Looking through the Health manual will tell more than I can in just a few words. The simple AF amp with a probe can be a good addition to a test bench. Especially for the bottom feeder without deep pockets.
This looks like the one I had as a kid. Notice it had a RF and AF input. The amp was strong enough I could clip an antenna to the RF input and receive our local station.
So you can build a high gain AF amp and a RF probe and be in business. The probe would be like this one.
This one is designed to be used with a voltmeter to read RF signals. A search will find more this is the idea. C1 would be small enough to block AF and large enough to pass RF.
Now how would you use it?
If you made this radio and it failed to produce output you could check the speaker with the AF probe. If you hear signal the speaker is bad otherwise check the input to the power amp. If you hear signal the power amp is bad otherwise check the input to the AF amp. If you hear signal the AF amp is bad otherwise attach the RF probe and check the detector input. If you have signal the detector is bad. Etc...
If you started at the first RF amp input and had signal and moved to its output you would expect to hear a louder signal. As you progress through you would be turning the volume down to a good listening level and expecting and increase. When you step over a stage and the signal drops you have found the problem area. Then you troubleshoot that stage......
Here they show the signals you would find in a superhet receiver. You just need to know when to look for AF or RF and use the correct probe.
So build an amp and probe and you are set to troubleshoot radios.
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