>
>> 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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