I should have conducted a web search first. SEMTECH continues to offer the
original SCH5000 H.V. rectifiers factory-direct and through distributors.
Anyone wanting to know the exact specifications of these diodes used in
older Alpha amplifiers can find it here:
http://www.semtech.com/pdf/rectifier/halfwave/schx.pdf
I'll plan on first checking with Alpha/Power for stock on Tuesday. Thanks
to everyone for their replies!
-Paul, W9AC
-----Original Message-----
From: Paul Christensen <paulc@mediaone.net>
To: amps@contesting.com <amps@contesting.com>
To: <amps@contesting.com>
Date: Saturday, September 05, 1998 2:36 PM
Subject: Alpha H.V. Rectifier Source
>In my continued pursuit of finalizing my Alpha PA-70V rebuild, I discovered
>that a nylon H.V. feedthrough jack between the power supply and R.F.
cabinet
>is causing my H.V. flashover, not the 3CV1500A7 as I originally suspected.
>In place of the nylon feedthrough, is now a glazed-porcelain James Millen
>"beehive" type, which I filled with 100% silicone clear RTV. If this
>doesn't take care of 4KV leaking to ground, I give up.
>
>I also noted that upon my last flashover, my glitch protection circuitry
did
>its job: I replaced a string of three 1N5408 diodes, not the plate ammeter.
>Unfortunately, a 50-ohm @ 50-watt H.V. lead resistor I recently installed
is
>AFTER the feedthrough. However, another failure occurred. One of the four
>H.V. diode "blocks" is shorted. It is marked...
>
>SEMTECH "SLIMPAC"
>SCH 5000
>
>Does anyone know if Alpha/Power is still carrying these? I believe my 77Dx
>used the same type. If I cannot obtain an exact replacement through a web
>search, would it be prudent to simply replace all four with a newer type?
>Does the "infamous" K2AW Silicon Alley have these? I measured the forward
>and reverse resistance of the remaining three H.V. "blocks" and they all
>measure identical. Is it safe to assume that they are not on the ragged
>edge of failure?
>
>In my search for a spare vapor-cooled 3CV1500A7, I not only found one
>new-in-the-box, but I also "coerced" the seller into letting me purchase
his
>new Alpha PA-70V which is in its original box with only a few hours on it.
>This is one of the few times when I really got lucky!
>
>To be safe, I'll probably change out the H.V. feedthrough, H.V. wiring and
>perhaps upgrade the plumbing as I had recently done using all Teflon
>components. Does anyone know the life expectancy of 20KV silicon rubber
>high voltage wire?
>
>-Paul, W9AC
>
>
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