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.
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.