Bridge rectifier (DB101) smoking (opto switch supply, 6.3VAC 3A)

[Duncan]

Question/issue for the hive mind:

I recently completed my SLO100 build (using C3 Amps boards, a custom/prototype Hammond power transformer, and the output transformer from a Peavey XXX).

When I powered the amp up (using a 150w lightbulb limiter), my bridge rectifier (DB101) for the switching started to smoke immediately (which caught me off guard since I was using my voltage limiter). Anyway, I learned that the DB101 is rated for 1A, and I realized I was throwing 3A at it.

In your opinion, should I try to source a new bridge rectifier rated for a higher amperage, or just use individual diodes to rectify instead?

Anyone have this issue before?

[sluckey]

You didn't give much information so let me guess...

You are powering a bridge rectifier for your switching power supply. Maybe from the filament string. But regardless, the PT winding has a center tap connected to chassis. And you also connected the negative terminal of the bridge to chassis. Boom! You blow up two of the diodes in the bridge. This happens because two of the diodes are directly across the PT winding. Dead short. This happens quite frequently. Just happened last week over on TAG forum. The problem (and the solution) is DON'T CONNECT THE NEGATIVE TERMINAL OF A BRIDGE RECTIFIER TO THE PT CENTERTAP!

If this is not your situation, please disregard and give us the details.

[sluckey]

I forgot to mention the DB101. The one that smoked is bad. After you fix the reason for the failure, replace with another DB101. A 1 amp bridge is plenty suitable for your use.

[Duncan]

You didn't give much information so let me guess...

You are powering a bridge rectifier for your switching power supply. Maybe from the filament string. But regardless, the PT winding has a center tap connected to chassis. And you also connected the negative terminal of the bridge to chassis. Boom! You blow up two of the diodes in the bridge. This happens because two of the diodes are directly across the PT winding. Dead short. This happens quite frequently. Just happened last week over on TAG forum. The problem (and the solution) is DON'T CONNECT THE NEGATIVE TERMINAL OF A BRIDGE RECTIFIER TO THE PT CENTERTAP!

If this is not your situation, please disregard and give us the details.

That sounds pretty much like what I’ve done ha. PT CT to the star ground, same with the CT for the switch windings.

I’ve attached the wiring diagram for the PT for reference.

[sluckey]

Should be a simple solution. Disconnect the winding CT, insulate the end of the wire, and tuck out of the way. It's not needed. Then replace the bridge and you should be ready to go.

I'm assuming you are using a separate winding for the switch power supply. If so, there's no need to bother with isolating any grounds.

[Duncan]

Should be a simple solution. Disconnect the winding CT, insulate the end of the wire, and tuck out of the way. It's not needed. Then replace the bridge and you should be ready to go.

I'm assuming you are using a separate winding for the switch power supply. If so, there's no need to bother with isolating any grounds.

Yeah, so my PT has a 6.3VAC winding for the heaters (7A) and an additional 6.3VAC for the switching (3A). Both have centre taps and if I’m reading you correctly, I should lift the CT of the switching winding from ground (where the CT’s for the other windings are going), yeah?

[sluckey]

yes