Date   
Re: Repairing my Tektronix 454 oscilloscope need some advice

Roger Evans
 

Indeed, but the period of a 50kHz is oscillation is 20us not 20ms so Ernesto's times 200 was actually correct.

Roger

Re: Scope auction

Bob Headrick
 

I see they also have a Tek 7854 in the previous picture, lot 19 in the catalog here: https://bid.tmcauction.com/auctions/catalog/id/23165/

I wish I was a bit closer to Sacramento.

- Bob Headrick

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Robert Simpson via Groups.Io
Sent: Sunday, February 16, 2020 7:40 PM
To: TekScopes@groups.io
Subject: [TekScopes] Scope auction

About the middle of the page:
https://www.estatesales.net/CA/Rocklin/95677/2475516

No connection, but is in a neighboring town.
That 7904A looks like it has 7S12 in it with modules Bob

Re: Scope auction

Bob Headrick
 

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Robert Simpson via Groups.Io
Sent: Sunday, February 16, 2020 7:40 PM
To: TekScopes@groups.io
Subject: [TekScopes] Scope auction

About the middle of the page:
https://www.estatesales.net/CA/Rocklin/95677/2475516

No connection, but is in a neighboring town.
That 7904A looks like it has 7S12 in it with modules Bob

Re: Repairing my Tektronix 454 oscilloscope need some advice

Chuck Harris
 

Wonderful! I just wanted to be sure that you and others were
aware of the issue.

Also, many of these HV diodes are designed to be used in old
color TV's, and CRT type monitors, so they need to be faster
than they would for the old style of transformer driven microwave
oven.

New style microwave ovens use inverters, and as such could be
pretty high frequency... I have never taken one apart.

-Chuck Harris

Ernesto wrote:

Hi Chuck,

You are very right about the importance of the diode recovery time. The specification on Amazon for this cheapy diode is Trr = 100 nS maximum. Other "fast" HV diodes specify 60 or 70 nS, not a big difference.
At 50 kHz the period of the rectified sine wave is 20 mS, 200 times longer than the Trr. During these 100nS the peak of the sine wave will barely comes down, so the operation should be safe. Indeed when I installed these diodes the efficiency of the supply increased, and it behaved correctly.

- Ernesto



Re: Repairing my Tektronix 454 oscilloscope need some advice

 

Thank you Jim!

I need to be more careful with my postings and avoid dumb mistakes! I try not to think that it is the years...

The period of a 50 kHz wave is 20 uS, not 20mS. So this period is still 200 times longer than Trr. And in Trr = 100nS, the wave has not significantly receded from its peak, so the capacitor will not be significantly discharged during this time.

Regards,
Ernesto

Re: Repairing my Tektronix 454 oscilloscope need some advice

Jim Ford
 

Hi, Ernesto.

Actually, 20 ms is 200,000 times longer than 100 ns. Just sayin'.

Jim Ford

------ Original Message ------
From: "Ernesto" <ebordon@...>
To: TekScopes@groups.io
Sent: 2/20/2020 6:41:48 PM
Subject: Re: [TekScopes] Repairing my Tektronix 454 oscilloscope need some advice

Hi Chuck,

You are very right about the importance of the diode recovery time. The specification on Amazon for this cheapy diode is Trr = 100 nS maximum. Other "fast" HV diodes specify 60 or 70 nS, not a big difference.
At 50 kHz the period of the rectified sine wave is 20 mS, 200 times longer than the Trr. During these 100nS the peak of the sine wave will barely comes down, so the operation should be safe. Indeed when I installed these diodes the efficiency of the supply increased, and it behaved correctly.

- Ernesto


Re: Repairing my Tektronix 454 oscilloscope need some advice

 

Hi Chuck,

You are very right about the importance of the diode recovery time. The specification on Amazon for this cheapy diode is Trr = 100 nS maximum. Other "fast" HV diodes specify 60 or 70 nS, not a big difference.
At 50 kHz the period of the rectified sine wave is 20 mS, 200 times longer than the Trr. During these 100nS the peak of the sine wave will barely comes down, so the operation should be safe. Indeed when I installed these diodes the efficiency of the supply increased, and it behaved correctly.

- Ernesto

Re: DS1742W-120 replacement adapter?

victor.silva
 

BTW, I downloaded KiCAD 5.1.5-3 and was able to completely browse the design files from the EEVBlog converter.
Very nice for the price (free).

--Victor

Re: DS1742W-120 replacement adapter?

victor.silva
 

On Thu, Feb 20, 2020 at 11:49 AM, Ken Eckert wrote:


JLCPCB
I like the Glitchworks option better. I seems to fit in the same footprint as the original DS1742W.
The board in the EEVBLOG link above is much bigger and requires an area next to the DS1742W to be free.

I will contact Glitchworks to see if they can make a DS1742W replacement.

--Victor

Re: Repairing my Tektronix 454 oscilloscope need some advice

Chuck Harris
 

Indeed, which is why I said a 9V battery, or two...

The diodes in these supplies are a little special in that
they need to be fast recovery diodes. They are working at
about 50KHz.

A common ordinary microwave oven makes its HV at 60Hz, and
can use very slow recovery diodes effectively. A slow diode
will drag a 50KHz supply down, appearing as a short circuit for
several tens of microseconds after the transformer's polarity
reverses.

-Chuck Harris

Ernesto wrote:

Hi Chuck,

Some HV diodes may need more than 9V to turn on. The ones I used in my HV supply need about 17V for a 2mA forwards current. they are some Chinese 20KV diodes used in microwaves (an overkill but cheap, at $7.49 for 8 of them at Amazon). He can use the +100V of the scope itself through a 100K resistor for a short measurement of 1mA forwards, then reverse the diode and measure zero current.

Ernesto

Re: DS1742W-120 replacement adapter?

Tom B
 

Hi Victor,

I would be interested in a few bare boards.

Tom Bryan
N3AJA

On 2/20/2020 1:54 PM, victor.silva via Groups.Io wrote:
Has anyone had a build of these made up and ten or so that they wish to sell?

If not, is anyone interested in going in on a group buy (of unpopulated boards)?

Thanks,
Victor

Re: Repairing my Tektronix 454 oscilloscope need some advice

 

Hi Chuck,

Some HV diodes may need more than 9V to turn on. The ones I used in my HV supply need about 17V for a 2mA forwards current. they are some Chinese 20KV diodes used in microwaves (an overkill but cheap, at $7.49 for 8 of them at Amazon). He can use the +100V of the scope itself through a 100K resistor for a short measurement of 1mA forwards, then reverse the diode and measure zero current.

Ernesto

Re: Repairing my Tektronix 454 oscilloscope need some advice

Brad Thompson
 

Victor via Groups.Io wrote on 2/20/2020 3:42 PM:

<snip> I have a doubt about the HV diodes... what do you think ? By the way how do you test HV diode,I understand you cannot do it with a regular tester.

Hello, Victor--

The high-voltage diodes likely consist of several diode junctions connected in series
to obtain a high reverse-breakdown voltage. You'd need a specialized test instrument to
measure reverse-bias leakage current and breakdown voltage. For example, stacking eight
junctions reverse-rated for 1000 volts each would produce an 8000-volt diode.

In this example, you can measure the high-voltage diode's forward-voltage drop by
connecting a current-limiting resistor (e.g., 1K Ohms) in series with the diode and a power supply
( 10 volts) whose voltage exceeds the estimated forward voltage drop of eight junctions
(e.g., 0.7 V *  8 = 5.6 volts.). Measure the voltage across the diode you're testing.

If the diode  doesn't exhibit forward conduction, it's  defective. Unfortunately,
this test won't diagnose abnormally low or intermittent reverse breakdown.

73--

Brad  AA1IP

Re: Repairing my Tektronix 454 oscilloscope need some advice

Albert Otten
 

Victor,
I would first of all test the waveforms at terminals 7, 9 and 10 and check that the amplitudes have more or less the same ratios to each other (and perhaps to the 1 V pp) as in my case. Your 52 V is really to low, so check it against the (negative) peak voltage at terminal 9. The secondary waveforms may show a slightly flat negative peak because of diode conduction, but only slightly. At terminal 9 the negative "flat" peak was about 5 V smaller than the "round" positive peak.
Can you measure the primary current? Perhaps your generator can show the current drawn?
For test HV diodes see the message by Chuck Harris or see message #163125).

Albert

On Thu, Feb 20, 2020 at 09:42 PM, Victor wrote:

Albert,
This afternoon, I was reviewing the measurement done yesterday and found a
problem (intermittent connection) with the cable connecting the wave generator
to the Q1430 collector. After repair it I test again my 454 and now with a
1Vpp on the collector of the Q1430, I get 52V at the HV test point.So, with
this result I believe my HV transformer is Ok. I have a doubt about the HV
diodes... what do you think ? By the way how do you test HV diode,I understand
you cannot do it with a regular tester.Tomorrow before made the test that you
recommend today. I would like to review the HV CRT circuit to see if any
resistor or capacitor are out of specs (transistors have been test and look
good).
Thank you,Victor

Re: Repairing my Tektronix 454 oscilloscope need some advice

Chuck Harris
 

Use a 9V battery, or two, in series with a 10K resistor, and
a low current meter.. then test in the usual way.

-Chuck Harris

Victor via Groups.Io wrote:

Albert,
This afternoon, I was reviewing the measurement done yesterday and found a problem (intermittent connection) with the cable connecting the wave generator to the Q1430 collector. After repair it I test again my 454 and now with a 1Vpp on the collector of the Q1430, I get 52V at the HV test point.So, with this result I believe my HV transformer is Ok. I have a doubt about the HV diodes... what do you think ? By the way how do you test HV diode,I understand you cannot do it with a regular tester.Tomorrow before made the test that you recommend today. I would like to review the HV CRT circuit to see if any resistor or capacitor are out of specs (transistors have been test and look good).
Thank you,Victor


-----Original Message-----
From: Albert Otten <aodiversen@...>
To: TekScopes <TekScopes@groups.io>
Sent: Thu, Feb 20, 2020 3:19 pm
Subject: Re: [TekScopes] Repairing my Tektronix 454 oscilloscope need some advice

Victor,

Today I did more waveform measurements.  I always viewed the primary voltage and primary current ( A6302 current probe) waveform and each time I tuned for resonance. Last time I made a frequency reading mistake (when you turn the FG504 knob cw the the frequency deceases...). Without other probes attached it was 27 MHz.  Probes at the secondary side lower the resonance frequency somewhat.
From the visible transformer right side 3 very short blank wires go to ceramic supports. From front to rear these are connected to winding terminals 7 (tripler circuit), 9 (cathode, D1452) and 10 (grid, D1440 visible). Resistances to GND: 547R, 243R and about 20k respectively.
Findings:
Always nice resonance with simultaneously primary voltage maximal, current minimal and no phase shift between these two.  In hindsight this could be expected when the primary side acts as a nice parallel RCL circuit with not too low Q factor. R was about 10 Ohm. Also each time the secondary voltage was in phase with the primary.
Amplifications, crude values:
from primary to 7: 375, to 9: 185, to 10: 195.
I did a more precise simultaneous measurement of negative peak at 9 and the DC voltage at HV TP (with DMM). The "loss" was about 10 V (of value about 80 V), looks realistically.
Anyway, it could be very informative to view those secondary waveforms.

Albert

On Wed, Feb 19, 2020 at 09:36 PM, Albert Otten wrote:


Victor,

Obviously there is not enough secondary HV, or a diode is bad. If you remove
the plastic cover of the HV box you can access at least one diode which is
connected to a hot winding end (I don't remember which one, I think it has
been mentioned in another recent 454 thread). With 1 V pp over the primary you
could view the wave form at that secondary winding, using a 10 M (and 10X)
probe. Then a bad (open) diode plays no role.
I estimated the primary impedance (about 10 R) by comparison of amplitude (1 V
pp) with the  open-circuit output amplitude of the 50 R generator. Did you
also do such? Maybe tomorrow I will (just for fun with my 7854) view both
voltage across and current into the primary. With the 7854 keyboard calculator
it's easy to determine reactive and real input power to primary. I guess it
will mostly be real power because of the (cold!) CRT filament load. (Of course
the phase shift between voltage and current can be viewed on an arbitrary
scope, without storage or calculator).
You might also view the collector waveform during normal operation. The 0.22 A
current seems to be small and probably indicates that Q1430 can not deliver
enough power to increase the oscillation to normal level; either because a
fault in the feedback circuit (resistor string to Q1414 etc.) or a too heavy
secondary load (shorted HV cap?) or ...(?)

Albert




Re: Tektronix 1L5 Crystal Discriminator

Jason A.
 

Thanks Tom! I'll open it up and take a look. My fear is that it would be potted inside. It's definitely worth a shot!

Re: Tektronix 1L5 Crystal Discriminator

fiftythreebuick
 

Jason, be sure to include the same part for a 3L5 in your searches. I believe they both have the same board in them, and I'm almost sure the discriminator is the same.

And before you give up, I'd open that thing up and see what's going on inside. I fixed a Collins crystal filter that was not too different from what's probably inside that one. You just never know!

Tom

On Thu, Feb 20, 2020 at 10:03 AM, Jason A. wrote:


Question #2 - does anyone have a 1L5 that is working you don't need anymore or
one you are parting out?

Thanks and best regards,

Jason

Re: Repairing my Tektronix 454 oscilloscope need some advice

Victor
 

Albert,
This afternoon, I was reviewing the measurement done yesterday and found a problem (intermittent connection) with the cable connecting the wave generator to the Q1430 collector. After repair it I test again my 454 and now with a 1Vpp on the collector of the Q1430, I get 52V at the HV test point.So, with this result I believe my HV transformer is Ok. I have a doubt about the HV diodes... what do you think ? By the way how do you test HV diode,I understand you cannot do it with a regular tester.Tomorrow before made the test that you recommend today. I would like to review the HV CRT circuit to see if any resistor or capacitor are out of specs (transistors have been test and look good).
Thank you,Victor

-----Original Message-----
From: Albert Otten <aodiversen@...>
To: TekScopes <TekScopes@groups.io>
Sent: Thu, Feb 20, 2020 3:19 pm
Subject: Re: [TekScopes] Repairing my Tektronix 454 oscilloscope need some advice

Victor,

Today I did more waveform measurements.  I always viewed the primary voltage and primary current ( A6302 current probe) waveform and each time I tuned for resonance. Last time I made a frequency reading mistake (when you turn the FG504 knob cw the the frequency deceases...). Without other probes attached it was 27 MHz.  Probes at the secondary side lower the resonance frequency somewhat.
From the visible transformer right side 3 very short blank wires go to ceramic supports. From front to rear these are connected to winding terminals 7 (tripler circuit), 9 (cathode, D1452) and 10 (grid, D1440 visible). Resistances to GND: 547R, 243R and about 20k respectively.
Findings:
Always nice resonance with simultaneously primary voltage maximal, current minimal and no phase shift between these two.  In hindsight this could be expected when the primary side acts as a nice parallel RCL circuit with not too low Q factor. R was about 10 Ohm. Also each time the secondary voltage was in phase with the primary.
Amplifications, crude values:
from primary to 7: 375, to 9: 185, to 10: 195.
I did a more precise simultaneous measurement of negative peak at 9 and the DC voltage at HV TP (with DMM). The "loss" was about 10 V (of value about 80 V), looks realistically.
Anyway, it could be very informative to view those secondary waveforms.

Albert

On Wed, Feb 19, 2020 at 09:36 PM, Albert Otten wrote:


Victor,

Obviously there is not enough secondary HV, or a diode is bad. If you remove
the plastic cover of the HV box you can access at least one diode which is
connected to a hot winding end (I don't remember which one, I think it has
been mentioned in another recent 454 thread). With 1 V pp over the primary you
could view the wave form at that secondary winding, using a 10 M (and 10X)
probe. Then a bad (open) diode plays no role.
I estimated the primary impedance (about 10 R) by comparison of amplitude (1 V
pp) with the  open-circuit output amplitude of the 50 R generator. Did you
also do such? Maybe tomorrow I will (just for fun with my 7854) view both
voltage across and current into the primary. With the 7854 keyboard calculator
it's easy to determine reactive and real input power to primary. I guess it
will mostly be real power because of the (cold!) CRT filament load. (Of course
the phase shift between voltage and current can be viewed on an arbitrary
scope, without storage or calculator).
You might also view the collector waveform during normal operation. The 0.22 A
current seems to be small and probably indicates that Q1430 can not deliver
enough power to increase the oscillation to normal level; either because a
fault in the feedback circuit (resistor string to Q1414 etc.) or a too heavy
secondary load (shorted HV cap?) or ...(?)

Albert

Re: DS1742W-120 replacement adapter?

Ken Eckert
 

The boards are extremely cheap from JLCPCB, online quote.

On Thu, Feb 20, 2020 at 10:54 AM victor.silva via Groups.Io <daejon1=
yahoo.com@groups.io> wrote:

Has anyone had a build of these made up and ten or so that they wish to
sell?

If not, is anyone interested in going in on a group buy (of unpopulated
boards)?

Thanks,
Victor



Re: DS1742W-120 replacement adapter?

victor.silva
 

Has anyone had a build of these made up and ten or so that they wish to sell?

If not, is anyone interested in going in on a group buy (of unpopulated boards)?

Thanks,
Victor