It's a relay. The main reason I want to hard key it is because it
sometimes clicks in and out on SSB when using the COR circuit and it's
annoying. I doubt it makes any difference without knowing the voltage
and current the amp is putting on it but the relay is this one here...
http://www.allelectronics.com/make-a-store/item/RLY-497/12-VDC-DPDT-RELAY/1.html
I will do as you suggest and take some readings. It appears I will at
least need the diode but I'm still unclear on where to put it exactly.
Tnx and 73,
Michael
On 12/1/2011 7:29 PM, Brian Lloyd wrote:
On Thu, Dec 1, 2011 at 4:01 PM, Michael Tondee
<[email protected] <mailto:[email protected]>> wrote:
I know this subject has been covered before but I'm reading a
couple of pieces of conflicting info on the web so I want to be
clear so I don't smoke anything on my rig. I have a homebrew 50
watt amplifier built from a PCB/ parts kit. The amp appeared in
QST several months back as the winner of the 2nd Homebrew
Challenge. It has a COR circuit which I have been using
successfully but I want to go to hard PTT control by the rig. The
amp keys by grounding the PTT. I have a switch wired in to
select between the COR circuit grounding the PTT or an external
source doing it via a 1/8 inch phone jack. I just need to wire
pin 3 of the Flexwire connector to the center of the phone jack,
correct? Or do I need to add another relay in the circuit? I also
see mention of a diode, where would this go, across the 1/8 inch
phone jack?
It is probably OK. That being said, what is getting keyed? A relay? A
transistor? A FET? A big-assed power contactor? The key points (pun
intended) are the open-circuit voltage that appears on the keying
circuit, and the closed circuit current. If the load is a relay then
you need a clamping diode to prevent the inductive flyback pulse from
taking out the keying transistor in the 1500.
So, take your multimeter, set if for volts, and place it across the
PTT input on the amp. That will tell you open-circuit voltage. Switch
the multimeter to current and connect to the PTT input on the amp
again. This will key the amp. Read the closed-circuit current. Compare
these values to the specs for the 1500. If either the voltage or the
current exceeds the maximum allowed for the 1500, you will need either
an additional transistor buffer or a relay between the 1500 PTT output
and the PTT input of the amp.
--
Brian Lloyd, WB6RQN/J79BPL
3191 Western Dr.
Cameron Park, CA 95682
[email protected] <mailto:[email protected]>
+1.767.617.1365 (Dominica)
+1.916.877.5067 (USA)
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