Every base station operator's worst nightmare. A "QSO with the clouds". Lightning. The customer who brought this to us just wondered why it produced no RF power. Seems he bought it like this.
Clearly this was not a direct strike to the antenna, but probably the result of having the antenna connected when the neighbor's tree was struck. An antenna will suck enough of the lightning stroke's RF energy to cause this sort of high-voltage surge.
I won't be removing the power-supply circuit board. The old relay gets removed with a sharp diagonal cutter. You'll have to shatter parts of the black plastic insulator to reach under it and clip all the lugs.
The only foil pads we will be using for the new relay are the two coil pads. The relay's spike diode gets removed so the new relay can mount flat to the pcb surface. A wire is soldered to each of the two pads for the relay coil.
Here is the new relay, ready to hook up. It's a Potter and Brumfield, or "TE Connectivity" type KUP14D15 12-Volt DC. It's sold with a clear polycarbonate case enclosing it, but that gets removed. The flexible pigtail for each of the two outside poles get unsoldered from the lugs so they can be connected directly to the center pin of each coax connector on the back panel.
The white wire leading to the input circuit gets unsoldered from the pc board, as does the output coax center conductor. No need to disturb the shield.
The center section of the relay serves to shut off the tube in receive mode by interrupting the circuit between the negative side of the high voltage and the center tap of the 5-Volt transformer winding that lights the tube's filament (cathode). The transistor that got remvoved here was part of Ameritron's "dynamic bias" circuit. The solder pad on its right leads to the Bee-Minus side of the high voltage. The white wire now installed there goes to the relay's center pole.
This customer will be using this amp for AM, so the factory's bias setup would not be suitable even if it still worked. This pc board has thirty 3-Amp rectifier diodes in series. The approx 20 Volts of "zener" bias it provides will hold the tube current down to a level that's safer for AM than the higher level used for sideband. The green wire with the yellow stripe is the center tap of the filament secondary winding. It gets a sleeve of insulation added because of the nearby stuff with high voltage on it.
Here's the stuff we'll use to attach the new relay to the pc board surface. This stuff is used by sign shops to hold together heavy stuff. The guy we got it from said it was used to hold serial-number plates onto diesel engines. Putting a layer onto the relay and onto the pc board surface allows burnishing it properly. Won't stick properly without applying proper pressure to the stuff.
The two relay coil wires emerge from under the VHB and connect to the new relay's coil lugs. The spike diode got removed to keep it out of the way. A new diode is seen wired across the new relay's coil lugs.
Here it is finished and ready to test. The white wire on the right leads to the tube's input-matching circuits. The new relay's center section has the white wire to the Bee-minus on the common lug and antother white wire to the bias board's "B-" pad on the normally-open lug.
There were two holes in the amplifier's center divider that line up perfectly with the brackets holding our bias board. Didn't have to drill holes to mount it. But the clamp holding the output coax was mounted too close to one of them and was in the way. It moves to the bracket screw on the bias board.
Big sigh of relief. Worked first time we tried it. I generally avoid bad-mouthing products that are still on the market, but the replacement relays we get from Ameritron have been a disappointment. The quality of the "TE" relays are just as good as they were when the name on the box was "Potter and Brumfield". To use the factory relay would make it necessary to remove the main circuit board. This is a definite PITA, so a method that leaves the pcb in place has a lot of appeal. One new relay we got from Ameritron and installed in a AL80B failed a couple of weeks later. Only took once to persuade me to adopt a better alternative.
73
Clearly this was not a direct strike to the antenna, but probably the result of having the antenna connected when the neighbor's tree was struck. An antenna will suck enough of the lightning stroke's RF energy to cause this sort of high-voltage surge.
I won't be removing the power-supply circuit board. The old relay gets removed with a sharp diagonal cutter. You'll have to shatter parts of the black plastic insulator to reach under it and clip all the lugs.
The only foil pads we will be using for the new relay are the two coil pads. The relay's spike diode gets removed so the new relay can mount flat to the pcb surface. A wire is soldered to each of the two pads for the relay coil.
Here is the new relay, ready to hook up. It's a Potter and Brumfield, or "TE Connectivity" type KUP14D15 12-Volt DC. It's sold with a clear polycarbonate case enclosing it, but that gets removed. The flexible pigtail for each of the two outside poles get unsoldered from the lugs so they can be connected directly to the center pin of each coax connector on the back panel.
The white wire leading to the input circuit gets unsoldered from the pc board, as does the output coax center conductor. No need to disturb the shield.
The center section of the relay serves to shut off the tube in receive mode by interrupting the circuit between the negative side of the high voltage and the center tap of the 5-Volt transformer winding that lights the tube's filament (cathode). The transistor that got remvoved here was part of Ameritron's "dynamic bias" circuit. The solder pad on its right leads to the Bee-Minus side of the high voltage. The white wire now installed there goes to the relay's center pole.
This customer will be using this amp for AM, so the factory's bias setup would not be suitable even if it still worked. This pc board has thirty 3-Amp rectifier diodes in series. The approx 20 Volts of "zener" bias it provides will hold the tube current down to a level that's safer for AM than the higher level used for sideband. The green wire with the yellow stripe is the center tap of the filament secondary winding. It gets a sleeve of insulation added because of the nearby stuff with high voltage on it.
Here's the stuff we'll use to attach the new relay to the pc board surface. This stuff is used by sign shops to hold together heavy stuff. The guy we got it from said it was used to hold serial-number plates onto diesel engines. Putting a layer onto the relay and onto the pc board surface allows burnishing it properly. Won't stick properly without applying proper pressure to the stuff.
The two relay coil wires emerge from under the VHB and connect to the new relay's coil lugs. The spike diode got removed to keep it out of the way. A new diode is seen wired across the new relay's coil lugs.
Here it is finished and ready to test. The white wire on the right leads to the tube's input-matching circuits. The new relay's center section has the white wire to the Bee-minus on the common lug and antother white wire to the bias board's "B-" pad on the normally-open lug.
There were two holes in the amplifier's center divider that line up perfectly with the brackets holding our bias board. Didn't have to drill holes to mount it. But the clamp holding the output coax was mounted too close to one of them and was in the way. It moves to the bracket screw on the bias board.
Big sigh of relief. Worked first time we tried it. I generally avoid bad-mouthing products that are still on the market, but the replacement relays we get from Ameritron have been a disappointment. The quality of the "TE" relays are just as good as they were when the name on the box was "Potter and Brumfield". To use the factory relay would make it necessary to remove the main circuit board. This is a definite PITA, so a method that leaves the pcb in place has a lot of appeal. One new relay we got from Ameritron and installed in a AL80B failed a couple of weeks later. Only took once to persuade me to adopt a better alternative.
73
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