Date   

Re: 547 scope HV transformer problem. One practical solution.

 

It is not only the enjoyment of the scope working, but also of the challenge of going around its HV problem.
I had incorrectly written that the plug-in on my scope is the 1A1, but it turns out the that one I have is the CA, an honorable senior dual-trace made 100% with vacuum tubes. I really like its design and the way it works competently. At the beginning waking up from the 40 years hybernation it was full of quirks, in part due to the old switches and the two gain potentiometers cracked and intermittently open. I shorted them out and I am waiting for replacements. But the more I use it the more quiet and behaved it becomes. This is the same with the whole 547. I had never cleaned it from some dirt accumulated in 40 years through the cover holes, many tubes are dirty, but I didn't dare to blow with compressed air or... god forbid ...wash it. But all by itself it is recovering from some shortcomings. The two time bases work fine, I can get delayed triggers, B intensified by A, trace separation, etc. etc. Retrace blanking and chopped blanking work fine. What a wonderful instrument!

One feature missing in the CA is a trigger signal from one of the channels so that one can use the alternate and chopped functions without having to trigger the scope externally. So I brought out the signal from the first stage of channel A, at the cathode of V3323, to the connector pin 5 through a 1K resistor, and this connects in the scope to the "Plug In" trigger input. This works fine, although as soon as I get a high voltage signal transistor or FET I will boost this added signal at the source with an emitter or source follower and send the signal with low impedance. Now the CA plug-in is perfect, it is all I need and I would not use an 1A4 if I had it. I don't know WHY Tektronix didn't add this single channel tool-module trigger, so easy to implement.


Re: 5116+5D10 intensity problem

Chuck Harris
 

The manuals on the internet are the old 1963 versions of
the P6015 manual. If you look at the picture, you should
notice that the connector on the compensation box is an
old PL259 UHF connector, like was used on the early 500
series scopes.

The manual that came with my P6015 is APR 87, and it has
two curves, one with Freon, and one without. The curve
with Freon shows 20KVDC or RMS from DC to 1MHz. With air
is 13KVDC or RMS from DC to 1MHz.

The old probe shows the same curve as mine, only it limits
the probe to 28KV, at less than 100KHz.

I am pretty sure that if you over voltage the probe, it
has a spark gap that will arc over before the probe is
ruined. Obviously, the spark gap will arc over at a higher
voltage with freon, and a lower voltage with air.

The patent indicates that R12 is suitable if the probe is
to be used and stored below 10C.

If I had a probe that was sans fluid, and I couldn't buy
more R114, I would either live with the 13KV limit, or
try another refrigerant with a high boiling point...
probably butane. SF6 is also bound to work.

[Please don't bother mentioning how butane is flammable.
Everyone already knows that. They should also know that
it isn't if there is no air in the probe... If you
fill the probe with liquid in the probe, you won't be
able to screw on the probe's cap before the butane has
boiled enough to totally displace the air.]

With SF6, you would have to fill with vapor only, as its
liquification pressure is too high.

-Chuck Harris


Harvey White wrote:

Ok, several things after searching the  manuals.

1) the liquid is fluorocarbon 114.  SF6 is used in the AWACS transmitter unless they
rebuilt it.

2) the P6015 has the liquid, the P6015A has a silicone filler and no liquid.

3) the P6013 (IIRC) may have neither and is rated for about 12KV or so, while the
P6015 is rated from 20KV to 30KV depending on circumstances.

4) I did not find the specs on the 6015 without dielectric fluid, not in the internet
material I have at the moment.


Harvey


On 2/17/2020 3:26 AM, Paul Cohen wrote:
Or maybe SF6 (nasty) gas which is used in HV

בתאריך יום ב׳, 17 בפבר׳ 2020, 10:22, מאת Yeun-Jung Wu ‏<
B0190@...>:

Hello Harvey:

Thank you for your hint on future diagnosis. I will start collecting more
information on epoxy coated transformer first.

5D10 seemed to work fine except read out information had been expanded
outside the screen. Now I understand why red LED "possible under-sampling"
would lit: I was using slow time base to watch two nearly identical 7kHz
since wave superimposed together to form a nice envelope. There were lot of
wave form variation during long accuqsition time but the available memory
space for storing waveform was limited. When I select faster time base such
that several cycles was within the range of one horizontal division that
warning went away.

More than 5 year's ago I bought a Tek high voltage probe from eBay. There
was an empty can supposed to contain liquid with high dielectric strength,
something similar to banned CFC freon. For 4.5kV maybe I can fill some
other liquid and give it a try.

Best Regards,

Yeun-Jung Wu







Re: 3D printable feet for TDS500/600/700

Mlynch001
 

Monty,

I will add my complement, you did an awesome job on that design. I just made some of the little "Bottom" feet for the 4XX series, I had a 465 that was missing some of those as well. I find all sorts of uses for the 3D Printer around that workshop and home.

Thank You for sharing!

--
Michael Lynch
Dardanelle, AR


Re: 3D printable feet for TDS500/600/700

Abc Xyz
 

Gulp!

On Tue, Feb 18, 2020, 8:43 AM Mlynch001 <@mlynch001> wrote:

JR,

I slice the STL file with CURA 4.4.1. Print in PETG, Nylon or ABS (I use
PETG with great success). Print "laid down" on one side so that minimal
support is needed.

Hope this helps.

--
Michael Lynch
Dardanelle, AR




Re: Repairing my Tektronix 454 oscilloscope need some advice

Albert Otten
 

(continued)
I did an easier and less risky test. F1437 tied to GND, wire to "P" disconnected. Sine wave generator FG504, same GND , 50 ohm output applied to Q1430 collector (no other termination). Viewed waveform at Q1430 collector at a scope. Kept amplitude pp up to only 1 V so Q1430 would never conduct.
Measurements:
Resonance at about 23 kHz, not very sharp but clear enough.
Amplitude 1 V pp at collector resulted in 77 V DC at the HV test point as measured with a 10M DMM.
Impedance was about 10 ohm.

Albert


Re: 3D printable feet for TDS500/600/700

Mlynch001
 

JR,

I slice the STL file with CURA 4.4.1. Print in PETG, Nylon or ABS (I use PETG with great success). Print "laid down" on one side so that minimal support is needed.

Hope this helps.

--
Michael Lynch
Dardanelle, AR


Re: 3D printable feet for TDS500/600/700

Monty Montgomery
 

Oh good. I was about to say I couldn't help with the 465 :-)

Thanks others for the compliments.

Cheers,
Monty


Re: 3D printable feet for TDS500/600/700

Abc Xyz
 

Thanks Mike! :)

On Tue, Feb 18, 2020, 8:34 AM Mlynch001 <@mlynch001> wrote:

On Tue, Feb 18, 2020 at 10:19 AM, Abc Xyz wrote:


Monty,

Great Job in those Feet! Now if I just had a File for 465 Feet...
JR

You need a file for the cordwrap feet of the 465 Series? That file is on
THINGIVERSE.

HERE: https://www.thingiverse.com/thing:1410827

I can e-mail you the STL File, as I have that as well.

I have printed dozens of these for my various 4XX Series scopes plus some
for my brother as well.

Hope this helps.


--
Michael Lynch
Dardanelle, AR




Re: 3D printable feet for TDS500/600/700

Mlynch001
 

On Tue, Feb 18, 2020 at 10:19 AM, Abc Xyz wrote:


Monty,

Great Job in those Feet! Now if I just had a File for 465 Feet...
JR

You need a file for the cordwrap feet of the 465 Series? That file is on THINGIVERSE.

HERE: https://www.thingiverse.com/thing:1410827

I can e-mail you the STL File, as I have that as well.

I have printed dozens of these for my various 4XX Series scopes plus some for my brother as well.

Hope this helps.


--
Michael Lynch
Dardanelle, AR


Re: help tek 475 power supply

Roger Evans
 

Roberto,

If everything works before Q1446 fails then the simplest explanation is that Q1448 has failed with its collector open circuit and Q1446 is passing all the current to the +15V output through the base emitter junction of Q1488. The regulator will still function to provide the correct +15V. Much more current will be drawn from the output of U1454A since there is less current gain in the regulator and U1454 will draw more supply current via VR1418 so VR1418 will also be hotter than normal.

Regards,

Roger


Re: 3D printable feet for TDS500/600/700

Abc Xyz
 

Monty,

Great Job in those Feet! Now if I just had a File for 465 Feet...

JR

On Mon, Feb 17, 2020, 10:34 PM Monty Montgomery <xiphmont@...> wrote:

Hi folks,

While putting a TDS7xx back together, I required several new feet, so
I modeled some. Files ready to print are at

https://www.prusaprinters.org/prints/22192-replacement-feetpads-for-tektronix-tds-500600700-s
for anyone who'd like them.

Cheers,
Monty




Re: help tek 475 power supply

Roberto
 

hi Roger
Yes, the track is there that performs all its functions, but after a few minutes the CRT backlight turns off and the reason is missing the + 15v, the voltages are all up when 2n222 fails even the 24v zener I noticed that it heats up
thank
Roberto


Re: 5116+5D10 intensity problem

Harvey White
 

Ok, several things after searching the  manuals.

1) the liquid is fluorocarbon 114.  SF6 is used in the AWACS transmitter unless they rebuilt it.

2) the P6015 has the liquid, the P6015A has a silicone filler and no liquid.

3) the P6013 (IIRC) may have neither and is rated for about 12KV or so, while the P6015 is rated from 20KV to 30KV depending on circumstances.

4) I did not find the specs on the 6015 without dielectric fluid, not in the internet material I have at the moment.


Harvey

On 2/17/2020 3:26 AM, Paul Cohen wrote:
Or maybe SF6 (nasty) gas which is used in HV

בתאריך יום ב׳, 17 בפבר׳ 2020, 10:22, מאת Yeun-Jung Wu ‏<
B0190@...>:

Hello Harvey:

Thank you for your hint on future diagnosis. I will start collecting more
information on epoxy coated transformer first.

5D10 seemed to work fine except read out information had been expanded
outside the screen. Now I understand why red LED "possible under-sampling"
would lit: I was using slow time base to watch two nearly identical 7kHz
since wave superimposed together to form a nice envelope. There were lot of
wave form variation during long accuqsition time but the available memory
space for storing waveform was limited. When I select faster time base such
that several cycles was within the range of one horizontal division that
warning went away.

More than 5 year's ago I bought a Tek high voltage probe from eBay. There
was an empty can supposed to contain liquid with high dielectric strength,
something similar to banned CFC freon. For 4.5kV maybe I can fill some
other liquid and give it a try.

Best Regards,

Yeun-Jung Wu




Re: 547 scope HV transformer problem. One practical solution.

John Griessen
 

On 2/16/20 4:43 PM, Ernesto wrote:
I have added a toggle switch on the side cover of the scope, close to the CRT. Now after initial power up, I wait for a reasonable time for the instrument to stabilize (something that takes time with the 1A1 plug in!) Then I turn on the display and make adjustments and measurements, and 5 minutes is plenty of time. Then I turn the display off
Sounds like a good way to enjoy your 547 while waiting for a transformer!


Re: 3D printable feet for TDS500/600/700

magnustoelle
 

wow, Monty, I am envy of your skills. Thank you for your generousity! 
Cheers,
Magnus


Re: 3D printable feet for TDS500/600/700

dnmeeks
 

Thanks Monty! Very generous to put it up for us to use. I need to check all my mainframes to see if I need any - I'm sure I'm missing some. If I print them I'll let you know how it turns out.
Dan


Re: help tek 475 power supply

Roger Evans
 

Can you explain what you mean when you say 'after a few minutes it turns off'? Do you mean that initially there is a trace on the CRT but after a few minutes it disappears? The 475 should show a light behind the V/div knob of the vertical channel that is selected - does this light stay on when the scope 'turns off'?

Can you measure the voltages on the low voltage DC supplies, +50V, +15V, +5V, -8V, -15V and also '+15 unregulated'. Do any of these these change between first turning the scope on and the 'turn off'? If the only problem is with the regulated +15V then we can trace the voltages through the regulator.

Measuring Q1446 in circuit may be misleading since there are many parallel components.

Regards,

Roger Evans


Re: 547 scope HV transformer problem. One practical solution.

Albert Otten
 

On Tue, Feb 18, 2020 at 07:34 AM, Ernesto wrote:


One detail that worried me somewhat is the initial very bright blur of the
image when turning the supply on. I am working on this issue.
Hi Ernesto,

Interesting story and solutions. Though I hope my 547 keeps going on without those HV problems!
The bright blur when turning on the HV supply is not amazing.
See message https://groups.io/g/TekScopes/message/108397. The cap mentioned is C562.
This cap has no effect when the 547 is already on and you switch off/on the HV at a later moment.

Albert


Re: help tek 475 power supply

Roberto
 

Thank Chuck Harris
I checked the tracks where the negatives seem to be going well, the tensions would all be there and the only problem is the one exposed in the previous message
Roberto


547 scope HV transformer problem. One practical solution.

 

Hi, I am a retired electrical engineer having designed electronic equipment for measurements in oil wells for over 30 years.

About 40 years ago I picked up a 547 scope with an 1A1 plug in left as surplus by my employer. It went into my garage, and it was never powered up. After some decades, I developed a fear of powering it up, concerned over the degradation of the large electrolytic capacitors in its voltage supplies. A few weeks ago I needed an oscilloscope to troubleshoot an old record player, and I decided to bring this ancient oscilloscope back to life.

I disconnected all the big capacitors and over hours raised their voltage with an external supply while monitoring leakage current. All of them got restored! I did some general inspection and studied the schematics of all the functional blocks. I removed the timer tube and powered up just the filaments to check on the tubes. All lighted up. I reconnected the capacitors and the timer tube, and removed the oscillator tube of the CRT supply. While monitoring the regulated supplies I brought up the power with a variac. They came up fine within specs, no smoke. I was able to activate the sweep generators and see the flashing on the neon beam position indicators.

Then I placed back the 6AU5 tube of the HV oscillator, powered up, and to my amazement I saw come on that beautiful sharp bright trace on the CRT. Overcome with emotion, tears rolled down my cheeks and I started playing with the controls using the calibration signal. The oscilloscope was basically WORKING! After 40 years of being dead!

After some short time the beautiful trace started to fade away, and I realized that I had a problem with the CRT high voltage. After investigating, I learned about the now classical problem with the HV transformer. First I replaced the vacuum diodes with silicon diodes, and the power consumption of the supply improved (as measured on the pentode grid 2), but the time to failure only increased slightly. I measured it as 15 minutes after power-up cold. The failure of the transformer is an insurmountable problem. I speculated that if clamping the pentode's grid 2 at a higher voltage than 125v the oscillator could provide more power, or I could easily replace the 6AU5 with a power MOSFET after some minor modifications, and then increase drastically the available power to the Hartley oscillator. But this could be a dangerous modification if it could burn out the transformer, and then this could end the life of the instrument since there are no replacements. I could still build a new larger transformer with a ferrite pot core that would fit in the available space, with sufficient space for reliable HV insulation of the windings (and NO impregnation). But I lack the basic design of the transformer, like the turn ratios of its winding, although I could measure them on a working transformer or calculate them from the existing design.

I realize that I have fallen in love with the 547. No other test instrument, be the 7000 series, the digital scopes, etc. have this effect on me. The scope is now in my office, and each time I see it my spirit lights up. So I searched for a solution.

First, I realized that the HV supply is overpowered. If the 325v unregulated supply (about 350v in my scope) is powered down, regulation is maintained until the voltage is down to 195v. The HV could be powered from the 225v supply instead, but this one simply regulates down the 325, so this does not save power but transfers some to the 225v regulator. My experiments with an external variable supply gave me an idea: while the scope is on, why not have a switch to turn on and off the HV power and so allow the scope to be used for an indefinite time, as long as the display is turned on only when needed, and maintaining an adequate low duty cycle.

I verified that the supply tolerates a 50% duty cycle of 5 minutes on and 5 minutes off. Or, a 10 minutes on followed by a longer period off. One can do a lot of measurements in 5 minutes. I have added a toggle switch on the side cover of the scope, close to the CRT. Now after initial power up, I wait for a reasonable time for the instrument to stabilize (something that takes time with the 1A1 plug in!) Then I turn on the display and make adjustments and measurements, and 5 minutes is plenty of time. Then I turn the display off, while doing other things. I am perfectly fine using the oscilloscope like this. Cycling the HV supply does not seem to affect the stability of the scope, the readings remain the same.

One detail that worried me somewhat is the initial very bright blur of the image when turning the supply on. I am working on this issue. First I have reduced the voltage to the supply by 120v with a string of 10 zener diodes, 12v 5w, which are dirt cheap on Amazon. With 230v the supply runs fine. Next I am building with a MOSFET and some timing components a means to raise these 230v slowly, and reduce this first bright flash in the first second of power on. I had measured that the current provided to the supply is 26mA, which doubled when it reached a safe degradation. So the consumption of the HV supply will stay below 25 watt, an amount of power easy to handle.

With this last modification I will be satisfied to have brought back to life this superb instrument, which I plan to keep in my office forever, for whatever little experimenting I will fancy to do.
I might try to improve it again whenever Chuck Harris is able to produce workable HV transformers, and I would like to be one of his clients.