[Amps] More instability problems

[N1BUG]

Once again I would like to thank everyone for your input on my amp 
woes. There was a massive pile of private responses, which I have 
not fully worked through in terms of replies. Each and every one is 
appreciated!

I have discovered I have two apparently separate issues:

1.) LF oscillation with no load on the amp output. It will sometimes 
succeed in taking off during the instant the bias and relays are 
switching from transmit to receive. I intend to work on LF 
bypassing, since I feel this amp should be stable even without a 
load. The current bypassing is woefully inadequate at LF. I will 
attempt to look at bias vs. relay timing to see if I have a problem 
there.

2.) Lack of tuned input. I should have known this bad decision would 
eventually come back to haunt me. The sudden, wild jumps in plate 
current, power out and even SWR (amp to antenna) while tuning are 
related to changes in input impedance driving my exciter into SWR 
protect! Sudden reduction of drive explains the plate current and 
power output jumps. The amp-to-antenna SWR jump is more perplexing. 
Apparently when the exciter goes into protect mode, spurs or 
harmonics are being generated by the system. This is not good.

The present input configuration is a 50 ohm RF load resistor with a 
.01 cap coupling to the cathode. I am trying (again) to figure out 
some practical method of adding tuned input to this amp but I am at 
a loss. Lack of space and switching problems are problematic.

73
-- 
Paul Kelley, N1BUG
RFI Committee chair,
Piscataquis Amateur Radio Club
http://www.k1pq.org