Date   

Re: Spectrum analyzer Tektronix 7L13 on mainframe Tektronix 7603

Attilio
 

Here I am,
I restarted with another external power supply and the frequency meter connected to the IF output of the oscillator and I have these results:
with control voltage at 17.5 V dc the frequency is 2095.050 MHz, with 20 Vdc it is 2097.600 MHz.
I made four more measurements: with a control voltage of 8.3 Vdc the frequency is 2072.019 MHz, with 12 Vdc it is 2085.740 MHz, with 15 Vdc it is 2091.650 MHz, with 16.5 Vdc it is 2093.122 MHz.
The absorbed current is constant at 28 mA.

I don't know, but I think the control voltage output from the PLL is a bit at the limit.
I suppose 20 Vdc for the oscillator is a limit not to be exceeded (with 20 V it reaches 2097.6 MHz), but the PLL stops at 17.6 V at the maximum.

--Cheers
Attilio


Re: 561 scope extender wiring?

Albert Otten
 

I meant ordinary wire except for the coax lines.

In my extender I used ordinary wire, not twisted or whatever.


Re: 2465B CRT board values

Chuck Harris <cfharris@...>
 

Hi Hirofumi,

One thing to note is that Tektronix didn't expect that you
would be able to get perfect results in the outer most
major divisions of the CRT graticule. I always try for
perfection, but if you have to have a little geometric
distortion, or less than perfect focus, that is where it
should happen.

-Chuck Harris



Hirofumi Momose wrote:

Hi Chuck,

Scopes, like the 2465B, have only a single electron beam to
draw all that is on the CRT screen. They do this by time
multiplexing the beam between the readout, and the traces.
Flicker less readout with single gun displaying multiple
traces, various timebase is a magic to me.

Especially, I feel a bit difficulty to get best result from
CRT adjustment is interact of geometry and edge focus.
To minimize the vertical edge curveture(CAL 08)
causes the edges to being some degree of defocus.
Focusing on edge causes the center to defocus...
All of these are interact at some extent and to get best result
needs 'dialog' with the scope.
But now, got satisfactory level.

Best regards,
Hirofumi JJ2PNX






Re: 561 scope extender wiring?

Albert Otten
 

Hi Charles,

You will have seen that the coax to pines 3 and 4 has a crossover between left and right connector. For fault finding in the 3T77A I would do as in the time base connector, that is with braid to pin 4. Don't connect the braid to the ground wire! The other coax at pins 18/19 is straightforward.
BUT as far as I can see the 3S2 makes no use of pins 3/4, so cannot trigger the 7T11A internally. In the 3S2 diagrams you can see that the trigger signal merely goes to the Trigger Out front panel connector.
In my extender I used ordinary wire, not twisted or whatever. Remember that you normally won't use the extender during (HF) calibration. IIRC all adjustments can be reached from the left and right side of the oscilloscope.

Albert


Re: Waking a slumbering 475

 

Steve Hendrix wrote:

I know of a new makerspace that would fit the bill, but where are you located?
I'm just outside Washington D.C.

I had thought that there were makerspaces near me, but they look like shared office space and don't say anything about 3D printing or other services.

-- Jeff Dutky


Re: 561 scope extender wiring?

 

I took a look at the schematic of the 561A. It appears that only pins 3/4 and 18/19 use coax to carry fast signals (trigger to timebase, strobe to sampling plug-in).
Still wondering what the deflection plates should use - would twisted pair be ok?


Re: Waking a slumbering 475

Weathers, W
 

Thank you to all who have responded to this thread. You have already given me useful information.

My intent is to take this slowly, as time allows. I did manage to slide the cover off the DM44 and tighten that loose (panel) jack nut.


Re: 549 transformer question

ykochcal
 

Hi
A time ago, I tried to rewind a 647 transformer, random ish wind with liquid
styrene coating on each layer, worked for a while but insulation failed the
way I did it(as the winding went from 2 wires to one I should have spaced
the one wire, I think I had too much voltage per layer.

In the process I took apart a 305 transformer.

The core is very brittle.

The core is gapped and I figured that because I broke both legs if they were
glued back together the thin layer of glue would just be a fraction more
gap.

The core broke in disassembly, but I measured it and the details are on a
document at http://snyders.site/Pages/Electronics_2015.html

Measurements of dimensions after dissection 1/23/15

305 Core Dim and connections Yel 15 0122.pdf

John

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of
Jean-Paul
Sent: Tuesday, February 09, 2021 2:42 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 549 transformer question

Hello again

We used many ferrite cores in SMPS and some HV designs since 1970s and have
a shelf of old stock, as well as the original printed catalogues. We used
Ferroxcube, Stackpole, TDK, in EI, EE, ER, and other shapes, most have no
gap, in usual power matériels for 20-50 kHz.

Most standard cores sizes are available today from Epcos, or TDK, in EU. US
sources are Fair Rite, TDK.

If you can post clear photos and dimensions I can look at what I have, we
might get lucky.

Happy to assist,

Kind Regards

Jon


Re: was 549 transformer question

Michael A. Terrell
 

Tom Lee wrote:

Hilarious! Nice improvisation with the Heathkit.

Tom

My motto is, Never piss off the Engineer!. When I got to basic I was told I
could be a cook or a truck driver. I told off an E8 and a Captain. I had
five medical 4F ratings, but was drafted because I worked in Electronics.
They told me I would be given the hardest electronics test in the Army and
that I would fail because no one had ever passed. It was 110 questions, and
you were given two hours, 15 minutes. The average score was 22/110, and
passing was 42/110. They gave me a copy with only 88 questions and laughed.
I finished it in 17 minutes, and my score was 82/88. The school wa


Re: Waking a slumbering 475

Steve Hendrix
 

At 2021-02-09 10:59 AM, you wrote:
Are you open to expanding your offerings? I've been looking (unsuccessfully) for a local MakerSpace with 3D printers, so that I could print a few things (e.g. some kickstands for DMM916s, top and bottom plates for TM500 plugins, TM500 latch release parts, and maybe see what can be done to produce press-on knobs for 2200 and 2400 series scopes).
I know of a new makerspace that would fit the bill, but where are you located?

Steve Hendrix


Re: 549 transformer question

Chuck Harris <cfharris@...>
 

Hi Roger,

We know everything about the cores, as the full Allen-Bradley
specifications are all over the net. It is A-B's "W5" material,
and the core shape is an E core.

A-B number for the ungapped half is: E1960S011A
A-B number for the gapped half is: E1960S021A.

The gap is 0.015" and on the center leg.

Le = 2.98" (effective length)
Ae = 0.271 sqin (effective area)
Ve = 0.812 cuin (effective volume)
Aw = 0.287 sqin (window area)

Saturation Flux Density 4900 Gauss @ 10 Oersteds @ 16KHz
Initial Permeability 2800 ui @ 16KHz
Core Loss (Pcl), (uW/cm3 -Hz) @ 1350 Gauss 2.5uW/cm3-Hz

TDK bought A-B, and liquidated them. TDK made everything that
A-B did, except the old fashioned cores, which they did not want
to make. A-B was bought to eliminate a competitor.

And being a gapped core, with 0.015"" gap, the core
material characteristics are relatively unimportant.

The problem is the core's shape. The core is of the E style,
but it has an octagonal center leg, and two rectangular outside
legs.

The dimensions are:

overall thickness = 0.52"
overall length = 1.960"
max winding diameter = 1.408"
outer legs = 0.52" x 0.267"
center leg = 0.52" x 0.488" (octagonal)

Initially, tektronix bought ungapped halves, and used 0.008" tape
to apply the gap to all three legs equally. Then they started buying
one gapped, and one ungapped half core, with 0.015" gap. And finally,
they got smart, and bought the cores gapped to 0.075", and assembled
them for 0.015" gap, simplifying inventory.

They used this same core for all of their tube scopes after the earliest
oil dunked scopes that operated at 1KHz (or should I say 1Kc?).


In modern magnetics, you have essentially four choices:

1) toroid
2) pot (cup) core
3) sectioned pot (cup) core
4) E core.

Toroid is out for the obvious reasons. Cup core is out because
the access to the winding area is limited, and the inner area
doesn't allow you to keep your winding away from the ferrite.
Sectioned pot cores have better winding access, but the legs are
still too close to the outer wrap of the winding for HV.

E core would be the best choice, except that square windings are
a really bad thing for HV, as the corner bends launch corona and
stress the wire insulation. So, you would have to use a round
former for the winding, and waste a lot of your winding space.

I have searched all the major companies, and none have anything
even close to suitable. Usually the dimensions are done to
maximize efficiencies for low voltage switchers, and A-B was
making HV cores.

Few of the owners of 500 series scopes own them as daily drivers.
They are more of a collector's item. It is desirable to have them
work, but it is also desirable to keep them as original as possible.

The old ferrite is best.

-Chuck Harris


Roger M wrote:

Hi Chuck,
Yes, I agree, the best solution is a rewind of the transformer.
Yet, in the continuum of poor, fair, good, better, and best, there
may be a method that is acceptable to the extent that its "good
enough".

This topic interests me but I have to admit I'm hampered by not
having even one failed transformer in my possession. In my life
I've owned and used a prototype 546 (for some 25+ years),
a rack mount 547 (some 15 years) and now a couple of recently
acquired bench model 547's. None of which have ever exhibited
the HV disease.

Some weeks ago I purchased some Tek parts needing a new home.
Among which are some apparently rewound 120-0308-00 transformers
at least one of which I'd swap for one in otherwise good condition
that has the thermal runaway issue.

On the topic of the unobtainable ferrite cores I should ask:
was Tek's vendor Stackpole? Do we know the mix type of the ferrite?
Not wanting to risk damage in disassembling a transformers I have
on hand, I assume the core is gapped at one or both of the center
legs. Have you noted what the gap dimension is?

Looking at what is currently (and readily) available, there's
the Ferroxcube core E47/20/16 in 3C94 material (for example).
Its too thick for direct fit into Tek's plastic HV enclosure,
but that's what a clamp jig and a Home Depot (Harbor Freight?)
diamond blade tile saw are for.

I plan to order some and "dink around" as time permits...

-Roger






Re: Selenium rectifiers in Tek equipment

Stephen Hanselman
 

My favorite PS used an old Burroughs transformer which I cut 4 turns off the
secondary. This meant removing 18" of 4in wide copper strap. That was fed
through a bridge to 50,000uF of filter cap. First time I turned it on the
bridge literally blew apart. Yup needed a bit of series R to "soften the
blow".

Great thread

Steve

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Tom Lee
Sent: Monday, February 8, 2021 11:50 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Selenium rectifiers in Tek equipment

Exactly. I never followed the lore because, as a teenager, I wasn't aware of
the lore. I foolishly replaced blown seleniums with whatever rectifiers I
had on hand from Poly Paks ("U test 'em and save"). Never had a problem, but
perhaps it was just dumb luck. When I later worked in TV repair, I learned
that I had violated proper procedure, but by that time, most gear with
seleniums had either been junked or upgraded. I've only replaced a few since
then, sometimes with added resistance to drop the voltage, but sometimes
not. Always in my own gear, so that I alone bear the risk.

Tom

Sent from an iThing, so please forgive the typos and brevity

On Feb 8, 2021, at 23:13, "Joe Laffey" <joe@thestable.tv> wrote:

On Mon, 8 Feb 2021, Tom Lee wrote:

The short answer is resistance. It's not only a matter of forward drop at
low currents (which the oft-quoted 1V number refers to; the drop at rated
current can easily be an order of magnitude higher). Selenium rectifiers
have considerable forward resistance (hundreds to thousands of ohms,
depending on the specific device), compared to the small number of ohms
typical of silicon rectifiers. So if you need to emulate selenium
rectifiers with silicon ones, you have to degrade the latter by adding
series resistance.

Not all circuits need such emulation, but the general practice among
old-time radio techs was to be conservative. "You'll pop the filter caps if
you don't have that resistance to soften the blow" is a common bit of lore.

I don't think you are going to harm modern caps with inrush current in
most cases (as you seem to indicate as well with your "lore" comment). The
transformer will usually help buffer this inrush. Old caps are a different
story, especially if you are one of those guys who thinks its wise to keep
20, 30, or 40+ year old electrolytic caps in your equipment (not I).

For me the easiest method is to measure the voltage with the selenium
rectifier in place (bring it up on a Variac). Then put a series resistor
after your silicon rectifier to lower the voltage to the same level (mind
the power rating for heat dissipation of course). Use Ohm's Law and then
adjust for tolerances or math errors ;-) You may even want to measure the
voltage at 117VAC input (or whatever the original expected line voltage was)
and then adjust the resistor value to match that output voltage at your
normal modern line voltage.

Most old equipment can handle fairly large swings in input voltages.
Though it may need to be re-aligned at modern voltages vs. old lower
voltages.

--
73
Joe Laffey





Re: 2445B 2467B - non Tek probes

Harvey White
 

I tried to find the one that I had taken apart, but without success.

I think that there are two types, possibly distinguished by the plastic color.

The one that I remember was light gray.  The plastic was in two pieces, the body and a ring at the end.  I seem to remember that the ring can be pried off.  Once that is done, the mechanical parts can simply be pushed out.

The second one that I just looked at was a black plastic.  In this case, the body apparently had the ring permanently attached. There are a number of small fingers that grab the back of the metal insert.  I suspect that you can just push out the connector using a defunct panel mount BNC shell.

Harvey

On 2/8/2021 10:47 PM, Jeff Dutky wrote:
Harvey,

I have been trying to figure out how to remove the plastic shell on the BNC connector and have not had any luck, even where i have connectors that are partly disintegrated. Maybe I have simply been too gentle in my investigations. If you can recall how this is done, I would be eager to know.

-- Jeff Dutky





Re: Selenium rectifiers in Tek equipment

Brad Thompson
 

Tom Lee wrote on 2/9/2021 2:50 AM:

Exactly. I never followed the lore because, as a teenager, I wasn't aware of the lore. I foolishly replaced blown seleniums with whatever rectifiers I had on hand from Poly Paks ("U test 'em and save"). <snip>
Hello, Tom and the group--

Polypak's other motto: "We bot [sic] thousands, no time to test."   In practice, one could learn a lot
from a homebrew curve tracer add-on for an oscilloscope and a bag of diodes-- intermittents and weird
breakdown characteristics showed up on screen. Also, sometimes a PolyPak would turn out to contain
pretty good surplus parts.

Back to selenium rectifiers: years ago, an industrial-controls company manufactured its own isolated interface
modules that used triacs as AC  switches for 120 and 240 VAC. To protect the triacs against voltage
spikes, the designer selected transient suppressors containing stacks of fingernail-size selenium plates
encapsulated in black epoxy and resembling candy gum balls (licorice flavor).

One lot of 240-volt interface modules exhibited a problem: the suppressors were bursting into flames, emitting
selenium fumes and stinking up the test area in the process.

The selenium "gum ball" manufacturer sent an engineer to investigate the problem, which turned out to contain several
smaller problems revealed in a meeting.

--The interface-module manufacturer didn't perform incoming inspection on the "gum balls".
--The "gum balls" were totally unmarked (their uneven surfaces precluded marking with ink stamps).
--The "gum ball" encapsulation process applied poorly-controlled amounts of epoxy.
--Overencapsulated  120-volt suppressors were mixed with 240-volt parts.
--The manufacturing group selected larger "gum balls" for installation in the 240-volt interfaces.

Someone at the meeting asked the "gum ball" engineer whether fumes from
the smouldering selenium parts was hazardous. "Of course not!" he replied,
"I've been working with selenium for years." ...And proceeded to cough a lung-shattering
liquid cough that completely spoiled his credibility.

Fortunately, GE had announced its line of metal-oxide varistors (MOVs) which were
better characterized and marked with part numbers.

73--

Brad  AA1IP

--


Re: Selenium rectifiers in Tek equipment

Kurt Rosenfeld
 


561 scope extender wiring?

 

Since I'm going to be working on this 3T77A plug-in for a while, an extender is necessary. Some years ago I acquired a pair of Amphenol connectors with the intention of building my own extender, but never got around to it.

Does anyone have a schematic so I don't have to figure it out from the 561 manual (I imagine most connections are simple pin-to-pin but do I use coax or twisted pair for the deflection signals?)

thanks

Charles


Re: Selenium rectifiers in Tek equipment

Dave Wise
 

?Coming to the party late, but I seem to recall that the instructions for one of the Se-to-Si Mod Kits stated that the purpose of the added resistance is to avoid excessive regulator input which will overheat the pass tubes. At least in some instruments, there are already resistors ahead of the reservoir caps which (a) reduce inrush and (b) furnish a handy point to estimate current.


Dave Wise

________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Tom Lee via groups.io <tomlee=ee.stanford.edu@groups.io>
Sent: Monday, February 08, 2021 11:50 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Selenium rectifiers in Tek equipment

Exactly. I never followed the lore because, as a teenager, I wasn't aware of the lore. I foolishly replaced blown seleniums with whatever rectifiers I had on hand from Poly Paks ("U test 'em and save"). Never had a problem, but perhaps it was just dumb luck. When I later worked in TV repair, I learned that I had violated proper procedure, but by that time, most gear with seleniums had either been junked or upgraded. I've only replaced a few since then, sometimes with added resistance to drop the voltage, but sometimes not. Always in my own gear, so that I alone bear the risk.

Tom

Sent from an iThing, so please forgive the typos and brevity

On Feb 8, 2021, at 23:13, "Joe Laffey" <joe@thestable.tv> wrote:

On Mon, 8 Feb 2021, Tom Lee wrote:

The short answer is resistance. It's not only a matter of forward drop at low currents (which the oft-quoted 1V number refers to; the drop at rated current can easily be an order of magnitude higher). Selenium rectifiers have considerable forward resistance (hundreds to thousands of ohms, depending on the specific device), compared to the small number of ohms typical of silicon rectifiers. So if you need to emulate selenium rectifiers with silicon ones, you have to degrade the latter by adding series resistance.


Re: Selenium rectifiers in Tek equipment

Matt
 

I purchased a Tek 575 Mod 122C curve tracer a couple of years ago from a Craig’s List seller. There was an original Instructional manual included along with instructions for a Mod kit (040-0223-00) which replaces the selenium rectifiers with silicon rectifiers. This Mod has not been incorporated into the curve tracer and I don’t have the necessary parts to do so. I don’t have the two ceramic strips that were used in the kit (#124-0089-00 Strip, cer, ¾ x 7 notches, clip mounted) or the bracket (#406-0815-00 bracket, silicon rectifier mounting) to mount the new silicon rectifiers. The remaining parts (the rectifiers, and solder lugs and spacers I figure can be obtained from Mouser. I know that I could mount the rectifiers on something other than the ceramic strips, but I am a bit anal (OK, perhaps more than just a bit) and I like to do it the right way.

If anyone has one of these Mod Kits available or just the ceramic strips, I would be interested in purchasing it.

It is interesting to note that the selenium rectifiers are being replaced with silicon rectifiers without any extra resistors for dropping the voltage as was suggested in this thread might be necessary.

As a youngster, I too recall salvaging a selenium stack from an old B&W TV, stripping the paint off and using the plates as a photo electric cell. The biggest challenge was figuring out how to fasten wires to the plates!


Re: Spectrum analyzer Tektronix 7L13 on mainframe Tektronix 7603

Attilio
 

Hi everybody,
sorry for the delay, I made some tests following Ed's instructions. By connecting the oscilloscope to the output of the oscillator control voltage coming from the PLL with the P446 connector disconnected, there is a signal that starts at + 1.6 Vdc rises up to 17.6 Vdc it remains there for 8 ms then it gradually drops to + 1.6 Vdc in 8ms then after about 200ms it repeats and so on. By connecting the P446 connector and the IF output to the input of the amplifier at 100 MHz, the signal on the P446 connector remains the one described above, then connecting the 1st LO output of the 7L13 to the 2nd LO input of the TR503 and tuning the center frequency of the 7L13 to have on the 1st LO output about 2200 MHz (FC at 109 MHz) the signal on P446 changes into an almost square wave that varies from + 14.6 Vdc to + 17 Vdc giving the idea that the PLL is working.
By connecting the 2nd LO output of 7L13 to the 2nd LO input of the TR503, the signal on P446 rises to + 17 Vdc and remains a straight line as if the output were saturated at the maximum level.
I think the problem is the signal level at the input of the 2nd LO of the TR503 (the 1st LO of the 7L13 comes out with + 10 dBm, while the 2nd LO comes out with - 5 dBm).
As soon as I can I do other tests, the problem is that I don't have an adapter to connect to the IF output of the oscillator to measure the frequency.

--Cheers
Attilio


Re: Waking a slumbering 475

 

Jeff (Davis),

Are you open to expanding your offerings? I've been looking (unsuccessfully) for a local MakerSpace with 3D printers, so that I could print a few things (e.g. some kickstands for DMM916s, top and bottom plates for TM500 plugins, TM500 latch release parts, and maybe see what can be done to produce press-on knobs for 2200 and 2400 series scopes). Would you be up for small runs like that?

-- Jeff Dutky

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