On Tue, 2007-03-06 at 15:55 -0500, Bill Acito W1PA wrote:
> Is there a "beefier" replacement for the single pass transistor on the back
> of the 252 supply?
>
> 2N5301; NPN, 40V 30A 200W
>
> I have to replace it every few years (good thing for crowbars), and was
> wondering
> if there was something available with a little more headroom in the TO3
> case.
>
> I have seen references to a J802 or EGC-181 or NTE-181, but assume they are
> direct replacements.
> Is there a 50A version?
>
> Bill
> W1PA
>
I've used 2N5302 for a bit more voltage head room. Dissipation is likely
limited by the power supply heat sink. Be sure to apply a minimum amount
of heat sink grease to the replacement transistor and heat sink. You
only want to fill the minute irregularities, a thick film or blob hurts
heat transfer.
I don't see anything with greater than 30 amps collector current in my
Mouser catalog. Its hard to get 30 amps through the emitter pin of the
TO-3 case without melting that pin as it is.
If there is a fuse at the input of the regulator, be sure it is a fast
blow or semiconductor rated fuse, otherwise its simply going to function
as an indicator the pass transistor has shorted because transistor
junctions melt faster than fuses. A slow blow fuse is a sure death
sentence for the transistor. Buss KTK fuses are fast and expensive. It
speeds up the fuse some to load it to name plate or higher. I protect
the PA transistors in my Corsair II with a 16 amp fuse, because it will
hold 20 amps indefinitely but will blow if I get the antenna tuner SWR a
bit too high. That's only happened a couple times. A regulator
protection fuse in the power supply must be after the filter capacitor,
else when the crowbar fires the pass transistor gets melted by the
energy stored in the filter capacitor.
--
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer
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