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Reg Mods Update

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There seems to be much interest still on the TDI-SL mods that our friend Reginald Sniff made. I often find old emails in my junk box from people trying to get the mods. I apologize for not replying as I find them late and often busy with day chores.
I will share what I still have left from my conversations with Reg many years ago. Most were over the phone as he had difficulty typing on the keyboard. I took notes and why I have the last picture with a summary of the three mods.



Thanks for the picture. I do have a few questions regarding my early model SL.

1- you had mentioned in another thread about doing something also with D20 and D21. We spoke only on changing C20, C21 and removing C56. What is the purpose of the D20,21 Mod?

2- Are C20,21 Polarized? what is the direction of flow ? ( thinking about building a board with a toggle switch to change from OEM to modified.} just in case the mod has an effect on my using my BIG coil.

3. If I did a board would the cables running from the capacitor board to the detector board need to be shielded?

I just ordered the Reidman battery.



EMAIL sent by Reg in response:

I mentioned mods  added in 2015 to the SL to correct a problem in Australia.  The mods to correct that problem included D20 and D21..  The D20 and D21 were part of that mod as was C56.  You can remove D20 and short out D21 with a simple jumper to complete the Aussie mods.  This will smooth out the ground balancing a little.

If you use the proper caps, C20 and C21 are not polarized.  Do not use polarized caps.

I don't recommend a board to be added.  Just tweak the Delay a little if the cap mod increases the sensitivity too much.

On the latest pic I sent you, you will see an arrow pointing to C42.  Adding a jumper across this cap will increase the gain and make very weak signals more reliable.  Adding a jumper is easy.  Simply look for two test points  TP2 and TP31.  They are near C42.  Simply add a jumper from one test point to the other jumpers C42 and takes care of the problem.  C42 and R75 are a high pass filter that isn't needed and causes problems.  Eric added them when he had a drift problem and thought they would help.  The drift was coming from some place else he later found out.




caps being removed are C20 &21, .47uf and will be replaced with .22uf. Use 50v Panasonic, or Rubicon Stacked Metal Film Polyester type ) from another post by Reg


Picture sent by Reg


My Summary of all three TDI-SL  REG mods






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Bear in mind that on SL's made since 2015 have D20, and D21 removed, and the jumper across the correct 2 legs of D21. This was a factory mod. if you want to perfor4m this mod on your pre-2015 model here's a pic showing which legs the jumper goes across on D21. It also shows D20, and C56, which can be removed.



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Both D20 and 21 are three-lead diodes. The jumper only goes across 2 of the 3 connections on diode D21. It goes across the bottom 2 connections in the pic, as shown. Also, everybody interested in this mod should understand these are very tiny components. They require a magnifying light, and good soldering skills, with a decent quality soldering station. At least IMHO...LOL I was a radar tech in the Air Force, and doing this mod taxed my skills. I've done 2 of Reg's mods to my 2013 unit, and I recommend them. At some point in then future I'm going to do the jumper across Test Points 2 and 31, too. I wasn't aware of that until Gilbert's post, so a shoutout to him, and a thumbs-up


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I'm thinking, Gil, that a switch for the hi-gain might be a nice feature.


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  • 5 months later...

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