Wiring Black Gates - How?

[Chris Doyle]

I have 300B PSE amps and have been steadily changing components for a while now. Having finally decided to take the plunge and swap the power supply smoothing caps for Black Gate WKZ types I'm now stumped due to them having 3 connecting lugs - 2 positive and 1 negative. Despite trawling a few web sites, including Jelmax's own strangled english special, I am none the wiser. I don't want to blow them up - they're too expensive - so, how do you wire these caps between the choke and O/P transformer? Any help would be appreciated - a doodle would be nice.

[NealG]

The negative terminal is the neg terminal for both halves of the cap. Think of it as two separate caps in the same can but with their negative terminals tied together. the positive terminals are the pos terminals of each individual cap.

Connect the neg terminal to PSU/cct ground and one of the pos terminals to one side of the choke and the other to the other side of the choke.

[Chris Doyle]

Thanks for the swift response but I'm afraid it makes me think I maybe asked the wrong question or perhaps used the wrong terminology - maybe they're not smoothing caps just power supply caps. The caps I'm after replacing are C9 and C10 on the 300B PSE power supply circuit diagram. They are wired in parallel between the choke and output transformer with negatives connected to earth and positives connected to each other via a 15k resistor and individually to the plate loads of the input and output valves.
I suspect I need to connect the two positive terminals on each Black Gate to effectively make both C9 and C10 two paralleled caps and then put the resistor between them, but this just begs the question why have two positive lugs on each capacitor.

[Paul Barker]

I don't have the circuit in fron t of me so there may be errors in my response due to that.

The Black Gates are designed so that you could use 100uF on one channel and 100uF on another with a common ground. OR you could decouple the two halves by a choke or a resistor (and I think you are describing this in the wad psu using 15k, though that is a very high value for a power stage, so it might me that the second stage of filtering is for the input stage, and the 15k aswell as decoupling is sized to correctly drop voltage).

What you cannot do, and I don't think that you are describing this, is stack the two halves on top of each other to share a greater B+ than they are individually rated for, because of the common ground.

[NealG]

OK I have the cct in front of me. The are smoothing caps/psu caps, the same thing. What I described is correct *except* instead of wiring either side of the choke you need to wire either side of R19.

I take it the WKZ you have is rated 500V and 100uF+100uF?

The WKZ is two caps in a single can with common neg terminal. C9 and C10 are the same; two separate caps but when in cct they also have a common ground when wired up in the amp. They effectively make a 100uF+100uF cap when wired in cct. Hope that helps!