Frank,
I remember those days. I think my soldering iron was the culprit and was causing cmos chips to fail, so I bought a much better soldering station and cured the problem.
As for the old CS 6, yes, it was quite a detector that could go down to 8 usec. It was able to do this because of the low power design and the very short pulse width at 8 usec. The detection of very small gold was superior to the TDI, but depth on larger gold wasn't close to the more powerful unit. Also, the old CS 6 required a DD coil to obtain the short delay.
Now, with a few mods, the TDI may just come close to matching that old CS 6 on the small gold without giving up the depth on the larger stuff and do it using a mono coil. Yes, you might have to switch from one mod idea to the other, but that isn't something difficult to do.
I am working with an associate and he has modified a TDI SL following my recommendations and that detector is really quite sensitive to the small stuff. Next, it has to be tried in the field to see if there are any negative drawbacks. Unfortunately, weather and time have not allowed this testing to occur.
I am thinking the changes have to be optional but because there are three of them, I am not sure just how to approach this without adding a bunch of switches and I am trying to avoid that. So, more thought process is required.
Reg