Re: Looking to ID a diode in a 1S1 sampling plug-in


Ah, thank you, I'll look in to replacing it with a FET and will see what I
have in stock. I presume I'll have to do some modifications to keep the
heater chain current right: it looks like that interacts with the +19V

While a FET may be practical, there's part of me that really likes the idea
of a plugin containing both a load of tunnel diodes and a Nuvistor, for
maximum use of obscure devices!


On Mon, 1 Mar 2021, 22:34 Tom Lee, <> wrote:

The 8056 is the most transistor-like of all Nuvistors. If you are not
insistent on preserving original factory innards, you can replace that
Nuvistor with a JFET. You can even plug it directly into the Nuvistor
socket, so no mechanical mods are necessary. For details on that, see
the tekwiki page on the 422. The MPF102 suggested for the latter is
probably not a bad choice here, either. The gm is a little on the low
side, but that shouldn't matter much here at all. You will have to
readjust the staircase DC level trimmer, but that's par for the course
even when replacing a Nuvistor with another Nuvistor.

-- Cheers,

Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070

On 3/1/2021 13:14, cmjones01 wrote:
I've had a look in my 1S1 and the tunnel diodes seem to be a mix of tiny
beads like the ones in the OP's photo, and the gold "top-hat" style
I've always associated with Tek tunnel diodes.

One explanation for the trace being stuck off the bottom of the screen is
also clear. The Nuvistor and a nearby transistor are entirely missing, so
there will be no staircase being generated. Typically, the Nuvistor isn't
the same as the ones in any of my other plugins so I can't even borrow
to try. Time to go shopping for an 8056...


On Sun, 28 Feb 2021, 02:49 Sean Turner, <> wrote:


Make no mistake, I am not wanting to solder on tunnel diodes unless I
absolutely must.

Thanks for the insights!


On Sat, Feb 27, 2021 at 11:37 AM, Ed Breya wrote:

Sean, I don't know about the other diodes discussed earlier, but I have
those tiny glob ones with the dot (in the picture) before, in Tek and
gear. They could be just a different version (stripline) package for
TDs, or they could be "back-diodes," which are a close relative. As I
back-diodes are even more heavily doped than regular TDs, so they are
in forward bias at zero volts, and the interesting part of their
exists around the zero-crossing, and includes that small region that
kind of like a crappy TD. Your mention of the weird curve reminded me.
don't assume they're bad TDs just yet, until you study it some more.
in the circuit description or schematics it may become more clear. I
recall what the usual TD part designations are, but somewhere in
there's a nice listing and summary of many TD numbers from the old
for that - it may explain what TD253 is supposed to be. Also, you can
look up
back-diodes, and see if the description matches the curve you saw.

You are right that this unit is a prototype. If the same phase
stages were used back then, as in more modern times, then "B11" should
be very
close to what went into production. The poor solder joints you
around those tiny diodes, may result from a couple of considerations.
those things are very delicate, so anyone soldering them in or out
they have to work fast - very fast - to get that iron tip out of there
even if the joint looks crappy, as long as it worked. Second, being a
prototype, these diodes may have been swapped out or had type changes
times during development, and the same soldering issues apply. This
could also
mean that those diodes are not necessarily the same part number that
ultimately used in production. But, you'd think they would be close at
Good luck in figuring it out.


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