Date   

Re: Shootout of Substitute SG504 heads = a better head.

 

David and Ancel,
My interests in the SG504 are slightly different. After my first attempt at
measuring the flatness of David's head it was pointed out nicely but firmly
that my methodology had some serious flaws. RF is not my area of expertise.
It would be accurate to say I don't have any area of expertise at all since
I have avoided becoming an expert in anything in favor of becoming adept at
as many things as possible (a jack of all trades).

Several years passed after my first attempt at measuring the flatness of
David's head when George Steen gave me one of his original SG504 heads. At
that point it became possible for me to do a better (still not perfect in
some people's eyes) test of David's head by comparing it to George's head.
By comparing the two I was able to eliminate many of the flaws that plagued
my first attempt. I learned a great deal from my earlier mistakes and was
able to make more accurate measurements the second time around.

Some might wonder why it would be worth concerning ourselves with
differences that are less than 0.1dB. The answer is simple - because we can.
Between the first and second time I did this test I became a lot more
rigorous, or less sloppy if you prefer, in how I made my measurements. The
criticism of my first attempt made me a better experimenter.

Having three different versions of the head, designed over a 40+ year
timeframe, is an opportunity to see what progress we have made in RF design.
Ancel produced what appears to be a great design in about a month. I would
guess David took longer when he did his about 10 years ago. I am sure George
took much longer 40+ years ago.

I would not be able to design anything like this on my own. But I'm learning
a great deal from testing what they have done.

Dennis Tillman W7PF

-----Original Message-----
Sent: Sunday, March 20, 2016 5:22 PM
Subject: RE: [TekScopes] Shootout of Substitute SG504 heads = a better head.

The build I have for your head uses a gold plated SMA launcher. Mine uses a
modified Nickel/brass BNC launcher. As you can note from the pic the SMA
launcher requires a SMA coupler to connect to the minicircuits SMA
attenuator whereas mine requires an BNC-SMA adapter to achieve the same.

Given that the SMA coupler I used is from Kirkby Microwave as part of the
cal kit for the VNA, I doubt it could be at fault as it has been quality
checked before shipping.
That just leaves the SMA launcher itself as compared to the BNC launcher,
the SMA launcher is not likely to be worse than the BNC launcher which is on
my head. SMA carries a much higher frequency spec. than BNC. The 0.2dB of
loss at 800Mhz looks like some kind of resonance dip as it improves
afterward. That implies some parasitics at work.

There is also the issue of the 10dB cross talk reduction gained by using
different schottky detectors in the new head. It is possible, that at that
frequency, the cross talk between the monoblock combined ref. detector and
the actual detector disturbs the leveling. But that's just a guess.

All in all though, I am satisfied that the design I have is more than
adequate and that both designs do the job.
I think rather than concern ourselves about 0.1dB improvement here or there,
the improvements in the DIY nature of the latest design matters more.

Given the availability of the components used in the new design as well as
the simple build construction any decent home workshop can economically turn
one of these new heads out and I figure that adds longevity to the Tek SG504
instrument lifetime and that's what the forum is all about.
------------------------------------
Posted by: mosaicmerc@...
------------------------------------


Re: Tek 2215

 

In a pinch that is a great idea. Using 1/2 watt resistors would be
even better.

I really think Tektronix ran the Allen-Bradley carbon composition
resistors too close to their voltage rating but apparently it worked
out well enough given that they lasted so long. Maybe they had
experience showing that they did not need to be voltage derated.

On Sun, 20 Mar 2016 23:38:57 -0400, you wrote:

Or you could use a pair of ~ 500k - 1/4 watt film resistors standing off the board for each of the 1 meg resistors. That would spread out the HV stress a bit more.

T


Re: Timebase and CRT Issues on Tektronix Type 545A

 

I have a Lavoie LA-265A which is a clone of the Tektronix 545A and
practically identical. I use the Tektronix 545A manual to work on it.

I agree with Craig because of what I am seeing in your photos; start
with the low voltage power supply outputs. Ignore the -1350 volt
cathode supply and +8650 volt PDA (post deflection acceleration)
supply for now.

It looks to me like one or more of the low voltage power supply
outputs is wrong and what you are seeing on the CRT is the result of
that and massive amounts of ripple causing improper operation.

The scan of the 545A manual at BAMA that vladimirshs mentions is
excellent.


Re: Tek 2215

 

Or you could use a pair of ~ 500k - 1/4 watt film resistors standing off the board for each of the 1 meg resistors. That would spread out the HV stress a bit more.

T

----- Original Message -----
From: David @DWH [TekScopes]
To: TekScopes@...
Sent: Sunday, March 20, 2016 11:17 PM
Subject: Re: Fwd: Re: [TekScopes] Re: Tek 2215



Oo! Oo! I know this one! *raises hand*

This has been discussed on the list before and on EEVBlog by me at
least once but I will quickly cover my recommendation.

The problem is the voltage rating and not the power rating of the
resistors. Tektronix used a string of inexpensive Allen-Bradley
carbon composition resistors so the voltage across any individual
resistor is within its voltage rating although barely. Later these
were replaced with specialized film resistors made by Mepco/Centralab.

Now you can probably get away with using standard carbon or metal film
resistors but their voltage rating is marginal in this application.
Higher power resistors generally have higher voltage ratings so do not
use a 1/4 watt resistor where a 1/2 watt will physically fit.

A better and actually very good option is to use a modern film
resistors intended for high voltage operation like a Vishay 1/4 watt
HVR25 (1.6KV) and 1/2 watt HVR35 (3.5KV) series. 500 volt 1/4 watt
and 700 volt 1/2 watt film resistors are also available but I would
not use anything with a voltage rating lower than that by preference.

On 20 Mar 2016 18:13:39 -0700, you wrote:

>I am still working on the rebuild and someone mentioned the replacing focus resistors network and want to know what resistors need to be replaced ??? I found the parts in the schematic but trying to make sure I get the right parts..


Re: Shootout of Substitute SG504 heads = a better head.

 

So you calibrated the SA by using a stable source (the SG504?) and a
Boonton 4210-4B to about +/-0.15dB and then used the SA to evaluate
the two different SG504 leveling head designs, right?

Why not just use the Boonton 4210-4B directly without the SA?

Do we have any details about how Tektronix determined the performance
of the SG504? The specifications say:

"Flatness is referenced to the NBS corrections of Tektronix standards.
Uncertainties of the NBS are not included in this specification."

Which I take to mean Tektronix sent their golden power meter or other
measuring instrument off to NBS and it was returned with a calibration
curve.


Re: Looking for a Broadband (>1GHz) Noise Source

 

Hi Mike,
Both links are excellent articles and precisely what I am looking for.
Thank you.
Dennis Tillman W7PF

-----Original Message-----
Sent: Sunday, March 20, 2016 2:00 PM
Subject: RE: [TekScopes] Looking for a Broadband (>1GHz) Noise Source

Dennis,
There was a ham construction article a while back, I think in qex, that used a noise.com diode. I think they will calibrate it for a ham at a steep discount.
http://bytecollector.com/archive/misc/BuildYourOwnNoiseSource.pdf
http://www.rf-microwave.com/datasheets/2581_generic_KIT-NS_01.pdf
73,
Mike
N2LYM

On Sun, Mar 20, 2016 at 04:42 PM, 'Dennis Tillman' @Dennis_Tillman_W7pF [TekScopes] wrote:
I am looking for a broadband noise source to use to test my Tek spectrum
analyzers with.
Ideally it should be flat to 1GHz and roll off above that would be
acceptable.
This one on Ebay (eBay item number:251953200778) caught my eye initially
until I saw it was not flat.
http://www.ebay.com/itm/251953200778?_trksid=p2060353.m1438.l2649

<http://www.ebay.com/itm/251953200778?_trksid=p2060353.m1438.l2649&ssPageNam
e=STRK%3AMEBIDX%3AIT> &ssPageName=STRK%3AMEBIDX%3AIT
Does anyone have a recommendation or suggestion for what I should look for?
Thanks, Dennis Tillman W7PF

------------------------------------
Posted by: n2lym <n2lym@...>
------------------------------------


Re: Tek 2215

 

Oo! Oo! I know this one! *raises hand*

This has been discussed on the list before and on EEVBlog by me at
least once but I will quickly cover my recommendation.

The problem is the voltage rating and not the power rating of the
resistors. Tektronix used a string of inexpensive Allen-Bradley
carbon composition resistors so the voltage across any individual
resistor is within its voltage rating although barely. Later these
were replaced with specialized film resistors made by Mepco/Centralab.

Now you can probably get away with using standard carbon or metal film
resistors but their voltage rating is marginal in this application.
Higher power resistors generally have higher voltage ratings so do not
use a 1/4 watt resistor where a 1/2 watt will physically fit.

A better and actually very good option is to use a modern film
resistors intended for high voltage operation like a Vishay 1/4 watt
HVR25 (1.6KV) and 1/2 watt HVR35 (3.5KV) series. 500 volt 1/4 watt
and 700 volt 1/2 watt film resistors are also available but I would
not use anything with a voltage rating lower than that by preference.

On 20 Mar 2016 18:13:39 -0700, you wrote:

I am still working on the rebuild and someone mentioned the replacing focus resistors network and want to know what resistors need to be replaced ??? I found the parts in the schematic but trying to make sure I get the right parts..


Re: OT: underground pipe locating

David DiGiacomo
 

On Sun, Mar 20, 2016 at 7:20 PM, John Miles <john@...> wrote:
This probably works because the ground density and/or topology is subtly
different where the object is buried, just as a consequence of the original
excavation. Machines compact the soil, etc. Focusing on the dowsing rods
takes your conscious attention away from the terrain, but your brain still
maintains its awareness at some level.
The simpler explanation is that it doesn't work any better than chance.

It's hard to put dowsing to a test, because it's just too hard to bury
something without leaving subtle cues behind that will persist for years. I
doubt the JREF would have taken the bet. It would have been fun to hear
Feynman's take on it.
The JREF did indeed put many dowsers to the test, and they all failed.
Example: https://en.wikipedia.org/wiki/One_Million_Dollar_Paranormal_Challenge#Example_of_a_test_.28dowsing.29

P.S. The JREF prize will be back this year or next.


Re: OT: underground pipe locating

Greg Muir
 

It must work with very subtle changes in soil conditions. I can even detect cable runs place by directional drilling techniques.

I do remember reading an article that discussed normal burial techniques and that the soil composition and/or terrain is obviously affected. That could be credible. But the minimal disturbance made by directional drilling makes for a minimal change in soil conditions that are undetectable on the surface.

Greg


Re: Tek 2215

 

The resistors are all 1 meg ohm and are R878, 879, 880, 881, 882, and 884. You can find them on the main board - A10 part layout - Figure 9-8. They are at coordinates 5-H.

HTH,
Tom

----- Original Message -----
From: jasontucker70@... [TekScopes]
To: TekScopes@...
Sent: Sunday, March 20, 2016 9:13 PM
Subject: Re: Fwd: Re: [TekScopes] Re: Tek 2215



I am still working on the rebuild and someone mentioned the replacing focus resistors network and want to know what resistors need to be replaced ??? I found the parts in the schematic but trying to make sure I get the right parts..


Re: OT: underground pipe locating

John Miles
 

This probably works because the ground density and/or topology is subtly
different where the object is buried, just as a consequence of the original
excavation. Machines compact the soil, etc. Focusing on the dowsing rods
takes your conscious attention away from the terrain, but your brain still
maintains its awareness at some level.



It's hard to put dowsing to a test, because it's just too hard to bury
something without leaving subtle cues behind that will persist for years. I
doubt the JREF would have taken the bet. It would have been fun to hear
Feynman's take on it.



-- john, KE5FX





From: TekScopes@... [mailto:TekScopes@...]
Sent: Sunday, March 20, 2016 5:00 PM
To: TekScopes@...
Subject: Re: [TekScopes] OT: underground pipe locating





That's amazing. It's a shame James Randi's Prize is no longer available
since he retired. You could have become a millionaire


Re: Tek 2247A [SN B029000] Recap and diode part list ?

Darren Ting
 

Hi Menahem Yachad

Great info and advice, appreciated.
However, for me to do those in 2247A is a challenge, this PCB board place in-between Main-Board and Processor board, all components lead hide in-between PSU PCB and Main Board making it not accessible to perform live probe as you suggested.
I have to solder wire lead to probe. a bit challenging in this unit


From: "@yachadm [TekScopes]" <TekScopes@...>
To: TekScopes@...
Sent: Sunday, 20 March 2016, 18:04
Subject: Re: [TekScopes] Tek 2247A [SN B029000] Recap and diode part list ?

  When I've had an issue like this, I connect my Fluke DMM to each capacitor lead, and check the voltage - plus or minus, stable or fluctuating.

Then scope the ripple on each lead (if one lead is GND, obviously there won't be any ripple!).


In a couple of seconds, I can determine whether a Regular or BP cap is needed, and what the appropriate voltage rating needs to be.


In older equipment, many times a cap with a voltage rating many times over the actual circuit voltage was required.
Why?
Simply, because an available cap with the correct voltage rating couldn't handle the ripple current.
There are many DISadvantages to using a capacitor with a vastly over-spec'ced voltage rating, but I'm not going to go into that here.








A Let's say Example (simplified for easy understanding):


Capacitor C1234 must dampen ripple of 1086mA, and it has 20.8VDC passing through it.


In the old days, Nichicon's "XYZ" series was the best there was for this circuit, and the 2200uF 25V was capable of only 763mA ripple.
But the XYZ 2200uF 50V could handle up to 1204mA, so that's what the designer specified in the BoM.


Today, Nichicon's HE 2200uF 25V can handle 2860mA, so EVEN THOUGH a 50V capacitor was previously installed (and so specified in the BoM), I am now going to install the 25V capacitor.


This decision would be valid for ONLY Nichicon's HE, because that is what I tested and verified.






To put it simply, you may NOT need a BiPolar in that position, and you may NOT need a 100V or 160V rated capacitor in there, AT ALL.


But you'd have to do some solid measurements to determine what really NEEDS to be in there, and if you'd like to take up that challenge, I would be very interested to know what you discover!


Menahem Yachad
Israel










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[Non-text portions of this message have been removed]


Re: Tek 2215

Jay
 

I am still working on the rebuild and someone mentioned the replacing focus resistors network and want to know what resistors need to be replaced ??? I found the parts in the schematic but trying to make sure I get the right parts..


Re: Shootout of Substitute SG504 heads = a better head.

mosaicmerc
 

I just did a quick check (5 min warm up) as it occurred to me that perhaps the 2nd harmonic was less in my design which made the detector see a lower overall amplitude and compensate the fundamental flatness a little better (a bit higher level).

Well at 650Mhz (6dB input) I can just see the 1300Mhz harmonic at - 44dBm down.
With my head we have a 5.74dBm fundamental level, David's shows a 5.66dBm level. Both show the same 2nd harmonic.

So that's just one less source of the difference although it doesn't answer specifically why there is a difference.


Re: Shootout of Substitute SG504 heads = a better head.

mosaicmerc
 

The build I have for your head uses a gold plated SMA launcher. Mine uses a modified Nickel/brass BNC launcher. As you can note from the pic the SMA launcher requires a SMA coupler to connect to the minicircuits SMA attenuator whereas mine requires an BNC-SMA adapter to achieve the same.

Given that the SMA coupler I used is from Kirkby Microwave as part of the cal kit for the VNA, I doubt it could be at fault as it has been quality checked before shipping.
That just leaves the SMA launcher itself as compared to the BNC launcher, the SMA launcher is not likely to be worse than the BNC launcher which is on my head. SMA carries a much higher frequency spec. than BNC. The 0.2dB of loss at 800Mhz looks like some kind of resonance dip as it improves afterward. That implies some parasitics at work.

There is also the issue of the 10dB cross talk reduction gained by using different schottky detectors in the new head. It is possible, that at that frequency, the cross talk between the monoblock combined ref. detector and the actual detector disturbs the leveling. But that's just a guess.

All in all though, I am satisfied that the design I have is more than adequate and that both designs do the job.
I think rather than concern ourselves about 0.1dB improvement here or there, the improvements in the DIY nature of the latest design matters more.

Given the availability of the components used in the new design as well as the simple build construction any decent home workshop can economically turn one of these new heads out and I figure that adds longevity to the Tek SG504 instrument lifetime and that's what the forum is all about.


Re: OT: underground pipe locating

Malcolm Hunter
 

That's amazing. It's a shame James Randi's Prize is no longer available
since he retired. You could have become a millionaire.

Malcolm


On 20 March 2016 23:50:51 "big_sky_explorer@... [TekScopes]"
<TekScopes@...> wrote:

I'll throw in my thoughts about dowsing for cables and pipes. Have been
using the technique for about 40 years now.

I use the technique described by Mr. Partridge. Two brass brazing rods
with one end bent at a right angle to form small handles. Hold them
loosely in your hands and walk slowly keeping the long extended ends
parallel directly in front of you and roughly parallel with the ground. If
you are reasonably at a right angle to the item underground, the rods will
spread apart when you pass over it.

A couple of caveats - you must hold the rod handles so the extended end
does not brush over the tops of your index fingers. It has to be friction
free. Also, many people will place their thumbs over the top of the
horizontal portion. A no-no. Again friction that hinders the movement.
Also, movement will occur if you are walking under overhead wires.

I have shown this to engineering colleagues, telephone outside plant
people, geologists and others. There was never an instance where I didn't
receive a "you're moving the rods" or "I don't believe it." The I would
let them try it. It ended up with quite a few believers.

But it is interesting to note that not all people could get a response.
That in itself is perplexing. Possibly because they were holding the rods
too tight or something else.

I have located underground cables and smaller wires, energized or no. I
also can locate (obviously) piping even of the plastic variety. I had one
instance where we were getting ready to install a radar site out in the
middle of nowhere. It obviously required some excavation and this was in
the days when there was no "call before you dig" services. As a fun
thought, I had brought my brazing rods so grabbed them and took off across
the field where we were going to do the work. About midway the rods
parted. No one believed that there was anything out there but, to be safe,
I drove a distance each way to check. Lo and behold, the telephone company
had buried a trunk cable right through the middle of the adjacent farmers
pastures and right through the property we were working at. The giveaway
was cable pedestals discovered about a half a mile in each direction of our
location. That was a narrow miss.

A friend asked if I could locate their buried septic tank because they
wanted to have a pumping company come to clean it out. First step was to
locate the piping coming out of the house. Then I walked along the axis of
it until the rods spread apart. That was the end of the tank. Then walked
from the opposite direction and located the other end. The owner knew the
company who built the tank so I called them to determine the location of
the cleanouts. From the spots where I marked the ends of the tank, I
measured in to the center of the cleanout ports, dug down 4 feet and was
directly on center.

Many say that it is disturbances in the earth's magnetic field from the
buried object that affects the rods. But I have been a little skeptical
about that due to the nature of the material int he rods that I use. I
don't think that there is enough strength int he field to induce any eddy
currents in the rods to have them possess any magnetic qualities. So I
will say that "only the Shadow knows."

So, I guess you will never believe it until you try it. Best thing is to
find someone who does it and learn their technique.

Greg


---In TekScopes@..., <telists@...> wrote :

On Sun, Mar 20, 2016 at 3:53 PM, David C. Partridge
<david.partridge@... mailto:david.partridge@...> wrote:
> I use two pieces of brazing wire bent into an L shape - you hold the
short pieces in your hand and the long bits stick out ahead of you.
>
> They will swing as you pass over the pipes. Don't mock it does work to
detect underground water pipes.


http://skepdic.com/dowsing.html





Re: OT: underground pipe locating

Greg Muir
 

I'll throw in my thoughts about dowsing for cables and pipes. Have been using the technique for about 40 years now.

I use the technique described by Mr. Partridge. Two brass brazing rods with one end bent at a right angle to form small handles. Hold them loosely in your hands and walk slowly keeping the long extended ends parallel directly in front of you and roughly parallel with the ground. If you are reasonably at a right angle to the item underground, the rods will spread apart when you pass over it.

A couple of caveats - you must hold the rod handles so the extended end does not brush over the tops of your index fingers. It has to be friction free. Also, many people will place their thumbs over the top of the horizontal portion. A no-no. Again friction that hinders the movement. Also, movement will occur if you are walking under overhead wires.

I have shown this to engineering colleagues, telephone outside plant people, geologists and others. There was never an instance where I didn't receive a "you're moving the rods" or "I don't believe it." The I would let them try it. It ended up with quite a few believers.

But it is interesting to note that not all people could get a response. That in itself is perplexing. Possibly because they were holding the rods too tight or something else.

I have located underground cables and smaller wires, energized or no. I also can locate (obviously) piping even of the plastic variety. I had one instance where we were getting ready to install a radar site out in the middle of nowhere. It obviously required some excavation and this was in the days when there was no "call before you dig" services. As a fun thought, I had brought my brazing rods so grabbed them and took off across the field where we were going to do the work. About midway the rods parted. No one believed that there was anything out there but, to be safe, I drove a distance each way to check. Lo and behold, the telephone company had buried a trunk cable right through the middle of the adjacent farmers pastures and right through the property we were working at. The giveaway was cable pedestals discovered about a half a mile in each direction of our location. That was a narrow miss.

A friend asked if I could locate their buried septic tank because they wanted to have a pumping company come to clean it out. First step was to locate the piping coming out of the house. Then I walked along the axis of it until the rods spread apart. That was the end of the tank. Then walked from the opposite direction and located the other end. The owner knew the company who built the tank so I called them to determine the location of the cleanouts. From the spots where I marked the ends of the tank, I measured in to the center of the cleanout ports, dug down 4 feet and was directly on center.

Many say that it is disturbances in the earth's magnetic field from the buried object that affects the rods. But I have been a little skeptical about that due to the nature of the material int he rods that I use. I don't think that there is enough strength int he field to induce any eddy currents in the rods to have them possess any magnetic qualities. So I will say that "only the Shadow knows."

So, I guess you will never believe it until you try it. Best thing is to find someone who does it and learn their technique.

Greg


---In TekScopes@..., <telists@...> wrote :

On Sun, Mar 20, 2016 at 3:53 PM, David C. Partridge
<david.partridge@... mailto:david.partridge@...> wrote:
> I use two pieces of brazing wire bent into an L shape - you hold the short pieces in your hand and the long bits stick out ahead of you.
>
> They will swing as you pass over the pipes. Don't mock it does work to detect underground water pipes.


http://skepdic.com/dowsing.html


Re: Tek 485 - Intensity at Max, Cannot Adjust Down

Tom Gardner
 

On 20/03/16 23:26, otrfan01@... [TekScopes] wrote:

Now, the trace is very bright (enough that if it is moved down onto the screen, it will occasionally trip the protection circuit and cause the power supply to cycle). The intensity control has no effect.

I have checked the DC restorer diodes with my DMM - all appear OK.
I am led to believe that is an insufficient test.

Would anyone familiar with this type of problem be able to advise next troubleshooting steps?
I recently had a similar problem on a 465, as discussed in the thread "Tek 465 intensity problem".

In my case the HV diodes and capacitors were OK, and the problem was that the grid pin/wire had visibly separated from the grid electrode.


Tek 485 - Intensity at Max, Cannot Adjust Down

wmactor
 

Hi,


I have been working on a non-functional 485 that I picked up. I discovered that the inverter was cycling rapidly on and off. I resolved an issue that was shorting out the +15V power line, which restored all power supply voltages to their correct levels.


Now, the trace is very bright (enough that if it is moved down onto the screen, it will occasionally trip the protection circuit and cause the power supply to cycle). The intensity control has no effect.


I have checked the DC restorer diodes with my DMM - all appear OK.


Would anyone familiar with this type of problem be able to advise next troubleshooting steps?


Thanks, Wayne


Re: Timebase and CRT Issues on Tektronix Type 545A

Craig Sawyers <c.sawyers@...>
 

545A Pics http://imgur.com/a/OxwlC
Offhand I'd be looking at the power supply, and the timebases (which hinge out for easy access).

Do you have a valve/tube tester?