[Amps] sb220 question after mods

[Vic Rosenthal]

N7uvh at aol.com wrote:
>  
> Hi guys...
>  
> Been working on a sb220.. did the rectifer and choke mods. Replaced with  
> Harbah parts.
> I have noticed that i don't have a idle plate and grid currant.  

You should never have ANY idle grid current.  If you do, your amplifier is 
oscillating or something is wrong with the metering circuit.  Zero signal plate 
current should be about 160-200 ma (for two tubes) for good linearity on SSB. 
If you are only running CW or RTTY, it will work fine at zero, although it will 
take more drive.

> i noticed that the right tube will glow some and the  left tube does not. 

One is weaker than the other or they are different brands (the Amperex ones have 
significantly different characteristics).  The one that is glowing is doing most 
of the work.  They can glow dull red, but if they glow bright orange or yellow, 
you are exceeding the dissipation rating.  Or, maybe one is a carbon anode type 
and the other is metal.

-- 
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco