EMRFD Message Archive 13256

Message Date From Subject
13256 2016-11-02 18:46:35 wb8yyy_curt Hycas Minor Instability Observed
Thanks for suggestions from several folk.  I may be experiencing much of the phenomena discussed. 

Finally getting expected AGC behavior, after getting regulator somewhat adjusted -- 8.43 volts.  (close enough or should I extend this closer to 9 volts?)

Occasionally the regulator will jump up to 11 volts or so -- possibly staying there or not.  Adjusting the variable capacitor in the input matching can improve the stability.  Also, I don't have this T50-2 inductor tacked down -- nor the output transformer for that matter. 

I do notice with no input signal, the AGC voltage is not stable -- it dances around a bit. 

I read others switching to a broadband transformer on the input.  Are there other things I should consider, other than obvious mechanical things, to improve stability?  Still I sense most of instability is electrical. 

Plan is to use this after a 4915 kHz crystal filter.  I don't mind putting a robust amplifier in front of the filter -- so willing to concede some in the front of the Hycas to stabilize it.  The adventure continues. 

73 Curt

13258 2016-11-03 09:00:53 vasilyivanenko Re: Hycas Minor Instability Observed
Hi Curt

Did you view Wes' pages? ; the latter discusses instability


The input matching network built with a lower Q inductor such as a molded choke [ what was supplied with the kit offered by Roger] -- or an L wound on a #61 material toroid can help  stop the stage from oscillating.

I built 2 with a molded choke [ QuL was ~50-60 ] , 1 with the L wound on a T37-61 and yet another with the L wound on a T68-6 but had to shunt it with a resistor to drop the Q and stop the IF strip from oscillating.

Your DC voltage regulator output V should remain stable.