Construction starts with applying the vinyl panel art because it serves as a drilling template as well as labeling the panels. With this article, we are introducing the idea of using custom-printed vinyl car wrap as a way to produce nice front-panels for electronic projects. It's tough, durable, attractive, accurate, full-color, self-adhesive and not hard to apply. Mine was produced from a PDF file by VVividvinyl.com for just $28 plus shipping. (Includes up to 12 x 54" of printing.) Made for use on vehicles where it must endure sun, dirt and rain for years, I expect it will be quite robust for this indoor, residential application.
Pinholes are made at the registration marks at the corners of the Top Panel. That's needed to see them on the back side.
Notches are cut to the registration marks where the panel bends. Those are needed so the vinyl folds around the edge neatly, as seen in slide-7.
The vinyl is flipped face down with the backing still in place and panel placement is checked.
We want to remove the backing from the top panel (the one in the middle) first since that is where first contact will be. The backing is pulled from the top and rear panels and cut off. Then the backing on the rear panel is put back in place. The adhesive is sprayed with slightly soapy water to temporarily inhibit sticking so we can align the position.
After the top panel is aligned, squeegied and flaps secured, it's on to the rear panel and flange. Then the front panel and skirt are done. Here, just the front flange remains to be covered.
The finished panel with bottom cover and vinyl artwork in place.
At left, polyethelene film (PE) protects the vinyl for the machining operations. The PE roll was supposed to have a temporary adhesive to hold it in place but it was very weak and didn't help at all. At right, paint masking tape is used to hold the PE in place.
Front panel holes are center-punched at left. At right, a hand held punch makes clean, quick and accurate work of the holes. Each punch size has a small point at the center which let's you quickly and accurately align to the indentations.
At left, the 3.2" throat of the hand punch covered all but 8 of the holes on the front and top panels. At right, after the other eight were drilled, drilling dust from the wooden backing board got up into the PE but it didn't cause a problem.
The hand punch could not help with the rear panel holes because of insufficient clearance to the flange at the bottom. Holes were drilled within the D-connector outline to admit a scroll saw blade.
The two large holes on the rear panel were made with a draw punch.
Above, offsets seem present at some of the punched holes but not really. The vinyl gets squeezed out or distorted, leaving it hanging over the edge of the holes a little. That's easily trimmed away, along with the rough edges of the drilled holes. Below, the draw punch distorts the vinyl a little at the edges of the large holes. after this photo was taken, I burnished-down the ripples and trimmed the edges as above.
Front and rear views of the finished panels. No worries about the rough D-hole: the flange of the connector covers it.
All chassis components are mounted here---ready for wiring! The AC adapter was mounted with contact cement. Since it remains pliable, the adapter can be pried-off for replacement, yet this gives a solid attachment. The close contact with the aluminum chassis provides heat sinking.
All prepped for chassis wiring.
The loop of wiring for pin-1 is seen here, roughly as recommended by Dr. Dekker. (Also, unbeaded wires connecting the left two and separately, the right two sockets have been done.) A drive line with bead runs to the left socket and a wire continues to the second socket. A beaded wire connects to the third, then a wire to the fourth and finally a beaded wire returns to the drive pole of the pin-1 connector. A beaded wire runs from the sense pole of the connector to the (octal) reference socket.
The pin connector lugs were too small for tinned, 18ga, stranded wires. At left, I made eyelets (with #22) wire to accommodate the wire. At right, connectors are seen in stages of completion. The upper, center-pin lugs are for sensing and lower are for drive.
Completed socket field wiring in all its glory! You can see some details of the service-position mounting of the main board. Think the beads are overkill? I didn't use them at first on the VTA and found 200MHz oscillations with tubes having Gm of 10000 or more. Tests pointed to the socket field wiring. Ended up having to pull out and redo all of the socket field wiring and that was a LOT more than 4 sockets!
Rear panel and power supply. The 65W AC adapter is affixed using contact cement. Its AC prongs on the left are connected using lugs from an octal tube socket. The terminal strip on the left handles connections of the AC line cord, the power switch and the AC adapter. A green wire goes to the single-point ground at the DC terminal strip on the right. It handles DC connections of the AC adapter, DC fuse and DC power choke. The DC terminals are (L to R): +19V after the choke, Single Point Ground, +19V before the choke.
The added heater regulator board is seen, installed. No heatsink has been added to the XL4005 chip on the switching regulator module yet.
Wiring is done except for the main board. The loose black cable is a shielded pair carrying the RS232 signals. It has to squeeze past the mains terminals on the left, so shielding seemed advisable. A plastic cover needs to be added over the mains terminals.
The completed µTracer/HR assembly. No cover for the mains yet. You might notice that instead of the screw-terminal connectors supplied with the main board, I used 0.1" headers as solder terminals. Nature abhors a connector.
A 0.22uF cap must be added to the bottom of the heater regulator board. It calms the ringy transient response of the switching regulator module. By the way, no worries about the two pads at the bottom cap connection; they are connected on top.
The heater regulator board is seen mounted in its service position.
The main board mounted in its service position.
An elevation view of the assembled µTracer/HR.
The finished rear panel. However, there was a small problem with the USB/RS232 adapter cable which plugs in here. It had threaded sockets which interfered with the screws holding the DB9 connector on the panel. The male adapter expects the female connector to have captive thumb screws which hold it in place. My solution was to cut off the threaded sockets of the adapter using a Dremel cutoff blade.
Shootout with the Vacuum Tube Analyzer! The µTracer seen at left with the computer monitor was compared with our own Vacuum Tube Analyzer (VTA) design, at right. Although the VTA is a far more difficult and expensive project, designed for maximum accuracy, the µTracer fared quite well.
The completed µTracer, setup for a Sovtek 6L6WXT. Results are shown in the article. Alas, the bottom cover of the unit has not yet had its "Tektronix-blue" paint job!
