[Amps] HV Diodes

[Hardy Landskov]

Manfred, et al
I believe the 1N4007 is actually manufactured as a PIN diode vs the PN 
configuration of the others in the same family.
I know it was when I was still at Motorola in the '90s.
73 Hardy N7RT


----- Original Message ----- 
From: "Manfred Mornhinweg" <manfred at ludens.cl>
To: <amps at contesting.com>
Sent: Tuesday, October 14, 2014 12:18 PM
Subject: Re: [Amps] HV Diodes


Carl,

 > ** IMO there is a balance point between using obsolete diodes and 
overkill.

Are you suggesting that the 1N4007 is obsolete? I just checked, and it's 
still
in full production by several companies, such as Diodes Inc, Fairchild, ON
Semiconductors, Vishay, and a few more. It's a highly popular diode, 
massively
used, and despite having been available for a long time, I haven't seen any
signs of it becoming obsolete.

To me, a device is obsolete when something better becomes available at the 
same
price, or something as good becomes available at a lower price, and thus the
sales of the original device fall, making the manufacturers discontinue it. 
As
far as I know, this hasn't happened to the 1N4007. But it has happened to 
almost
all tubes...

So, I would look for a balance point between reliability and cost. Given the 
low
cost involved, indeed 1N5408 diodes might be that sweet spot, despite being 
huge
overkill. My point was to illustrate that technically the 1N4007 diodes 
should
be fine for legal limit ham amplifiers using bridge rectifiers, but a bit 
tight
for those using voltage doublers. There was no intention to force any of you 
to
use them! So, please don't eat me alive... ;-)

 >> Let's assume a pretty big amplifer, solid legal limit, CCS, which is 
more
 >> than any ham needs. The power supply might deliver 3500V at 0.8A. Each
 >> diode string in a bridge rectifier will then see a peak voltage that 
might
 >> reach 4000V in the event of line overvoltage, and an average current of
 >> 0.4A at full output.
 >
 > **  That is an obsolete assumption with RTTY and data modes having many
 > users these days. Even AM linear is pushing it.

Sorry, Carl, I don't understand you here. What exactly did you mean by 
"obsolete
assumption"? If I base my calculation on a 1500W CCS amplifier, in what way
would this be obsolete, or too weak for a ham running RTTY? In fact it still 
has
some headroom, because no ham RTTY operation is continuous in the long term,
even RTTY bulletins might last only 10 to 20 minutes!

Or did you mean that 0.4A average current per diode is too low, for an 
amplifier
running 1500W in RTTY? It isn't! If that amplifier runs on 3500V and 0.8A,
giving 2800W input and 1500W output, meaning a 53% efficiency, then each 
diode
in the bridge rectifier carries 0.4A average current. That's a fact, not an
assumption! The actual average current will be slightly different, depending 
on
the amplifier's efficiency, and the voltage it works at, but will hardly get
much above 0.5A, unless you have a lousy efficiency, run illegal power, or 
use
tubes that need a very low supply voltage.

The current will be peaky, due to the capacitive filter, but the average 
will
still be just that low value. The peaks might be around 3A, but such 
repetitive
peaks are within the safe operating area of a 1A diode, as long as the 
average
current is low enough.

 > ** I detest when someone who should know better starts championing the
 > lowest denominator.....the cheapskates that infest the hobby at the amp
 > level. Keep it to QRP where nobody gets hurt (-;

ROFL. Seems that we two represent opposing poles! I absolutely love getting 
the
most bang for the buck, and building legal limit amplifiers that cost under 
500
dollars, total. And which work well, too. Remember that old adage? "A piece 
of
engineering is the product of material and brains. The more you use of one, 
the
least you need of the other." I like using lots of brains, and little 
material!

And yes, I built QRP equipment for the first several years of my ham career. 
The
2SC1969 was my preferred output device, but I also sometimes ran a few 
2N2222 in
parallel to deliver one watt... I made many intercontinental contacts using
power levels under 5W, into simple dipoles or quarter wave verticals. Mainly 
on
ten meters. And many of them in FM! When the other guy has good ears, you 
don't
need a kilowatt. On the other hand, a kilowatt gets heard better in many
situations. As an old QRPer, I do know that!