Rugged 807 & 1625 tubes

The good old 807 and 1625 tubes can take a real beating.

One night decades ago, when I was working DX on CW with the shack lights off, the room suddenly lit up. The cathode-keyed 807 final was white hot! I let go of the key and cut the power.

Since I was monitoring the exciter signal, I was unaware of a break in the drive and had continued to send.

After the rig had cooled and the fault rectified, it was back to normal operation again. I still have that tube.
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Lightning jolt

It was a typical summer afternoon in the year 1977.

I was working CW on 40m - my homebrew EL84 rig feeding a straight dipole antenna with telephone drop wire as feeder.

Meanwhile the sky became overcast and there was a continuous rumble as I continued to work.

All of a sudden I received a jolt through my Junker key followed by the crash of a thunderbolt.

Without a thought I yanked the feeder off its sockets and threw it on the floor. My heart missed a beat when I saw the arc that followed between the banana plugs and the cement concrete floor.

The following morning's local newspaper headline was 'Lightning stuns football players'. It was a direct hit at the nearby football field. Fortunately only a couple of the players had fainted and there were no casualties.
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Drake TR-4C - receive problem

The old workhorse seldom gave problems on transmit.

A frequent receive problem was the receiver going dead on switching back to receive from transmit.

The problem was solved by replacing custom C145 (4 electrolytic capacitors housed in a can) with individual capacitors.

Capacitors drying out was the root cause.
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Yaesu FT-747GX / FT-757GX - failure to power up

Every Yaesu FT-747GX / FT-757GX user would have been flummoxed by the rig refusing to power up only to discover later that the MOX button had been left actuated.

It's a safety interlock to prevent the rig from going to transmit on power-up.
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Yaesu FT-747GX - PTH problems

A batch of Yaesu FT-747GX transceivers, produced in the 1990s, is plagued with PTH issues.

They show up as intermittent problems in receive and transmit and finally lead to total failure.

The faulty boards are the filter selection board (for receive) and the power module (for transmit).

In the filter selection board, faulty PTH connections result in the switching diodes failing to connect the required filter.

Similarly, in the power module, the result is a break in the drive to the bases of the driver transistors.

The solution is to solder jumper wires across the faulty PTH junctions.
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Injection moulding machine problem

It was a crisis call for a table-top injection moulding machine. Clear acrylic meter faces were being moulded and the output quality had deteriorated overnight.

The controls were fairly simple, the key ones being those for temperature control of 3 zones. Temperature setting was through potentiometers with graduated dial plates. The instruction manual had a chart listing the 3 settings for various plastics.

The easiest way to check whether the temperature controllers were working was to connect bulbs across the heating elements and observe the change in the switching while changing the settings. All 3 tested okay.

When I was mulling over the problem the owner excused himself for a while.

Then 'Eureka'! I turned the knobs fully anticlockwise and the pointers were not at 'zero'.

All I had to do then was to loosen the knobs to rectify that.

After changing back to the settings for acrylic, the machine was back in business!
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Speaker vibration/distortion

A Radio Cassette Recorder was received for repair.

The problem: Speaker vibration/distortion within days of its purchase in another city.

On opening the set, a cockroach was found perched on the back of the voice cone. It appeared to enjoy the vibration, for it wouldn't budge even with the volume turned high.

Without getting into details, out went the cockroach and along with it the vibration/distortion.

It was my fastest repair job, ever!
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