Yes, you know the problem, I hestated because there is so much
mis-information on audio-fool sites. I just tend to take a
precautionary approach when I can to extending tube life. But running
the CRT heater warm is an alternative to full cold soft start. My
current scope clock which is under development switches the HT/EHT and
the heater to off. When it starts up (again PIR sensor) the heater
takes 7 seconds to full voltage, then at 10 seconds the EHT is applied.
The 7 seconds is set by a capacitor in the hardware, the 10 seconds is
software controlled.
Grahame
On 10/08/2014 12:49, Morris Odell wrote:
Yes, I'm switching both the EHT and the heater. I would be surprised
if cathode stripping is an issue considering the very small beam
current in a CRT compared to, say, a power amp tube. Keeping the
heater warm is a form of soft starting. I did that in my E1T clock
where it starts from cold with about 60% heater voltage applied and
then full HT and heater volts kick in about 10 seconds later.
Morris
On Sunday, August 10, 2014 7:07:18 PM UTC+10, Sgitheach wrote:
Morris
Are you switching off the HT/EHT to the tube when the heater is
off as well? My understanding is that it is not good to switch
the heater on while there is full HT on any thermal valve/tube.
You might take the opportunity to "soft start" the CRT heater - I
can PM you a schematic I'm using if you wish?
Cheers Grahame
On 10/08/2014 10:00, Morris Odell wrote:
Hi all,
Latest progress on the Sperry radar clock - I found a very
helpful transformer manufacturing shop whose owner was happy to
vacuum impregnate and bake the howling transformer for me. Alas,
it only made a very small difference, if any. It sounds like the
problem is magnetostriction in the core so there's no easy
solution. I've rubber mounted it to try to stop the rear chassis
panel from acting as a sounding board but that's all I can do I
think. Hopefully it will be quieter when it's all buttoned up.
Right now I'm working on a PCB which will contain a PIR motion
detector and also a Xbee wireless receiver to pick up the GPS
data that I have sent around my house.
I also have a question - among other things the PIR motion
detector switches the power to the CRT heater. Is it worth
dribbling a little bit of current through the heater when it's
off so that it heats up faster when the PIR senses an observer?
If so, how much? The CRT heater draws 300 mA at 6.3 volts when
it's working but takes about a minute to get to full emission.
Will preheating it like that shorten its life significantly?
Any opinions much appreciated,
Thanks, Morris
On Monday, July 14, 2014 7:02:47 PM UTC+10, Morris Odell wrote:
Hi all,
I've got the clock displaying time now. The video shows it
upside down on the bench so it's at a few minutes past 12.
That howling power transformer is a distraction, I'll have to
wrap it in some sound absorbing material especially as I like
to add Westminster chimes to my clocks :-).
The next step is to put it all together and tidy it up!
https://www.youtube.com/watch?v=tL3840bE9Cs
Morris
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