[Collins] Thoughts on the "New Filament Saver Device for the 30L-1"

[Dr. Gerald N. Johnson]

On Tue, 2009-11-17 at 14:28 -0800, Eugene Hertz wrote:
> Very interesting! If it were me, and I couldn't restrap the power transformer, I would just stick a variac in front of the amp and call it a day :) (but what fun would that be, you ask?)
> 
> 73 Eugene W2HX
> 
A variac works well so long as its set and forgotten and no little (or
big) inquiring visitors turn that knob to see what it does. Many variacs
are wired to also raise the input voltage, to sometimes 140 volts and
that's definitely not an improvement for a 115 volt radio. The
buck/boost transformer once its wired and buttoned up, won't be changed
by accident or on purpose. And often the buck/boost transformer is less
expensive than the variac.

In his home brew linear, one ham near here with many decades of
broadcast experience, built in a small variac for the tube filaments so
he could bring them up slowly and always set them to the exact voltage
no matter how far the line voltage wandered. He gets great lifetimes
from his PA tubes that way.

-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer