>
>Since the parasitic debate has died down, maybe we can get it going again!
>
>I offer the following two experiences to the group for comments and/or
>discussion.
>
>In the past year, I have put together two amps with *NO* parasitic
>suppression of any kind.
>
>Case #1: 4 x 813's
? Bzzzzzzt. You said no suppression. 813s have built-in VHF
suppression. No fair!
>in TCGG, started out to be 160 through 40. Had a unique
>layout problem that fried (arced) band switches which had hi-pot tests that
>exceeded twice the anode voltage. Turned out not to be any kind of an
>oscillation at all. Temporarily fixed by removing band switch and fixed on
>160. Details on request, but how about you guys dry-labbing this one and
>see if you can guess what was going on? This amp was deliberately built
>with no parasitic suppression of any kind. I knew going in that the 813's
>wouldn't be bad boys, and I was right. Easy 1500 out with a muffin fan for
>cooling and only 20 bux for the tubes, not too bad.
>
>Case #2: 4CX1000A amp converted to a YC-156. The sheer physical size of
>this jug with handles made this a mechanical nightmare. Tank is an air
>variable and roller coil. Anode "C" plus strays, etc., make it barely able
>to tune on 20 mtrs. That's OK, don't need more then one band per amplifier
>anyway! I fix tuned the cathode network for 40 just to get it going. I was
>scared that the high gain/bandwidth of this tube would make it be one of
>the "bad boys". I did not put any parasitic suppression in at first. My
>thought was to see what it did, then design an appropriate fix. The
>parasitic anode resonance dipped at 80 Mhz.
? Where is the screen resonance? What is the rated feedback-C for a
YC-156?
>I turned it on the first time
>expecting to use the fire extinguisher. Was I wrong! It is absolutely
>stable under any conditions I could come up with. Of course that may change
>if and when I run the anode supply up. My present limit is about 3100v. The
>tube is capable of 6.5kv operation.
>
? I have never heard of a 4-1000A amplifier that had a parasite with a
3kV anode supply. A 6.5kV test might be interesting, Larry.
>......
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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