[AMPS] Screen protection WHAAAATTTTTT!!!!

[measures]

>
>
>Conrad Writes ... 
>
>> 
>> 
>> Rich wrote
>> 
>> >>Transistors that C/E short offer zero protection.
>> 
>> Ok so sense the voltage drop across a resistor across the screen supply,
>> feed the transistor via an opto isolator,make the transistor trip a fast
>> relay in the primary of the supply transformer.This is better and more
>> reliable than a fuse surely.
>> 
>
>Make that trip a fast zero crossing solid state relay in the primary 
>of the screen supply.  The SSR should "open" at the zero voltage point 
>and, with the proper MOV to limit the inductive kick-back spike, should 
>be the quickest, most reliable protection.  

The screen in an 8171 is rated at 275w.  Instanteous protection would 
interfere with tuneup.  A fast acting fuse works. .  

>Frankly, I would sense screen
>current, screen voltage, as well as plate current and trip both the 
>plate and screen supplies in the event of a fault.  I might even use 
>a big SCR (screen) or triggered spark gap (plate) to discharge the 
>supplies to limit the fault (if I could justify the CO$T). 
>
Glitch resistors work well enough. More complicated is not mo betta.  

-  Rich..., 805.386.3734, www.vcnet.com/measures.  
end


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