If you knew as much about amp history as you may not know about other ham
items you would know that Alpha has used potted diode blocks since the
1970's. And Ive replaced my share as likely have others, including my own
76PA 3 holer and especially, the 77 series.
Instead of continuing the guesswork why dont you ask Alpha what is inside?
OTOH I stated "almost universal" knowing exactly your reply, and Alpha is
far from high volume compared to others using 1N5408's.
Next?
Carl
KM1H
----- Original Message -----
From: "Manfred Mornhinweg" <manfred@ludens.cl>
To: "Amplifier Mailing List" <amps@contesting.com>
Sent: Thursday, October 16, 2014 3:47 PM
Subject: Re: [Amps] HV Diodes
Carl,
> Suffice it to say that the real world of tube type ham amps uses the
> 1N5408
> almost universally no matter what the configuration.
Do the Alpha 8410, 9500, 8406, and the 89 belong into the real world of
tube type ham amps? I would say, they do. And they don't use the 1N5408
but instead use a potted bridge rectifier, rated at 5kV peak inverse
voltage and 2A total forward current. I don't know with certainty what's
inside it, but 4 strings of 5 each 1N4007 diodes would have exactly those
ratings. Instead a bridge made from 1N5408 diodes would have a rating of
6A total.
This is it:
http://www.rfconcepts.com/REPLACEMENT-PARTS-LISTED-BY-ALPHA-PRODUCT/Blowers-and-Fans_2/HV-Bridge-Rectifier
Maybe it doesn't use the 1N4007, but then certainly it uses some other
diode very similar to it, and not at all like the 1N5408.
They rate it for 50A surge of 8.3ms duration, which might mean the diodes
inside are slightly beefier than the 1N4007, or maybe the difference is
just due to to larger thermal mass thanks to the potting. If different,
this could be 1N5622 diodes, which have that 50A surge rating. But that
diode has a slightly higher voltage drop, which isn't consistent with the
bridge's rating for voltage drop - while the 1N4007's is consistent with
it!
I suspect this bridge is simply made from 1N4007 diodes, nicely potted,
and sold for $150...
Take $2 worth of diodes, a little plastic case, 4 blade terminals, 20
drops of solder, and a few grams of a good epoxy potting resin, put it all
together, and sell it for $150 to hams. Hmm, I should get into that
business! ;-)
On the other hand I do admit that several other amps I checked, indeed use
bridges made from 1N5408 diodes. But the Alphas are too important an
exception, to ignore them!
Manfred
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