Repair/Restoration of a Tek Type 561B

[med6753]

The latest project here is this basket case Tek  Type 561B. If I didn't get it REAL cheap I would have passed it by. It came with Type 3A72 Vertical plug-in and Type 2B67 Time Base plug-in.

Front panel. It's all there just needs a good cleaning and sticker residue removed.



Handle missing. I have leather strapping plus leather tools. Used them to successfully make new handles for a Type 535A. Both cabinet halfs are banged up and scratched. Will hammer out the dents and repaint.



A look inside. It's complete but absolutely filthy. Before any testing will give it a complete dry clean.




Front view of the plug-in's. Not too bad but inside tells a different story. Tube raiders struck. Both plug-in's stripped of all their tubes. I knew this when I went to look at it and decided to go forward anyway. The Type 3A72 has a B/W of only 650Khz. Pathetic. So I'll go out on Ebay for a better Vertical plug-in. The Type 2B67 Time Base plug-in is a decent unit but it would cost hundred's to re-tube it. So I'll also look for another Time Base plug-in.




So once cleaned up next step is to check the filter caps for shorts. The Type 561B mainframe is actually pretty simple compared to other Tek's. It's basically a power supply, HV supply, and CRT. The vertical and time base circuits are all in the plug-in's. So I'm going to concentrate on getting the mainframe complete before investing in plug-in's.

I'll update this thread as I make progress.     

[jxjbsd]

Thank you very much. I can see the wonderful repair process. I saw a 3a75 plug-in for $90, and the seller said it was an electronic tube hifi amplifier . But there is only 4m bandwidth.

[med6753]

The cleaning process completed.

The front panel came clean with all sticker residue removed except for a few scuffs. There was a clear plastic lens between the CRT face plate and the bezel that had deep scratches so I removed it. It may affect the light distribution of the scale illumination but that's no big deal.



The covers have been removed and cleaned. Currently out for dent removal and repaint. The interior is now clean. Compare that with yesterday.




This is the power supply/calibrator board. In order to gain access to the filter capacitors this board and all that perimeter wiring has to be removed. So I've decided rather than pulling it out and checking for shorts I'm going to do a mass replace. I am not an advocate of  “re-forming” capacitors, especially ones 50 years old. It's false economy. Better to replace.



I did some quickie checking and both the line fuse and the HV fuse are good. So that is very encouraging. I am also going to check the four TO-3 transistors on the rear heatsink. Next installment should have the covers painted and replaced.   

[Specmaster]

Thats a great transformation, almost as good as new 

[med6753]

Mechanical restoration essentially complete. The original remnants of the broken handle assembly were damaged beyond repair so it was removed. I have other alternatives in mind for a replacement. And the line cord needs a new strain relief.

Next step is the electrical repair/restoration. The replacement capacitors have been ordered and should arrive Tuesday. Will provide an update when that process begins.   

[Specmaster]

What a difference a nice coat of paint makes

[Kosmic]

Yep, looking good 

I need to do the some thing on my Power designs PSU. They used also the same color as Tek on their casing.

[Cubdriver]

Nice work, Mike.  Shame that the tube vultures picked it clean.  Mostly 6DJ8s missing?

-Pat

[med6753]

Nice work, Mike.  Shame that the tube vultures picked it clean.  Mostly 6DJ8s missing?

-Pat

Yep, between the 2 plug-in's at least 10 of the tubes were 6DJ8 "Bugle Boys" which drive the audiophools rabid with delight. Along with several 6BL8's and 6AU6's. And I'm finding plug-in's going for stupid money on Ebay that have been raped too.   

[Cubdriver]

Yep.  I accidentally bought some from a tube rapist.  Was searching for a 3-series time base and found two plus a vertical one for pretty cheap as a buy it now.  They'd been stripped, of course, but I snagged them anyway figuring that ultimately I'll re-tube them.  After placing the order, I did a "see seller's other auctions" search only to discover he was also selling tubes from various Tek scopes.     

Part of me feels bad for in effect 'encouraging' him, but at the same time I may have saved those plug ins from the landfill.  I dunno.  I'm not looking forward to buying the tubes though, because yeah, it needs a bunch of them!

-Pat

[jxjbsd]

If you can buy electronic tubes made in China, you can replace them. Replace 6dj8 with 6n11, about $5-10 each, the performance is the same. Other types of electronic tubes should be inexpensive.

[mnementh]

 

mnem
sssh. I'm not really here.

[coromonadalix]

Nice to see dedicated people 

[jdragoset]

Very nice work.
Don't toss the CRT face plate.
It can be buffed out or even plastic headlamp-lens restored.

[nixiefreqq]

ahhhhhhh.   that's the stuff.

[med6753]

More work on this Type 561B.


Got the power supply board removed. A chart and lots of pictures for the approx 40 wires that had to come off. Once removed and cleaned with IPA issues reared their ugly head. Evidence of some capacitor leakage corrosion. Evidence of some prior repairs. And in the lower left a burn and bodge repair. It looks like a resistor burned and rather than replaced was bypassed. I'll investigate further after completing the re-cap of the board.




Here are the capacitor cans that were hidden behind the power supply board. They will all be removed and replaced with new on terminal strips on opposite side. I used this technique on the Type 535A restore and it worked well.



I found reasonably priced (and complete) Type 3A6 Vertical plug-in on Ebay that should arrive this week. Still looking for a Time Base that is complete and reasonably priced. 

[Specmaster]

Oh dear that looks nasty, I hope that the board is not a multilayer otherwise you could be wasting your time and money recapping it. I'd check the board out first and see how many layers it is, keeping my fingers crossed that is repairable.

[med6753]

Oh dear that looks nasty, I hope that the board is not a multilayer otherwise you could be wasting your time and money recapping it. I'd check the board out first and see how many layers it is, keeping my fingers crossed that is repairable.

It's only 2 layer. Top side and bottom side. I checked out the circuit. It's for the -100VDC supply and it also supplies voltage to HV oscillator. The resistor was a 1.2 ohm in series between the transformer and the rectifier stack. Those 2 smaller diodes are replacements. I am going to assume the repair worked and for now I'll leave it. When I get it all back together I'll pull the fuse for the HV oscillator and make sure the -100V is OK. Then install the fuse and give it full beans and see what happens. 

[Cubdriver]

Damn!!  There's something to be said for multi-pole connectors, huh?  Nice work, Mike.

-Pat

[David Hess]

If you can buy electronic tubes made in China, you can replace them. Replace 6dj8 with 6n11, about $5-10 each, the performance is the same. Other types of electronic tubes should be inexpensive.

The performance may not be the same if Tektronix was grading the tubes.  Details would be in their common parts design catalog but I do not have the one for tubes.

[m2circuits]

The 561 is a great scope. I have the original 561 with the tube PSU, and use it regularly. It's particularly useful for tube audio applications.

If you're looking for an easier way to replace the multican caps I designed these PCBs a few years ago. They are available here: https://www.thetubestore.com/Multi-Capacitor-PC-Board

I restored a 561 with them and it was way easier than restuffing or using terminal strips. Here's a link to a blog I wrote about the project:
https://m2sbench.wordpress.com/2019/06/02/tektronix-561-oscilloscope-repair/

Cheers

[Specmaster]

Oh dear that looks nasty, I hope that the board is not a multilayer otherwise you could be wasting your time and money recapping it. I'd check the board out first and see how many layers it is, keeping my fingers crossed that is repairable.

It's only 2 layer. Top side and bottom side. I checked out the circuit. It's for the -100VDC supply and it also supplies voltage to HV oscillator. The resistor was a 1.2 ohm is series between the transformer and the rectifier stack. Those 2 smaller diodes are replacements. I am going to assume the repair worked and for now I'll leave it. When I get it all back together I'll pull the fuse for the HV oscillator and make sure the -100V is OK. Then install the fuse and give it full beans and see what happens. 

Well t seems that you have it  well under control so no need to be scared now that you've done your homework it'll be fine you'll see.

[med6753]

Quick update. The re-cap of the supply board is complete. There were only 4 electrolytics to change.

But I discovered an interesting flaw and a clue as to why that 1.2 ohm resistor was burnt. C31 is specified as a 6.8uf/100V. But it's installed across the -100VDC bus. Now granted, older electrolytic capacitors had a wide voltage tolerance but that's cutting it damn close. And apparently the original did fail as evidenced by corrosion in that section of the board. And what was installed was a 7uf/250V as a replacement. That makes sense and I think it explains the cooked and bodged rectifier stack for the -100VDC supply. And of course my replacement capacitor is 6.8uf/100V as specified in the parts list. I installed it for now but it can't stay there. New electrolytics do NOT like over voltage in the least. I'll order a higher rated cap and I may in fact pull that one and install a 10uf/150V + as a temporary measure.

Tomorrow I'll start on the cans.       

 

[Specmaster]

You could always leave the 10uF 150V cap there once you swap it out for 100V 6.8uF cap. going up in value slightly is perfectly OK and a 50% headroom in voltage is adequate I'm sure.

[med6753]

You could always leave the 10uF 150V cap there once you swap it out for 100V 6.8uF cap. going up in value slightly is perfectly OK and a 50% headroom in voltage is adequate I'm sure.

Yep, I know. I do that quite often. These old Tek's have some odd ball capacitor values in them that can be hard or impossible to source.

For example: 180uf/250V. If you can find them they are super expensive. 220uf/250V standard value works a treat.