Tektronix 214 Miniature Storage Oscilloscope
Another eBay find, I don’t remember how much I paid, it wasn’t much. A replacement set of Ni-Cad batteries from BATTS4LIFE also on eBay at $40.40 including shipping, was probably comparable. I also paid $25 for a original manual. The scope actually came with a manual on DVD but I find it much easier and more pleasant to have a hard copy. Here it is sitting on a sheet of 8.5 x 11 for scale:
The Tektronix 214 was introduced I believe, in 1973. It is a two-channel storage oscilloscope, the only storage oscilloscope that I have. The bandwidth is DC to 500kHz while the time-base operates from 500mS/div to 5μS/div in 1-2-5 ranges, that can by increased to 1μS/div using the variable control.
The Y channels have the usual 1-2-5 attenuators over a range of 1mV/div to 50V/div, a notably wide range, I like the very high sensitivity. There is no invert or algebraic addition which does which limit its functionality quite a bit for me. The input capacitance is around 140pF and since the probes are hard-wired, this cannot be reduced using a X10 probe, again, this does limit the range of applications, even at audio frequencies. The switching automatically changes from chop to alternate mode with applied signal frequency.
The triggering system provides a pre-set position that keeps the time-base running without a signal applied. The variable level control allows the user to move the trigger point from the up slope to the down slope, if required.
To my delight, a new set of batteries was all that was required to breath life back into this marvel of mechanical engineering. I emphasise the mechanical engineering since the electronic design was most likely not the major challenge. The quality of fit of the plastic parts is astonishing, the toolmakers must have been the very best! Here it is pulled apart:
I found heavy corrosion on the negative wires and connectors from the battery packs. In fact one connector crumbled to pieces, I managed to clean the remains and under a magnifying glass and soldered a new wire to what remained. Together with Deoxit it proved to be enough. The original wire was so corroded that I was unable to solder to it, I guess Tektronix did not use de-oxygenated wire. There are two battery packs each comprised of five A size Ni-Cad cells for 6V each. I was able to detach the wire assembly from the second pack and re-use it. The replacement batteries are slightly fatter than and slightly shorter than, the originals. I had to cut the rounded ends out of the moulded plastic caps and then I used sticky back foam tape to pad the ends, inside the caps. It took one trial assembly to get this just right. The board on the control panel, which houses most of the functional electronics connects to the motherboard by a long row of gold-plated pressure contacts and the height of the battery packs is the controlling factor in these making good contact. I was surprised again at how easily this worked out, which speaks volumes for the quality of the mechanical design and manufacture. Here is the battery pack, the re-built pack on the left, the original cells in the middle and the original pack on the right:
I need to study the storage tube technology, the tiny CRT in this thing is another amazing piece of mechanical engineering. The screen is 2 1/32″ x 1 7/32″ divided into 0.203″ divisions, 10 horizontal and 6 vertical. Here is the screen end showing the signature of the guy who production tested it.
Since I wrote this, I thought to see what state the batteries were in one day and found that it would not display dual traces. Each channel worked individually and so I surmised that the Alt/Chop multi had failed. This is a DM74L72N chip so I looked on ebay and sure enough found some for sale and bought two. Replacing the chip restored the dual trace function however, I have no clue as to why the chip failed.