Linear amplifier keying circuit

Description

Here we have for sale a single unit (1) of the RF-sensing circuit used to activate the antenna-transfer relay of a linear RF-power amplifier, using the transmitter's RF power as the trigger.
Whew! It's a keying circuit, folks. It's built to work with a negative-ground powered DC relay. Works okay with relay-coil voltages from 12 Volts to 35 Volts DC.
Hookup is pretty self explanatory. The two pads marked "SSB" get wired to a SPST switch, and prevents relay chatter using that mode.
Okay, so the price is a little high. Blame it on the reality of retail-sale overhead costs. I have also listed sale lots of two and five units. This brings the unit price down to nearly half what this single-unit sale costs. But nobody wants to buy five of them without trying it out first.
Your relay will be powered by a wire that feeds DC power from your standby switch. The solder pad marked "Out" connects to the other side of the relay coil.
The metal tab on the power transistor will typically be bolted to a grounded metal chassis. If you mount it differently, a wire should be added from the pad marked "Ground" to the circuit ground in the amplifier. In a solid-state amplifier, the transistor's metal tab may be simply soldered to a circuit-board ground foil, if there is room to do it that way.
It's really intended for AM transmitters. It will reliably sense a carrier power of 1/4-Watt or less at 28 MHz. The sensitivity is lower at lower frequencies.
The 4.7k 2-Watt resistor supplied with this board is installed between the solder pad marked "In" and the center pin of the amplifier's input or "Radio" socket.  This resistor allows it to tolerate power levels from the radio up to about 150 Watts PEP, or about 35 Watts average RF power.
If you need to increase the sensitivity, you can substitute a resistor as low as 1K ohms, but the upper limit of power it can tolerate will also be reduced.
This is a technical product that requires technical knowledge to use successfully. Of course, any dimwit can blow it up, so feel free.
There are NO RETURNS AT ALL FOR ANY REASON OF ANY KIND!
No matter how good they sound.
We ship no later than the second business day following receipt of cleared payment. I ship USPS First-Class mail with tracking.
!!!! NOTE !!!!
Shipping to destinations outside the US are by the Ebay GSP or Global Shipping Program.
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No, I will NOT ship direct if you are outside the USA and its colonies.
GSP ONLY!! GSP ONLY!! GSP ONLY!!
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And if you don't know what it is, you probably don't need it.
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Please.