Vintage Tektronix 067-0532-00 resurrection project

[Addicted2AnalogTek]

About a decade ago I purchased a neglected 067-0532-00 calibration fixture off of the bay of fleas. The unit had no covers, the 7119 tube was scavenged from it, and worst of all: the alumina(?) shaft that connects the dial plate to the oscillator capacitor had been shattered. At that time I disassembled the oscillator and recovered the pieces of the shaft. I also epoxied the shaft back together. I know that this is less than ideal, but I decided to run with it for now in order to see if I can get the unit to function. What follows will chronicle my adventure with this unit.

Here is a link to the manual for the unit:  http://w140.com/067-0532-00.pdf

I began by laying out all of the oscillator parts. Since I lost the disassembly documentation I decided I'd try to match wear patterns on the six shims that are installed in two packs of three shims.





Making some progress with the oscillator reassembly:



Note the 2C43 transmitting triode:


The reassembled unit with a couple new 30D capacitors:






I checked all of the transistors on a 7CT1N and all tested good. So far, so good..
Before installing the tubes and time delay relay, I powered the unit up and observed the power supply voltages and ripple:

The 450V supply measured 485V with no load
The -11V supply measured -12.6V before adjustment and -11.2V after adjustment, which is now maxed out.
The 6.8V supply measured 6.82V.

The ripple on the -11V and 6.8V supplies seem in spec according to some single ended measurements.

I proceeded to install the tubes and relay and power up the unit again, which didn't result in a release of any magic smoke! 

However, there was absolutely no output from the detector head, which was no surprise as I had already had a staring contest with the filter board.

Upon probing the signal path, I found that the 3Mhz oscillator had a strong, correct output. The 65-500Mhz oscillator also had output, although at varying amplitudes. So why no output from the detector head?  Well, the signal exists up to the input to the filter board, but no such signal (or none whatsoever) exists at the output.

Time to pull the filter board:



Yep, peep those "unobtanium" SPDT reed relays! 
All of the coils were measured and appear to be in working order. 
All of the reed switches were measured for resistance on the N/C contacts and some have a couple ohms of contact resistance. Two have no contact.
I connected my leads to the N/O contact and actuated them with a neodymium magnet and found that two will not make contact. The same two that had no contact in the N/C position.

The two failed reed switches reside in the top left coil (K199 - directly before the output to the detector head) and the bottom right coil (K111 - the first relay after the signal input to the filter board).

The reed switches of those two relays were then CAREFULLY desoldered and removed:


It appears that they're a standard physical size that is readily available. ~2.54mm x 14.7mm.
I tried to find a Tektronix Electro-mechanical parts book to get the electrical specs, but I've had no such luck.  I don't know much at all about reed switches, so it's time to get an education. From a quick look, I think the main thing I'll need to pay attention to is the AT (Ampere-turn) ratings.

 I just couldn't help myself, though, so I've already ordered a handful of various SPDT N/O N/C reed relays to experiment with.

More to come...

[WB8PFZ]

The oscillator unit looks like a General Radio unit.

[Addicted2AnalogTek]

I'm quite certain that it is. The schematic just says "Tek Modified" and references part number E119-0132-01.  The 067-0532-01 manual has a section dedicated to the oscillator unit, which is  labelled "General Radio type 1369-9000 UHF Oscillator".

Might as well add some update information:
I've ordered some reed switches to experiment with from the MDRR-DT line of Hamlin/Littlefuse SPDT reed switches.
Pull-in ranges purchased are 10-15 AT, 15-20 AT, and 15-25 AT. 

[Addicted2AnalogTek]

So far, so good.

I replaced the 260-0721-00 SPDT reed switches with Littlefuse P/N: MDRR-DT-15-25-F
(For search reference, these reed switches are inside of coil Tek P/N: 108-0358-00).





SUCCESS!!
The following photo is of the 3Mhz reference output at 1V.

In the 3Mhz mode, and after a little adjustment of the R34 Amplitude Cal pot, the output shown on the scope is correct in all ranges.

However, there is still work to be done.
When the 65-500Mhz oscillator is switched in, I have correct output frequency in all ranges, but the following issues exist:

Correct voltage output only up to 1.5V and only up to 77Mhz, which is where the 300Mhz filter is switched in. With any selection above 1.5V there is no additional change in amplitude.
Correct output voltage only up to 1V with the 108Mhz and 180Mhz filters switched in. With any selection above 1V there is no additional change in output.
Output voltage with the 108Mhz, 180Mhz, and 300Mhz filters switched in varies in amplitude but does not exceed 0.5V.

I think the contact resistance in the old reed switches is problematic and I have added four more to my next parts order, which will be placed tonight. I don't think that alone is going to wrap up this project, though. I'm sure I'll have other issues to sort out, and as much as I'd like to avoid it, I'll probably open the oscillator can again and replace the 2C43 tube and the shaft that I epoxied back together.

More to come in a week or so...

Note: BOLD text is edit.