Date   

Re: Typical scope CRT anode current range?

Ed Breya
 

John, I could measure the actual current in one (rather complicated to do properly)*, but I'm hoping to find some sort of spec if possible. I don't need it to be high in precision - I just need to know what's a reasonable load for measuring the anode voltage with the CRT running. I've got a real nice 200 megohm divider on hand that would take about 100 uA. If it's too much, I'd go to 300 or 500 megs with a bit more complexity.

*Please do not attempt to measure the anode current by simply interrupting the CRT connection. In principle, you can put a current meter in the anode line, but since the common-mode voltage is around 20 kV, the whole meter circuit will be hot with this. The measurement will be wrong, the whole thing will be buzzing with corona discharge, and you'll be risking damage to the meter, the scope, and yourself. You need special equipment for this. I have the facility to do this, but would have to build it up from various HV stuff on hand, and I'd rather not.

There is a proxy for the anode current that is accessible with some grief, inside the scope. The bottom of the HV multiplier can be interrupted, and with some interpretation, the current can be estimated.

Ed


Re: Typical scope CRT anode current range?

John Williams
 

I suppose it would be possible to measure this, although I have not done that. It could be done by unsoldering the power supply end of the lead to the pda and putting a meter in series. Might try that later. One could make a graph at different intensity settings etc. Sounds like a good project if it snows tomorrow. Stand by for that.


Typical scope CRT anode current range?

Ed Breya
 

Does anyone know offhand, the typical or specified PDA anode current operational range for scope CRTs, say for example, in a 7904? I'm guessing up to a few hundred uA at full/max brightness, but don't know for sure.

Ed


Re: 7904A / 7A26 / 7D15 for sale $150

David Berlind
 

As someone that lives close to Salem, I'll just report that the supply of Tek gear in this neck of the woods exceeds the demand. Especially with regularly recurring swapfests at MIT. And so, in my view, based on the buying and selling I've done around here, $150 is on the high side.

On February 14, 2019 9:54:49 AM "Daniel Koller via Groups.Io" <kaboomdk=yahoo.com@groups.io> wrote:

First, one needs to find out if it floats!
Dan

On Wednesday, February 13, 2019, 4:55:51 PM EST, Dennis Tillman W7PF <dennis@ridesoft.com> wrote:

My daughter spotted this 7904A / 7A26 / 7D15 for sale for $150 in a thrift
shop in Salem MA.

The address is

Witch City Consignment and Thrift Store

Downtown Salem, MA



She has no connection with this item and neither do I.

A 7904A for $150 is a great price.



Dennis Tillman W7PF






Re: OT: Baird Atomic #123 G-M scaler manual? OT!!

Artekmedia <manuals@...>
 

Dan

Try asking out on the yahoo group Manual_Exchange

Dave
manuals@artekmanuals.com

On 2/14/2019 10:03 AM, Daniel Koller via Groups.Io wrote:
Hi all, this is grossly Off Topic, but I figure folks here might have a lead.
  Does anyone know where I can find a service manual or even just a schematic for a Baird Atomic 123 G-m (Geiger-Mueller) scaler?
  It looks like the one in this link:https://www.tubeclockdb.com/on-ebay/180-baird-atomic-geiger-gm-counter


  I have checked BAMA and Archive.org, but had no luck there.   Anyone have any suggestions of other places to look, or does someone happen to have the manual?
    Thanks, and I will take replies off-line.
  Dan


--
Dave
Manuals@ArtekManuals.com
www.ArtekManuals.com


OT: Baird Atomic #123 G-M scaler manual? OT!!

Daniel Koller
 

Hi all, this is grossly Off Topic, but I figure folks here might have a lead.
  Does anyone know where I can find a service manual or even just a schematic for a Baird Atomic 123 G-m (Geiger-Mueller) scaler?
  It looks like the one in this link:https://www.tubeclockdb.com/on-ebay/180-baird-atomic-geiger-gm-counter


  I have checked BAMA and Archive.org, but had no luck there.   Anyone have any suggestions of other places to look, or does someone happen to have the manual?  
    Thanks, and I will take replies off-line.
  Dan


Re: 7904A / 7A26 / 7D15 for sale $150

Daniel Koller
 

First, one needs to find out if it floats!
  Dan

On Wednesday, February 13, 2019, 4:55:51 PM EST, Dennis Tillman W7PF <dennis@ridesoft.com> wrote:

My daughter spotted this 7904A / 7A26 / 7D15 for sale for $150 in a thrift
shop in Salem MA.

The address is

Witch City Consignment and Thrift Store

Downtown Salem, MA



She has no connection with this item and neither do I.

A 7904A for $150 is a great price.



Dennis Tillman W7PF


Re: SIGSALY 1942 ADC recreation with tubes

Trevor
 

Jon-
Interesting project.

The oscilloscope in the photo of one of the original machines appears to be a DuMont 2551, not the beloved Tektronix we discuss here, but hey, Tektronix was not born yet back then.
Reading about the SIGSALY was a good diversion this morning:
https://www.nsa.gov/about/cryptologic-heritage/historical-figures-publications/publications/wwii/sigsaly-start-digital/
Trevor

On Wednesday, February 13, 2019, 7:34:11 AM EST, Froggie the Gremlin <jonpaul@ix.netcom.com> wrote:

Hello All:
Perhaps off-topic,

Please see my SIGSALY 1942  ADC recreation with tubes, in February IEEE Spectrum:
Printed magazine has the first link article.

https://spectrum.ieee.org/geek-life/hands-on/rebuilding-a-piece-of-the-first-digital-voice-scrambler
https://spectrum.ieee.org/geek-life/hands-on/sigsaly-analogtodigital-converter-construction-and-debugging

Your comments and feedback appreciated.

Jon


Need another 475 part ...

Mike Harmon
 

Thanks to Tom Jobe for the current calibration loop for the 475 that I'm helping a friend get working!

I have just discovered another drop-related problem with the scope. The horizontal position pot (right next to the current loop), is also damaged beyond repair. It's a dual-shaft square pot, with a 10K pot in the panel position and a 1K pot in the rear position. I even dismantled the pot thinking there might be a chance I could fix it. Nope, it's toast! Also the knobs that I thought might work won't fit, so I guess I need the knobs as well.

I don't expect people to send me this stuff without being paid for it. Please let me know and I'll send you green stamps or PayPal, or whatever works for you.

This friend isn't technically skilled enough to get into a component-level repair, so I'm trying to help him get this scope up and running. He's a young guy and this is his first scope. I guess I got him into this, because I told him he would be better off getting an older professional-grade scope than to spend his money on a plastic uni-board, SMT offshore scope. So much for my big mouth!

If anyone can help, I will be most appreciative!
Mike Harmon, WB0LDJ
mharmon at att dot net


Re: OT capacitor question

 

I will be using a wire wound 5W inrush current protection series resistor. I'll measure its inductance when it arrives. Since the mains freq is just 60Hz the inductance will have negligible effect....I can probably increase the resistor's inductance by bonding a soft iron 'nail' to the body to squash HF noise. The soft iron will also help with heat dissipation (3 to 4 W). I understand that motor related line noise can reach 30Mhz.

It will be an interesting result, using the resistor as an inductor. I can probably do some testing with my function gen to define the noise attenuation. Plus there's the MOV across the line and neutral doing some capacitive snubbing as well.

Ancel


SG 504 levelling heads availability

 

Hi All:
Getting these lemo connectors is getting harder every day.
But here are 2 more calibrated heads if u need.
https://www.ebay.com/itm/132801983494
thx Ancel


Re: 2465B, 2467B CAL, restoration - U800 cooling

 

I just threw together a hackaday.io project regarding my own 2465A scopes.
It might have some usefulness here.
https://hackaday.io/project/163890-tektronix-2465-series-servicing


Re: 2467B "CT TEST 86 FAIL 02" Error

thespin@...
 

I've connected, in the appropriate positions, ribbon cables C and E, and the pair of coaxes D, and on the opposite side of the instrument, a rather wide ribbon cable that passes through the side of the chassis. Seems like everything is connected OK. What's the next thing to check?

On Tue, Feb 12, 2019 at 10:16 AM, Chuck Harris wrote:


It usually means you have left a connection undone. Check
the connections to the CTT board that pass through the chassis
to the motherboard side of the scope. (Ribbon and two coax).

-Chuck Harris

thespin@gmail.com wrote:
Hey All,

After repairing the power supply on a 2467B, it boots up but to the error of
"CT TEST 86 FAIL 02."

The options manual indicates this failure corresponds to "In Trigger After
Delay mode with the delay time set longer than the delay, there was no sweep.
Check B AUX TRG and HO at U6190 and output O1 at U6140." Is this a failure
that others have seen? Could I have left a cable loose somewhere? U6190
appears to be some sort of gate array, and I'm not sure where I'd find a
replacement. I'm also not sure how to get at the B AUX TRG/HO/O1 signals on
the specified ICs, as the board needs to be installed face down to be powered
by the power supply. Maybe I should install little wires or pieces of coax to
bring the signal out?

Best,
Evan




Re: Tektronix 577-177 test jig measurements.

Jared Cabot
 

Hi,

Yep, I got that 3/4" (19.01mm in metric land) no worries.
The other measurements make sense too, I just gotta remember to recalibrate myself in inches when working on this stuff. :D

That drawing that Glydeck posted looks to be exactly what I need. I'll compare it to the drawing I made and see how far off I was....

Tom, if you could email me some of those photos, that would be great. I always like seeing different ways of doing stuff so I can get new ideas or see things I didn't think of. :)
I plan to make some of my own adapters with stacked PCB's spaced by brass standoffs to make a kind of sandwich. Standard base with banana jacks on ground floor, 1st floor will be the specific layout to the test socket in question and second floor will have cutouts and mounting holes for mechanical support of the test sockets and also labels etc.


Re: Tektronix 577-177 test jig measurements.

tom jobe <tomjobe@...>
 

After further thought, I remembered that I had a box with many bits and pieces left over from repairing quite a few broken Tektronix test fixtures years ago.
In the box were sketches of the various parts I had made complete with dimensions, which brought back some of this from memory.
The banana pins on the back of the original Tek test fixtures get centered by the threaded part of the screw that fastens them into the test fixture body, and in the extreme case I measured today, the screw diameter over the threads is 0.020" smaller than the largest hole in the test fixture bodies I measured, so the center to center dimension of any two banana pins can easily be off of the nominal 0.750 center to center dimension by 0.020" or 0.5 mm, which is not good.
Obviously I had seen this problem before, because I had accurately made the five hole pattern in a piece of 1/2" thick steel plate with the holes slightly smaller than the original test socket holes, and used that as an assembly jig for the test fixtures. With the five pins slightly loose in the test fixture body, the test fixture was plugged into the steel piece and had the banana pin screws tightened to get them close to the nominal spacings. You could do the same thing by loosening the pins a little and plugging the test fixture into your curve tracer before gently re-tightening the screws in a gradual fashion like it was a cylinder head on an engine.
On the small Kelvin test fixtures there are four small #2-56 threaded screws that come from the backside that hold the top cover plate on. Be careful about how much re-tighten these screws on re-assembly as the threaded boss will break off of the backside of the test fixture cover plate very easily... as you probably know all too well if you have worked on these test fixtures.
I had several used test fixtures I had bought with these threaded bosses pulled off of the cover plates, so I made some threaded brass pieces that had a head on them like a nail. They dropped through the holes I drilled in the original cover plate corners and were secured with epoxy on assembly. This arrangement used the original style of tiny #2-56 screw fastening from the underside of the test fixture.
If anyone is interested in any of this, I will provide some dimensions and photos of whatever you want to see, but only directly to the person who requests it. If you want to share this information or think it needs to be posted elsewhere, you can do that.
tom jobe...

On 2/13/2019 1:23 PM, tom jobe via Groups.Io wrote:
Hi Bob,
I checked the two 575's I have and they fit the later style test fixtures that have the Kelvin connectors quite well. I also checked the with some 'Pomona' brand dual banana plugs so that I was only testing two banana plug sockets at a time, and again all seemed well.
Measuring the center to center spacing of the banana plugs on multiple test fixtures showed them to have a range of center to center dimensions of about 0.745 to 0.755 inches or  18.92 mm to 19.18 mm.
The nature of banana plug hardware seems to be very forgiving of small errors in the center to center spacing.
tom jobe...




On 2/13/2019 10:16 AM, bobkrassa wrote:
Dennis is correct about the standard 3/4" spacing for dual banana plugs, but on my 575 it is a little difficult to insert the later 576/577 fixtures as the pins on the fixtures seem to be just a bit more than 3/4" apart. Loosening the plastic nuts on the 575 helps but does not allow full insertion.  Seems as though this may have been discussed some time ago on this group.

Bob Krassa ACØJL




7904A / 7A26 / 7D15 for sale $150

 

My daughter spotted this 7904A / 7A26 / 7D15 for sale for $150 in a thrift
shop in Salem MA.

The address is

Witch City Consignment and Thrift Store

Downtown Salem, MA



She has no connection with this item and neither do I.

A 7904A for $150 is a great price.



Dennis Tillman W7PF


Re: Tektronix 577-177 test jig measurements.

tom jobe <tomjobe@...>
 

Hi Bob,
I checked the two 575's I have and they fit the later style test fixtures that have the Kelvin connectors quite well. I also checked the with some 'Pomona' brand dual banana plugs so that I was only testing two banana plug sockets at a time, and again all seemed well.
Measuring the center to center spacing of the banana plugs on multiple test fixtures showed them to have a range of center to center dimensions of about 0.745 to 0.755 inches or  18.92 mm to 19.18 mm.
The nature of banana plug hardware seems to be very forgiving of small errors in the center to center spacing.
tom jobe...

On 2/13/2019 10:16 AM, bobkrassa wrote:
Dennis is correct about the standard 3/4" spacing for dual banana plugs, but on my 575 it is a little difficult to insert the later 576/577 fixtures as the pins on the fixtures seem to be just a bit more than 3/4" apart. Loosening the plastic nuts on the 575 helps but does not allow full insertion. Seems as though this may have been discussed some time ago on this group.

Bob Krassa ACØJL


Re: Tektronix 577-177 test jig measurements.

Glydeck
 

Jared,

I posted a detailed PDF of the 577 / 576 spacing, including the safety switch probe.

Here at TekScopes-groups.io
https://groups.io/g/TekScopes/files/576_577TestFixture.pdf

Added to page 32 of the PDF Manual on TekWiki - w140.com
http://w140.com/Tek_177_service.pdf

Hope this helps,

George

On Feb 13, 2019, at 10:16 AM, bobkrassa <bob@krassa.com> wrote:

Dennis is correct about the standard 3/4" spacing for dual banana plugs, but on my 575 it is a little difficult to insert the later 576/577 fixtures as the pins on the fixtures seem to be just a bit more than 3/4" apart. Loosening the plastic nuts on the 575 helps but does not allow full insertion. Seems as though this may have been discussed some time ago on this group.

Bob Krassa ACØJL



Re: Tektronix 577-177 test jig measurements.

bobkrassa
 

Dennis is correct about the standard 3/4" spacing for dual banana plugs, but on my 575 it is a little difficult to insert the later 576/577 fixtures as the pins on the fixtures seem to be just a bit more than 3/4" apart. Loosening the plastic nuts on the 575 helps but does not allow full insertion. Seems as though this may have been discussed some time ago on this group.

Bob Krassa ACØJL


Re: OT capacitor question

Michael A. Terrell
 

Another problem is that the capacitive reactance goes down as the frequency goes up. That allows spikes and line noise to cause failures on circuits with large, switched inductive loads.


Michael A. Terrell

-----Original Message-----
From: ppppenguin <tekscopes@borinsky.co.uk>
Sent: Feb 13, 2019 9:51 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] OT capacitor question

I don't like them much either but they can be an economic solution. I'd far rather have a double wound transformer or, if appropriate, a switchmode PSU, but these are expensive solutions compared to a capacitor dropper.

AFAIK, the 2 main failure modes of capacitor droppers as proposed by the OP are:

1: Short circuit cap. This will toast the equipment that's being supplied and might be a fire hazard. A fuse or other device must be there to fail open circuit before it gets out of hand.
2: Gradual reduction of the capacitor value as it safely absorbs transients and blows away more and more of the foils. Eventually the kit will stop working as it won't get enough power.

22241 - 22260 of 176601