Repair/Restoration of a Tek Type 561B

[med6753]

This project is like a see-saw. Two steps forward and one step backward.

The Amplitude Calibrator is fixed. Turned out to be a dirty switch. Deoxit took care of it. This is surprising because the calibrator uses the +125V supply as it's source and that's the section of the PSU that had the spectacular flames and smoke the first time I installed the PSU board and accidentally swapped 2 wires and applied +300V to that area.

The 3A3 plug-in has successfully had it's gain and DC balance adjusted on both channels. The gain on both channels needed to be increased an equal amount apparently due to the decreased sensitivity of the weak CRT.

I made an offer on Ebay for a Type 3B3 Time Base plug-in that was accepted because.......

The Type 2B67 Time Base has gone out to lunch again and now refuses to trigger as before.  Was working fine and suddenly quit. I also have the Type 3A6 Vertical plug-in which has a trace on each channel that I can move vertically up and down but if you apply a signal it's a flat line. In order to troubleshoot these plug-in's I need an extender cable so I can access the component sides of each. I can fairly easily make one but the issue is the connectors. They are Amphenol 24 pin connectors but I have no idea what the Amphenol P/N is. I can salvage a male off a junker plug-in but the female side is the issue. Google search on the Tek P/N revealed a source but rather than list a price they want you to submit an RFQ. Oh goody, I wonder how far I'll have to bend over and spread them when I submit it. 

Speaking of the CRT. There's one on Ebay right now. Supposedly brand new. They want $100 USD plus shipping. They're nuts.  That's more than I paid last year for a CRT for the 7904. Granted, that one was used but still...I think a 561B CRT is worth maybe $50 USD at most. But this project has already turned into a semi money pit and unless the old CRT takes a complete dump it's staying in place. I got this entire Type 561B real cheap but it certainly ain't cheap now. But I'm a sucker for old Tek's.        

[tautech]

Keep those knees firmly together mate ! 

[David Hess]

The 3A3 plug-in has successfully had it's gain and DC balance adjusted on both channels. The gain on both channels needed to be increased an equal amount apparently due to the decreased sensitivity of the weak CRT.

CRT deflection does not change with age or use but acceleration voltage directly affects it.

CRT deflection sensitivity varies between units and 560 series plug-ins directly drive the CRT so the plug-ins need to be calibrated for each mainframe.  In most other Tektronix mainframes, the plug-ins drive internal amplifiers which are standardized for a specific sensitivity.

[med6753]

The 3A3 plug-in has successfully had it's gain and DC balance adjusted on both channels. The gain on both channels needed to be increased an equal amount apparently due to the decreased sensitivity of the weak CRT.

CRT deflection does not change with age or use but acceleration voltage directly affects it.

CRT deflection sensitivity varies between units and 560 series plug-ins directly drive the CRT so the plug-ins need to be calibrated for each mainframe.  In most other Tektronix mainframes, the plug-ins drive internal amplifiers which are standardized for a specific sensitivity.

I realize 560 series plug-in's directly drive the CRT. And that's why the gain adjustment is on the front panel. Except this 3A3. For some reason I guess driven by it's design the gain adjustments are inside. Not convenient if you need to move this plug-in to another scope.

But even the 500 series as well as the 7000 series plug-in's had gain adjustments on the front panel even though they drove an internal amplifier rather than the CRT directly.     

[David Hess]

I realize 560 series plug-in's directly drive the CRT. And that's why the gain adjustment is on the front panel. Except this 3A3. For some reason I guess driven by it's design the gain adjustments are inside. Not convenient if you need to move this plug-in to another scope.

But even the 500 series as well as the 7000 series plug-in's had gain adjustments on the front panel even though they drove an internal amplifier rather than the CRT directly.

But the variation in gain for the 500 and 7000 series is much less.  In practice the gain does not need to be adjusted between mainframes if they are standardized.

[med6753]

Been a while since I updated this thread and this repair/restoration is pretty much complete. There's still a few plug-in's that need repair but my immediate objective was to get the mainframe fully functional with functional vertical and time base plug-in's. That has been accomplished and as a bonus it also has a replacement CRT which is at least 2x brighter than the original which suffered from low emission.

Thanks to fellow blog member nixiefreqq I was able to get another Type 561B with Type's 3A74 and 3B4 plug-in's. This scope was from his local CL and he picked it up for me. It had been stored in a very damp environment for years and was in fair to poor condition. The Type 561B and 3B4 will be for parts. In fact, the 561B has already given up it's CRT which is in excellent condition and as mentioned above is nice and bright, and sharp. The Type 3A74 Vertical plug-in appears to be in decent shape and will eventually be checked out.

The scope has gone through several burn-in cycles with no issues. So this one is a wrap.   

[bitseeker]

Congrats, med! Such a cool scope.