27 Jul
2007
27 Jul
'07
4:03 p.m.
On 27 Jul 2007 at 23:29, Tony Duell wrote:
From my days in repairing _old_ colour TVs, I seem to
remember that the
valve that gave off the most Xrays wasn't the HV rectifier (a GY501 in
most UK sets) but the 'Shunt Stabiliser' (often a PD500). This was a
big triode connected between the EHT line and chassis, and formed an
adjustable load on the EHT supply. The idea was to keep the total load
(and thus the EHT voltage) constant as the CRT beam current
changed.
I seem to recall the early color sets here had X-ray warning stickers
on the HV regulator cage (and it was always a metal cage), but you
rarely saw them on the monochrome sets. 6KB4 was the most common
type--a large, octal-based unit with a peculiar cup-shaped grid more
or less completely covering the cathode at the bottom of the tube and
about a 3/8" air gap between that and the long tubular anode (like
that on a 1B3, but much larger) connected to the top cap. Rated for
something like 20-30KV if memory serves and about 30W plate
dissipation.
Cheers,
Chuck