[Amps] HV Diodes

Carl km1h at jeremy.qozzy.com
Thu Oct 16 17:13:16 EDT 2014

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.



----- Original Message ----- 
From: "Manfred Mornhinweg" <manfred at ludens.cl>
To: "Amplifier Mailing List" <amps at 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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