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On Wed, Apr 7, 2021 at 04:43 PM, Jim Adney wrote:

The wire actually is white, with a brown and a red stripe. Guess why?

Because, using the resistor color code, brown-white translates to 12, the CRT
pin number it goes to. And for pins 1-9, I'll bet there will be only one
stripe.

Nice catch, I wouldn't have gotten it without your hint. Was this standard Tek
practice?

Using the resistor color code, brown-white would translate to 19. The brown-red combination on a white background indicates 12 - or 21. The CRT socket however only has 14 pins. The background color is not used and yes, below 10 only one color is printed on the (white) background.
Yes, this was standard Tek. Often, the harmonica connectors (the linear ones, pushed onto rows of pins on a PCB) are molded in colors indicating the last digit of the socket number.
HP (Agilent) had a similar habit, using color codes for the PCB ejectors.

Raymond

On Wed, Apr 7, 2021 at 3:35 PM Albert Otten <aodiversen@...> wrote:

On Thu, Mar 25, 2021 at 05:17 PM, cmjones01 wrote:

I couldn't find any information in the manuals as to why this resistor
is there. Why is it? To avoid ground loops?

561B (mentioned by keantoken) manual page 3-5 bottom left: "R183, which is about ten times the resistance of the braid of a 42-inch coax cable, cancels any ground loop current that may exist between the CAL OUT connector and some other instrument chassis." I didn't look in other manuals.

Thank you for confirming this, Albert. My previous message got
somewhat mangled in transit so I'll try to post the text again here:

Further to this discussion on the 0.25R anti-ground-loop resistor on
tube-era calibrator outputs, I looked further in to why my 127's
calibrator output ground seemed to be open-circuit.

It turned out that there was actually a manufacturing error. There's
an arrangement of plastic bushes and fibre washers to keep the
calibrator socket's outer from being in contact with the front panel.
In my 127, one of the fibre washers was in the wrong place, so the
bottom of the volts/millivolts divider chain was connected to chassis
ground, and both ends of the 0.25R resistor R898 were also connected
to chassis ground. The calibrator socket outer wasn't connected to
anything at all. It was completely floating. The paint seals on the
screws were still intact, so it must have left the factory that way in
1960.

The only reason I noticed is that in my office the power sockets have
no ground connection, so when by chance I powered the 127 from a
different outlet to the scope I was testing it with, they had no
common ground connection via their power cables. Trying to view the
calibrator output it seemed to be imposed on about 100V of mains hum,
which I blamed on a faulty cable. But the cable was blameless. It was
an actual Tek assembly error! I guess nobody had ever noticed due to
never having tried to connect the calibrator to an ungrounded device.

I've moved the offending washer now and the wiring matches the
schematic diagram. It all works as it should now.

Chris

On Tue, Apr 6, 2021 at 05:25 PM, Raymond Domp Frank wrote:

The wire actually is white, with a brown and a red stripe. Guess why?

Because, using the resistor color code, brown-white translates to 12, the CRT pin number it goes to. And for pins 1-9, I'll bet there will be only one stripe.

Nice catch, I wouldn't have gotten it without your hint. Was this standard Tek practice?

On Thu, Mar 25, 2021 at 05:17 PM, cmjones01 wrote:

I couldn't find any information in the manuals as to why this resistor
is there. Why is it? To avoid ground loops?

561B (mentioned by keantoken) manual page 3-5 bottom left: "R183, which is about ten times the resistance of the braid of a 42-inch coax cable, cancels any ground loop current that may exist between the CAL OUT connector and some other instrument chassis." I didn't look in other manuals.
Albert

Received the 7603 trigger select board and swapped the suspect IC, U2404. My 7704A is now fully functional for trigger. R2409 measures 910 ohms as it should. The voltage on pin 11, the common substrate voltage for the 2 ICs is now -4.1V as on the schematic.

These Siemens motors can be found NIB occasionally. Here’s one: .

Further to this discussion on the 0.25R anti-ground-loop resistor on
tube-era calibrator outputs, I looked further in to why my 127's
calibrator output ground seemed to be open-circuit.

It turned out that there was actually a manufacturing error. There's
an arrangement of plastic bushes and fibre washers to keep the
calibrator socket's outer from being in contact with the front panel.
In my 127, one of the fibre washers was in the wrong place, so the
bottom of the volts/millivolts divider chain was connected to chassis
ground, and both ends of the 0.25R resistor R898 were also connected
to chassis ground. The calibrator socket outer wasn't connected to
anything at all. It was completely floating. The paint seals on the
screws were still intact, so it must have left the factory that way in
1960.

The only reason I noticed is that in my office the power sockets have
no ground connection, so when by chance I powered the 127 from a
different outlet to the scope I was testing it with, they had no
common ground connection via their power cables. Trying to view the
calibrator output it seemed to be imposed on about 100V of mains hum,
which I blamed on a faulty cable. But the cable was blameless. It was
an actual Tek assembly error! I guess nobody had ever noticed due to
never having tried to connect the calibrator to an ungrounded device.

I've moved the offending washer now and the wiring matches the
schematic diagram. It all works as it should now.

Chris

Dave,

Happy to be of service.

-- Jeff Dutky

Well,

I finally got me some 2N3442s from mouser.

Good news: the HV sparking problem was definitely cause by the 75V regulator going short.

Bad news: there appears to be no vertical deflection. But, there's a caveat to that. I'm pretty certain the problem lies downstream of the front end amplifiers because the channel 1 out signal is present and responds to vertical position control when viewed on another oscilloscope.

Another symptom is that the spot is about 1 cm long in the X dimension when the time base is slowed down. I'm hoping the 75V rail going high didn't take out a bunch of stuff!

Sean

Going to get this on the bench again this weekend and tinker with it. I couldn't get the shaft to come free; was afraid of breaking something. Will need to examine again.

Sean

That dang Jeff Dutky keeps making me spend money on test equipment!

LOL.

Last I'd checked there wasn't any availability. R&L has them now! Get 'em while their hot!
Dave

Jonathan Pyle wrote:

I don't have a function generator that can produce frequencies in the hundreds of MHz,
and I don't have a spectrum analyzer that can test the frequency response of the RF probe.

Good News! You can remedy both deficits by the acquisition of a TinaSA:

The TinySA is a spectrum analyzer that can operate on signals between 100 KHz and 960 MHz (in two ranges), it can generate sine waves up to 350 MHz, and square waves up to 960 MHz, and it fits in the palm of your hand.

Make sure you buy from one of the reliable sources:

When I bought mine, earlier this year, I paid less than $60. I bought through the Zeenko store on AliExpress. It did take more than a month or the item to arrive, as I did not pay or expedited shipping.

-- Jeff Dutky

Charles --

I tested the RF probe from Ukraine that I got on eBay ().

I tested it with my 1S1 and my Leo Bodnar 30 picosecond pulse generator (10 MHz) and found that the measured risetime through the RF probe was around 300 picoseconds, which is the same as when the pulse generator is plugged directly into the 1S1.

However, the RF probe did add a lot of "ringing" to the waveform. See the photo in this album:

/g/TekScopes/album?id=262713

I'm not sure this is a fair test, though, because a 30 picosecond risetime contains frequencies well beyond the stated bandwidth of the probe (1.5 GHz), so maybe that messes things up?

The RF probe comes with a nice telescoping needle probe point, but I desoldered it because I thought it might introduce noise. Removing it did not have any noticeable effect. I soldered an SMA socket to the RF probe input for purposes of attaching the pulse generator without any long leads. (The pulse generator wants 50 ohms so I used a T and a 50 ohm terminator.)

I did another test with a 10MHz signal from my Koolertron function generator (low cost Amazon product) through a 3-foot BNC cable (well within the bandwidth of the probe). The waveform looks the same through the RF probe, just noisier.

I don't have a function generator that can produce frequencies in the hundreds of MHz, and I don't have a spectrum analyzer that can test the frequency response of the RF probe (see the eevblog post above).

For $21.20 including shipping I think it's a pretty handy device. (Shipping to the U.S. took only eight days.)

Also consider that some of us are pretty good at 3D printing blowers
that will fit onto a case fan hub ;-)

Monty
(the other one)

On Tue, Apr 6, 2021 at 9:03 PM cheater cheater
<cheater00social@...> wrote:

Don't forget that PC fans are good and bad. If you want something good
buy Noctua, or, in a pinch, BeQuiet.

On Wed, Apr 7, 2021 at 2:28 AM durechenew via groups.io
<durechenew@...> wrote:

Thank you, Raymond and Siggi, for taking the time to answer to this post. Unfortunately the motor of the blower is beyond repair (back side bushing is completely broken), therefore the whole stuff must be replaced. I've seen a blower that might be appropriate for the purpose, beside the obvious (and, as Siggi said, undesired) regular fan. I'm quite aware of all the issues (I recently put a fan on a 2235 and, yes, I had to go from 8V to 5V - for a 12V motor - to get a decent noise. For fan I was considering making some additional holes in the back cover to allow for easier flow; but no decision yet.
TT

Don't forget that PC fans are good and bad. If you want something good
buy Noctua, or, in a pinch, BeQuiet.

On Wed, Apr 7, 2021 at 2:28 AM durechenew via groups.io
<durechenew@...> wrote:

Thank you, Raymond and Siggi, for taking the time to answer to this post. Unfortunately the motor of the blower is beyond repair (back side bushing is completely broken), therefore the whole stuff must be replaced. I've seen a blower that might be appropriate for the purpose, beside the obvious (and, as Siggi said, undesired) regular fan. I'm quite aware of all the issues (I recently put a fan on a 2235 and, yes, I had to go from 8V to 5V - for a 12V motor - to get a decent noise. For fan I was considering making some additional holes in the back cover to allow for easier flow; but no decision yet.
TT

On Wed, Apr 7, 2021 at 02:54 AM, Raymond Domp Frank wrote:

I thought they were part of the focus circuit (and they are, if I'm not
mistaken).

That's done to improve focus tracking (making focus less dependent on beam
current i.e. screen brightness).

Please forget my above remark. It's wrong.

Raymond

On Wed, Apr 7, 2021 at 01:25 AM, Dave Peterson wrote:

I thought they were part of the focus circuit (and they are, if I'm not
mistaken).

That's done to improve focus tracking (making focus less dependent on beam current i.e. screen brightness).

Raymond

On Wed, Apr 7, 2021 at 02:33 AM, Dave Peterson wrote:

But that's assuming the above links actual go to the pictures added. The forum
system is definitely weird: the new added pictures are not in any kind of
order relative to the existing album pictures. So just hoping for the best
here.

The links are fine. I just wouldn't add the quotes because they are of no help, at least not to me, neither in Firefox nor in Chrome. Either highlight the whole url, including the trailing digits, and open in a new tab (right click) or have groups.io send messages as mail as well. In messages, you may just click the links; they are complete, at least in Thunderbird.

Raymond

On Wed, Apr 7, 2021 at 01:25 AM, Dave Peterson wrote:

I can't even hazard a guess as to the meaning of the wire color. I won't be
the slightest bit surprised to learn that there is meaning to the wire
coloring. Consider it an aspect of Tek design that I haven't contemplated yet.

Hi Dave,
Spoiler alert! Don't look any further if you want to think about it a bit more, but

here's the giveaway:

Brown and red stripes for the wire connected to pin 12 of the CRT, etc. Strictly following standard color code. Pin numbers below 10 have just one stripe on a white background.

Raymond

Uploaded a couple of new pictures, though I see that the one Raymond uploaded does also show VR1434/C1434. Just didn't realize yesterday those were the pin 12 drivers.

This one shows the same diagram with the two components highlighted: "/g/TekScopes/photo/262670/3203258?p=Name,,,20,0,0,0"

This one is a close up without the annotations that should make them more visible: "/g/TekScopes/photo/262670/3203259?p=Name,,,20,0,0,0"

But that's assuming the above links actual go to the pictures added. The forum system is definitely weird: the new added pictures are not in any kind of order relative to the existing album pictures. So just hoping for the best here.

Dave