On Sun, 18 Oct 1998 11:18:40 +0100 Chris W Tran <chris.tran@zetnet.co.uk>
writes:
>
>Sunday 18th October 1998
>
>Hello all
>
>I've got a few tired 4CX1000A ex-broadcast 'pulls', and
>want to revitalise them a bit, if it's possible.
>
>Speaking to my friend Bob Kerr GM4FDT, he quoted from the 1925
>Admiralty Handbook about how to revitalise Thoriated-tungsten
>cathodes/filaments (as used in the larger Eimac tetrodes)
>- run the filament for a few hours/days with all other voltages
>disconnected - extra Thorium migrates to the surface and the
>emission will increase. Also, as the filament reaches the end
>of its life, the filament voltage can be increased by say 5% to
>improve emission.
>
>Does anyone know of a similar procedure which would give new
>life to the 'Oxide-coated unipotential' cathodes of the
>4CX1000A/4CX1500B series ?
>
>73 Chris GM3WOJ/GM8V
><chris.tran@zetnet.co.uk>
Back in the 60's there was an article on rejuevaniting indirectly heated
TX tubes. If memory serves it required filament voltage and momentary
applications of a positive voltage between cathode and grid. In a 6146
that was about 250V and it brought many of my old duds back to life.
I may be able to find that article and I'm sure there are others out here
that have experience.
73 Carl KM1H
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