Hi Paul,
There's no 6A equivalent part to the JTX1N5554. Problem is, JAN parts must
be hermetically sealed by spec, and to make a 6A glass or ceramic dual-plug,
metalurgically-bonded part is nearly impossible because the slug diameter
gets to be too large, so the small mismatch in the thermal coefficient of
expansion between the die, the slugs and the glass or ceramic body can cause
cracking under surge conditions. It's been tried for decades without
success.
So, "we" use paralleled 3A hermetic parts like the 5554's previously
described to provide lower Rthj-L and ~6A rectified current rating and ~250A
Ifsm surge rating, or go to non-hermetic parts which do not suffer the
coefficient mismatch problems, or go to custom power hybrid modules (thick
film hybrids using large dice eutectically bonded to a CRS case). Problem
with the hybrids is they get very, very expensive and it's difficult to
assemble them so they'll stand off more than a few kV, because the die to
metal substrate (or pin seal) dimension is so small.
Heatsinking does help the K2AW assemblies. I use thermally conductive
grease to mount the K2AW modules on aluminum heatsinks, and then mount the
heatsinks to my chassis, if I'm pushing them. However, I cannot envision a
"legal" amateur amplifier that needs to push them, since even 3500V at 1.5A
is -- ahem -- quite a lot of power-?
73!
Steve WB2WIK/6
"Each success only buys an admission ticket to a more difficult problem." --
Henry Kissinger
> -----Original Message-----
> From: PAUL HEWITT [SMTP:wd7s@att.net]
> Sent: Monday, November 19, 2001 10:01 AM
> To: Steve Katz
> Subject: RE: [AMPS] 8877 rectifier board considerations
>
> Hi Steve
> Nice tip on the diodes. Do you have any
> numbers for 6-amp 1kv?
> I've always been afraid of over
> stressing the K2AW stacks with high
> current. I have used them ,(on a
> heat-sink) with good results at 1.5 amp
> Thanks, Paul
>
> PAUL HEWITT
> WD7S PRODUCTIONS
> QRO HOMEBREW COMPONENTS
> http://wd7s.home.att.net
>
>
>
>
> Hi Jim,
>
> I surely wouldn't bother with the setup
> costs of prototyping PC boards for
> an array of diodes...the off-the-shelf
> prototype boards in all the
> electronics hobby stores will do the job
> just fine. I'd probably use
> JTX1N5554's as the rectifiers,
> though....1000 PIV, 3A, 150A surge, very
> low
> leakage (<1 uA @ 1 kV, and typically far
> less), excellent diodes available
> new surplus for pennies each. The "JTX"
> designates "JAN Tested Extra" and
> indicates the parts are 100% burned in,
> including a 168 hour reverse stress
> test at elevated temperature, to weed
> out questionable parts. Worth the
> extra few cents. These are also
> dual-plug metalurgically bonded parts as
> opposed to soldered die construction,
> and thus withstand most extremes
> better than commercial equivalent parts.
>
> Of course, then, the K2AW modules which
> cost pennies per kV make me question
> why I'd ever bother building a HV diode
> stack...
>
> WB2WIK/6
>
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