Signal tracer & probe build + questions - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

David G4EBT · 2nd Dec 2025, 1:48 pm

I post 18, I said "I've attached a block diagram of the stages".

I hadn't noticed that for some reason, it didn't appear as an attachment and it's too late to edit the post so I've attached it below. It depicts the stages of a superhet rather more clearly than looking at a circuit diagram or reading my verbose explanation of the principle of the superhet.

Hope that helps.

Jameson · 2nd Dec 2025, 2:08 pm

Thanks David thats good info. I should really thou, before anything else, confirm that the RF part of my combined AF/RF probe is doing what it should (the AF is good at least). Should I be receiving RF when probing onto my sets tuneable variable capacitor (the one with the transparent body with vanes inside) ? With MW on and the volume of the set to zero im receiving nothing with the probe/tracer combo ! I will make a dedicated RF probe and compare !

Al (astral highway) · 2nd Dec 2025, 9:40 pm

Hi Jameson, as I suggested, you should be hearing a hash noise if you probe at point C in David's handy illustration. So yes, it suggests something's off with your build at the moment.

No harm done, below is about the lowest component count probe you can make, if you want to try a quick lash-up to get the idea of it...good luck!

Jameson · 2nd Dec 2025, 10:25 pm

That's great I do need to make another to confirm. Ive made a decision with myself to leave the set I have for now and have ordered an Elenco AM/FM kit to practice on, it will make things easier for me as its laid out for a novice like myself and has instructions of where/what to test and the expected results which will keep me more than happy. Thanks for the input..... tbc !

https://uk.robotshop.com/products/elenco-am-fm-radio-kit-combo-ic-transistor

David G4EBT · 3rd Dec 2025, 8:46 am

Quote:

Originally Posted by Jameson

That's great I do need to make another to confirm. Ive made a decision with myself to leave the set I have for now and have ordered an Elenco AM/FM kit to practice on, it will make things easier for me as its laid out for a novice like myself and has instructions of where/what to test and the expected results which will keep me more than happy. Thanks for the input..... tbc !

https://uk.robotshop.com/products/elenco-am-fm-radio-kit-combo-ic-transistor

That's an excellent decision - it isn't cheap but it's more than just a kit - it's a training course. There's a useful YouTube video which shows how to use a signal tracer/injector such as the Velleman K7000 to fault-find transistor radios, which uses the Elenco AM/FM kit radio to demonstrate the technique here:

https://www.youtube.com/watch?v=QePKurE0atA

It explains very clearly what to expect at various points when using both the tracer and injector on a working transistor radio so that on a faulty radio, you can quickly narrow down which stages are working and where the faults are. The kit is built on a printed circuit 'breadboard' with graphics of all of the components shown. It comes with a 64-page manual on constructing and setting up the radio, including a training course of 56 pages, divided into 9 lessons:

• Audio Amplifier
• AM Detector
• AM IF
• AM Amplifier
• AM Mixer & Oscillator
• FM Detector
• 1st FM IF
• 2nd FM IF
• FM RF Stages

Make sure you use a pencil-tipped soldering iron and follow the instructions to the letter.

You build a section, then the manual tells you how it works, and how to test it before you move on to the next stage. It tells you how to test with just a multi-meter, and for those who have an oscilloscope and a signal generator, how to use those for tests.

A PDF of the 64-page comprehensive training manual can be downloaded at this link:

https://cdn.robotshop.com/media/i/ibo/rb-ibo-489/pdf/am-fm-r...t-combo-ic-transistor-datasheet.pdf

It has a lot of practical advice for anyone interested in how a radio works, whether or not they buy the kit.

For restoring vintage valve radios, using a signal tracer/injector for fault diagnosis, there's a useful video here:

https://www.youtube.com/watch?v=maIJC4J_jZw

About ten years ago, an acquaintance built the kit and I made a little wooden base for it, and the 'magic wand' tuning aid. Some pics attached.

Good luck with the kit!

Jameson · 3rd Dec 2025, 11:08 am

Yep found this kit while browsing this forum, and will be invaluable for me at this stage, also will able to put the signal generator to use !

2nd Dec 2025, 1:48 pm	#21
David G4EBT Dekatron Join Date: Feb 2003 Location: Cottingham, East Yorkshire, UK. Posts: 6,176	Re: Signal tracer & probe build + questions I post 18, I said "I've attached a block diagram of the stages". I hadn't noticed that for some reason, it didn't appear as an attachment and it's too late to edit the post so I've attached it below. It depicts the stages of a superhet rather more clearly than looking at a circuit diagram or reading my verbose explanation of the principle of the superhet. Hope that helps. Attached Thumbnails __________________ David. BVWS Member. G-QRP Club member 1339.

2nd Dec 2025, 2:08 pm	#22
Jameson Triode Join Date: Nov 2019 Location: Kent, UK. Posts: 49	Re: Signal tracer & probe build + questions Thanks David thats good info. I should really thou, before anything else, confirm that the RF part of my combined AF/RF probe is doing what it should (the AF is good at least). Should I be receiving RF when probing onto my sets tuneable variable capacitor (the one with the transparent body with vanes inside) ? With MW on and the volume of the set to zero im receiving nothing with the probe/tracer combo ! I will make a dedicated RF probe and compare !

2nd Dec 2025, 9:40 pm	#23
Al (astral highway) Dekatron Join Date: Nov 2006 Location: Bristol Posts: 3,617	Re: Signal tracer & probe build + questions Hi Jameson, as I suggested, you should be hearing a hash noise if you probe at point C in David's handy illustration. So yes, it suggests something's off with your build at the moment. No harm done, below is about the lowest component count probe you can make, if you want to try a quick lash-up to get the idea of it...good luck! Attached Thumbnails __________________ Al

2nd Dec 2025, 10:25 pm	#24
Jameson Triode Join Date: Nov 2019 Location: Kent, UK. Posts: 49	Re: Signal tracer & probe build + questions That's great I do need to make another to confirm. Ive made a decision with myself to leave the set I have for now and have ordered an Elenco AM/FM kit to practice on, it will make things easier for me as its laid out for a novice like myself and has instructions of where/what to test and the expected results which will keep me more than happy. Thanks for the input..... tbc ! https://uk.robotshop.com/products/elenco-am-fm-radio-kit-combo-ic-transistor

3rd Dec 2025, 11:08 am	#26
Jameson Triode Join Date: Nov 2019 Location: Kent, UK. Posts: 49	Re: Signal tracer & probe build + questions Yep found this kit while browsing this forum, and will be invaluable for me at this stage, also will able to put the signal generator to use !