[TMC] C708 in PS-4

[triodes at optonline.net]

Larry,

Is it a PS-4 or a PS-4A? The two units are significantly different. I have a PS-4A that I have extensively serviced and brought back to it's as-built configuration, and I am quite familiar with the unit at this point. It was the victim of several Hammy Hambone dumbass modifications that I pulled out, plus the control relay was completed zorched which I subsequently replaced. She works like a charm now and does everything she is supposed to do. I'll be using this PS-4A in conjunction with my RFD-1A and a homebrew 3000 VDC power supply. I don't ever expect to find the PS-5 HVDC supply for the PAL-1KA, and since I have the HV magnetics from a Gates BC-1G 1KW AM broadcast rig I stripped for parts years ago, I'm currently building my own version of the venerable PS-5.

At any rate, if it is a PS-4A, C-708 is a 0.1 uf @ 1000 WVDC hermetically-sealed paper-in-oil bathtub capacitor. It is used as part of several of the RC snubber networks included within the PS-4A power supply. My guess is the same RC values are used within the protective snubber networks in the PS-4 as well.

I pulled these specs from my PAL-1KA technical manual.

The PS-4A has the major advantage of an electronically regulated screen supply for the PL-172A and the 6146 driver stage screens, and the inclusion of a circuit breaker to protect the grid circuit within the HPA stage. My guess is that relatively few PS-4s were built, and the majority of the production was the PS-4A. I think it is a superior circuit overall for the intended application, when compared to the PS-4.

I hope that this helps.

73,

Bruce, W2XR

----- Original Message -----
From: LARRY D GODEK 
Date: Wednesday, May 25, 2011 10:38 pm
Subject: [TMC] C708 in PS-4
To: tmc at mailman.qth.net

> 
> This cap, C708 is uspposed to be across a set of relay contacts 
> in the PS-4 medium-low voltage power supply for the PAL-1 type 
> linear amps. It's the same amp as used with the SBT-1 KW rigs. 
> On any of the schematics i have it shows C-708 but it's not in 
> the parts list. No capacitor has that high a number assigned to 
> it yet it's on the schematic. I know it's a .1 but what value 
> voltage. I want to change out the one in my supply to protect 
> the grid from burning up in the event plate voltage doesn't come 
> on or drops off without kicking out the grid voltage relay.
> 
> I looked on various schematics on K4OZY's web page, again not 
> finding a part number such as this in any parts listing. I 
> even printed out a new copy of a PS-4 which is totally different 
> than the schematic i have with my books. Unless i pull that 
> beast out of the rack i'll never know which version i really have.
> 
> Anyone have any info on the C708 cap? 
> 
> Larry
> W0OGH
> 
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