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561 scope extender wiring?


 

Since I'm going to be working on this 3T77A plug-in for a while, an extender is necessary. Some years ago I acquired a pair of Amphenol connectors with the intention of building my own extender, but never got around to it.

Does anyone have a schematic so I don't have to figure it out from the 561 manual (I imagine most connections are simple pin-to-pin but do I use coax or twisted pair for the deflection signals?)

thanks

Charles


 

I took a look at the schematic of the 561A. It appears that only pins 3/4 and 18/19 use coax to carry fast signals (trigger to timebase, strobe to sampling plug-in).
Still wondering what the deflection plates should use - would twisted pair be ok?


Albert Otten
 

Hi Charles,

You will have seen that the coax to pines 3 and 4 has a crossover between left and right connector. For fault finding in the 3T77A I would do as in the time base connector, that is with braid to pin 4. Don't connect the braid to the ground wire! The other coax at pins 18/19 is straightforward.
BUT as far as I can see the 3S2 makes no use of pins 3/4, so cannot trigger the 7T11A internally. In the 3S2 diagrams you can see that the trigger signal merely goes to the Trigger Out front panel connector.
In my extender I used ordinary wire, not twisted or whatever. Remember that you normally won't use the extender during (HF) calibration. IIRC all adjustments can be reached from the left and right side of the oscilloscope.

Albert


Albert Otten
 

I meant ordinary wire except for the coax lines.

In my extender I used ordinary wire, not twisted or whatever.


 

I had an "interesting" afternoon. First I made the extender (including running coax for the other pins even though it looks like you're right and the 3S2 doesn't use them).
Then I slipped while measuring the voltages at the plug-in and took out the regulator in the 561A. Actually the +300 was wide-open, almost to the +420 unreg. That took a while to find - because the added diode (to prevent the grid on the 6AS7 from going positive) that shorted was 1) not in the manual OR the change info in my copy and 2) well-hidden under the resistors on the ceramic strips! Fixed that.
Moved the extender and another "zap". One tiny strand of braid had touched the 120 VAC next to it. Replaced the scope fuse and cleaned THAT up.
Plugged the extender cable back in - nothing working on the plug-in... then red glow and bubbling from the 561A!! Fried half of R667. Then I realized I'd plugged the cable into the wrong edge connector on the back of the 3T77A. Why did Tek make them identical.... sigh.
Time for a break.


Albert Otten
 

Hi Charles,

The diode is shown in the 564 schematic, being added at 564 S/N 2980. From the serial numbers of my 564s I conclude that this must have been somewhere in 1964.
You undoubtedly were the first person with such bad luck ...


Albert

On Wed, Feb 10, 2021 at 02:35 AM, Charles wrote:


I had an "interesting" afternoon. First I made the extender (including running
coax for the other pins even though it looks like you're right and the 3S2
doesn't use them).
Then I slipped while measuring the voltages at the plug-in and took out the
regulator in the 561A. Actually the +300 was wide-open, almost to the +420
unreg. That took a while to find - because the added diode (to prevent the
grid on the 6AS7 from going positive) that shorted was 1) not in the manual OR
the change info in my copy and 2) well-hidden under the resistors on the
ceramic strips! Fixed that.
Moved the extender and another "zap". One tiny strand of braid had touched the
120 VAC next to it. Replaced the scope fuse and cleaned THAT up.
Plugged the extender cable back in - nothing working on the plug-in... then
red glow and bubbling from the 561A!! Fried half of R667. Then I realized I'd
plugged the cable into the wrong edge connector on the back of the 3T77A. Why
did Tek make them identical.... sigh.
Time for a break.