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If anyone's looking for one, there's a new listing for a 1S1 sampling plug-in.

Good price, untested, but it has tubes. Sampling diodes seem to be there too. Perhaps this will end up on someone's bench who will try to get it to work?

Well, at least this one has tubes. I'll give it a try.....
Thank You for the heads up.

Mark

In the photos on eBay, I see a circuit board mounted on clips on the reverse side of the horizontal board, which I don't have in my 1S1 and that I haven't seen in pictures of the 1S1 on-line. I don't know if that is a user modification or maybe a feature of later serial numbers.

I noticed that too. My 1S1 doesn't have that board either, and it
doesn't look very Tek-like. I was going to suggest it might be
something to do with substituting for the 8056 Nuvistor, but that
still seems to be in place. Odd.

Chris

Yes, one of my 1S1s has that add-on board. It says 'Heater regulator'
Board 670-1054-00
It has a 151-0148 on a heatsink Q609 but not mentioned in my manual
070-0475-00

Tim

If people don't bid it up. LOL!

I might try to get it, so I have something to compare my prototype 1S1 to. I'm still deep in studying the schematics and theory of operation to uncover why literally nothing works on it.

Sean

That's an approved Tek mod which became standard on later production. It's a current regulator for the tube heaters.

Instruments with the mod have a more stable Memory Balance which doesn't have to be recalibrated when you move from one mainframe to another.


Make sure it's doing its job, mine was mis-assembled in a way that shorted it out, so the tubes were too bright.


From my notes:


SYMPTOM: Drift in MEM BAL, with drastic readjustment needed when switching extenders
or mainframes.

CAUSE: The heater current regulator was shorted, maybe since the instrument was new!
There was no insulation on the transistor pins, and E was touching the heat sink and
shorting to C. The heat sink is anodized, but I guess there's a weak spot in the hole.

POOR FIX: Reposition the heat sink. DONE.
BETTER FIX: Put insulation on the pins. Has to endure soldering heat briefly.

ALSO: There was no heat sink grease!

...

Adjust in the following order.
(a) BRIDGE STANDOFF for 2V positive or negative input without baseline lift;
(b) BRIDGE BALANCE for no baseline shift across mVOLTS/CM;
(c) SNAPOFF CURRENT for 350ps risetime;
(d) MEMORY GATE WIDTH for maximum loop gain;
(e) MEMORY BALANCE for no baseline shift across SMOOTHING;.

Until you've performed the above steps, comparing loop gain is meaningless.
After performing the above, my 1S1 maximum loop gain is 1.18 .

...

Dave Wise?
________________________________
From: [email protected] <[email protected]> on behalf of jhpyle via groups.io <jhpyle@...>
Sent: Monday, March 08, 2021 4:14 AM
To: [email protected]
Subject: Re: [TekScopes] 1S1 on ebay

In the photos on eBay, I see a circuit board mounted on clips on the reverse side of the horizontal board, which I don't have in my 1S1 and that I haven't seen in pictures of the 1S1 on-line. I don't know if that is a user modification or maybe a feature of later serial numbers.

Anyone got a link for this mod? Schematic?

In the Mod Summary, it's Mod M14377, effective S/N 2770. It replaces R606 and R607 with a 180mA current regulator using a temperature-compensated zener diode and a TO-66 Silicon power transistor on a heat sink. The document was incomplete when it was created, because it leaves out the new resistors. I would not recommend trying to recreate this mod, just remove R607 and install an LM317 on heat sink. For 180mA you want 7 ohms of resistance; I'd use 8.2 ohms 1/2 W and add R in parallel.?


HTH,

Dave Wise

________________________________
From: [email protected] <[email protected]> on behalf of snapdiode via groups.io <snapdiode@...>
Sent: Monday, March 08, 2021 6:28 PM
To: [email protected]
Subject: Re: [TekScopes] 1S1 on ebay

Anyone got a link for this mod? Schematic?

So who got the 1S1... there were 8 bids and it went for $104!

Guilty as charged. LOL! I need another one so I can hopefully have a reference to compare things I find in my prototype 1S1 to.

Sean

I received it...seller did a great job packing it. It appears to be functional, certainly moreso than my prototype one. I think it will need some caps done as well, but having a mostly working one will be a massive help troubleshooting!

Sean