On Mar 8, 2005, at 1:34 AM, Rick and Theresa Low wrote:
Several times in the past week Iâ•˙ve observed unusual behavior from
this single 3-500Z amplifier and need to know if this looks like the
tube is about to go belly up on me, or if there is some circuit factor
thatâ•˙s causing this behavior:
1. First turn on, plate current indicates about 200-250 mA without
amplifier going into transmit mode.
My guess is a filament to grid short since 250mA on standby sounds like
0v bias and it's normally c. 25v on Standby. I would test the grid-fil
BD voltage with a high-pot to find out what's what. .
I turn ON with the standby switch in STBY. Stays this way for about 3
to 5 seconds, then zero current.
2. At seemingly random times during T/R operation, plate current meter
shows same 200-250 mA, input circuit shows HI SWR on the driver rig,
and of course, no RF output. Cannot clear by cycling T/R relay---PTT.
I turn off, wait about 10 seconds minimum, then turn on and get the
same ╲First turn on╡ behavior above.
De Rick I0/N6CY Gaeta IT JN61sf
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Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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