Date   

Re: HV transformer equalizing loop

Albert Otten
 

and the pictures (I hope...)
Albert


HV transformer equalizing loop

Albert Otten
 

and the pictures...
Albert


HV transformer equalizing loop

Albert Otten
 

Continued from the "647 HV transformer" thread as a new topic.

More surprises...
Since I also have 564s with 2 original 5642 diodes I decided to also measure one of these. I measured and measured again, but all the time I saw no real difference between the two legs. I also saw no equalizing loop. Mysterious. So I digged up the remaining 564, again draw wires trough the holes and (big relief) this time the empty leg showed much higher induction voltage than the heater leg.
I opened the first 564 again for comparison and yes, there *was* an equalizer loop, but quite different from what I expected. Having seen those heavy insulated wires for the heaters I expected something similar for such a loop. But no, it's a simple thin copper wire, see attached pictures, and why not.
All transformers have the same number -275. The one with loop is in the most recent 'scope. In my opinion all are beeswax types.

The heater side voltage for the transformers without loop was 0.86-0.88 V, against 1.10 V for the one with loop. A considerable difference, and both well below the nominal 1.25 V. (All HV voltages have been calibrated in recent years but I didn't check again.)
Following Chuck I wonder whether the designers were aware of this, though it is hard to believe they were not. Maybe the low voltage was intended to be low to increase life time?

Albert

===
Intriguing thing those equalizing "8" windings. Chuck (private mail) suggested that these would perhaps first of all serve to equalize the heater voltages. I happens that one of my 564's has one 5642 and one semiconductor diode (done by previous owner), without equalizing loop. I guided additional wires through both holes of the EI-core and did waveform and rms voltage measurement at these.
heater side leg: 0.9 V
empty leg: 1.4 V
The heater current tries to prevent flux changes, so to some extend these prefer the empty leg and hence the induced voltage is higher there.
With a 6.8 Ohm load at the empty leg side wire the heater side voltage increased to 1.0 V.
The 'scope works normally with calibrated HV IIRC. So the low 0.9 V (rounded up from 0.88 V) heater voltage seems sufficient for normal emission of the 5642.

Albert

===
Further evidence of this is the flux equalizing loop that got
added for the 545B/547/647... later transformers. Most (all?) of
the scopes had an odd number of 5642 rectifiers, and as such an
odd number of filament windings. Because they were using the EHT
to source the filament voltage, they put the windings on the outer
legs of the transformer core, 3 on one leg, and 2 on the other.
That causes a flux imbalance in the core, ...
(---)
To compensate for this imbalance, they added a single shorted
turn to link the two outer legs of the core. The turn was
arranged so that if one side was more heavily loaded than the
other, it would steal some extra current from the lightly loaded
side to even up the balance.
(---)
-Chuck Harris


Re: 155-0012-00 datasheet

 

I am just pointing out that high speed design techniques should be used to
prevent oscillation and achieve the IC's rated performance. It can be clocked
as slowly as you like but there may be maximum rise and fall times which should
be observed for the digital inputs and operating them in their active region may
cause oscillation. Treat it like slow ECL or a video operational amplifier.

On Sun, 08 Dec 2013 11:50:39 +0000, you wrote:

There is a really good explanation (including basic truth table) of just
how this part works in the 7834 Manual. It is much more detailed than
the 7844 manual that I have been using.

As to the speed issue, I agree the chip is built for speed, but it looks
as though it can be clocked slowly using the A Gate input from a slow
running TB and all other inputs, except the intensity current sink input
on pin 16 and current sink output to the Z Axis Amp on pin 8, held
statically HI or LO as required. Or am I too simple here?
Chris HJ
On 06/12/2013 17:00, David wrote:

The 155-0012-00 operates in the 100+ MHz range (250 MHz?) so lead
length and
decoupling can be critical.

The current sink output from pin 8 is usually going to operate into
the emitter
of a cascode transistor at the input of the z-axis amplifier which is
the case
with the 7844. The low emitter resistance, about 5 ohms, plus the 47
ohm series
resistor is only going to allow very small voltage changes at pin 8.

The voltages at the three inputs, pins 1, 2, and 16, will behave the
same way
with their voltages reflecting the logic control signals from pins 15
and 5
instead of their input currents.


my 7k standardizer on ebay

 

291031469805


Jerry Massengale


Re: 647 HV transformer

Chuck Harris <cfharris@...>
 

Tektronix built their transformers in a very expedient
way: The entire transformer, epoxy or wax, was dipped
into the potting tank. So, the beeswax transformers are
covered with beeswax, and the epoxy are covered with a
thin coating of epoxy.

Also, all of the tek beeswax transformers that I can recall
have a pair of reddish brown micarta plates that sandwich
the coil. The epoxy varnished transformers are more compact.

My 545B/547 transformers only have the coil vacuum
impregnated with beeswax.... a lot less messy.

-Chuck Harris

Cliff White wrote:

Is there any way to tell if a Tek transformer has wax or epoxy? I have a small
suspicion that the tranny in my 536 has been replaced -- Possibly with one with
epoxy. Were replacement transformers ever made with epoxy?


Re: 545 HV won't oscillate 100% of the time.

bonddaleena@...
 

I have replaced literally BUCKETS full of BBOD, Bumblebees, wax caps, etc. I have NEVER seen a single one that would pass a leakage test at rated voltage.
They might 'test' fine for VALUE on my NIST traceable bridge, but they all leak at HV.

As the Prez would say:

"PERIOD!"

ha ha

ron
N4UE



-----Original Message-----
From: Don Black
To: TekScopes
Sent: Sun, Dec 8, 2013 4:17 am
Subject: Re: [TekScopes] 545 HV won't oscillate 100% of the time.

 
Oops. I meant eBay bumblebee and black beauty caps, not tubes. Freudian slip??

Don Black.

On 08-Dec-13 8:09 PM, Don Black wrote:
 
I hope you get it sorted out Dan but I was being facetious about the eBay tubes advertised as tested good. I wonder what tests were done? I noticed another ad for similar caps saying they were tested OK on a bridge. No mention of leakage or if the bridge had to be adjusted for losses. Maybe I'm just getting cynical in my old age.

Don Black,

On 08-Dec-13 10:33 AM, Daniel Koller wrote:
 
Hi all,
  My caps probably are bad.  When I first got the scope around 1980, I learned about "black beauties" and had to replace them in the power supply, but I think I recall being told that the bumble-bee types were fine, so those stayed in.  Now it looks like I have leakage from them in the HV power supply.  See the attached photo here: http://groups.yahoo.com/neo/groups/TekScopes/photos/albums/158207078/lightbox/1517700781
The two shiny black 0.001 uF caps stand out because they are coated in oil.  You can't see it on the photo, but there is a film of liquid oil between the middle cap and the 56K resistor below it.  Those two are coming out but being a big fan of "don't mess with it if it ain't broke" I might leave the other caps in unless there is an obvious failure. Mind you, my scope works well when it does turn on.

But I've had some other modifications it seems.  What's that square cap on the left and the 2.2K resistor doing there?  I'll have to trace the circuit to see where they were put in and why.  Maybe that was a long ago patch for the oscillator failure?  Or the cause of it now?

I see now why I had originally thought my scope was much younger than it is - before I learned from the group here that the "brown" Teks were pre-1954.  There is this circuit board in my scope:
http://groups.yahoo.com/neo/groups/TekScopes/photos/albums/158207078/lightbox/1026393052
Someone seems to have made factory improvements circa 1967.   What was in its place before this?  Is it possible my additional HV circuit components were placed in the same upgrades/refurbishment?

Back to the shop.  I've got an hour before guests arrive!

Dan

On Saturday, December 7, 2013 10:58 AM, Don Black <donald_black@...> wrote:

>I'm not so sure. Yours may be faulty, these are tested good so they must be a rare animal.
>
>Don Black.
>
>On 08-Dec-13 2:31 AM, Daniel Koller wrote:
>

>>I'll check and see what's in there.   And when I take them out, I'll sell them on e-bay to an audiophool!!
>>http://www.ebay.com/itm/4-TUBE-AMP-CAPACITORS-0-1uF-400V-Sprague-Bumblebee/171185528791?_trksid=p2047675.m1982&_trkparms=aid%3D333005%26algo%3DRIC.FIT%26ao%3D1%26asc%3D177%26meid%3D3232141210003616509%26pid%3D100009%26prg%3D1088%26rk%3D1%26rkt%3D5%26sd%3D181276706729%26
>>
>>(No affiliation with the seller!)
>>
>>Dan
>>
>>On Friday, December 6, 2013 11:27 PM, Chuck Harris wrote:
>>
>>>Most of the time with the 545, the problem is the
              black beauty oil/paper
>>>tubular capacitors used for the HV filters.  They
              always go bad, and if
>>>they haven't been replaced, you must replace
              them.  Ceramic is fine.
>>>
>>>There is also a BB cap that is in series with the grid
              feedback winding,
>>>and another in parallel with the plate winding.  Both
              must go.
>>>
>>>-Chuck Harris
>>>
>>>Daniel Koller wrote:
>>>> Howdy,
>>>>
>>>> The recent discussions on HV repairs has me
              thinking I should look into the issues
>>>> in my 545 (not A or B, old style square case).  
              It works very very well, but
>>>> about half of the time, increasingly more, the HV
              circuit will not oscillate.  If
>>>> I pull the plug-in out and drop it back in, it
              will work.  I know this is not a
>>>> recommended option!  Alternatively, if I shut it
              off and wait for it to cool, it
>>>> will work when I turn it on with about the same
              probability, or a little less.
>>>> Once the scope is on it's up to spec.
>>>>
>>>> The 6AU5 is not brand new, but is good.  It was
              replaced recently with no
>>>> improvement.
>>>>
>>>> So, suggestions as to where to start on this
              intermittant problem are welcome.  Is
>>>> there anything I should look for or measure that
              might indicate what is getting
>>>> tired?
>>>>
>>>> Dan
>>>>
>>>
>>>
>>>
>>>
>>
>
>
>>________________________________
>
>   This email is free from viruses and malware because avast! Antivirus protection is active.  
>
>
>
>




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Re: 155-0012-00 datasheet

Christopher Hilton-Johnson
 

There is a really good explanation (including basic truth table) of just how this part works in the 7834 Manual.  It is much more detailed than the 7844 manual that I have been using.

As to the speed issue, I agree the chip is built for speed, but it looks as though it can be clocked slowly using the A Gate input from a slow running TB and all other inputs, except the intensity current sink input on pin 16 and current sink output to the Z Axis Amp on pin 8, held statically HI or LO as required.  Or am I too simple here?
Chris HJ

On 06/12/2013 17:00, David wrote:
 

The 155-0012-00 operates in the 100+ MHz range (250 MHz?) so lead length and
decoupling can be critical.

The current sink output from pin 8 is usually going to operate into the emitter
of a cascode transistor at the input of the z-axis amplifier which is the case
with the 7844. The low emitter resistance, about 5 ohms, plus the 47 ohm series
resistor is only going to allow very small voltage changes at pin 8.

The voltages at the three inputs, pins 1, 2, and 16, will behave the same way
with their voltages reflecting the logic control signals from pins 15 and 5
instead of their input currents.

On Fri, 06 Dec 2013 14:49:53 +0000, you wrote:

>I have now had a chance to look at the datasheets kindly sent me. With
>that & David's informed explanation, I can now make something of what I
>have seen so far and can experiment further.
> Incidentally although the block diagram looks odd (At a glance I see
>no pin 8 on the block diagram, but two pin 6s. I also cannot find any
>pin 10, but two pin 14s) the other information is very useful.
>I can see myself making an extension set for this IC so I can work
>outside the scope.
>Thanks again
>Chris HJ
>On 05/12/2013 23:20, David wrote:
>>
>> This IC works by adding and subtracting currents so the measured
>> voltages depend
>> on the output shunt resistances which may be zero.
>>
>> The voltage or current into pins 6 and 7 add together to set the
>> maximum output
>> sink current into pin 8. The current into pin 10 subtracts from the
>> magnitude
>> of the output sink current into pin 8. The sink currents from pins 16,
>> 1, and 2
>> subtract from the current from pin 10 so they have the effect of
>> increasing the
>> magnitude of the current drawn into pin 8.
>>
>> I do not quite understand how the chopped blanking input at pin 6
>> works since it
>> seems like its logic is backwards.
>>
>> On Thu, 05 Dec 2013 22:39:14 +0000, you wrote:
>>
>> >Does anyone have a datasheet for the widely used mainframe Z Axis logic
>> >chip (155-0012-00)?
>> >If so can they contact me off list - thanks
>> >I am trying to understand why pin 10, an input, has a signal the
>> >amplitude of which varies with the intensity control and why pin 8, the
>> >output to the z Axis amplifier, which should have such a signal, does
>> not.
>> >Thanks
>> >Chris HJ

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Re: 545 HV won't oscillate 100% of the time.

Don Black <donald_black@...>
 

Oops. I meant eBay bumblebee and black beauty caps, not tubes. Freudian slip??

Don Black.

On 08-Dec-13 8:09 PM, Don Black wrote:
 

I hope you get it sorted out Dan but I was being facetious about the eBay tubes advertised as tested good. I wonder what tests were done? I noticed another ad for similar caps saying they were tested OK on a bridge. No mention of leakage or if the bridge had to be adjusted for losses. Maybe I'm just getting cynical in my old age.

Don Black,

On 08-Dec-13 10:33 AM, Daniel Koller wrote:
 

Hi all,
  My caps probably are bad.  When I first got the scope around 1980, I learned about "black beauties" and had to replace them in the power supply, but I think I recall being told that the bumble-bee types were fine, so those stayed in.  Now it looks like I have leakage from them in the HV power supply.  See the attached photo here: http://groups.yahoo.com/neo/groups/TekScopes/photos/albums/158207078/lightbox/1517700781
The two shiny black 0.001 uF caps stand out because they are coated in oil.  You can't see it on the photo, but there is a film of liquid oil between the middle cap and the 56K resistor below it.  Those two are coming out but being a big fan of "don't mess with it if it ain't broke" I might leave the other caps in unless there is an obvious failure. Mind you, my scope works well when it does turn on.

But I've had some other modifications it seems.  What's that square cap on the left and the 2.2K resistor doing there?  I'll have to trace the circuit to see where they were put in and why.  Maybe that was a long ago patch for the oscillator failure?  Or the cause of it now?

I see now why I had originally thought my scope was much younger than it is - before I learned from the group here that the "brown" Teks were pre-1954.  There is this circuit board in my scope:
http://groups.yahoo.com/neo/groups/TekScopes/photos/albums/158207078/lightbox/1026393052
Someone seems to have made factory improvements circa 1967.   What was in its place before this?  Is it possible my additional HV circuit components were placed in the same upgrades/refurbishment?

Back to the shop.  I've got an hour before guests arrive!

Dan

On Saturday, December 7, 2013 10:58 AM, Don Black wrote:

>I'm not so sure. Yours may be faulty, these are tested good so they must be a rare animal.
>
>Don Black.
>
>On 08-Dec-13 2:31 AM, Daniel Koller wrote:
>

>>I'll check and see what's in there.   And when I take them out, I'll sell them on e-bay to an audiophool!!
>>http://www.ebay.com/itm/4-TUBE-AMP-CAPACITORS-0-1uF-400V-Sprague-Bumblebee/171185528791?_trksid=p2047675.m1982&_trkparms=aid%3D333005%26algo%3DRIC.FIT%26ao%3D1%26asc%3D177%26meid%3D3232141210003616509%26pid%3D100009%26prg%3D1088%26rk%3D1%26rkt%3D5%26sd%3D181276706729%26
>>
>>(No affiliation with the seller!)
>>
>>Dan
>>
>>On Friday, December 6, 2013 11:27 PM, Chuck Harris wrote:
>>
>>>Most of the time with the 545, the problem is the
              black beauty oil/paper
>>>tubular capacitors used for the HV filters.  They
              always go bad, and if
>>>they haven't been replaced, you must replace
              them.  Ceramic is fine.
>>>
>>>There is also a BB cap that is in series with the grid
              feedback winding,
>>>and another in parallel with the plate winding.  Both
              must go.
>>>
>>>-Chuck Harris
>>>
>>>Daniel Koller wrote:
>>>> Howdy,
>>>>
>>>> The recent discussions on HV repairs has me
              thinking I should look into the issues
>>>> in my 545 (not A or B, old style square case).  
              It works very very well, but
>>>> about half of the time, increasingly more, the HV
              circuit will not oscillate.  If
>>>> I pull the plug-in out and drop it back in, it
              will work.  I know this is not a
>>>> recommended option!  Alternatively, if I shut it
              off and wait for it to cool, it
>>>> will work when I turn it on with about the same
              probability, or a little less.
>>>> Once the scope is on it's up to spec.
>>>>
>>>> The 6AU5 is not brand new, but is good.  It was
              replaced recently with no
>>>> improvement.
>>>>
>>>> So, suggestions as to where to start on this
              intermittant problem are welcome.  Is
>>>> there anything I should look for or measure that
              might indicate what is getting
>>>> tired?
>>>>
>>>> Dan
>>>>
>>>
>>>
>>>
>>>
>>
>
>
>>________________________________
>
>   This email is free from viruses and malware because avast! Antivirus protection is active.  
>
>
>
>





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Re: 545 HV won't oscillate 100% of the time.

Don Black <donald_black@...>
 

I hope you get it sorted out Dan but I was being facetious about the eBay tubes advertised as tested good. I wonder what tests were done? I noticed another ad for similar caps saying they were tested OK on a bridge. No mention of leakage or if the bridge had to be adjusted for losses. Maybe I'm just getting cynical in my old age.

Don Black,

On 08-Dec-13 10:33 AM, Daniel Koller wrote:
 

Hi all,
  My caps probably are bad.  When I first got the scope around 1980, I learned about "black beauties" and had to replace them in the power supply, but I think I recall being told that the bumble-bee types were fine, so those stayed in.  Now it looks like I have leakage from them in the HV power supply.  See the attached photo here: http://groups.yahoo.com/neo/groups/TekScopes/photos/albums/158207078/lightbox/1517700781
The two shiny black 0.001 uF caps stand out because they are coated in oil.  You can't see it on the photo, but there is a film of liquid oil between the middle cap and the 56K resistor below it.  Those two are coming out but being a big fan of "don't mess with it if it ain't broke" I might leave the other caps in unless there is an obvious failure. Mind you, my scope works well when it does turn on.

But I've had some other modifications it seems.  What's that square cap on the left and the 2.2K resistor doing there?  I'll have to trace the circuit to see where they were put in and why.  Maybe that was a long ago patch for the oscillator failure?  Or the cause of it now?

I see now why I had originally thought my scope was much younger than it is - before I learned from the group here that the "brown" Teks were pre-1954.  There is this circuit board in my scope:
http://groups.yahoo.com/neo/groups/TekScopes/photos/albums/158207078/lightbox/1026393052
Someone seems to have made factory improvements circa 1967.   What was in its place before this?  Is it possible my additional HV circuit components were placed in the same upgrades/refurbishment?

Back to the shop.  I've got an hour before guests arrive!

Dan

On Saturday, December 7, 2013 10:58 AM, Don Black wrote:

>I'm not so sure. Yours may be faulty, these are tested good so they must be a rare animal.
>
>Don Black.
>
>On 08-Dec-13 2:31 AM, Daniel Koller wrote:
>

>>I'll check and see what's in there.   And when I take them out, I'll sell them on e-bay to an audiophool!!
>>http://www.ebay.com/itm/4-TUBE-AMP-CAPACITORS-0-1uF-400V-Sprague-Bumblebee/171185528791?_trksid=p2047675.m1982&_trkparms=aid%3D333005%26algo%3DRIC.FIT%26ao%3D1%26asc%3D177%26meid%3D3232141210003616509%26pid%3D100009%26prg%3D1088%26rk%3D1%26rkt%3D5%26sd%3D181276706729%26
>>
>>(No affiliation with the seller!)
>>
>>Dan
>>
>>On Friday, December 6, 2013 11:27 PM, Chuck Harris wrote:
>>
>>>Most of the time with the 545, the problem is the
              black beauty oil/paper
>>>tubular capacitors used for the HV filters.  They
              always go bad, and if
>>>they haven't been replaced, you must replace
              them.  Ceramic is fine.
>>>
>>>There is also a BB cap that is in series with the grid
              feedback winding,
>>>and another in parallel with the plate winding.  Both
              must go.
>>>
>>>-Chuck Harris
>>>
>>>Daniel Koller wrote:
>>>> Howdy,
>>>>
>>>> The recent discussions on HV repairs has me
              thinking I should look into the issues
>>>> in my 545 (not A or B, old style square case).  
              It works very very well, but
>>>> about half of the time, increasingly more, the HV
              circuit will not oscillate.  If
>>>> I pull the plug-in out and drop it back in, it
              will work.  I know this is not a
>>>> recommended option!  Alternatively, if I shut it
              off and wait for it to cool, it
>>>> will work when I turn it on with about the same
              probability, or a little less.
>>>> Once the scope is on it's up to spec.
>>>>
>>>> The 6AU5 is not brand new, but is good.  It was
              replaced recently with no
>>>> improvement.
>>>>
>>>> So, suggestions as to where to start on this
              intermittant problem are welcome.  Is
>>>> there anything I should look for or measure that
              might indicate what is getting
>>>> tired?
>>>>
>>>> Dan
>>>>
>>>
>>>
>>>
>>>
>>
>
>
>>________________________________
>
>   This email is free from viruses and malware because avast! Antivirus protection is active.  
>
>
>
>





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Re: 647 HV transformer

alexeisenhut@...
 

Eh, just noticed there's a nice database system right here.
Just click on database ^^^^ up there somewhere.


Re: 647 HV transformer

alexeisenhut@...
 

Maybe we should keep a database of 547s by S/N and if they had the transformer rebuilt?
Might be good come selling time.
https://docs.google.com/spreadsheet/ccc?key=0Akq_eqQcegmedGxheXl5aFRhU3FnQm9LOEpsamdFLXc&usp=sharing


Re: How to open a scope?

Reed Dickinson
 

I have experienced that same problem also.  Go to Harbor Freight and buy a 'slim Jim' or use a long piece of hacksaw blade.  The slim Jim is a long piece of tough thin steel used to open car doors.  Slide the slim Jim or bladeinside the case and work it around until you feel an obstruction.  Then examine the outside and look carefully for any anomolies in the outside case.  The screws holding the handle might be loose and catching on the chassis as you try to slide it out.  Pulling the handles outwards might make it clear.

Good luck

Reed Dickinson


On 12/7/2013 12:34 AM, machineguy59@... wrote:
 

The handles on some scopes can be damaged/bent and get hung up on the chassis rear plate as the case slides out.  Sometimes you can feel the handles bind when the case stops moving.  Try pushing the case back in slightly and then pull the handles out as you try to remove it again.  You might be able to feel if the handles bind up as the case slides. 



Re: 647 HV transformer

Cliff White
 

Is there any way to tell if a Tek transformer has wax or epoxy? I have a small suspicion that the tranny in my 536 has been replaced -- Possibly with one with epoxy. Were replacement transformers ever made with epoxy?



Respectfully,
Cliff White, W5CNW
w5cnw@...

On 12/06/2013 12:13 PM, Chuck Harris wrote:
 

To my knowledge, there are no "good" 547/545B transformers made
by tektronix. They all will fail given time, and the right environmental
conditions... unconditioned space, basements, etc. are really bad
for 547 transformers... as is lack of use.

There are quite a few 547's that have transformers made by Bill Schell,
and by me. They should be good for the long haul. There are so many
out there that surely some have changed hands by now.

-Chuck Harris

David wrote:
> Your hypothesis fits with other design choices that Tektronix made and most
> other companies make. Minimizing R&D expense by reusing existing designs with a
> minimum of alteration is great up until the loss of institutional knowledge
> causes problems. It is easier to quantify an initial hard dollar expense in
> time and money versus a later speculative loss that can only be estimated until
> it is too late by which time the loss has already occurred and is ongoing.
>
> Maintaining institutional knowledge is an expense with no immediately
> quantifiable benefit.
>
> I have not attempted to refurbish my 547 yet because I have no immediate need to
> use it until I get a uniquely useful plug-in for it like a sampler, TDR, or
> spectrum analyzer. Did any 547 oscilloscopes *not* have the bad epoxy
> transformer?
>



Re: 545 HV won't oscillate 100% of the time.

Daniel Koller
 

Hi all,
  My caps probably are bad.  When I first got the scope around 1980, I learned about "black beauties" and had to replace them in the power supply, but I think I recall being told that the bumble-bee types were fine, so those stayed in.  Now it looks like I have leakage from them in the HV power supply.  See the attached photo here: http://groups.yahoo.com/neo/groups/TekScopes/photos/albums/158207078/lightbox/1517700781
The two shiny black 0.001 uF caps stand out because they are coated in oil.  You can't see it on the photo, but there is a film of liquid oil between the middle cap and the 56K resistor below it.  Those two are coming out but being a big fan of "don't mess with it if it ain't broke" I might leave the other caps in unless there is an obvious failure. Mind you, my scope works well when it does turn on.

But I've had some other modifications it seems.  What's that square cap on the left and the 2.2K resistor doing there?  I'll have to trace the circuit to see where they were put in and why.  Maybe that was a long ago patch for the oscillator failure?  Or the cause of it now?

I see now why I had originally thought my scope was much younger than it is - before I learned from the group here that the "brown" Teks were pre-1954.  There is this circuit board in my scope:
http://groups.yahoo.com/neo/groups/TekScopes/photos/albums/158207078/lightbox/1026393052
Someone seems to have made factory improvements circa 1967.   What was in its place before this?  Is it possible my additional HV circuit components were placed in the same upgrades/refurbishment?

Back to the shop.  I've got an hour before guests arrive!

Dan

On Saturday, December 7, 2013 10:58 AM, Don Black <donald_black@...> wrote:


I'm not so sure. Yours may be faulty, these are tested good so they must be a rare animal.

Don Black.

On 08-Dec-13 2:31 AM, Daniel Koller wrote:

 
I'll check and see what's in there.   And when I take them out, I'll sell them on e-bay to an audiophool!!
http://www.ebay.com/itm/4-TUBE-AMP-CAPACITORS-0-1uF-400V-Sprague-Bumblebee/171185528791?_trksid=p2047675.m1982&_trkparms=aid%3D333005%26algo%3DRIC.FIT%26ao%3D1%26asc%3D177%26meid%3D3232141210003616509%26pid%3D100009%26prg%3D1088%26rk%3D1%26rkt%3D5%26sd%3D181276706729%26

(No affiliation with the seller!)

Dan

On Friday, December 6, 2013 11:27 PM, Chuck Harris <cfharris@...> wrote:

Most of the time with the 545, the problem is the
              black beauty oil/paper
tubular capacitors used for the HV filters.  They
              always go bad, and if
they haven't been replaced, you must replace
              them.  Ceramic is fine.

There is also a BB cap that is in series with the grid
              feedback winding,
and another in parallel with the plate winding.  Both
              must go.

-Chuck Harris

Daniel Koller wrote:
Howdy,

The recent discussions on HV repairs has me
              thinking I should look into the issues
in my 545 (not A or B, old style square case).  
              It works very very well, but
about half of the time, increasingly more, the HV
              circuit will not oscillate.  If
I pull the plug-in out and drop it back in, it
              will work.  I know this is not a
recommended option!  Alternatively, if I shut it
              off and wait for it to cool, it
will work when I turn it on with about the same
              probability, or a little less.
Once the scope is on it's up to spec.

The 6AU5 is not brand new, but is good.  It was
              replaced recently with no
improvement.

So, suggestions as to where to start on this
              intermittant problem are welcome.  Is
there anything I should look for or measure that
              might indicate what is getting
tired?

Dan



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Re: 536 HV Dropping Off (and other random issues)

Albert Otten
 

I would certainly test HV again with the CRT still removed. CRT anode lead well insulated.

Albert


Re: 647 HV transformer

Albert Otten
 

(coninued)
I forgot to mention (well, thought of it later on) that both heater windings in the 564 are at the same transformer leg. The other leg is empty. So there is no need to equalize. I didn't expect this, otherwise I would have chosen a 564 with two 5642s.

Albert


Re: 536 HV Dropping Off (and other random issues)

Cliff White
 

We seemed to have started a trend of HV threads!

Thanks for the clarification on the transformer test and the center tap of the primary. I guess I need to read up on Hartley oscillators!

I went ahead and pulled the CRT to check the anode connection. There was a little dust around it, but not too much. I've cleaned it up anyway. On that note, are there any tests y'all recommend while I have the CRT disconnected?

Also, is it possible I'm dealing with the same transformer epoxy issue? Maybe because of a replaced transformer? Is there a way to identify what material the transformer is potted in? I noticed the CRT appears to have been replaced -- The CRT itself has a property sticker on it, one on the neck and one on the base.


Respectfully,
Cliff White, W5CNW
w5cnw@...

On 12/05/2013 04:39 PM, kaboomdk@... wrote:
 


Hi Cliff,
  Wow, that's a neat test.  Seeing the primary voltage and the secondary change in lockstep sure seems to vindicate the transformer.  The voltages should remain in the same ratio as the turns ratio, unless perhaps you saturate the core and then it deviates further from an Ideal transformer.

One other thing to try might be to remove intensity circuit by removing V842 (at least partially and connecting an 8MOhm resistor across that transformer winding to give it a similar load as it has now.
That will leave nothing but the CRT anode circuit on the HV side.   On that note, is the anode clean, without dust around the connection point?  Are we are sure there are no discharge paths over the surface of the CRT?

Before you do that, measure the voltage across the intensity pot as Albert recommended.  

What have we done to vindicate R804, R805?  Still assuming all the caps are good.

Dan

---In TekScopes@..., wrote:

I ran another wire through the transformer once like you mentioned. I used another scope and calculated the RMS value. It started at 1.9 and went down to 1.0. Note that the circuit is still cut at R855, which might be causing the higher voltage. Also I think my winding is closer to a full turn than the real filament winding.

I then put a scope probe on the primary side of the transformer (AC-coupled). I set up the monitor scope such that both signals were stacked (appeared to be only one trace) by adjusting the variable v/cm control on one channel. When the fade out happened, they went down exactly together. I *think* this means the transformer's efficiency isn't changing. True? If so would that mean the transformer is not at fault, I think, although I'm not to certain about this part. Can anyone offer insight to that?

Then I added a diode clamp from pin 6 of V816 to the +100 supply. Note that the circuit is still cut at R855. Here's the values in that scenario.

Primary (pin 5, V800): 415ish to 325 (p-p)
"Filament" (my "winding"): 1.7 to 1.3 (rms) (compare that to the first time w/o clamp above)
DC Output (junction of R855 and C855): -950 to -630 (dc)
R807 (referenced to transformer end): 10.03 to 9.67 (dc) Should I measure this with the scope also? I can use my Type W differentially.



Respectfully,
Cliff White, W5CNW
w5cnw@...
On 12/05/2013 05:30 AM, aodiversen@... wrote:
 

Well, that rules out a possible tube fault at the primary side.
The diode heaters nominally receive 1.25 V AC from the single-turn "windings" through the transformer. This is 50 kHz AC (no DC component), so your DMM must be suitable for that frequency. It would be nicer, if possible, to guide an additional well insulated wire through the transformer and then view the induced voltage at an other 'scope. In my opinion you can only find a decrease to some 75% of nominal.
I don't know whether V800 can deliver more and more power when the screen voltage rises so extreme. Hence my suggestion to clamp the screen with a diode to the +100V supply. Then the change in primary AC swing during warming up will indicate whether the secundary load increases or decreases. Perhaps the AC swing reduces like before or even further now, for sure indicating now an increasing load at V800. But then the secundary load decreases  (less heater power and less power at the DC outputs, assuming again you already eliminated possible DC leakage by cap replacements). Hence that would imply leakage in the the secondary windings or leads. Again the reasoning is that the DC outputs collapse because of the reduced heater voltages, not because of the reduced secundary HV voltages.
I would also monitor the voltage across R807. At higher load the anode current will increase. (BTW I think R807 would burn out when its resistance increases dramatically.)

BTW did you measure DC across the Intensity pot? Should normally be slightly over 100 V.

Albert

 




Re: bama edebris manual uploads

alexeisenhut@...
 

That's good.
Sent it just now. It's just a manual for the 1S1 plugin but it's just so awesomely well done by a really good guy I have to share it.


Re: How to open a scope?

danishcah@...
 

My 465's also hang up solid on the grounding tab extension(s) and or the screwhead, as these protrude right out to the inside surface of the case. These can be found on any of the 4 sides, some of mine have been removed or just the tab removed, leaving a "stud" sticking out for no other reason than to catch on the case...  Dana  d:)>

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