D-104 Switch Contacts

Keith Rowland k4kgw at MINDSPRING.COM
Sun Jan 10 06:23:38 EST 1999

Wow!  11 replies so far, all appalled that I should be thinking of
holding 120-volts in my hand...and rightly so.  I thank everyone for
their replies, but mostly for the concern shown for my safety.

I can see that I should have explained the purpose of the question about
the current-carrying capacity of the D-104 PTT switch.  I am building a
QRO AM transmitter which contains several rather hefty 120VDC relays in
the RF section, the modulator, and the VFO, each of which are separate
units.  These relays perform all the functions needed to go from receive
to transmit, including antenna changeover, shorting the modulation
transformer secondary and disabling the modulator low-stages B+ in CW
mode, and breaking the B+ power transformer center taps in receive mode
in the RF stage power transformers, and so on.

In order to control that many large relays requires that the relay that
controls them has to be fairly substantial itself.  I have some6 and 12
VDC relays on hand that will do this job, but their coils draw about 30
ma. I figured that if the D-104 switch would handle 300 ma. at 120-v, it
surely would take 30 ma. at 6 or 12 volts, hence my alarming question!

Again, thanks to all who responded, and be assured that I didn't get to
be 70 years old and spend many of those years aroound multi-megawatt
radio and TV broadcast transmitters without having a healthy respect for
high voltage!!!  : )

73 all,


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