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 Signal Tracers

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Cliff Jones
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PostSubject: Signal Tracers   2011-02-15, 1:03 pm

This topic of Signal tracers will field questions comments and uses.
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Signal tracers are very useful when you are trying to find and isolate a non working stage in a radio, it will work on all three stages of a radio. R.F., I.F. and audio.

The signal tracer has a diode that can demodulate a signal into audio. It has an audio amplifier and a speaker.

The best way to use it is to start at the antenna, then the antenna coil, then if present the R.F. amplifier, then going to the mixer tube and I.F. coils, then the detector tube and finally the audio tube, then audio transformer with speaker as the final test point.

Or you can go the opposite route.

The Idea is to find either when you loose the signal, or find it. When you get the results you are trying to hear, then you have an idea where the problem lies.

Then you start removing components for testing to resolve the problem and look for bad connection, or even affraid wrong connections (horrors)

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Cliff Jones
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PostSubject: Re: Signal Tracers   2011-06-01, 11:26 pm

One Signal tracer has a high voltage that is used to see if components are starting to fail. Sounds like it could be very useful.

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PostSubject: Re: Signal Tracers   2011-06-03, 2:33 am

To "fine tune" a little, put the tracer's probe on one of the antenna's connectors to begin, and adjust the radio's tuner dial around the band. If the oscillator section, and hence the A and B supply circuits, are working, you should hear a variety of stations through the tracer's amp.

Next, put the tracer's probe on the input grid of the first tube, which will either be the RF Amp, or the converter tube. If audio is present, then move to the plate (output), and then to the next stage's input grid, and so on, until the demodulation stage, at which point you will need to switch to an AF amplifier.

For Transistor sets, the inputs are the Transistor Base connections, and the outputs -at least before demodulation, are at the Collector. Many Transistor amplifiers use dual Emitter stages connected to each side of the AF transformer for their output.

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Cliff Jones
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PostSubject: Re: Signal Tracers   2011-06-03, 10:22 am

There are two thoughts of signal tracing a radio. One is start at the antenna, and work towards the audio, and then there is the reverse of working through the audio and proceeding back to the antenna.

There is no preferred way, as both have advantages.

I would make sure that the signal tracer is used on radio that has isolation. I don't know if most signal tracers are operated with a internal power transformer or not, However I would suspect that most do, just for common sense.

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PostSubject: Re: Signal Tracers   2011-06-03, 1:01 pm

It's ALWAYS a good idea to use an isolation transformer when working on an AC powered set, and double that when working on an AC/DC, since the chassis is usually hot. Tube signal tracers will need AC power, while there are simple solid state models that operate by battery.

Personally, I like to use a simple circuit that I built into a pen barrel, consisting of a Diode and a cap, the output of which goes to a small Rat Shack IC amplifier, powered by a nine volt cell.

For anyone who wants to make one, just Google "simple signal tracer circuits".

AFA testing the audio section, I will usually feed a signal to the center, or high side of the volume control, to see if I get an amplified output.

Although I have a generator (two, actually), I will often just use a Transistor radio's output, by plugging an earphone-less connector with both leads into the earphone jack, grounding one lead, and connecting the other to the volume control.
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Cliff Jones
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PostSubject: Re: Signal Tracers   2011-06-03, 2:01 pm

OK that's great info.
I just thought of a question on the solid state tracer, is the any built in protection for use on High voltages encountered in a tube set?
And another thought, rather than use a speaker or Earphone per/say for the solid state tracer, would a Piezo speaker work?

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PostSubject: Re: Signal Tracers   2011-06-03, 2:55 pm

The capacitor in the front end of the tracer provides for DC blocking, so voltage doesn't matter. Take a look at the Pill Bottle Tracer Probe, toward the bottom of this page; it's similar to what I built; in fact, the last circuit on the page is what I built;

[You must be registered and logged in to see this link.]

I'm not sure if a Piezo speaker by itself would work for tracing, as an amplifier would be needed, if that was the question. AFA using that type of speaker for an amplifier's output, you would have to experiment with it.
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Cliff Jones
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PostSubject: Allied Radio Knight KG 690 signal tracer   2011-09-08, 7:48 pm

Found in a vintage and antique shop for $6.99 Shocked
A Knight KG 690 Signal Tracer.

I couldn't find the manual until I ran across a Ham on ARF.
I found That another Model # 83y135 that is the same unit.
Here is a free Booklet [You must be registered and logged in to see this link.]

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FrankB
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PostSubject: Quick and Dirty Signal Tracer   2015-02-21, 10:45 pm

A signal tracer for those on a real low budget can be made from any AM radio. Tube or solid state.
Personally, I prefer the tube type with a power transformer to isolate it from the power line.

Just feed the signal into it thru a  .01-.005 mfd 1KV or greater capacitor, attaching to the volume control at the middle terminal of it.

Another thing is that the tube radios are way more forgiving it you hit a HV AC connection in the set.

If you use a non- power transformer radio, be sure to connect it to an isolation transformer. Do not ground to the ground wire either. Just connect to hot and neutral.

If using a battery powered xistor radio, no isolation transformer is required, but do NOT hook radio to a wall wart or external power supply.
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