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I managed to get the screen looking a little bit better in the corners. After having a closer look, it turns out the clear plastic screen behind the blue filter was filthy on the edges and after a cleaning, the CRT still isn't sharp overall but the corners are much improved. While taking the front bezel off, I also managed to snap one of the knobs under the CRT by being a cavalier and just pulling on the knob (oops). I used a little bit of heat on the rest of them and didn't have any issues. Lesson learned. Any one have a spare knob or 2? haha.

Jay

Rick,

I echo what Paul says. One thing you can do is look for a donor 576. As you know from reading through the messages, the older 576's have issues with the HV (brown) transformer. I got one of these and had a replacement HV transformer professionally made. The CRT is bright and sharp and appears to have low hours.

I have a theory that the ones with HV transformer issues will have low hours on the CRT, as the HV transformer issue is difficult to troubleshoot and usually only shows up when the transformer has warmed up a bit. I would have never guessed or thought to look at the HV transformer with out the help of this group (and some members of this group that have moved over to Tekscopes2). So my theory is, the older 576s developed an issue with the HV transformers, and service was attempted (unsuccessfully) and then put on the junk pile or relegated to a back closet somewhere.

If you keep an eye out on eBay (high priced mostly ... but not always ... you can have eBay email you everytime a new 576 listing shows up) and other places (craigslist, facebook, swap meets, etc) for ones with the brown transformer and really beat up, you can get a donor at a good price (less than the kit mentioned a few months ago), plus you will get some other parts too. I agree it is still a risk the CRT will be well used or damaged, but the two "brown transformer" ones I have gotten have really good CRTs)

I hope you find one.

Dave

Possibly the 5ADP1 crt, as suggested by Walter.

There are videos out there on Tek's CRT production line. They are very interesting. With
sufficient resources you could probably duplicate a tube, however it would be cost prohibitive
(you'd also need a complete machine shop, glass shop, ceramic setup and high vacuum lab,
among other things). I daresay going through the learing curve would take a few years.

There are hobbiests that make their own vacuum tubes though, so there is that.

The way to address this today is to digitize the signals and use a microcontroller to write
the display to an LCD panel. (You could also just tap out the signals to an XY display if
you wanted to stick with a CRT and use an overlay with the grid on it).

Because most of the controls have contacts to display the values along side the screen, you can
also tap into those and have your microprocessor do various calculations for you on the fly.

IIRC, there was someone about a year ago who advertized a product, might have been a kit, that
converted a 576 to a wiz bang computer controlled curve tracer. I looked at it at the time, but
it was too pricey for a cheap hobbiest like me. I ended up getting an actual computer controlled
Tek curve tracer (a Tek 571) which does most of what I need to do although it lacks the super
wizbang features. I got that for a few hundred.

There's probably space for a simple minded display replacement that would duplicate the 576 CRT
display without adding all of the other stuff. I think about that from time to time, but it's
not high on my project list. The problem is, once you have a processor involved, it's hard
not to do everything else.

Paul

--
Paul Amaranth, GCIH | Manchester MI, USA
Aurora Group of Michigan, LLC | Security, Systems & Software
paul@... | Linux/Unix - We don't do windows

hi Bob,

question:

Tek 576 CRT specifications, design, x-rays, ... alternatives
garp66
11:27am #209592

Does anyone have any design specifications or technical information on the CRT used in the Tek 576 CT ?
- anyone have Xray images of that tube ?

I understand for the many posts in Groups io that it was a "special" crt tube,
but looking for technical details to attempt to kludge -swap in- some other CRT,
in place of my dying 576 crt tube....
thinking there must be some way to do this in some fashion.

thanks,
rick

Find R830 - a 3M3 resistor, it's towards the back of the scope, to the right of the EHT module. Use your DMM on continuity/beep then resistance to check by buzzing out from the intensity pot, scope powered off obviously. R830 is connected to C829/830.
Pop your DMM onto DC resistance/mV then put/clip your probes across the 3M3. If the CRT is faulty & has a control grid/cathode short the voltage reading across R830 will be over 1v say. The reading should be very, very low.

I think that's right, not an expert on CRT's but it's how normal valves are tested, EG 1meg resistor to g1 voltage source from g1 to cathode. Please chip in & confirm/clarify please folks. Andy.

Does anyone have any design specifications or technical information on the CRT used in the Tek 576 CT ?
- anyone have Xray images of that tube ?

I understand for the many posts in Groups io that it was a "special" crt tube,
but looking for technical details to attempt to kludge -swap in- some other CRT,
in place of my dying 576 crt tube....
thinking there must be some way to do this in some fashion.

thanks,

I have a 7J20/J20. I haven't used it in a while. It's on my "to do" list.
But I am grateful when I run across application notes for it.

DaveD
KC0WJN


On Mon, May 19, 2025 at 14:05 garp66 via groups.io <Bean595939=
[email protected]> wrote:

A .pdf of the 1976 Applied Optics 7J20 paper was randomly uploaded to
the Files section.

-- Who in this group still has a Tek 7J20 RSS ?

-- Is anyone familiar with the differences / similarities of the Tek
7J20 vs.
the Hp 70k 70950a / 70951a / 70952a series ?

A .pdf of the 1976 Applied Optics 7J20 paper was randomly uploaded to the Files section.

-- Who in this group still has a Tek 7J20 RSS ?

-- Is anyone familiar with the differences / similarities of the Tek 7J20 vs.
the Hp 70k 70950a / 70951a / 70952a series ?

Gordon,

What I do to test crts that do not have a socket for a tester is to use the 12 pin adapter, small test clips to make contact with the connectors for the heater, G1 and G2 then hook them up to the respective pins on the crt. A wire or paper clip that can be shoved into the entrance of where the wire goes into the socket works. There should be enough room where the wire goes in and the socket to do this. Set the heater for 6.3V and use a b/w setting. I do have a Hickok tester that has an adapter for the 12pin crts and I have used a male plus with wires that are tinned on the ends to use test leads to test crts. My Hickok will show leakage in ohms, if there is any leakage. A crt tester has a feature to clear a short from K to G1. That you make sure to do with the heater off! This is not 'shooting' the crt, only removing a short or high leakage. 'Shooting' is when the heater is raised in voltage then a condenser is discharged through K-G1.

Mark

On Sun, May 18, 2025 at 04:29 PM, Mark Vincent wrote:

you can increase the heater voltage 20-30% higher

I was never a fan of increasing the voltage on a CRT filament, even temporally.
I always thought that that was a good result for CRT manufacturers, parts sellers, and techs, but not consumers.
Power is proportional to the square of the voltage... and power here is heat.
So on a filament some hours on it, that's going to do some irreversible damage.
It's not going to do the cathode any good either.
No one makes these CRTs any more.
That's a good reason... IMO... not to abuse them... even innocently.
It's not so easy to get a replacement... except, and perhaps, from a parts mule.
'Some display' wagered against a 'potentially better display' is... IMO... much better than 'no display'


--
Roy Thistle

Tom & Darla,

This is clearly a huge task and everyone here hopes the best for you. I'll keep you in mind for future Tek and HP parts needs.

In the meantime, since you asked for feedback, I went to your website and have a few suggestions.

1) It's unnecessary to repeat the Tek part number in the second column. It's extra work for you, without adding any utility, and it takes up room for useful info. It's just clutter. Likewise, don't repeat info from column 2 in column 3. Redundancy is not a good thing, it dilutes your message.

2) When I try to "walk" thru your Tek part pages, say going from page 1 to page 2, using the links at the bottom of each page, I get forwarded to BOTTOM of page 2, but it would be better to get sent to the TOP of page 2. That way I can scan down that page and end up with the links to the next and previous pages. I didn't try "walking" backwards, but in that case, ending up at the bottom of the previous page might be good. Another way to deal with this might be to have those page links at the top as well as the bottom of each page.

3) When I've scanned a few pages this way and then click on my browser's Back button, I get sent all the way back to your home page, losing any progress I might have made, looking for something specific.

4) The search function seems to only look at the Tek part number. It finds those nicely, but sometimes it might be useful to be able to search for things that show up in other columns, like 2N3904 or TO-3.

5) Some of the prices look pretty optimistically high. It will be a lot of work to figure out reasonable prices for everything. Parts that are currently available from normal distributors will need to be cheaper than parts that are NLA anywhere else.

6) Photos of non-transistor parts would be really useful, but I know that adds a lot of work to your effort. I would not bother with photos of most transistors, since almost anyone looking at your web site will already know what a TO-92 transistor looks like. Transistors in odd cases might still benefit from a photo.

I hope you find these suggestions useful, but you are free to take them with a large grain of salt. They are worth no more than what you paid for them.

thanks for reading,

--
Jim Adney
Madison, WI USA

On Sun, May 18, 2025 at 04:29 PM, Mark Vincent wrote:

use a Tadiran 2.4A/hr axial type

The part speced in the Tektronix documents (070-6863-00) is an Eagle Picher LTC-7P Battery.
The Tadiran is the same chemistry; but does not have... AFAIK... internal reverse charging current protection.
The LTC-7P does... which I suppose makes it a 'battery module'... more than just a battery.
As well... and at least... the modern LTC-7P is encapsuled... if not potted? ... in Ryton.
IMO... that encapsulation, along with the internal reverse charging current protection... means that leakage is less likely.
There is reverse current protection in the scope... but, if it fails... the memory backup battery may become pressurized, and 'explosively' vent... in other words leak.
But for some reason Tektronix chose the LTC-7P
Both the Tadiran, and the Eagle Picher... AFAIK... have 'lifetimes' of 10 years... and ought to be replaced after that.
I would think the Tadiran would be at risk of leaking after that 10 yeartime period?
Given the above... I don't see the point of the Tadiran.
The LTC-7P is the 'right' part, and is available... so why not use it?
That Tadiran is more expensive; but, so is a new PCB, if it leaks.
--
Roy Thistle

Here is another possibility for Linux/MAC...

There is a GPL'd version of the host software for the CGR101, a two channel scope that used to be sold by Syscomp Design:



It's written in Tcl/Tk, which is an interpreter, and runs on Linux, Windows, and Mac.

The CGR101 has a similar serial interface as the curvebug, and the host software already supports menus to auto-detect or manually select the right /dev or COM port. In operation, it polls the scope and plots the two channels, just like the curvebug.

The host software supports a lot of other stuff in the CGR101 like function gen, pulse gen, and logic I/O, but that functionality can be removed, leaving just what's needed for the curvebug.

It could be an alternate starting point for anyone who is interested in doing a Linux or Mac implementation. I think most of the work is deleting code.

The above version on github is out of date. I have a newer version and can provide it to anyone who is interested, please PM me. I used to have a CGR101, but no longer. Syscomp Design is out of business, and their code does not seem to be out there anymore. They had a lot of devices written this way and provided the source to all of them. It's a shame if it's all been lost.

-mark

On Sun, 18 May 2025 at 22:32, Jay Czaja via groups.io <jmczaja=
[email protected]> wrote:

Is there anything else I can use as a substitute for the tunnel diode
pulser? or is there anyone in the NJ area that has one?

My limited understanding is that you need a 250mV rectangular wave with a
risetime much less than that of the 2465.

Leo Bodnar's step generator is currently the traditional answer, but I have
not checked the amplitude/frequency is suitable for the 2465.



If a 2.5V/300ps risetime into 50ohms is acceptable then you could - with
care about the layout and decoupling - use 74lvc1g gates.

On Sun, May 18, 2025 at 02:32 PM, Jay Czaja wrote:

Is there anything else I can use as a substitute for the tunnel diode pulser?

Well you could try a fast pulse generator based on avalanche breakdown of bipolar junction transistor... if you believe the specs.
AFAIK... ideally you want a scaled delta function, to measure the un-attenuated (so mV range) transient response of the 2465B's vertical amplifiers

--
Roy Thistle

It turns out that a friend has a Sencore CR70 CRT checker, but it doesn't seem to cover many scope tubes. Does anyone know if there's a way to use it to check the 547 crt?

Thanks
Gordon

Depends on what you mean by “broke”, Luca. If you mean uh, yeah, it seems like it’s working, then it could mean it’s not broke. But it would be foolish to assume that something inside one of these vintage pieces we all love so much isn’t in imminent danger of going kablooey. That could be another definition of “broke”.

Jim Ford
Laguna Hills, California, USA

Hi Larry,
The battery I used was a LTC-7PN 3.5v 750mAH from eBay. I paid $25 with free shipping (US). Unfortunately the vendor is out of stock and there are many of this battery listed on eBay for ridiculous prices... also it's a Lithium battery, not a LIPO as incorrectly said above.

If you were asking about the procedure to replace it, you have to keep at least 3vdc going to the ram chip that holds the calibration. If it looses power the calibration settings will be lost and the scope will have to be recalibrated which is not an easy job for most of us.

I soldered the leads from a battery holder to on the back of the A5 PCB to the resistor and diode that go to the battery (see photo) , two AA 1.5v batteries supplying 3v to the ram chip while I soldered in the new battery. and then removed the AA battery leads.

Firstly, I want to say thanks to Steve for his good words, and clarify that his "Thank You" was unsolicited.

In this day and age, the simple words "Thank You" are generally considered surplus and unnecessary, and when someone does say "Thank You", it is considered unusual, and raises eyebrows - what's his ulterior motive?
The opposite was true 50 years ago, and perhaps this "modern progressive" society might do well to come full circle again.

Looking back over previous posts, I noticed that Vendors of valuable items are encouraged and welcomed - such as Ram's U800 replacement PCB from India. And why shouldn't we encourage and thank those vendors who do a really good job of enhancing the usability of our scopes?

And, on the opposite side of the scale, we are not shy about calling out the charlatans - example - the fake 2465's with butchered 2445 PCB's from California.

IMHO it's very healthy to air opinions or reviews of one's good or bad experience, as long as it is firstly Personal, and secondly Based on fact.

Just my 2 cents!

Menahem