[R-390] B+ Dropping Resistance (was Drill a Hole...)
Bill Hawkins
[email protected]
Mon, 19 May 2003 16:49:50 -0500
Drew Papanek wrote:
"Some have claimed that delaying application of B+ until after heater warmup
is of benefit only to extend life of thoriated tungsten (transmitting type)
tubes and is not necessary for indirectly heated tubes as used in R-390
series. It is noteworthy, however, that Tektronix tube type oscilloscopes
(which use indirectly heated tubes) have B+ delay feature."
Well, Tek used a number of regulated supplies and all were based on the
value of the -150 volt regulator [Warning - Do not adjust -150 unless you
are prepared to realign the entire scope]. This was reason enough to delay
the application of high voltage. Another reason is that the no-load voltage
across filter caps (and wiring) is higher than the loaded voltage. I don't
think that either concern applies to our favorite receivers.
Anybody nostalgic for a 535/545 series scope? I have 5 of them.
Regards,
Bill Hawkins