[AMPS] SB221 Tuned input Question

[2]

>
>Greetings
>
>Allow me to display [some of] my ignorance here. Is the tuned input 
>circuit in these amplifiers for the benefit of the driving transceiver to 
>allow it to see the proper impedance, or is it to act as an attenuator for 
>out of band sporadic or impure emissions for the benefit of the amp? 

Principally to provide a match to facilitate driving the cathodes.
>
>My question arises because I have an sb 221 which I have had sitting 
>around for a while after buying it from the son of an SK. The builder did 
>not build it to spec, as he left out the CB filter, the ALC circuitry, and 
>the relay. Looking yesterday at the rf input, he took it past all the 
>tuned input circuitry and straight to the final tube, through one cap. My 
>plan is to correct all this, but his method got me to wondering about the 
>tuned input
>
The SB-221's tuned inputs are designed to work with the CB filter in 
place.  After the CB filter is removed, the optimal tuned input values 
change.  This subject is covered in "Circuit Improvements for the Heath 
SB-220 Amplifier" in Nov/Dec. 1990 *QST*.  The manuscript for the article 
is on my Web site.  

>Would the amp perform OK in this configuration 

No

>or would you be likely to 
>create some damage? 

No

> I plan to change it anyway, but am curious about the 
>answer.
>
cheers, Randy

-  R. L. Measures, 805.386.3734,AG6K, www.vcnet.com/measures.  
end


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