little board had a cracked solder joint, and intermittantly the bias would go nuts and blow the HV fuse.

[Enzo]

Yes, whenever I am in one of those amps I check it. Even if it is not shorted, if it looks like it was hot, out it goes. And if there is any complaint like low power, hum, won't bias evenly,or a number of other things, that is the first place I look.

Loss of bias doesn't usually blow fuses, unless it causes the tube to short