Repair/Restoration of a Tek Type 561B

[med6753]

Received the 3A6 Vertical Plug-in. Not too dirty and complete but there was some shipping damage.

The front panel. The detent for the Channel 1 variable is broken at the pot. I have the broken piece and it should be repairable.



View inside. This is a true “hybrid” plug-in and represents the revolution in electronics packaging that was taking place in 1960's. First we have two sub-minature 7586 high frequency vacuum tubes called “nuvistors”. When FET's appeared around the same time they became obsolete. In between the nuvistors are discrete transistors. And in the background conventional 7 and 9 pin minature vacuum tubes. I believe the Tek 500 series and plug-ins were the last designs to incorporate vacuum tubes in their design. Everything beyond that went either discrete solid state or starting in the early 1970's to IC's. 



Damage. Both output peaking coils have broken posts on the top. One looks like it happen before and was glued. It appears all the coil wire is there and in tact. So I will remove the coils and carefully glue the wires and use emory paper on the wire ends to solder additional wire and reattach them to those large resistors. It will take time and careful prep but it should work.

[med6753]

Started on the can replacement. Three done so far. 2 more to go.



The vanquished.



With those cans removed there are more areas accessible to clean out the remaining dirt.

[Cubdriver]

Mike, if your inclination is to shitecan the cans, perhaps I could prevail upon you to save them and at some point I'll send you what it should cost and you could to mail them to me.  I'll then restuff them and keep them ready to swap out on mine to save time, as I like to do things the hard way.   

-Pat

[med6753]

Mike, if your inclination is to shitecan the cans, perhaps I could prevail upon you to save them and at some point I'll send you what it should cost and you could to mail them to me.  I'll then restuff them and keep them ready to swap out on mine to save time, as I like to do things the hard way.   

-Pat

It wasn't just an inclination....it was an absolute intention to shit can them.  But if want them I'll save them and send them to you. I should finish with the other two by tomorrow so next week if you want them that soon. Contact me via PM.   

[Cubdriver]

Mike, if your inclination is to shitecan the cans, perhaps I could prevail upon you to save them and at some point I'll send you what it should cost and you could to mail them to me.  I'll then restuff them and keep them ready to swap out on mine to save time, as I like to do things the hard way.   

-Pat

It wasn't just an inclination....it was an absolute intention to shit can them.  But if want them I'll save them and send them to you. I should finish with the other two by tomorrow so next week if you want them that soon. Contact me via PM.   

Yes, please save them for me.  I'll be in touch via PM; hitting the sack now.

-Pat

[med6753]

Re-cap of the cans finally complete. Took longer than anticipated because of the tight area.

Backside view of the new capacitors on terminal strips.



Front view. The power supply board can now be reinstalled then will apply power. That will be next installment.



Pat, send me a PM and I'll get the old caps on their way to you early next week.

[med6753]

Update of this Type 561B restoration. Two major set backs and some progress.

First major set back: Yes, I should have used a series lamp limiter upon first try at power up. I didn't and I paid the price. Even though I triple checked the perimeter wiring on the power supply board I did swap 2 wires with very similar color codes. The result was approx 300V applied to an area that should only see 125V. Yes, a lot of flames and magic smoke. The carnage was 4 blown transistors and 4 carbon comp resistors vaporized. 3 of the transistors are common types still available. But the TO-3 series regulator is Tek spec and unobtanium. I was able to cross reference a sub but thanks to forum member cycle_collector he had a stock in the vast stash of Tek parts he has for sale. Thanks to him I have an exact replacement. I hope to have all repairs completed in a few days.

The next setback: One of the broken peaking coils on the 3A6 Vertical plug-in is open which makes the plug-in unusable. Replacement unobtanium. Looking for an alternative but what complicates matters is that it's a 3 wire center tapped adjustable coil. I haven't totally given up bodging some sort of fix but in the meantime I found a reasonably priced 3A3 that I should have in a few days.

Some progress: The 2B67 Time Base plug-in which was stripped of all it's tubes will now be put into service. It's tube complement is one – 6BJ7, two – 6BL8, and six – 6DJ8. I had the 6BL8's on hand. The 6BJ7 cost $10 USD and will arrive early next week. But the score was I won an Ebay auction for five – 6DJ8 for the sum of $19.50. They are Sylvania marked non-Bugle Boy not matched but tested which is why they were cheap. Audiophools frown on anything other than Bugle Boys. As far as I'm concerned I'm sure they will work just fine. And I was able to scrounge one more 6DJ8 so all this plug-in needs is the 6BJ7.     

[Cubdriver]

Great score on those 6DJ8s, Mike!   

-Pat

[med6753]

How quickly fortunes change. The Type 561B is repaired and now powers up. No drama, no magic smoke.


The 4 voltages (+300V, +125V, -12.2V and -100V) are just about on the mark without any plug-ins installed. I will make final adjustments after both plug-ins are in place.

I even have a spot of the CRT which says I have HV. (I turned the intensity down after the pix so as to not burn a spot in the phosphor)

Next step. Awaiting delivery of the 3A3 Vertical plug-in and the 6BJ7 tube for the 2B67 Time Base plug-in.

Sorry for the lousy focus. Camera phone doesn't do well on close ups.

[Smoky]

These two plug-ins were included with an old 310 oscilloscope I bought at a garage sale.

Parts are missing from both. One is a 3A1 and the other is 3B1. Both are corroded from the North Carolina humidity.

I do see about six coils with three wires on them.

I'll be happy to pull them and even measure them on my LC53 or LC102 if needed.

[med6753]

These two plug-ins were included with an old 310 oscilloscope I bought at a garage sale.

Parts are missing from both. One is a 3A1 and the other is 3B1. Both are corroded from the North Carolina humidity.

I do see about six coils with three wires on them.

I'll be happy to pull them and even measure them on my LC53 or LC102 if needed.


(Attachment Link)

I just checked the 3A1 service manual and yes, peaking coils L361 and L371 on your plug-in are the same P/N as used on the 3A6. Tek P/N 114-151. I would greatly appreciate getting them from you. Hit me up with a PM and we'll talk.  Thanks!

[jxjbsd]

These two plug-ins were included with an old 310 oscilloscope I bought at a garage sale.

Parts are missing from both. One is a 3A1 and the other is 3B1. Both are corroded from the North Carolina humidity.

I do see about six coils with three wires on them.

I'll be happy to pull them and even measure them on my LC53 or LC102 if needed.


(Attachment Link)

It seems that there are many friends who like old-fashioned Tektronix oscilloscopes. I need to save money, buy a bigger house, or stop collecting oscilloscopes

[med6753]

These two plug-ins were included with an old 310 oscilloscope I bought at a garage sale.

Parts are missing from both. One is a 3A1 and the other is 3B1. Both are corroded from the North Carolina humidity.

I do see about six coils with three wires on them.

I'll be happy to pull them and even measure them on my LC53 or LC102 if needed.


(Attachment Link)

It seems that there are many friends who like old-fashioned Tektronix oscilloscopes. I need to save money, buy a bigger house, or stop collecting oscilloscopes

Once you start collecting you can't stop. And the Type 561B is small compared with this monster. 

[jxjbsd]

So I only collect things from the transistor era. The small size is one aspect, mainly because Tektronix oscilloscopes with electron tubes are hardly seen in China.

[med6753]

More work on Type 561B mainframe....

The original incandescent pilot lamp was burnt out. It uses miniature colored lamps that I didn't even bother to look for. Replaced it with this LED assembly. But the lamp operated on 6.3VAC so the LED required the addition of a diode, capacitor, and current limiting resistor. This is the result.

The mainframe is now complete and the balance of the restoration is pending the arrival of the parts for the plug-ins.   

[med6753]

The new carrying handle. Forgot all about it. Replaces the original which was damaged beyond repair. I have to notch the covers to clear the mounting screws.



No deliveries today because of our National Memorial Day. 

[med6753]

The Type 3A3 Vertical Plug-in arrived as well as the 6BJ7 tube for the Type 2B67 Time Base Plug-in.

The Type 3A3 is very clean and appears complete. Deoxit'ed the switches and controls.




Time to install and power up as a complete unit.

[med6753]

Close but no cigar. The PSU voltages are set. The -100VDC is the only adjustment and it serves as a reference for the other PSU voltages and they are in spec.

With both plug-in's installed there is no trace. If I pull the Type 3A3 I get a trace. The Type 2B67 is sweeping but that is also intermittent. So progress but additional troubleshooting is needed.



At least there's no magic smoke. 

[med6753]

Troubleshooting the Type 3A3 Vertical Plug-in and found the issue.

One vertical deflection plate had +165V on it (normal). The other vertical deflection plate had -76V on it (definitely not normal).

See schematic. R679 (8K/3W) is open killing the B+ to pin 9 of V674.



The open resistor is top far left. I'll have to see if I can cobble something together from my parts stash. 

[med6753]

Progress and more issues have shown up.

Replacement of the 8K/3W resistor in the Type 3A3 Vertical Plug-in fixed the no trace issue. Now have full control of a base line trace both vertically and horizontally.

The Type 2B67 Time Base refuses to have trigger lock. Comes close but then drifts. Extremely touchy adjustment of the Stability and Trigger Level. In order to troubleshoot this I may have to build up an extension cable so the plug-in can be operated outside the scope to gain access to the component side. But I'm going to hold off until the Type 3A6 plug-in is repaired in case there is a compatibility issue with this Type 3A3.




Other issues:

The Calibrator is totally dead. I suspect it might have gotten fried when there was the fireworks. That's low priority right now.

Bigger concern is the CRT. It's not as bright as it should be and it is displaying what is called “double peaking”. As you turn up the intensity it gets brighter, then darker, then brighter. That is a sure sign of a worn out CRT with many hours on it. I will be checking the CRT bias and HV but I doubt that's the problem. The CRT is near end of life but right now still usable with a sharp, if someone dull, trace. 

[med6753]

A public thank you to fellow forum member Smoky. He generously sent me 2 new peaking coils for the Type 3A6 Vertical plug-in. Now installed and this plug-in is ready for testing.

But unfortunately the Type 561B mainframe has a new issue that must be worked out first. More later.

[med6753]

One step forward, 2 steps back. Another setback on this restoration.

The CRT may not be defective. Measured the HV and it's -1.6KV. It should be -3.3KV. Adjustment of the HV control yielded no difference. Decided to check the primary side of the HV oscillator and I accidentally shorted the collector of the TO-66 output transistor to ground. The 125ma HV fuse blew and I was hopeful that's all that went out. Not the case. Lost that transistor. Got one coming from Ebay but this project is on hold until it's replaced.

I suspect the low HV is due to an open resistor in the focus divider. It's a very common issue. So while I'm waiting for the replacement transistor I'm going to pull the entire HV assembly and check all the resistors.   

[Cubdriver]

Damn.  We need to get you some test prods with everything but the very tip insulated!  I hope that the transistor was all that it took out and you can get back to business once the replacement arrives.  That's gotta be frustrating!   

-Pat

[med6753]

It wasn't the test lead. I was going to scope the oscillator signal after verifying all the DC voltages were correct. I went to clip the ground lead on the chassis not realizing I was right near where the transistor was mounted. Saw a little spark and had an "aw shit" moment. The ground clip also contacted the collector of the TO-66 transistor. HV fuse blew but it was too late. 

[Cubdriver]

It wasn't the test lead. I was going to scope the oscillator signal after verifying all the DC voltages were correct. I went to clip the ground lead on the chassis not realizing I was right near where the transistor was mounted. Saw a little spark and had an "aw shit" moment. The ground clip also contacted the collector of the TO-66 transistor. HV fuse blew but it was too late. 

The protection circuit obviously failed, then.  Normally the semiconductor blows to protect the fuse!

-Pat