SB-102 15m "ghost"

[EP Swynar]

Hi Joe,

If your drive to the 6146's is fully counter-clockwise, and you're STILL
getting maximum RF output out of the tubes, then you have a self-oscillating
final pa stage...

You can confirm this by listening to your signal on another receiver, both
before you retard the drive control, and then again after. I'll wager that
in the "after" setting, the signal will have disappeared from the second
receiver, or, if it's still there, it'll be all raspy sounding, &
unsteady...

If you have a frequency counter, read the output frequency with the final
"normally" driven, & then again with the drive control fully
counter-clockwise. I'll bet it'll be different.

Try this: "jiggle" the bandswitch around the 15-meter position, with the rig
putting out RF with the drive control retarded, and watch what happens. It
may well drop off & act normal again, dependent upon the placement / final
resting position of the bandswitch. That same thing happened to my
SB-102 --- I guess the "torque" effect of the long shaft in the bandswitch,
& all those wafers, resulted in a "lag", or "less-than-fully-seated" wafer
in one of the assemblies, resulting in sometimes weird & wonderful things.
As I recall, it was on 15-meters, too...

~73~ Eddy VE3CUI - VE3XZ


********************************


----- Original Message ----- 
From: "jsloss" <k7mks at COMCAST.NET>
To: <HEATH at LISTSERV.TEMPE.GOV>
Sent: Monday, November 12, 2007 8:10 PM
Subject: SB-102 15m "ghost"


> In TUNE mode all is well on all bands except 15.
>
>  Grid current peaks w/ DRIVER and plate current dips as it should.  BUT
when I move the CW GAIN full CCW I still have RFoutput w/ Ig and Ip,.  On
all other bands, in TUNE, rotating the DRIVER  reduces Ig and Ip as it
should.  Havwe replaced 6CL6 to no avail.
>
> If it acted this way on all bands I figure there would be a common problem
for all bands.  But with only 15m acting up I feel it is time to seek
counsel of those on this reflector.
>
> While I'm here does anyone have any comments or cures for "hot" running
tubes especialy the IF's and 6CL6.   An internal fan may be the only answer.
>
> Thanks,
>
> Joe k7mks
>
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