Michael - The open circuit voltage is about -65, and the current is less than a mA. No need for any protection.
If you're feeling adventurous, you can lick your finger and key the transceiver by putting it across the key.
The TO was around when many (most?) transmitters were cathode keyed, with hundreds of volts and full PA current!
73, Garey - K4OAH Glen Allen, VA Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line and TR-4/C Service Supplement CDs <www.k4oah.com> Michael A. Kelly wrote:
Howdy everyone, I have a Hallicrafter's TO Keyer that I am using with a TR-4CW. According to the Hallicrafters manual there is a section that reads: "The mercury-wetted relay contact rating is 5 amperes maximum, or 500 volts maximum, the product not to exceed 250 volt-amperes with contact protection. For example, the maximum allowable voltage with a 5-ampere load is 50 volts (5A X 50 V =250 VA); the maximum allowable current with a 500-volt supply is 0.5 ampere (500V x 0.5A = 250 VA). Except for very light loads (under 2 MA and 50 V), the relay must be provided with a contact protection network consisting of a capacitor and resistor in series. The network prevents possible arcing which would eventually destroy the contacts." Anyone want to venture what the approximate current load would/should be when the rig is keyed, or what is the open circuit load voltage at the keying points? They give the example using the chart after measuring the voltage at 150V and the current at 50 MA would generate needing a protection network consisting of a 0.001 uF capacitor (limiting capacity) in series with a 750 ohm resistor. Surely folks have already done the checking using a TO Keyer with a TR-4anything and can tell me what is a good guess for capacitance and resistance needed? Thanks, Michael NZ4D
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