To: | "R. Measures" <r@somis.org> |
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Subject: | Re: [Amps] Ten-Tec Centurion |
From: | Bill Fuqua <wlfuqu00@uky.edu> |
Date: | Thu, 11 Nov 2004 10:24:35 -0500 |
List-post: | <mailto:amps@contesting.com> |
At 07:06 AM 11/11/2004 -0800, R. Measures wrote: On Nov 11, 2004, at 6:13 AM, Bill Fuqua wrote: You are assuming that the cathode plate capacitance is the only path for feedback. I don't know anything about this amplifier but often there is only one 2C contact relay and serves to switch both the input and outputs. And there is lots of opportunity for feedback in that area. I have seen amplifiers become unstable at HF operating frequencies due something as simple as lacing the wrong wires together. In one case the HV wire to the final of a transmitter was laced nicely in a bundle of wires that feed other lower level buffers etc. Simply removing the HV wire from the bundle and moving it some distance away solved the problem. I realize that this does not necessarily apply to this situation but it is an example. Also, the .3pf is not much if the cathode is loaded but unloaded is another question. You typically have a tuned circuit there that unloaded may present a high impedance at resonance. Remember TGTP oscillators. It can happen in grounded grid amplifiers. In my experiences, VHF parasitic suppressors reduce the chances of having one, but they do not eliminate them. I can't understand how a VHF parasitic suppressor could reduce chances of HF oscillation if they are practically lossless at operating frequency. At one time I may have agreed with you but after giving it some thought over the years I must disagree. 73 Bill wa4lav _______________________________________________ Amps mailing list Amps@contesting.com http://lists.contesting.com/mailman/listinfo/amps |
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