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Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members. |
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25th May 2021, 12:28 pm | #21 | ||
Heptode
Join Date: Jul 2020
Location: Larkhall, South Lanarkshire, Scotland.
Posts: 671
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Re: Signal tracer help needed
Quote:
Jay
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25th May 2021, 12:37 pm | #22 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: Signal tracer help needed
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25th May 2021, 12:50 pm | #23 | |
Heptode
Join Date: Jul 2020
Location: Larkhall, South Lanarkshire, Scotland.
Posts: 671
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Re: Signal tracer help needed
Quote:
Youtube video of the tracer build and testing on a valve set for anyone interested https://www.youtube.com/watch?v=PbsnI0uM5BM
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25th May 2021, 1:23 pm | #24 | |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: Signal tracer help needed
Quote:
Lawrence. Last edited by ms660; 25th May 2021 at 1:40 pm. Reason: correction |
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25th May 2021, 1:55 pm | #25 | |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,899
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Re: Signal tracer help needed
Quote:
There are other RF probe circuits which are more economical on capacitors etc. Have a look at some of the Marconi and HP valve voltmeters (there's one in the AVO CT38 for example...) an input coupling capacitor, then a shunt diode to ground and then a load resistance to ground. The coupling capacitor and the dc path of the circuit under test acts as the filter capacitor as well. David
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25th May 2021, 2:05 pm | #26 |
Heptode
Join Date: Jul 2020
Location: Larkhall, South Lanarkshire, Scotland.
Posts: 671
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Re: Signal tracer help needed
All very useful & helpful info fellas, But i'm still wondering why the guy in the video had good results with his version of the circuit without any of the modifications mentioned in this thread ?
jay
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25th May 2021, 2:14 pm | #27 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: Signal tracer help needed
Try the right type of diode, the parts list calls for a 1N34a type if I read it right.
Lawrence. |
25th May 2021, 2:16 pm | #28 | |
Heptode
Join Date: Jul 2020
Location: Larkhall, South Lanarkshire, Scotland.
Posts: 671
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Re: Signal tracer help needed
Quote:
Cheers Jay
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Help!! I've been electrocuted by a glass thing that glows |
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25th May 2021, 3:49 pm | #29 | |
Heptode
Join Date: Jun 2019
Location: Oxfordshire
Posts: 740
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Re: Signal tracer help needed
Quote:
Well it's always best to try a circuit out with a sig gen and scope if you're not sure. Here's a quick mockup of the circuit of the probe. It uses an 1N4148 as it was handy. The anode of the diode D1 is driven by the sig gen (and Ch1 of scope). The cathode of the diode goes to a 1000pF cap C1 going to ground. Then a 10nF cap C2 is connected from the cathode of D1, the other end goes to scope probe Ch2 (pic 1) With the sig gen set up for 1MHz modulated by a 400Hz tone and 0.1Vpp, and the scope set to 50mV/div you can see that little or nothing is present on the output (pic 2). Not really surprising as the diode forward voltage is about 0.6V so it won't conduct. If we then turn the sig gen up to 1Vpp, there is a little bit of life on the output... but mostly RF still (pic3, ch1 set to 500mV/div) Adding a 10K resistor in parallel with C1 (pic 4) so there is a DC path to ground you can see a rectified output (pic5). So the DC path makes a lot of difference. |
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25th May 2021, 4:03 pm | #30 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: Signal tracer help needed
I think the two threads should be merged or at least the relevant posts in the other one in the link below should be merged with this thread:
https://www.vintage-radio.net/forum/...d.php?t=179602 Lawrence. |
25th May 2021, 4:37 pm | #31 |
Heptode
Join Date: Jul 2020
Location: Larkhall, South Lanarkshire, Scotland.
Posts: 671
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Re: Signal tracer help needed
Interesting keith, I Do have a scope and signal generator, But never thought of trying that, I suppose i expect circuits to work straight off, But thats seldom the case. It seems to be working more to my satisfaction now, When i get time i'll mount the circuit in a tin to shield it and feed the probe via a BNC Socket.
Homebrew probe. Using shielded cable, Diode is inside PL259 Plug. |
25th May 2021, 4:40 pm | #32 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: Signal tracer help needed
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25th May 2021, 4:42 pm | #33 | |
Heptode
Join Date: Jul 2020
Location: Larkhall, South Lanarkshire, Scotland.
Posts: 671
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Re: Signal tracer help needed
Quote:
Cheers Jay
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Help!! I've been electrocuted by a glass thing that glows |
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25th May 2021, 4:45 pm | #34 |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: Signal tracer help needed
Coaxial cable capacitance, that could de-tune a tuned circuit quite far, and all circuits are potential dividers so double whammy.
Lawrence. |
25th May 2021, 4:47 pm | #35 | |
Heptode
Join Date: Jul 2020
Location: Larkhall, South Lanarkshire, Scotland.
Posts: 671
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Re: Signal tracer help needed
Quote:
Jay
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Help!! I've been electrocuted by a glass thing that glows |
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25th May 2021, 4:59 pm | #36 | |
Heptode
Join Date: Jul 2020
Location: Larkhall, South Lanarkshire, Scotland.
Posts: 671
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Re: Signal tracer help needed
Quote:
Jay
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Help!! I've been electrocuted by a glass thing that glows |
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25th May 2021, 5:16 pm | #37 | |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: Signal tracer help needed
Quote:
Lawrence. |
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25th May 2021, 5:21 pm | #38 | |
Dekatron
Join Date: Apr 2011
Location: Cornwall, UK.
Posts: 13,454
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Re: Signal tracer help needed
Quote:
Lawrence. Last edited by ms660; 25th May 2021 at 5:26 pm. Reason: extra info |
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25th May 2021, 5:24 pm | #39 | |
Heptode
Join Date: Jul 2020
Location: Larkhall, South Lanarkshire, Scotland.
Posts: 671
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Re: Signal tracer help needed
Quote:
Inside the body of the PL259 plug to which the probe is attached, (Plug at the top of the pic,) Other end will attach to the tracer via a BNC socket
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25th May 2021, 5:31 pm | #40 |
Heptode
Join Date: Jul 2020
Location: Larkhall, South Lanarkshire, Scotland.
Posts: 671
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Re: Signal tracer help needed
Tip of the probe in pic below. The diode is shielded inside the body of the plug.
Jay
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