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Barry,

These are a bleeder for the cathode circuit and partial divider for high voltage and focus circuit. I replaced mine with 1W 1% types and spaced them off the board. The 1W types I use are about 1cm in length, not 3,68 x 8,74mm types.

You will find the two 22meg resistors to be well out of tolerance. Use VR37 Vishay types.

Mark

Without looking, that sounds like the typical "focus string" divider that probably includes the focus pot somewhere, to get the right operating voltage for the function, and it possibly does other things too. Carbon composition resistors are often used for this, and they tend to drift upwards over time. Your idea to mount the replacements with more board clearance is sound.

It's also possible that strings of resistors are used for feedback in high voltage regulator circuits, but if so, they would be better grade metal film resistors. Tek hardly ever did this for CRT HV regulation - they used instead a carbon or metal film resistor network on a ceramic substrate. You can usually spot this part easily in the circuit.

Ed

Hi All,
I've a TM504 with 4 modules for sale.
Also a Scopemobile Type 204. The TM504 tucks nicely into the 204.
Both can be seen here:


Local sale & PU only.

Please respond privately off group. I will not respond here, to preserve the bandwidth/protocol of the group.

Thank you - Bob

In my latest 7704A, I noticed the chain of nine 300K resistors (R4261 - R4277 and, possibly, R4279) in the CRT circuit have drifted significantly high (~20%) making what should be a total of 2.7M about 3.2M. It's rather obvious they've been running quite warm (discoloring on the PCB) and I'm going to replace them with some breathing room between the new resistors and the board but it got me to wondering what function those provide. I looked over the circuit description and didn't see those mentioned so it made me curious and, perhaps, someone could enlighten me. I presume they're probably a more-or-less standard part of a CRT circuit and that's why they're not called out in the circuit description but not sure.

Thanks,
Barry - N4BUQ

I'm doing some work with interfaces & doing some research on the test equipment & interfacing.

I'm interested in both serial & parallel & the various types of test equipment, breakout boxes, line monitors & "Smart Cable" interface aids.
I haven't managed to find a manual for a Parallel Breakout Box even though I've seen photos of them.

Breakout boxes & line monitors are available on ePay etc but most do not have the manuals with them.

I am sure that there are members with lots of experience & that may even have manuals laying around.
I'd appreciate if members could look to see if they do have manuals & contact me if they have specific hints on interfacing.
I have seen the occasional comment about equipment that will damage test equipment or is particularly difficult to interface but haven't found a single repository so I'm starting to put it together for myself.

I'm also interested in the link between the Wavetek & Beckman Industrial brands for their breakout boxes.
The products appear to be the same although Beckman uses the "Easy Bob" terminology.
One breakout box I've seen is Beckman but the manual with it is Wavetek.

Many thanks,
Brian Symons.

Should have mentioned, these are Tek scopes.

I should have mentioned - if you use a simple LED deal, use a different color for each direction. The signal will be brief, and it's easier to discern which color flashed, than which of two same ones close together did.

Ed

When one object dumps charge to another with enough energy to make a spark, then you don't need any sophisticated instruments to tell the polarity. A couple of anti-parallel-connected LEDs will suffice. Electrostatics was pretty well figured out by brilliant minds long ago, with comparatively crude instruments, way before tubes and transistors and ICs. Except for scientific curiosity, there's no need to recreate it (aka reinvent the wheel) to answer the question.

Any DMM in its voltage mode can sense the currents flowing in an electrostatic situation, so just bring a handheld DMM in its lowest VDC range, clamped with those anti-paralleled LEDs or regular diodes, and have at it. Use a simple, cheap DMM, like a Harbor Freight one, in case you accidentally discharge into a bad spot. Or, just leave out the DMM and use the LEDs. Don't forget the clipboard, paper, and pen to record the results, and try to look cool while doing it. Don't use a phone - keep it well away from all this activity.

One thing that may help is to look at the various HBM (human body model) electrostatic specifications, to get an idea of magnitudes involved. You can only store so much energy in practical conditions.

Ed

On 5/7/2024 7:35 PM, cheater cheater wrote:

Hmm... anything less rare? Anything I could take with me on the go?

Gold leaf is the standard for electroscopes because it can be beaten far thinner than other metals. It has been the standard for leaf electroscopes since British physicist Abrahm Bennett used it in 1787. There are pith ball electroscopes which are less sensitive than gold leaf electroscopes.

As I said upstream, if you need to detect the direction of the current you need a sensitive galvanometer.

--
Dale H. Cook, Member, NEHGS, AGS, MA Soc. of Mayflower Descendants;
Massachusetts State Coordinator for the USGenWeb? Project;
Administrator of

Hello,

I and a friend changed out the batteries in my newly purchased 2712 today. The GPIB battery was totally dead on an unloaded meter... The other battery had 3.xx left. Both batteries were swapped with new ones. They fit perfectly on the board! Thanks to all that answered and suggested batteries here! Also, thanks to whoever told me to hurry once you put in the GPIB board battery, the 2712 got powered up maybe 3 to 5 minutes after the GPIB battery was soldered in place.

When I run the self normalization all seems good until I get:

Amplitude Normalization Failed

The scope appears to be working well, I hang an antenna off it, and transmit with an HT on 146.52, and see a waveform, the right width, etc...

My God Tek builds nice equipment... There is not even any dust in the unit, save a tiny amount near the end of the CRT HV. All the boards look brand new, nothing has leaked, and it was even calibrated in 2015 by Tek...

So what does the Amplitude Normalization failed mean in terms of repair, and/or operation? Do I need to worry? Is there something else I should do, and try again?

--
73, and thanks,
Dave (NK7Z)

ARRL Volunteer Examiner
ARRL Technical Specialist, RFI
ARRL Asst. Director, NW Division, Technical Resources

Hmm... anything less rare? Anything I could take with me on the go?

On Wed, May 8, 2024 at 12:12?AM Dale H. Cook via groups.io
<bridgewaterma@...> wrote:

On 5/7/2024 4:43 PM, cheater cheater wrote:

also why buy aluminium leaf? why not use alu foil?

Aluminum foil is far too thick. An electroscope needs minimum mass, and
that means leaf, not foil. The repulsive force in an electroscope is far
too low for foil to work.

For detecting direction of current flow you want a sensitive
galvanometer, of the type used as a detector for instruments such as a
Leeds & Northrop Type K-3 Universal Potentiometer. You would probably
need an adjustable current limiter of fairly high resistance to avoid
damaging the galvo.
--
Dale H. Cook, GR/HP/Tek Collector, Roanoke/Lynchburg, VA

On 5/7/2024 4:43 PM, cheater cheater wrote:

also why buy aluminium leaf? why not use alu foil?

Aluminum foil is far too thick. An electroscope needs minimum mass, and that means leaf, not foil. The repulsive force in an electroscope is far too low for foil to work.

For detecting direction of current flow you want a sensitive galvanometer, of the type used as a detector for instruments such as a Leeds & Northrop Type K-3 Universal Potentiometer. You would probably need an adjustable current limiter of fairly high resistance to avoid damaging the galvo.
--
Dale H. Cook, GR/HP/Tek Collector, Roanoke/Lynchburg, VA

Looking for a nice crack free front cover for the 465/475 scopes with DM44 or the 468. Thanks.

Hair on the wheels and some plastic of the wheels rubbing together generate lots of ES charge. Sort of like a van de graaff generator.

OK, so looking into it, a gold leaf electroscope will detect the
presence of _a charge_, but what i want is to figure out the _sign_ of
the current when an item is discharging into another item. I don't
think a gold leaf electroscope will do that, but i might be wrong. let
me know.

also why buy aluminium leaf? why not use alu foil?

On Mon, May 6, 2024 at 5:03?PM Glenn Little via groups.io
<glennmaillist@...> wrote:

Google provided this:

I built one in jr high school.
Very easy.
You can use aluminum leaf available at a sign maker.

Glenn

On 5/5/2024 9:56 PM, cheater cheater wrote:

How do you make one?

On Mon, May 6, 2024 at 12:41?AM jspencerg via groups.io
<jspencerg@...> wrote:

It is easy to make an electroscope. Walk around store with your finger on the electrode and observe when you get charged. Wear a foil hat if you don't want to answer any questions.

--
-----------------------------------------------------------------------
Glenn Little ARRL Technical Specialist QCWA LM 28417
Amateur Callsign: WB4UIVwb4uiv@... AMSAT LM 2178
QTH: Goose Creek, SC USA (EM92xx) USSVI, FRA, NRA-LM ARRL TAPR
"It is not the class of license that the Amateur holds but the class
of the Amateur that holds the license"

Hi,
I'm looking for a Keithley 2000 motherboard.
Mine has some broken PCB tracks but I can't fix it.
The PCB is multilayer.
Thanks if anyone can help me.
Mauirzio

Is anyone looking for a 575? I have two spares and need the room. PM if interested. I am in Kentucky.
ThanksJeff Kruth

Hi,
I'm looking for a Keithley 2000 motherboard.
Mine has some broken PCB tracks but I can't fix it.
Thanks if anyone can help me.
Mauirzio

Bob Koller <fourdesigns@...> added folder */TG2000 SOFTWARE*

*Description:*
TG2000 SOFTWARE



---

The following files and folders have been uploaded to the Files area of the [email protected] group.

* /TG2000_SW.zip ( /g/TekScopes/files/TG2000_SW.zip )

*By:* Bob Koller <fourdesigns@...>

*Description:*
TG2000 SOFTWARE

I just uploaded the SW, check the files section.

Enjoy!