Safety?
The Tek 577 can produce up to 1.6kV collector voltage with a fair amount of current, so getting in contact with the DUT – especially if it has a metal body – can be very harmful.
So Tek has build in a safety feature in the 177 test fixture. If the collector supply is >=100V a pin in the fixture has to be activated to enable the high voltage. The original safety lid activates this switch with a pin when the lid is closed.
However almost all of these lids are lost or broken – my Tek came without. Of course you can deactivate the switch (there is a how to in the 177 service manual how to rewire the fixture) or you can create an insert which presses the switch all the time (found some on eBay).
I really did not want to do this, since 1.6kV is a lot….so why not use modern printing tech to recreate a lid?
Design
I tried to replicate the original design as close as possible, which is not easy since pictures of the original are also rare.
The one in the picture above is from a TekWiki image.
Above you can see the design I came up with. Its dimensions and notches fit to the fixture, so that you can fully open the lid without interfering with the knobs of the instrument.
The hole in the front left is for a plastic pin which will activate the security switch once the lid is closed. The notches and holders on the back and the front make it possible to easily mount and dismount the lid.
The hinges needs some 2mm x 10mm pins as axis. You can buy them ready to use or just make some on your own from a 2mm axis.
Printing
I printed several draft versions of the model on my H2D printer, but finally I used PCBWay’s SLA print service to make a really nice one. A 50-year-old Tek 577 deserves that!
The result is absolutely amazing – almost factory like quality, this really does not look like 3D printed.
That’s how it should look like!
Is the model available?
Sure! You can download it here for free. You will need two 2mm x 10mm axis for the hinge and the plastic (or metal pin) to activate the security switch. I added one to the print model for your convenience.