[Amps] SB220 Sick

[TexasRF at aol.com]

Jay, you might want to make sure the bandswitch shaft hasn't slipped and  
the input part is not on the band you think it is on.
 
73,
Gerald K5GW
 
 
 
 
In a message dated 4/7/2010 12:48:15 P.M. Central Daylight Time,  
pcb4u at verizon.net writes:

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


_______________________________________________
Amps  mailing  list
Amps at contesting.com
http://lists.contesting.com/mailman/listinfo/amps