3B3 Time Base Interesting Problem


unclebanjoman
 

If you don't have a 6BL8 handy, you can try using the one used in the delayed sweep circuit (V261, the Miller integrator circuit is identical)

Remember that tunnel diodes cannot be tested as a normal diode with some diode tester. A curve tracer (and GREAT precautions) is mandatory.
Apart from that an excessive current from the digital multimeter could burn it, they would result as a short in both directions, so it's impossible to determine they are good or not.

To check if they work just see with an oscilloscope if they switch (approx 200/300 mV between OFF state and ON state).
Do not unsolder them unless you are reasonably sure they are faulty. They are very delicate and almost impossible to find.

Max


 

Thank you Max, I will indeed revisit the 6BL8. I checked all the tubes and they seemed fine on my Philco 7052 (which is a re-badged Hickok 533A). However, it may have been marginal. Too, I have ran across too many tubes that look good on the tester, yet fail to work properly in some Tek circuits.

All the tunnel diodes are in place (I looked to make sure they had not been made off with). However, They have not been checked. Will check the tube first, then address the condition of the TD's.

Thanks again.

On 5/31/22 07:42, unclebanjoman wrote:
Hi Jerome,
I read only now your post.
The symptoms you describe are different faults.
The first, trace moving backwards at very low time/div is due to the miller run-up not working properly. The culprit is in the V161 tube: If the gain of the pentode section drops due to aging, the Miller run-up shows exactly this behavior.
Put in a new 6BL8 (replaceable with a ECF80 also) and the sweep section will return fully functional.

Regarding the second problem (no sweep triggering): check first if all tunnel diodes are present.
Due to their rarity, they are often plundered. It happened to me with my 3B4: fully functional but the tunnel diodes had been removed. Result: a very poor and insensitive trigger.
If they're in place trace the trigger signal path starting from V13. On the schematics there are some waveforms that will help.

I hope I have given you useful information.
With instruments of such type you need to be prepared for the fact that sooner or later there will always be one (of tubes) to replace.

Max




unclebanjoman
 

Hi Jerome,
I read only now your post.
The symptoms you describe are different faults.
The first, trace moving backwards at very low time/div is due to the miller run-up not working properly. The culprit is in the V161 tube: If the gain of the pentode section drops due to aging, the Miller run-up shows exactly this behavior.
Put in a new 6BL8 (replaceable with a ECF80 also) and the sweep section will return fully functional.

Regarding the second problem (no sweep triggering): check first if all tunnel diodes are present.
Due to their rarity, they are often plundered. It happened to me with my 3B4: fully functional but the tunnel diodes had been removed. Result: a very poor and insensitive trigger.
If they're in place trace the trigger signal path starting from V13. On the schematics there are some waveforms that will help.

I hope I have given you useful information.
With instruments of such type you need to be prepared for the fact that sooner or later there will always be one (of tubes) to replace.

Max


Jim Adney
 

On Wed, May 11, 2022 at 10:12 PM, Bruce Atwood wrote:

Check that the blanking (unblanking) is working correctly. Your backwards trace motion could be retrace.
If your physical comparison of your two 3B3s reveals nothing, my money would be here, with Bruce's suggestion.


Jim Adney
 

On Wed, May 11, 2022 at 04:44 PM, Jim Adney wrote:

I always thought the 3B4 was the better timebase plugin. Should I take a better look at the 3B3?
Now that I've taken a better look, it appears that the 3B3 is a better timebase than the 3B4. It originally cost about 1.5x the price of a 3B4 because it has a nice delayed trigger and sweep.. Looks to be the best of the 3 series timebase plugins. I have several extra 3B3s, so I could be persuaded to part with a couple.


Joel B Walker
 

I mistyped the model number. 067-0591-00.


Bruce Atwood
 

Check that the blanking (unblanking) is working correctly. Your backwards trace motion could be retrace.


 

Let me look at the 3A6 Jim, that is one plugin I am not familiar with. I am certainly interested though. Send me an email at jeromeleach17 at gmail.

On 5/11/22 17:47, Jim Adney wrote:
Another plug-in that is difficult to find in restorable condition in the 3A1.
The better choice is the 3A6, which is just a 3A1 with a delay line, so the scope can display the event that triggers the sweep. I've only got one 3A1, but I have several 3A6s, all in good cosmetic and working condition. Make me an offer.




Jim Adney
 

Another plug-in that is difficult to find in restorable condition in the 3A1.
The better choice is the 3A6, which is just a 3A1 with a delay line, so the scope can display the event that triggers the sweep. I've only got one 3A1, but I have several 3A6s, all in good cosmetic and working condition. Make me an offer.


Jim Adney
 

I would love to have a 3B3. I have been halfway looking for one to jump in my lap, but it hasn't happened yet.
I've got several 3B3s, all in good working and cosmetic condition. Make me an offer.

I always thought the 3B4 was the better timebase plugin. Should I take a better look at the 3B3?


Joel B Walker
 

I have a 3A1. It's pretty nice. I also have a couple of 2A63's, a 3A74, a 3A9, a 3L5, a Nelson-Ross PSA321, and a Nelson-Ross Model ??. Can't remember the model number. Have a 067-0581-00 calibration adapter on the way. I have looked on the 'bay for a 3B3, and have seen a couple. I missed what looked to be a really nice one. There is one on there that looks like the owner didn't know about the locking screw to remove it from the scope. It appears to have been pried out with a crowbar.


 

The 2B67 is a decent, although basic, timebase. I don't have one, but I do
have a 67, which is the predecessor of the 2B67. Just doesn't have single
sweep. Until I got the 3B4 restored, that was what I had in the 561A.

Another plug-in that is difficult to find in restorable condition in the
3A1. Been looking for a candidate for several years now with no joy. My 3A1
resides in the 564B, but like my working 3B3, is beat up pretty badly.

On Wed, May 11, 2022, 10:37 AM Jerome D Leach via groups.io <jeromeleach17=
gmail.com@groups.io> wrote:

I certainly don't have all the 560 series time-bases, but I have a few. As
for usefulness, the 3B3 is at the top. Pretty much next is the 3B4.

And I can feel your pain Joel. I don't need another 3B3, but I have looked
at several up for sale in the past few years. ALL of them were pretty much
trashed. I recall one that looked like it spent some quality time with the
fishies.

On Wed, May 11, 2022, 10:12 AM Joel B Walker <joelandjoyce@...>
wrote:

I would love to have a 3B3. I have been halfway looking for one to jump
in
my lap, but it hasn't happened yet. All I have for my 561A and R564B Mod
121 for timebases is 2 2B67's.










 

I certainly don't have all the 560 series time-bases, but I have a few. As
for usefulness, the 3B3 is at the top. Pretty much next is the 3B4.

And I can feel your pain Joel. I don't need another 3B3, but I have looked
at several up for sale in the past few years. ALL of them were pretty much
trashed. I recall one that looked like it spent some quality time with the
fishies.

On Wed, May 11, 2022, 10:12 AM Joel B Walker <joelandjoyce@...> wrote:

I would love to have a 3B3. I have been halfway looking for one to jump in
my lap, but it hasn't happened yet. All I have for my 561A and R564B Mod
121 for timebases is 2 2B67's.






Joel B Walker
 

I would love to have a 3B3. I have been halfway looking for one to jump in my lap, but it hasn't happened yet. All I have for my 561A and R564B Mod 121 for timebases is 2 2B67's.


 

All suggestions a comments are help Joel, and I take them into
consideration. When I hook it back up to the scope with the extender, the
voltage checks will find the problem, if it is rail related.

On Wed, May 11, 2022, 12:00 AM Joel B Walker <joelandjoyce@...> wrote:

To me, with all the different symptoms that are seemingly unrelated to
each other, would seem to point to a power supply rail within the plugin
that is either dead or way off spec. Just my opinion, of course.






Jim Adney
 

Yes, I've another 3B3. I use it in my 564B, and of course, it sweeps correctly.
Okay, so we know the problem is within the 3B3. I'd start by putting your two 3B3s side by side and comparing the wiring of the plugin connector. Start with the 2 wires for the horizontal output. If those have been switched, check the others, since you now know that someone put these back somewhat randomly.

Make sure you don't get confused and start changing the good 3B3. Unless it's obvious, mark the good one GOOD. ;-)


Joel B Walker
 

To me, with all the different symptoms that are seemingly unrelated to each other, would seem to point to a power supply rail within the plugin that is either dead or way off spec. Just my opinion, of course.


 

As to the issue with the plugin, it has me rather baffled. Been thinking about pulling my good 3B3 from the 564B, and literally comparing them to see if anything is different. The two plugins are not that far apart in serial number, so should be pretty much identical.

After doing a comparison, my plan is to get out the extender and start doing voltage and signal tracing and see where that leads.

The symptoms are: Trace only extends from the right edge of the CRT to the last vertical graticule line before the center line of the CRT.

Trace will not trigger, but can be moved with horizontal control.

Trace disappears when Coupling lever is put into AC or DC positions.

Time/Div control appears to work, as does the Variable control. Can slow it down to clearly see the calibrator square wave.

There appears to be action when switching to Delay or Intensify.

As already stated, the trace when slowed down to say, .1 seconds, the dot progresses from the right edge of the CRT to that aforementioned graticule line, then repeats. However, when the trace stops, it leaves a constant bright spot at the end.

On 5/10/22 09:26, Jerome D Leach via groups.io wrote:
Thank you for the response Jim. Yes, I've another 3B3. I use it in my 564B,
and of course, it sweeps correctly. The 3B3 in the 564B works well, just
pretty beat up. The one I'm working on is much nicer, with no evidence it
has been tampered with. Apparently came from the Mayo Clinic (has their tag
on the rear panel).

On Tue, May 10, 2022, 8:55 AM Jim Adney <jadney@...> wrote:

The interesting part is that as the trace sweeps, it is going backwards,
or
from right to left. I verified this behavior by slowing down the sweep.
The
dot indeed is going backwards.
Do you have another time base that tracks correctly, Left to Right? If
not, it's possible that the wires to the horizontal deflection plate pins
have been swapped. That would be an easy fix.

If you have other timebase plugins that sweep correctly, then you'll have
to figure out where this 3B3 went wrong. I've got several 3B3s and the
manuals, so I may be able to help if you get into this.







 

Thank you for the response Jim. Yes, I've another 3B3. I use it in my 564B,
and of course, it sweeps correctly. The 3B3 in the 564B works well, just
pretty beat up. The one I'm working on is much nicer, with no evidence it
has been tampered with. Apparently came from the Mayo Clinic (has their tag
on the rear panel).

On Tue, May 10, 2022, 8:55 AM Jim Adney <jadney@...> wrote:

The interesting part is that as the trace sweeps, it is going backwards,
or
from right to left. I verified this behavior by slowing down the sweep.
The
dot indeed is going backwards.
Do you have another time base that tracks correctly, Left to Right? If
not, it's possible that the wires to the horizontal deflection plate pins
have been swapped. That would be an easy fix.

If you have other timebase plugins that sweep correctly, then you'll have
to figure out where this 3B3 went wrong. I've got several 3B3s and the
manuals, so I may be able to help if you get into this.






Jim Adney
 

The interesting part is that as the trace sweeps, it is going backwards, or
from right to left. I verified this behavior by slowing down the sweep. The
dot indeed is going backwards.
Do you have another time base that tracks correctly, Left to Right? If not, it's possible that the wires to the horizontal deflection plate pins have been swapped. That would be an easy fix.

If you have other timebase plugins that sweep correctly, then you'll have to figure out where this 3B3 went wrong. I've got several 3B3s and the manuals, so I may be able to help if you get into this.