[AMPS] Recycling filament

Fri, 27 Jun 1997 08:36:33 +0000

> >I have to agree with Peter, I can't imagine a 723 being a "good 
> >choice" for an IC near strong RF fields. 
> 
> Instead of trying to imagine, why not try trying to see if it works, Mr. 
> Rauch?

I've had bad luck with 723's unless they are in a well shielded 
area and everything is bypassed quite well.

The shielding and layout is probably more important than the 
specific value of bypass component, especially since the series 
resonant frequency varies greatly with different components and lead 
lengths.

Time would be better spent describing a proper layout and 
bypassing, especially since Peter is right. The 723 is very 
sensitive to EMI (even from HF). 

> >But ignoring all that, why would anyone want to re-start the whole 
> >filament cycle if the power line just faulted for a few seconds? 
> >
> If the warmup delay is not re-started, the solution becomes somewhat more 
> complex.  How are we to know what percentage of under-voltage for X 
> seconds requires Y seconds of makeup preheat?.  The safest, simplist 
> thing is to initiate a restart.  

I wouldn't think so. It would be just as simple to set a timer's 
threshold at the proper filament voltage, and simply disable the 
timer by letting the trigger ramp down with the voltage. Then it 
would only have to ramp up a ting bit to re-start.

> >Cathode temperature would drop at the nearly the same rate as it 
> >takes to rise. If the line totally removed voltage for ten seconds, 
> >it would only require a ten second warm up to be back at full 
> >temperature.
> 
> Perhaps.  Perhaps not.  There is nothing in the Eimac specs. about this 
> matter.  Better to be safe than sorry, methinks.  

The refrigerator and air conditioner start at the same time, the 
lights flicker, the filament drops to 4.65 volts for just a second, 
and you now have to wait wait three minutes to talk.

Makes sense to me (not).

I find this all a remarkable conundrum. Here's a fellow who 
recommends REMOVING electron grid overload protection because 
"it might fail during a glitch", but who recommends adding a 723 to 
protect the filament for undervoltage and to regulate and protect the 
screen grid.

Which way is it? Are all these little chips Devils or are they 
Saints?  This seems like a case of "do it my way, it's the only right 
way".

73, Tom W8JI 

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