mark wrote:
>1). Does this 50% periodic filament voltage reduction stresses the
>tube? 2). What is the recovery time from 50% to 100% caloric output of
>the filament (for a step up voltage)? 3). What happens, if by accident,
>HV and DRIVE is applied while the filament is still ramping up?
To answer #2, it depends on the tube and the voltage reduction you have
applied. Fortunately you can measure the recovery time - or the warm-up
time from cold - by measuring the heater current. The heater acts as its
own resistance thermometer, and with a high-resolution DMM you can see
the current change slow down until it settles at the final value.
There must be a small time lag between the heater temperature and the
electron-emission temperature of the cathode surface, but the
measurement should get you close.
There was a discussion of heater voltage reduction for the 4CX1500 in an
article on a "Luxury Linear" by K5AM in QEX a few years ago. He found no
harmful short-term effects. But since this is not a topic that the tube
manufacturers seem to have explored, data on long-term effects may
simply not exist.
--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek
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