Ampeg SVT CL preventative maintenance question - to fil transformer fuse? or not to?

[tubeswell]

Sorry, I thought that you mentioned Zener diodes in your first post.

Yeah there were 15V clamping zeners in that circuit as well, which I also replaced (along with the 4 x 220uF filter caps). But the 1N4007s were definitely fried, they all measured short circuit in each direction.

[tubeswell]

+...It's not the running current that damages them, it's the "startup" jolt that can reach 6x the running current. ...

Hmmm... This must have been what caused the 1N4007s rectifying the +/-15V supply (that is fed off one of the other the filament transformer secondaries) to fry. - in combination with the higher resistance from the oxidation on the terminal connector. A spike caused by the extra resistance going back through the 6.3 winding (with 11.1A running current - 70VA, which could have been 6 x as high = 420VA?) into the 14V winding - an impedance ratio of 0.45:1 (and any voltage spike would have doubled)??

[Enzo]

6.3mm is 1/4" i believe, which is what all mine are sorted as.

Doesn't have to be insulated, you can use a bare one and put a blob of silicone on top of it to prevent it touching the chassis if that is a danger.

Juan, his connectors are the 6vAC connections to the tube socket board, not the multi primary connections.

[tubeswell]

The amp owner has since told me he's happier if the leads are soldered straight onto the output tube board's 6V lugs, so that's where its heading.

[Leo_Gnardo]

The amp owner has since told me he's happier if the leads are soldered straight onto the output tube board's 6V lugs, so that's where its heading.

Good choice. One less thing to go wrong. Two actually, those spade/flag connectors. A couple of cases I've seen, the plastic covering had half-melted & turned toasty brown. "What's that smell?"

[tubeswell]

The 1N4002s in the filament supply on the pre-amp board were short circuit too. Probably a consequence of the charred 6V terminal lug on the power tube board methinks. One day I'll find all the faults and it'll be fixed. :-)