Sampling head extender missing coax connectors


Shipping rates from Canada really suck.
So does the wait time from China...



Me either.
I finally ended up drilling a small hole in the PC board and mounting a sturdy solder lug, to which I fastened the coax connector and then soldered.. It took quite a bit of fiddling to get it properly lined up with the hole in the casting in all three axes, too. At least nobody can see the hack job inside the case ;)

But it is now a useable extender. I'm still not sure how well the trigger pickoff will work at really high frequencies (due to the rigged junctions at the connectors), but I doubt I'll ever work with anything that fast, or on the extender. I really just wanted it for repairing sampling heads.


That's good, I still don't understand the mindset of the person cutting the coax.


Got them today (also run-over by a hand truck as I posted)... no damage though.

The end that mates with the sampling head was easy - it snaps into the hole. Since the coax was a little short where some fool had cut it off, and I have no ferrules for these, I rigged it with a piece of #26 Teflon wire through the center and the shield quickly tacked to the connector barrel. There'll be a little impedance bump there but I think the trigger pickoff will still work.

Same issue on the "box" end that inserts into the plug-in - cable a few mm short and no ferrule. The problem is that the connector needs to sit flush with the end casting from the inside, and the casting's hole is too small to pass the connector through anyhow. I will need to fab some kind of mounting bracket to the PC board inside, likely how it was done in the first place... maybe use epoxy or (non-acid) RTV to secure it to the board. Not the casting, I'd never be able to take it apart again the other way.

"Missouri engineering" meets Tek engineering! Unmolested extenders are going for $100+ on that auction place. Forget it.


Weird, I just mailed a part to Massachusetts and it got there in two days.


Not yet :(
As I mentioned in the 3T77A thread, mail from Canada to the US is even slower than usual these days. Still waiting on the hybrid for my S-4 head that Walter sent, too.


Did the connectors ever show up?


The sampling heads have the trigger out connector mounted directly to the PC board anyway, so looking inside wouldn't have helped. Hopefully the hole is the same size as in a D-sub connector and it just snaps in.


No problem, I'll figure something out! I have various crimp tools, and a friend who used to install alarm systems and cable TV and still has the tools.

I'm more concerned about mounting the connectors. I don't have anything to inspect for the original mounting scheme (except my more expensive S-2 head and since it works, I do not want to mess with it). But it almost has to be a snap-in since there are no marks where a nut or spring clip would have been.

Guess that's what JB Weld is for :D


Snapdiode would like to tell you that an important thing has been overlooked: the need for a ferrule and crimping tool to properly terminate the cable to the connector. I do not have these ferrules... You're on your own basically as to how to attach the ground braid of the cable to the connector. I suppose a brass tube of some sort, if you still have hobby shops in your area, would work, and delicate squishing with pliers will do the job.


Thanks for the heads-up. Snapdiode is sending me a couple of coax contacts that hopefully will fit - they sure look the same.
I'll check transient response with the head directly in the plug-in and on the extender to see how different they are.
Of course I have to install new diodes first... ;)

Albert Otten

Be aware that the missing trigger connector affects the Transient response of the S-1. The transient response amplifier (Q13/Q17) will do almost nothing.
The 7S12 cannot be triggered internally by the sampling head. However, the 7S12 trigger connector is still present and terminated to GND via 51R.


On Mon, Feb 15, 2021 at 01:37 AM, Charles wrote:

The extender is still partially useful to start debugging the S-1 once I get
the Schottky diodes from Digikey, assuming that doesn't fix it right away.


PM me


If you have a male and a female (since I need one for each end of the extender) ;) I'd happily pay postage.

D-sub coax contacts can be had, for example:

For almost $16 for just one pair. Plus postage!
I'm going to check my cable bin, maybe there are some coax contacts as mentioned...


Meh, I creatively destroyed my connectors to get the contacts inside. Why not, I don't even know how or why I have a 7W2 in my box of shiny things. If they fit, I can ship them to you for the price of postage.


"They could be dsub coaxial contacts, as used in 13W3 connectors. I'd have
to measure it. me."

If they are then those same contacts were used in some of the old Sun
and SGI monitors and you might be able to get one of the video cables and
rob the connectors out of it. HP also used the same contacts in various
extender and unit interconnect cables.

On Sun, Feb 14, 2021 at 7:27 PM snapdiode via <snapdiode=> wrote:

Whoever did that did a pretty despicable thing... This connector kind of
looks like a SMB but isn't. The manual seems to suggest it is built of
parts intended for other things.

The inner female conductor is a DM53740-5001 which still exists today

...which says it's meant for RG187 or RG188 coax, which leads to these

They could be dsub coaxial contacts, as used in 13W3 connectors. I'd have
to measure it. me.


I'll look for your album, thanks.

The NorComp contacts are proving elusive (DigiKey lists them as "obsolete" and no price. Of course).

However, it appears that other manufacturers also make similar coaxial contacts, for example:

I might as well chase this mirage while I'm waiting on Schottky (and tunnel) diodes ;)


I think that will be the bigger problem, naturally the connectors need to be mounted at the right distance to work... Check out my exciting photo album.


Those look good, but I wonder how the contacts were originally mounted in the extender cable. There is no mark where a nut or clip would have been, and no separate bracket. Perhaps it's a push-in lock (as it works in the D-sub connector body)?