[AMPS] TL-922 Filament Transformer Protection

[Peter Chadwick]

Tom says:

>One cure is to park the resistor outside the suppressor coil, and 
>series tune it with a small mica cap. That not only increases 
>current through the resistor at VHF, it decreases resistor current at 
>HF. 

Another method which is very effective at reducing the current in the
resistor is to use a one or two turn link in the plate circuit, coupled to a
parallel resonant tuned circuit tuned to the parasitic frequency, with a
resistor across that. As in the older editions of the ARRL handbook. It also
allows tuning out the reactance of the resistor.

I suspect that winding the choke over the resistor was a practice started
when resistors were generally either carbon composition or the earlier
carbon rod types, which were essentially non inductive; it saved space.

>Since inexpensive non-inductive carbon resistors are getting nearly 
>impossible to find

Even EXpensive ones seem impossible to find!

73

Peter G3RZP




--
FAQ on WWW:               http://www.contesting.com/ampfaq.html
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm