SB 220 symptoms

[john w. king]

My SB 220 is working and putting out about 1100 watts however the tuning
controls have moved from their former positions when loaded up. The tuning
and loading is the same on a dummy load as when on my 40 meter antenna.

The plate cap is more at the beginning of the 40 meter range than previously
when tuned to resonance.

The loading control produces maximum output with capacitor at MINIMUM and as
the cap is increased to the right, the output drastically drops off.

The grid current is about 200ma when the plate current is 500 ma. to 600 ma.
with 100 watts of carrier as drive and an output from the SB220 is 1000-1100
watts D.C. Output.

The amp is working but there is just something about its' tuning that tells
me that it isn't functioning just right. The grid RF chokes and caps are not
suspect because they have long been removed and replaced with small
resistors that place the grids about 2 ohms above ground. The tuning is
smooth without drastic  meter excursions and the tubes barely show any color
with 1100 watts out.

I have had on the air report of minor distortion on low frequency audio
component of my signal. It is described as a minor popping on low freq part
of my signal.

Any ideas about the strange tuning up? 73, John, K5PGW

-----------------------------------------------------------
This list is a public service of the City of Tempe, Arizona
-----------------------------------------------------------

Subscription control - http://www.tempe.gov/lists/control.asp?list=HEATH
To post - HEATH at LISTSERV.TEMPE.GOV
Archives - http://interactive.tempe.gov/archives/HEATH.html