[Amps] SB220 Sick

[Steve Katz]

Does it show no drive/output on all bands?

Make sure the bandswitch shaft to the input circuits is properly aligned
with the output tank position.  "No drive" (and of course no output) can
be that the wrong input circuit is selected for the bandswitch
position...

WB2WIK/6


-----Original Message-----
From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com]
On Behalf Of JayKay
Sent: Wednesday, April 07, 2010 8:44 AM
To: amps at contesting.com
Subject: [Amps] SB220 Sick

HI all

Need some help. I have a friends SB220 that does not accept RF drive.
Following info

1) Plate voltage good at tubes
2) Looks like 30 ohm parasitic resistors/cap (aftermarket) are good,
both tubes 
3) Relay closes...TUNE position plate idles at 100ma
4) When relay closed I do have a DC path from RF input via relay to tube
just prior to .01uf coupling capacitor.
5) In standby RF path good from INPUT to OUTPUT
6) Tubes do not glow blue
7) The tubes appear OK (physically), passed the "shame next to ear" test
8) No grid current
9) Driving rig (TS950) shows INFINITE SWR which (to me) indicates an
open or short (RF wise) in input.
10) 5 volt zener OK when relay energized

I am thinking it could be the .01uf coupler to the filaments

Thoughts?

Jay
W2IJ


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