Boy,
I'm sure glad we ran those lowdown, dirty rotten CBer's off of here so
that we could get down to some serious technical mind-bending 8+)........
Mike(y)
W3SLK
----- Original Message -----
From: measures <2@vc.net>
To: Amps <amps@contesting.com>
Sent: Saturday, September 02, 2000 12:57 PM
Subject: RE: [AMPS] Problem with SB-220 Bias Diodes
>
> >
> >> The reason why I say enlightening is because in my field of electrical
> >> engineering that includes the design of commercial power systems,
> >> lighting, traffic signal instrumentation etc., the engineering
principals
> >> are cut and dried and there is no interpretation of basic applied
> >> engineering principals such as voltage drop and system fault analysis.
In
> >> the field of RF Power Engineering it appears, however that their is
great
> >> deal of room for interpretation.
> >
> >There isn't actually much room for interpretation. Everything can be
> >confirmed by physics, math and proper measurement.
> >
> >The problem is getting people to understand the problems,
> >because they are complex. Most people want a simple "one thing
> >causes all" answer rather than the truth, that in a complex system
> >many things interact.
> >
> >> Both Richard Measures and Tom Rouch are very intelligent, highly
skilled
> >> and respected engineers within the RF Power Engineering community. The
> >> have both contributed many publications advancing the knowledge base in
> >> this field and have both contributed to the "design" and "development"
of
> >> products at the commercial level. Having said that however, it is
> >> disturbing that their various 'egos' interfere with the presentation of
> >> their information.
> >
> >I wasn't aware that Rich designed any commercial products, but
> >that shouldn't matter at all to anyone. It's what a person SAYS and
> >how well he can explain it that are key to proving his technical
> >abilities.
> >
> True enough. Also, what a person tosses off is important.
>
> >> Here is a basic summary of what I should do to improved the performance
of
> >> my SB-220 based on information posted in this group.
> >>
> >> 1. Replace the existing bias diodes with diodes having a 3A rating.
> >
> >You have plenty of diode rating for ICAS, but if you want to improve
> >the biasing stability use a zener...especially a low power zener
> >with a transistor wrap-around. A zener will have a sharper
> >clamping action and make a more stable bias source than a string
> >of rectifiers.
> >
> The issue is glitch surviveability.
>
> >That may not be a major issue in amateur service, but zeners
> >around 5 volts also have a nearly zero temperature coefficient. I
> >can't understand why people use rectifiers for zeners.
> >
> Three amp diodes can withstand 200a. 10W, 5V zeners can not.
>
> >> 2. Increase the L in the existing parasitic suppressors.
> >
> >Increasing the L will help make the parallel R a bigger part of the
> >anode circuit, if you have a VHF stability problem.
> >
> Increasing L-supp decreases VHF gain and increases 10m dissipation in
> R-supp.
>
> >> 3. Add current limiting protection in the form of a ten ohm RCD 175P
> >
> >Yep, then when the tubes arc the current will be limited by ESR of
> >the electrolytics, circuit wiring, and the ten ohm resistor (actually
> >20 ohms would be better, if you can use two resistors in series).
> >
> >> series HV pulse rated resistor. 3. Replace the existing 3-500Z tubes
with
> >> new tubes (I would assume that you would recommend getting good quality
> >> Amperex 3-500ZG instead of the generic Chinese variety?).
> >
> >The later Amprex tubes have a tendency to develop filament to grid
> >shorts, but that is a non-catastropic failure.
>
> A cathode/grid short is catastropic. It instantly reduces drive to zero.
> .....
>
> later, Tom
>
> - Rich..., 805.386.3734, www.vcnet.com/measures.
> end
>
>
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