Date   

Lazy man's guide to 2467B HVPS cleaning and re-cap

vdonisa
 


The subject says it all, I felt too lazy to do a complete disassembly of the board (i.e. remove the top panel / assembly) so I found out that if you don't mind the board being held captive by the high voltage cable, you can still do the cleaning & re-cap work on it.

Short self-explanatory photo guide posted here:

http://groups.yahoo.com/group/TekScopes/photos/album/1649030095/pic/1700662428/view

New caps are Nichicon UBT1V101MPD, same physical size / capacity/ voltage as the ones I found in place. Except the new ones are rated 5000h/125C, should last for a while :-)

Cheers,
Valentin VE3VDO


Re: Why X1 probes have low bandwidth

Dave C <davec2468@...>
 

However, since I am still working where I work, I cannot share details.  After I am no longer working there, I don't know how long my non-disclosure agreement may apply.

Needless to say -- "same thing different day"

73
Jim N6OTQ

-=-=-=-

Your NDA includes discussion about observations of what management does (or not)? It's usually limited to your field of technical expertise, in my experience. 

Dave


7904A and X-Y Display -- Help !

jsternmd
 

My 7904A seems to work fine for routine use with my various Vertical amps and timebases. However, I can't get it to work in X-Y display. I have a 7A26 in right vertical and a 7B70 in the left (A) Horizontal slot with nothing in the B-horizontal slot. As I understand the instruction manual, the 7B80 should be switched from Timebase to Amplifier and external/DC selected but when I do this the 7904A "A" slot light next to the Intensity control goes out and the "B" light comes on and the display is lost. There is nothing in the B slot. Also the Horizontal Mode button selected for A or B lights up correctly but has no effect on the getting anyt display. If I try to reverse things by putting the 7B70 into the B horizontal slot with the A slot empty, it works normally as timebase with B light on but as soon as I switch it to Amplifer mode, the B light goes out and the A light comes on. I tried to input two simple sine wave signals 90deg out of phase but cannot get anything on display. I also have a 7B80 with X-Y option and it shows the exact same behavior switching from timebase to X-Y.

Any advice approeciated.

Jerry
K1JOS


Re: Mystery capacitors in 2467B HVPS

 

On Sun, 14 Apr 2013 02:25:05 -0000, "vdonisa" <vdonisa@yahoo.com>
wrote:

Hi All,

I am staring at the schematic of the 2467B HVPS, more specifically to the A9C4363 and A9C4470 capacitors. Tek has specified them as "CAP,FXD,ELCTLT:0.22UF,5%,35V,1KHZ" Vishay Sprague tantalum caps.

Unfortunately I cannot find any datasheet for them that would enlighten me on why this particular choice for a tantalum 0.22uF/35V capacitor. This value could had been easily found as ceramic or film. They already have 22 Ohms resistors in series with them so Tek was not relying on their ESR exclusively.

So why this particular choice? What is special about these caps? What does the "1KHZ" spec refer to?

There must have been a reason, please enlighten me!

Thanks,
Valentin VE3VDO
Charge!

The .22uF capacitor lowers the impedance (2KOhms) driving the
oscillator but also introduces an additional 90 degrees of phase lag
into the regulator control loop before the unity gain crossover point.
The 22 ohm series resistor adds a frequency compensation breakpoint to
keep the regulator stable.

Notice that the operational amplifier feedback time constants
(0.0047uF and 110KOhms=308Hz and 2200pF and 220K=329Hz) are pretty
close to the output impedance time constants (0.22uF and
2KOhms=362Hz). At high frequencies (0.22uF and 22Ohms=33KHz), the 22
ohm resistor adds phase lead to keep the feedback loop stable.
Tektronix probably had problems with overshoot during startup.

They did not use high dielectric constant ceramics because their high
voltage and temperature coefficients of capacitance and high tolerance
would have altered their carefully tailored frequency response too
much. C0G type ceramics would have been expensive. I think a film
capacitor would have worked but it would have been larger than the
tantalum they specified.

I suspect the 1 KHz specification refers to a test frequency or
guarantied specification at 1 KHz.


Re: Tek 576 Curve Tracer Repair

George
 

Greetings,
I have one of these and would like to know if there suggestions laid out as to how to use this Transistor curve tracer to test vacuum tubes
. I looked at several threads but no luck. Also any downloads in files or attachments to give examples or instructions. I am just getting small pieces as to how this idea works?
Thank you in advance,George

--- In TekScopes@yahoogroups.com, "c1ferrari" <sonic_liberation@...> wrote:

Hi all,


I bought a 576 from eBay with a Tektronix cal from Dallas which expired 01-DEC-10. Everything was going well and I was learning how to use the instrument...until today.

I was attempting to characterize 6C33C tubes when smoke began to emanate from the top array of ventilation ports on the machine's left side. Immediately, I attenuated the Variable Collector Supply and switched the machine off.

I did not observe any POP or other sound in connection with this event.

Now that I've recovered, somewhat, my equilibriium -- I'm writing the post to ask this august group if there is anyone, any resource in my neck of the woods -- San Diego, that can take a look at my beloved Tek 576 CT.

Please, let me know.


Very best regards,

Sam


Re: 7000 Series Plug-Ins For Sale

Don Black <donald_black@...>
 

Oh dear, I'd sure be interested in some of them but from Australia it's too far to swim.

Don Black.

On 14-Apr-13 9:20 AM, Richard Solomon wrote:
 
I have the following Plug-Ins that are excess to my needs:

7A11
7A13
7A15
7A22 (2)
7B50 (2)
7B51
7B53A
7B85 (2)
7B87

Take your choice, $15 each, pick-up ONLY in Vail, AZ
20 miles SSE of Tucson

73, Dick, W1KSZ



Re: Any advice on 547 power supply repair?

Chuck Harris <cfharris@...>
 

Hi George,

It is my intention to start making 647 transformers in the
same manner as the beeswax impregnated 547 transformers. I
am in the process of redesigning my winding machine to make
it easier and more reliable to wind all manner of different
style transformers. When I get that done, and have the
process perfected, I will make an announcement.

It might help me to speed up the process if a nice bench top
647A that needs a transformer were to find its way into my
stash... kind of like happened with a 547 and 545B..., but
regardless, it will happen one of these days.

-Chuck Harris

G. K. wrote:

Chuck, Would you take on the task of re-winding the high voltage transformer in a
647A? I have a near mint condition unit which runs for about 45 min until the
transformer gets hot and the fuse in the 2N3055 collector blows. - George



________________________________ From: Chuck Harris <cfharris@erols.com>


535 on Boston Craigslist

sipespresso <sipespresso@...>
 

I have no affiliation with the seller.
http://boston.craigslist.org/nwb/atq/3741630290.html
-Kurt


Mystery capacitors in 2467B HVPS

vdonisa
 

Hi All,

I am staring at the schematic of the 2467B HVPS, more specifically to the A9C4363 and A9C4470 capacitors. Tek has specified them as "CAP,FXD,ELCTLT:0.22UF,5%,35V,1KHZ" Vishay Sprague tantalum caps.

Unfortunately I cannot find any datasheet for them that would enlighten me on why this particular choice for a tantalum 0.22uF/35V capacitor. This value could had been easily found as ceramic or film. They already have 22 Ohms resistors in series with them so Tek was not relying on their ESR exclusively.

So why this particular choice? What is special about these caps? What does the "1KHZ" spec refer to?

There must have been a reason, please enlighten me!

Thanks,
Valentin VE3VDO


Re: Any advice on 547 power supply repair?

G. K. <glkinst@...>
 

Chuck,
Would you take on the task of re-winding the high voltage transformer in a 647A? I have a near mint condition unit which runs for about 45 min until the transformer gets hot and the fuse in the 2N3055 collector blows. - George

 

From: Chuck Harris
To: TekScopes@... 
Sent: Saturday, April 13, 2013 4:44 PM
Subject: Re: [TekScopes] Re: Any advice on 547 power supply repair?
 
That's kind of like asking what can I do to keep the rising
flood water out of my house, other than building a dike,
putting in sand bags, or moving the house... Pray?

The problem is the secondary gets lossy, which makes the
transformer run very hot... so hot that it will melt the
polyethylene filament windings, if they touch the center
EHT winding. When the core gets hot, it gets very lossy,
and the inductance of the primary and secondary coils
drops, which causes the HV to drop, which causes the HV
regulator to push the oscillator tube's screen grid to
maximum voltage. A little hotter, and the oscillator just
quits. Usually you can count on replacing the oscillator
tube and its plate resistor... if your 547 doesn't have
the screen voltage limiter modification.

Replacing the 5642's with silicon diodes will eliminate
about 5W of heat from inside of the plastic HV compartment,
and will usually allow the transformer to last a little
longer. Because of the lower current draw from the EHT,
you will have to adjust the screen resistor to lower the
gain of the hv regulator. I have been told that the
rectifier replacement only delays the inevitable replacement
of the EHT.

I have been told that the late Jim Williams was of the
belief that if a transformer could be dried out before it
was run in the lossy state, it could sometimes be saved.
He championed the idea of putting a 100W light bulb inside
of a new (to him) scope, and putting a blanket over it and
allowing it to cook for a couple of days to a couple of
weeks. That said, Jim Williams bought dozens of replacement
transformers from an early 547 rewinding pioneer, Bill Schell.

I gave up trying to "fix" the transformers and spent my
limited time and energy on learning how to rewind them.

Unlike the legendary 547 transformer winder Bill Schell,
I made sure that my windings were fully compatible with
the original... no need to replace the 5642's, or adjust
the screen resistor to use my transformers. There
are pictures in the pictures section of this group.

Send me any old tektronix EHT with that style core, and
$100 US, and I will send you a rewound transformer
anywhere in the world.

There are plenty of folks on this group that can tell you
of their experiences with transformer replacement.

-Chuck Harris



Re: Stacked 7000s

 

Dave,

The wattage ratings on the mainframes may give you a clue.
Also, the mix of plugins among mainframes may make a difference.
If any plugin slots are empty, that could affect airflow unless the slot has a blank panel in it.

HankC, Boston, WA1HOS

--- In TekScopes@yahoogroups.com, Dave Daniel <kc0wjn@...> wrote:

Also, can anyone tell me in what order one would rate the power
dissipation of these 'scopes (e.g., which ones get hotter than the
others)?. My 7904A and 7854 don't get very hot. The 7104 and 7934 have
failed power supplies, so I don't know if they run noticeably hotter.
The four 'scopes I am speaking of are

7104
7904A
7934
7854

Cheers,
DaveD

On 4/13/2013 6:39 PM, Dave Daniel wrote:
Has anyone had any problems running 7xxxx 'scopes stacked two high? I
am thinking of stacking my 7104, 7904A, 7934 and 7854 in a 2 x 2 pile.
I'm not sure if I would need two 'scopes running concurrently. The
fans, where they exist, move air horizontally. Perhaps the bigger
problem would be that one shouldn't have them side-by side?

Cheers,
DaveD


7904 for sale

Dave Daniel
 

All,

I have a 7904 that I would like to sell. I'll probably include two 7B53A timebases. I'll have to see which of the pile of 7B53As I have that are working; I need to keep two good ones. If I have four good ones, I'll include two with the 'scope. Otherwise, it'll be none, or non-working timebases (buyers choice). No vertical amplifiers. Shipping within the continental US only (also UK but I think it would be prohibitively expensive to ship). Packaging would be well-done, but would add to the cost.

The instrument was working when I last had it on the bench (it was my main 'scope between about 1997and 2012), but has not been calibrated lately. I will verify basic operation if someone is interested just in case it got annoyed with me after having been replaced by my other 7xxx 'scopes. I do know that the light behind the LEFT vertical mode switch does not work (anyone realize that a typo in this last results in "doe snot" ? Ewwwwww). The 'scope has no options.

If you are interested, please make an offer. Buyer will have to pay for shipping. I don't want a lot for it; I'd be satisfied just to cover the cost of one of my other recently-purchased 7xxxx 'scopes, which were less than almost all that have been listed on eBay for the past year or so. I'm basically trying to give it a good home while making some space and covering some of the cost of my Tek 'scope addiction.

I bought this 'scope from a guy in Denver. it was calibrated when I bought it, and the guy actually decided to drive it up to Longmont, CO rather than ship it so it would not get damaged. I was impressed with his desire to deliver a quality used 'scope.

If anyone is interested in buying it, I can post photographs.

Cheers,
DaveD


Re: Stacked 7000s

Dave Daniel
 

Also, can anyone tell me in what order one would rate the power dissipation of these 'scopes (e.g., which ones get hotter than the others)?. My 7904A and 7854 don't get very hot. The 7104 and 7934 have failed power supplies, so I don't know if they run noticeably hotter. The four 'scopes I am speaking of are

7104
7904A
7934
7854

Cheers,
DaveD

On 4/13/2013 6:39 PM, Dave Daniel wrote:
Has anyone had any problems running 7xxxx 'scopes stacked two high? I am thinking of stacking my 7104, 7904A, 7934 and 7854 in a 2 x 2 pile. I'm not sure if I would need two 'scopes running concurrently. The fans, where they exist, move air horizontally. Perhaps the bigger problem would be that one shouldn't have them side-by side?

Cheers,
DaveD


Stacked 7000s

Dave Daniel
 

Has anyone had any problems running 7xxxx 'scopes stacked two high? I am thinking of stacking my 7104, 7904A, 7934 and 7854 in a 2 x 2 pile. I'm not sure if I would need two 'scopes running concurrently. The fans, where they exist, move air horizontally. Perhaps the bigger problem would be that one shouldn't have them side-by side?

Cheers,
DaveD


Single wide 7K plugin Frames Wanted

 

Hi,

I need 7K plugins frames parts. top and bottom rails, Side panels, ALL latch parts, rear plastic bracket. I do not need knobs,pots,switches,pwbs. No double wides.

Please contact me of-list. Am willing to trade

Jerry Massengale


Re: Planning 2467B LVPS re-cap

vdonisa
 

Hi David,

Agreed on both points.

There is an "optimal" point up to which you can increase voltage and improve on all parameters, and going past that you get worse ripple current rating so you know where to stop. Also there are physical limitations on the case size, it has to fit on the PCB, and also you should have lead spacing <= hole spacing (I don't find it acceptable to bend the terminals inwards).

As for the 10u/100V vs 10u/160V example you mentioned, here were the candidates:

http://groups.yahoo.com/group/TekScopes/photos/album/1314606778/pic/405367259/view 

Since the schematic calls for 3 x 10u/100V and 1 x 10u/160V, and taking into account the characteristics shown in the photo, and that we're trying to maximize on ripple current and endurance spec, and we don't need to go past 105 Celsius spec, it made sense to use the Nichicon CA for all 4 caps of 10uF.

As for your second point, I am definitely aware of that, and particularly the Panasonic EEU-FR comes in two variants, with or without an "L" postfix in the part number, the "L" indicates a taller slimmer case, with different ripple / endurance specs, I have used both variants in my list depending on all specs including lead spacing.

Rest assured that the list was carefully researched and a good starting point for a re-cap project, improving on it will take many hours of datasheet reading :-) and/or access to some capacitors that are not usually stocked by mouser/digikey/newark.

Thanks again gentlemen for all your help,

Valentin VE3VDO


--- In TekScopes@..., David wrote:
>
> On Sat, 13 Apr 2013 02:54:52 -0000, "vdonisa" vdonisa@...
> wrote:
>
> >A few notes:
> >
> >- some capacitors (100, 180 and 270u - the ones that are the most stressed) may look ridiculously oversized in voltage; it was deliberate and had nothing with the voltage itself but with the case size instead; a modern 100uF/25V is pretty tiny and won't dissipate heat very well - this is generally also reflected in its ripple current and endurance ratings; I went for some larger capacitor cases in order to improve on these specs;
>
> I do the same thing for the same reason although if you check the
> manufacturer's specifications, higher voltage does not always yield a
> higher ripple current rating. There is often a significant rise in
> ESR and sometimes lowering of ripple current rating going from 100
> volts to 160 volts because the electrolyte is changed.
>
> Sometimes you can find the same capacitance and voltage rating in two
> different case sizes with one having a much higher ripple current
> rating.
>


Re: 7912AD

Dave Daniel
 

On the other hand, here is what might be either a working but dented 'scope, or a reasonably priced parts mule. eBay #310650437070.

DaveD

--- In TekScopes@yahoogroups.com, "Steve" <ditter2@...> wrote:

--- In TekScopes@yahoogroups.com, "Craig Sawyers" <c.sawyers@> wrote:

Anyone up for a look at something just a bit overpriced? EPay 230881279002

Craig
The other humorous (maybe not so) point is the shipping policy. Like many other small surplus resellers, this company states that they will" gladly ship nearly anywhere in the world".

What many of these small companies fail to check out is that all technology is subject to export classification from the USA, and some items such as this digitizer, are actually extremely controlled, requiring an individual export license be obtained for each sale to other than a tiny handful of "friendly" countries. Even when sold to one of these, you had better have strong evidence that the digitizer is being purchased to really be used in that country, and not be an agent who will pass it on to a banned country. The fines for noncompliance are pretty steep – they would essentially put most small companies under.

While some may say this is just other example of government over regulation that harms small business, I don't agree. The export classification system in the US is relatively easy to follow, and if I were a surplus dealer, I would weigh the relatively small potential for export business with the hassle of checking each item for export restrictions. As an alternative, you could easily specialize in one of the majority of categories that have no restrictions.

In the case of the 7912AD, its main application while Tek sold it was to the government labs for nuclear weapon design testing. While the technology is somewhat dated by today's standards, the digitizer has many features that simplify data collection in this application. I really would not see these going to countries with rogue regimes that would use them for developing their own weapons.

Steve


Re: Any advice on 547 power supply repair?

Chuck Harris <cfharris@...>
 

That's kind of like asking what can I do to keep the rising
flood water out of my house, other than building a dike,
putting in sand bags, or moving the house... Pray?

The problem is the secondary gets lossy, which makes the
transformer run very hot... so hot that it will melt the
polyethylene filament windings, if they touch the center
EHT winding. When the core gets hot, it gets very lossy,
and the inductance of the primary and secondary coils
drops, which causes the HV to drop, which causes the HV
regulator to push the oscillator tube's screen grid to
maximum voltage. A little hotter, and the oscillator just
quits. Usually you can count on replacing the oscillator
tube and its plate resistor... if your 547 doesn't have
the screen voltage limiter modification.

Replacing the 5642's with silicon diodes will eliminate
about 5W of heat from inside of the plastic HV compartment,
and will usually allow the transformer to last a little
longer. Because of the lower current draw from the EHT,
you will have to adjust the screen resistor to lower the
gain of the hv regulator. I have been told that the
rectifier replacement only delays the inevitable replacement
of the EHT.

I have been told that the late Jim Williams was of the
belief that if a transformer could be dried out before it
was run in the lossy state, it could sometimes be saved.
He championed the idea of putting a 100W light bulb inside
of a new (to him) scope, and putting a blanket over it and
allowing it to cook for a couple of days to a couple of
weeks. That said, Jim Williams bought dozens of replacement
transformers from an early 547 rewinding pioneer, Bill Schell.

I gave up trying to "fix" the transformers and spent my
limited time and energy on learning how to rewind them.

Unlike the legendary 547 transformer winder Bill Schell,
I made sure that my windings were fully compatible with
the original... no need to replace the 5642's, or adjust
the screen resistor to use my transformers. There
are pictures in the pictures section of this group.

Send me any old tektronix EHT with that style core, and
$100 US, and I will send you a rewound transformer
anywhere in the world.

There are plenty of folks on this group that can tell you
of their experiences with transformer replacement.

-Chuck Harris

Bene's Mails wrote:

What can I actually do to increase the HV output apart from replacing the
rectifier-diodes into silicone-types (already done) and replacing the tubes of the
HV Supply (too) or rewind the transformer (what is too expensive for me at the
moment.

ben

From: Chuck Harris Sent: Saturday, April 13, 2013 3:02 PM To:
TekScopes@yahoogroups.com Subject: Re: [TekScopes] Re: Any advice on 547 power
supply repair?


That is, of course, why tektronix added the screen grid clamping diode to the
later model 547's... one of many indications that they knew that the epoxy
impregnated transformers were very lossy, and likely to get worse... Another
indication is the previously unnecessary balancing winding for the asymmetrically
distributed 5642 filament load. And another is the cutout in the bottom of the
plastic HV box for an unused transformer core heatsink. And yet another is
lowering the oscillation frequency from 65KHz to 50KHz... and there are still more
indications if you look at other scope models that inherited the 547's HV
compartment.

I have found that new rewound beeswax impregnated transformers result in screen
voltages around 65V vs. good epoxy impregnated transformer's 100V.

-Chuck Harris

Albert wrote:
Hi Ben,

An indication for that (or for a weak oscillator tube) would be a very high
screen voltage of the oscillator tube, probably clamped at 125 V. Normally that
voltage is well below 100 V.

Albert

Hm, I think then it was one of the less degenerated. I can imagine, that this
is also the reason why the HV still don’t reach it’s specified value.

ben


--- Some transformers that are only mildly affected by the epoxy degradation
will reduce their leakage after being heated, but even at their best, a good
epoxy impregnated 547 transformer is about 10x more lossy than one of my
transformers impregnated with beeswax. --- -Chuck Harris


7000 Series Plug-Ins For Sale

Richard Solomon <dickw1ksz@...>
 

I have the following Plug-Ins that are excess to my needs:

7A11
7A13
7A15
7A22 (2)
7B50 (2)
7B51
7B53A
7B85 (2)
7B87

Take your choice, $15 each, pick-up ONLY in Vail, AZ
20 miles SSE of Tucson

73, Dick, W1KSZ


Re: Why X1 probes have low bandwidth

 

The period is not important except that it needs to be long enough to
show lower frequency effects. It does not need to be any faster than
the oscilloscope sweep rate which is limited by the trigger hold-off
time.

50kHz is usually good but you can raise it if it makes the display
brighter.

The PG502 is a little marginal for this kind of test because it does
not have aberrations much lower than the SC504. The fast rise and
fall outputs of a PG506 would be idea. A calibrated tunnel diode or
avalanche pulse generator would work also.

On Sat, 13 Apr 2013 16:54:56 -0400, Ray <w4byg@att.net> wrote:

David,
Thank you for your comments.

I have a FP-502 which I've never used. I also have a precision 50 ohm
sampling termination which I can attach the scope probes to at the
generator output.

Would you care to suggest initial settings of the PG in order to check
the scope probe bandwidths to 100 MHz? I would think I should use the
.1 nsec range for a 10 MHz period.

Ray, W4BYG

On 4/13/2013 3:16 PM, David wrote:
If you have a fast transition time reference pulse generator then you
can test them while connected to the oscilloscope. The bandwidth may
not exactly match but if the transient response is flat, I would
declare victory.

The cheap Chinese 100 MHz x1/x10 Aidetek brand probes I picked up have
worked fine when tested on every oscilloscope I have used them with so
far.

On Sat, 13 Apr 2013 12:05:52 -0400, Ray <w4byg@att.net> wrote:

Fascinating article and comments. It brings up a question for me.

My SC-504 was bought used in good condition, but did not come with
original probes. It supposedly has an 80 MHz BW.

I have tended to use on it my probes from my 465 or probes made by
Leader, model LP-101X, both of which are supposedly 100MHz probes. Both
have adjustable compensation at the scope end of the cables and both
seem to compensate the reference square wave OK.

I'm now wondering how compatible these really are at RF frequencies for
the SC-504?

Your attention is appreciated.

Ray, W4BYG

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