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1S1 Sampling Unit risetime #photo-notice

 

In case anyone is interested in the 1S1 Sampling Unit, I uploaded some pictures of a risetime test:

/g/TekScopes/album?id=261760

The time/cm is set to 0.1 nanoseconds/cm and the scope displays a risetime of approximately 300 picoseconds, which is actually faster than the recommended 330-350 picoseconds that the manual suggests. (I should probably do all the calibration steps and adjust snap-off current for 340 picoseconds.) Anyway, I think a ~300 picosecond risetime is pretty good for a 55+ year old vacuum tube oscilloscope.

I am driving the input with a USB-powered "fast risetime pulse generator" from Leo Bodnar Electronics () connected through an SMA to GR-874 adapter. The actual risetime is 29 picoseconds.

I was worried when I got the 1S1 from eBay that it would have lots of problems, e.g., maybe the tunnel diodes would have drifted and stopped working, but this unit performs perfectly, as far as I can tell. I replaced the EMT, EMC, and PTM capacitors but that's it. It takes a long time to warm up and when it is cold the trace is noisy and drifts vertically all over the place, but once everything warms up it is quite stable. I thought sampling would compromise the quality of the trace but it really doesn't. Sure, the trace is made up of dots, but Tektronix made such good CRTs, those dots are finer than the pixels of a modern LCD screen (or so it seems to me).
 

That's really nice to see, and encourages me to get my 1S1 going. I
have a replacement 8056 nuvistor on the way (decided it was more
sensible for me to pay EUR8 for a valve than spend time fiddling
around with a FET substitute). What are the EMT, EMC and PTM
capacitors? I didn't come across those terms in my scan of the manual
so far.

Chris

On Thu, Mar 11, 2021 at 6:13 AM Jonathan Pyle <jhpyle@...> wrote:

In case anyone is interested in the 1S1 Sampling Unit, I uploaded some pictures of a risetime test:

/g/TekScopes/album?id=261760

The time/cm is set to 0.1 nanoseconds/cm and the scope displays a risetime of approximately 300 picoseconds, which is actually faster than the recommended 330-350 picoseconds that the manual suggests. (I should probably do all the calibration steps and adjust snap-off current for 340 picoseconds.) Anyway, I think a ~300 picosecond risetime is pretty good for a 55+ year old vacuum tube oscilloscope.

I am driving the input with a USB-powered "fast risetime pulse generator" from Leo Bodnar Electronics () connected through an SMA to GR-874 adapter. The actual risetime is 29 picoseconds.

I was worried when I got the 1S1 from eBay that it would have lots of problems, e.g., maybe the tunnel diodes would have drifted and stopped working, but this unit performs perfectly, as far as I can tell. I replaced the EMT, EMC, and PTM capacitors but that's it. It takes a long time to warm up and when it is cold the trace is noisy and drifts vertically all over the place, but once everything warms up it is quite stable. I thought sampling would compromise the quality of the trace but it really doesn't. Sure, the trace is made up of dots, but Tektronix made such good CRTs, those dots are finer than the pixels of a modern LCD screen (or so it seems to me).
 

Hi Chris,

In the parts list at the end of the manual, "EMT" and "EMC" are the acronyms that Tektronix uses to refer to electrolytic capacitors. On the 1S1, these are the power supply filter caps and there is also a small electrolytic on a switch as well. PTM is the acronym they use to refer to "paper or plastic, tubular, molded" capacitors. These are the bright yellow axial capacitors in the 1S1. Electrolytic capacitors definitely go bad over time, but whether "PTM" capacitors go bad over time probably depends on whether they are actually paper capacitors. The ones in the 1S1 probably aren't paper, but thought I should replace them anyway just to be on the safe side.

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