Did the TDI SL sweep speed mod this morning

[Jim in Idaho]

Bit the bullet and did the sweep speed mod this morning. Made a huge difference in the acceptable SS. I ran the 1 grain gold bar past the 8 x 6 Sadie coil before doing the mod, and there was a relatively slow, specific sweep speed that gave the best signal. Too fast, and the signal completely disappeared. After the mod, the SS made almost no difference. Fast, slow, the signal was steady. No change in indicated depth in the air test. Threshold was still smooth. I'll post a video of the before/after tests later on. I changed the filter caps (C20, 21) from .47ufd, to ,22ufd. A friend in Florida, who is a civilian tech working for the Navy, was kind enough to send me a few matched pairs of the caps. Without his encouragement, and help, I probably never would have tackled this. Now I'm really glad I did. One tool I'm glad I had was my fly-tying magnifying light. My eyes don't focus like they did when I was young, and that magnification allowed me to see the soldered spots, to be sure I had done a thorough job.
Jim

[eclipse]

C20 and C21 are integrator caps and they don't need to be matched.

[Carl-NC]

C20 and C21 are integrator caps and they don't need to be matched.

Uh, yes they do.

[Andi68]

How accurate must the values be?

[Jim in Idaho]

As I understood Reg S. they're supposed to be within 1%. The overall capacitance isn't critical, but the relative capacitance is.
Jim

[Jim in Idaho]

I posted a video comparing the sweep speeds, before and after the mod.
Jim
https://youtu.be/SOkYbMkm56c

[Carl-NC]

Yes, 1% is sufficient.

[eclipse]

The integrators are single ended and you can adjust the gain of the Geb channel anyways but yeah 1% match is very easy to achieve with good quality caps. Only polypropylene or PPS high quality capacitors can be used.

[WM6]

The overall capacitance isn't critical, but the relative capacitance is.

Jim

Hi Jim

Can you explain what this practically mean?

What mean here overall capacitance and what relative capacitance? Relative to what?

Sorry, but my I cannot help with my English to understand this sentence. Thanks.

[Jim in Idaho]

The idea of the mod is to reduce the factory capacitance of .47ufd to .22ufd. If the new capacitors you use are .23, or .21 it doesn't matter as long as they are within 1% of each other. The critical detail is that they be nearly identical, not that they be precisely .22ufd. Hope that makes sense.
Jim

[waltr]

Yes, 'match' value to each other.
The other part, which was not mod'ed, is the resistors parallel to the integrator caps should be matched and also the input series resistors.

This is all to match the two integrator channels to have the exact same Time Constant and response.

Thanks for posting Jim.

[Andi68]

Thanks

[Carl-NC]

This is all to match the two integrator channels to have the exact same Time Constant and response.

Correct, the 2 channels have to be time-aligned or you'll never get the GB to quite work. Gain doesn't have to match because the GB control deals with this, but it can't deal with delay mismatch.

[6666]

Hi Jim

Can you explain what this practically mean?

What mean here overall capacitance and what relative capacitance? Relative to what?

Sorry, but my I cannot help with my English to understand this sentence. Thanks.

What it means is the modification needs two .22ufd capacitors that measure within 1% of each other
so buy a few .22ufd caps and measure the capacitance and find two within 1% of each other, it does not matter if the values that you finish with are not exactly .22ufd, all that matters is if you have two that are within 1% of each other and then they will be MATCHED. (Australian English )

[Mark-VA]

This is actually the next upgrade for my SL. I recently completed my upgraded battery and was very pleased with the increased depth the extra voltage/current gives. Thanks to Jim of Idaho for all your help and encouragement.