> >By far the biggest stress in amateur service is the
> > constant thermal cycling of the filament
>
> That's where the rheostat comes in handy - assuming proper
> proportions, it limits surge current.
> Of course, so does a suitably designed surge limiting filament
> transformer, but that can be a bit more expensive.
Not really, a suitable current limiting transformer costs LESS than
a transformer that allows excessive starting current. You do have to
allow for temperature rise, however, and not box it in.
> >provisions would have to be made for monitoring voltage
> >accurately
>
> I assumed external metering, but point taken, especially on cost.
Oh sure! Let the guy use his handy $25 dollar VOM to set voltage!
I've seen six cases of low cathode emission in the past 18 years in
8877's. In five of those cases, the filament systems were modified
to reduce voltage and they missed by a few percent.
73, Tom W8JI
w8ji@contesting.com
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