[Amps] SB220 Sick

[TexasRF at aol.com]

I know now, but when I started the answer and before being interrupted six  
times, there was no answer. I didn't think about going back to see if 
anyone had  answered before hitting the send button. Very sorry for any 
aggravation caused  by this oversight and I will definitely try to be more aware in 
the  future.
 
One added thought: the band switch index on these old amplifiers get dry  
and stiff. If the index is at the rear of the assembly (can't remember if the 
 SB220 is or not)  it puts extra stress on the shaft turning torque  
requirements. That can lead to a slipped shaft.
 
Now, the next question is: how to free up one of these indexes?
 
73,
Gerald K5GW
 
 
 
 
In a message dated 4/7/2010 1:14:18 P.M. Central Daylight Time,  
stevek at jmr.com writes:

Already  said that!

WB2WIK/6




-----Original  Message-----
From: amps-bounces at contesting.com  [mailto:amps-bounces at contesting.com]
On Behalf Of TexasRF at aol.com
Sent:  Wednesday, April 07, 2010 11:10 AM
To: pcb4u at verizon.net;  amps at contesting.com
Subject: Re: [Amps] SB220 Sick

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


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