[Amps] B- switching.
craxd
craxd1 at ezwv.com
Mon Sep 20 11:28:15 EDT 2004
Angel,
You don't really need a vacuum relay, I used (model#
EC12-NC/NO/DT-12-0-5-BD) from a company named Ross Engineering. They
make open frame relays with a switching capability of 10Kv @ 450 mA on
their smallest size. This will de rate to 5Kv @ 900 mA, or 2.5 Kv @ 1.8
amperes. There's also sealed reed relays available from Ross with a
switching ability of 5-15Kv @ 3 amperes. The first relay mentioned was
used to switch the B- . You can use vacuum relays if you want to pay the
cost though. The only time the primary would be opened is with a HV
safety switch being thrown, and the capacitor bank being discharged
quickly after the primary opened. On lower secondary voltages, I have
switched the secondary ac feeding the rectifiers with good results. This
being anywhere from 1Kv to 1.5Kv. Ac will not arc near as bad as DC due
to the cycling current through 0 volts extinguishing the arc. The
contact rating has to be correct to do this as HV relays are different
than the DPDT relays in use at other places. The one from Ross has is a
solenoid type with a large air gap and rods for the contacts. These full
round surfaces act to kill out arcing from a sharp point. The shorting
contact is a round washer. The air gap is about 5/8" to 3/4" which also
helps kill the arcing. Most DPDT relays with 10 amp contacts only have
about a 1/16" to 1/8" gap at the most. In doing this, a HV relay is a
must. The screen voltage can be switched with a DPDT relay and10 amp
contacts with no problems.
Will Matney
Hi
Will Matney wrote:
>>In any amps I've made, I did kill the B- lead for the HV until the
>>antenna relay pulled in even though it was biased to cutoff on idle.
>
>
How do you do this? Switching several Kilovolts must surely be done with
an expensive vacuum relay?
You certainly cannot switch the HV transformer primary on and off every
time you cycle between xmit and receive, because of the HV capacitor
current inrush.
73
Angel Vilaseca HB9SLV
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