>Rich says:
>
>>The only tubes which seemingly have this limitation are the 3-400Z and
>>3-500Z.
>
>I believe there's a limit on all filament type tubes, but it may be that
>manufacturers figure that only on the ones for ham use do you have to stress
>the point.
The 3-400Z and 3-500Z have no midpoint fil.-helices support This
makes them vulnerable
>In the days of tubed TV receivers here, when 99.99% were all
>series heaters and half wave rectifiers (and live chassis!), it was quite
>common to use a negative temperature coefficient thermistor in series with
>the heater chain to limit surge current. By using it in series with the HT
>rectifier, you also limited the limited the switch on surge ( that was for
>selenium HT rectifiers - indirectly heatad tube rectifiers let the tube
>cathode get hit)
>
>> No further increase in output occurs when filament potential is
>> >increased above what is needed to secure full emission.
>
>So what?
Your "wind up" story does not hold water.
> We all know that, but this is a case where we aren't talking
>science or fact or whatever - just 'mo' is better', to misquote you! So the
>thing would get wound up. Just like bright emitter tubes in BC receivers in
>the early 1920s. (No I'm not that old, but I have books that are).
>
>>A simple rheostat would be a cheap fix.
>
>Sure. Especially if round the back so that it wasn't too easy to get to.
Good point
>
>Not inside, because then it might not get adjusted when it needed it. But I
>figure it would still get misadjusted. You can't beat Murphy
Yea, verily .
>......
cheers, Peter
>
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