I'm not sure what this is all about, but the Semtech diode string used 3A
diodes internally, having Vf = 1V/cell @ 3A and about .8V/cell at 1A, so
there were a variety made using different qtys of cells. I recall Henry
used these for their inherantly high surge current capability (150Apk, 8.3mS
rating), but that wasn't the only reason. The other reason was that at the
time, Semtech didn't make any high powered Zeners, and the Semtech salesman
was good friends with the people at Henry, so they give him the business.
The salesman is quite a famous 20m DXer, Mel, W6FDR (ex-WB6FDR). I recall
all this because at the time, I also worked for Semtech.
-WB2WIK/6
"If everything seems under control, you're just not going fast enough." -
Mario Andretti
> -----Original Message-----
> From: Marv Gonsior [SMTP:w6frmarv@dslextreme.com]
> Sent: Friday, July 19, 2002 2:09 PM
> To: amps@contesting.com; 2
> Subject: [Amps] Diode Bias Strings
>
>
> >>>At 08:01 AM 7/19/02 -0700, Richard Measures wrote:
> >>>
> >>>>The Semtecc diode string in question appears to be a 10 diode
> >>>>unit. No, it was a 10V unit, according to Henry and the Semtech p/n
> >>>>was their SA5534. So, now we are talking about an ~18 diode device as
> >>>>used in the Henry 3-K Classic X.
> >>>
> >>>> >I would like to ask the proponents of series rectifier diode strings
> if
> >>>> >they have ever measured the developed bias between the minimum and
> full
> >>>> >power conditions?
> >>>>
> >>>>Yes. Please tell us about the results.........one 5408,
> >>>>or? Previously, when I asked you for test data on your recommended
> >>>>diode biasing , your response was that I "didn't need no stinkin'
> >>>>data." Why now?
> >>>>
> >>>> >I've done it with a Henry 3-K Classic X, using and 8877,
> >>>> >and the bias soared about 6V from zero to full signal.
> >>>>
> >>>>V sounded a bit high, You bet it was high and you can't compare a
> >>>>Semtech assembly with a sample of one 5408. BTW, the early Henry 2-Ks
>
> >>>>used a 50W, 6V Zener.
> >>>
> >>>>so this morning I tested a 1n5408/3A diode for fwd
> >>>>V-drop using 8877-sized currents, assuming a ZSAC of 0.1A and a signal
> >>>>max Ik of c. 1.2A. At 0.1A, the V-drop was 0.734v. At 1.2A, the
> V-drop
> >>>>was 0.813V. Thus, with a 10-diode string, the change in bias V for
> an
> >>>>8877 would be 0.79V from zero-sig to max-sig. For improved IMD, and
> >>>>less chance of overdrive with more than 78w drive, add a few ohms in
> >>>>series with the diode-string to increase V-drop at max sig.
> >>>>
> >>>> >Read that power limiting that must result in additional distortion
> >>>> products.
> >>>>
> >>>>A diode has more V-drop as current increases. A resistor has even
> more
> >>>>V-drop as current increases. A resistor can be added in series with
> the
> >>>>cathode to create RF-NFB. (which I read in Svetlana, Eimac, and RCA
> >>>>pubs).
> >>>
> >>>>- Marv - Does more RF-NFB increase or decrease IMD? We all know the
> >>>>answer to that one but you have to know the net effect of the ratio of
>
> >>>>the biasing distortion to the negative feedback afforded by the
> resistor.
> >>>>
> >>>> > I couldn't wait to dump Henry's Semtech diode pack and put in a
> >>>> 50W,12V Zener. IMHO,
> >>>>
> >>>>Humble ? Yes, humble and it is not obvious that you know much about
> that.
> >>>>
> >>>> there is nothing worse than diode strings as a biasing element.
> >>>> > Further, just ask the G-land 6M ops what they think of the bricks
> >>>> >that find their way into cluttering up the band with relatively high
>
> >>>> levels
> >>>>of splatter resulting from diode bias. Ian et al, are you listening?
> >>>>
> >>>>The red herring. Now, don't tell me that you've gotten into fishing?
> >>>
> >>>73,
> >>>
> >>>Marv, W6FR
>
>
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