Re: Low output from 2nd crystal filter and SA602 product detector

Posted by n7zf on Feb 02, 2011; 4:25am
URL: http://elecraft.85.s1.nabble.com/Low-output-from-2nd-crystal-filter-and-SA602-product-detector-tp5979986p5983646.html

I am using a 50-ohm Relm dummy load.  My Astron power supply is set to 14.0 volts, which is what I remember reading somewhere in the K2 manual.  At 5 watts power, the K2 was shutting down.  

At 2.0 watts, the current is 1.5 amps and the voltage drops from 13.8 to 13.4 per the internal voltmeter.

At 5.0 watts, current is 2.1 to 2.3 amps (depending on band), voltage drops to 13.2.  The expected current per the '40-meter transmitter alignment' procedure is 1.3 to 1.6 amps, so I am about 50% too high.

At 10.0 watts, current is 2.7 amps, voltage drops to 13.1 vdc.

The low pass filters all appear good on the analyzer:
80m: min SWR is 1.04 @ 3750 kHz, max is 1.48 @ 4000 kHz
60/40m: min SWR is 1.09 from 7000 to 7080 kHz, max is 1.4 @ 60m
30/20m: max SWR is about 1.25
17/15m: 17m SWR is 1.4, 15m SWR is 1.2-1.3
12/10m: 12m SWR is 1.35, 10m SWR is 1.2-1.3
In all cases the SWR is very high at the 2nd harmonic of the lower band.

That was a very enlightening exercise, by the way, Don.  Thanks for that tip.

Visual inspection of T1 thru T4:  as far as I can see, without removing them, they look correct.  I probably could have wound T1 a little tighter.

DC measurements at the base of Q7 and Q8 are .631 and .632 volts -- right at the maximum.  

I will continue taking voltage measurements in the power amp circuit.

Bob