In a recent post the 7A29 was recommended as a much better plugin that the 7A19 which apparently has a poor reputation among members of TekScopes. I don't disagree with that assessment. But if you know a few of the details behind its remarkable development and its strategic importance to Tek you might appreciate it more. Tek was always known for how much attention they paid to the "Human Factors" of their products. Howard Vollum's goals for the 7000 series forced the "Human Factors" engineers to get much more creative. The result was a totally new look in scopes. In 1969 Tek introduced their brand new 7000 series lab scopes at the 1969 WESCON industry trade show in San Francisco. Tek's new top of the line 150MHz 7704 was 3 times faster than their current 547 lab scope. Tek was justifiably proud of the 7000 series. Here are a few examples of the new features Tek was so proud of: * The new triggering control (one of Howard's requirements) combined the level and slope into one knob can turn through 360 degrees. This made it possible to trigger anywhere on a waveform while the knob showed the corresponding level and slope of the trigger point. * The Tek 7704 had 4 plugin slots for much greater flexibility. It could display up to 4 signals simultaneously at two different sweep speeds. * The new scopes had lighted push buttons to make them easier to use. At the same show HP introduced their new line of lab scopes. But it quickly became apparent that the new HP scopes were superior in many ways. Here are two features that proved to HP that they had the superior products: * The new HP scopes had much better specifications and they cost much less than the 7000 scopes. * When you applied an AC signal that went from low frequency up to the limit of the scopes triggering capability the HP scope triggered perfectly across the entire frequency range without ever missing a trigger point. By comparison the 7000 trigger setting had to be constantly adjusted to get it to trigger. HPs triggering capability was so good it left Tek embarrassed by their trigger circuits. HP wasted no time touting the superior performance and lower cost of their new lab scopes with an industry wide advertisement. Within Tek this became known as the HP "Foxtail" ad. It didn't mention Tek but it mocked the new features of the 7K scopes as irrelevant "bells and whistles". One of those bells and whistles was Barrie Gilbert's revolutionary on-screen readout. I uploaded this ad to TekScopes at /g/TekScopes/files/Infamous%20HP%20%22Foxtail%22%20advertisementInternally the WESCON show was described as a big success to the Tek employees. But Howard Vollum and the rest of management knew they were in trouble. The 7K introduction was a flop. What Tek did next would cement their reputation as the industry leader in oscilloscopes for decades to come. The ultimate goal of the 7000 series was never meant to be the 150 MHz 7704 that was introduced at WESCON. The 7000 series was designed from the beginning to have the capability to go much faster. But faster scopes could not be done with discrete parts. Tek would have to develop their own 1GHz+ analog IC process to make faster scopes. That would be extremely difficult. Meanwhile the 7000 design team was working on the next mainframe scope and plugins to leapfrog HP. The 7704 was 3X faster than the previous 547 50MHz lab scope. The next scope was going to be 10X faster if they could do it. Thor Hallen, an excellent vertical amplifier designer was given the task of creating a vertical amplifier with 500MHz performance in the 7904. That meant his design had to have a standalone bandwidth in excess of 700MHz. The amplifier was required to use the new ICs Tek was making. Thor had less than 2 1/2 years to do this. When the date was decided for the announcement Tek still couldn't make the ICs Thor was supposed to use to achieve the unheard of specs the 7A19 had to meet. The ICs were nowhere to be seen. At the last minute Thor had to substitute discrete transistors for the ICs and still make it work at 500MHz in the 7904 it would be announced with. I have that 7A19 plugin in my collection that Thor made, with the transistors Thor used, for the announcement. As if that wasn't enough, all by himself, Thor designed the 7A19 Option 4 plugin which has variable delay so two extremely fast signals can be displayed at the same point in time on the CRT. The 7A19/7A19 Opt 4/7B90/7934 combination was the fastest lab scope ever made and it was ahead of its time in 1972. In spite of the inferior performance of the 7000 products Tek announced at WESCON 3 years earlier, engineers liked what they saw and wanted features like on-screen readout. Ironically the bells and whistles HP mocked in the Fox Tail" ad were a strong selling point for the new 7000 series. By the time Tek introduced the 7904, HP was no longer crowing about their superiority in scopes. The development of the 7A19 and 7A19 Opt 4 by Thor Hallen is an astounding achievement for 1972. Its 500MHz performance in the also astounding 7904 lab scope was so much faster than anything else at the time that Tek reclaimed the crown as the undisputed leader in oscilloscopes. They kept the crown for over 20 years after that. Dennis Tillman W7pF -- Dennis Tillman W7pF TekScopes Moderator
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Re: Advice about buying a 7904
I'm in central Arkansas, so T&M gear "near me" is in Dallas. Except for my 577 everything I've bought has been shipped. Picking up the 577 was a 6 hr drive each way. But I had bought $1000 of the wrong LED 4 ft fluorescent replacement lamps and return shipping would have cost as much as the 577. So the 577 was effectively free. Paid for by the LED lamp shipping charges.
I had one casualty with a poorly packed DDA-120. I now give very specific instructions about packing. But I've gotten 2 dozen major instruments shipped without damage including a 7104.
My LeCroy DDA-125 is almost jet engine level.
Have Fun!
Reg
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Re: Mystery part Type 576 Curve tracer.
They are to keep the HV caps spaced apart the right amount, and prevent them from rattling into each other from (severe) mechanical shock and vibration. You don't really need them if the unit won't be banged around too much, but since you have them anyway, they should go back in place. I don't recall what retains them - Tek sometimes used a gob of silicone goop, and sometimes a rubber "mouse tail" wrapped around them, that was pulled through holes in the board.
Ed
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I'd seen specs like that but hadn't thought of it that way. A 10uF +150% - 100% would then be in spec at 10uF to 15uF. That makes a lot more sense now!
Thanks,
Barry - N4BUQ
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----- Original Message ----- From: "Chuck Harris" <cfharris@...>
To: [email protected]
Sent: Friday, May 29, 2020 12:10:20 PM
Subject: Re: [TekScopes] 475 questions
Hi Eric,
I think in the case of the +150% - 100% rated capacitor,
they were using the "-" as a hyphen, not a minus sign.
I think they meant to convey that the capacitor could range
in value from 150% of the marked value to 100% of the marked
value... otherwise it makes no sense to me.
In most cases, the range is as you would suppose.
-Chuck Harris
Eric wrote:
Bruce,
There are 2 fundamental differences that need to be taken in to account
when
replacing “vintage” caps. And I use the term vintage loosely. One is
tolerance. In
the worst case I can remember a capacitors value was +150% -%100 tolerance.
The means
<snip>
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Tektronix Application Notes
The Tek web site has a lot of newer material available but it's hard to find application notes from the classic era - which I define as roughly up to the marketing alliance with R&S and Advantest.
Up to that point, Tek made some of the most awesome spectrum analyzers available - it was sad to see the product line discontinued.
I remember a discussion about application notes on this list many years ago. At that time Stan Griffiths said he was still trying to secure permission from Tektronix to publish them.
I never saw a followup but I do see a few application notes on TekWiki so perhaps it would be OK now to create a collection of these before they are lost to time.
What I think would be great would be an itemized list by product lines: 5000, 7000, 11000, spectrum analyzers etc.
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Re: Advice about buying a 7904
I find all of the fans get quieter as I get older.
I wonder why that is?
-Chuck Harris
Bob Koller via groups.io wrote:
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The fan on my 7904A is very quiet, a non issue on mine at least. I suggest that the most important thing will be finding the best instrument available around your location. Packing properly is difficult and shipping is expensive.
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Re: Mystery part Type 576 Curve tracer.
If they are part of the curve tracer, they should appear in
the mechanical parts list with a description like, insulating
washer...
-Chuck Harris
Michael W. Lynch via groups.io wrote:
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All:
Now that I have got my 576 working reliably, I was going to start calibration and I found a pair of what appear to be silicone washers laying in the bottom of the unit. I have no idea where these are supposed to go.
The color is a translucent and slightly off white.
The parts are very soft and pliable.
The appearance is like that of silicone or a similar rubber like material.
The dimensions are 22mm OD x 8mm ID x 2.25mm H (or thick).
There is no appearance of any adhesive residue on these parts.
These were laying at the bottom of the unit and had a layer of dust on top.
Photo is here: /g/TekScopes/album?id=247763
This unit is a very Low Serial number unit B0100169 and this is the one that I used as my "Test Mule" for the HV transformer project, it is in pristine condition inside. The unit seems to work just fine (other than needing a calibration) and I have not done anything else to disturb the internal parts of the unit, other than the HV Supplu cover and board. I do not believe that I dislodged these, since they appear to have been laying in the bottom of the unit for quite some time.
Any ideas what these might be or where they need to be installed?
Thanks in advance. .
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Re: Advice about buying a 7904
Yeah, the fans in my HP 8566A spectrum analyzer and 8350B sweeper are pretty darn loud, too.? Don't have a 7904A to compare, just a 7904.? FWIW.?Jim Ford?Sent from my Verizon, Samsung Galaxy smartphone
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-------- Original message --------From: fiftythreebuick <ae5i@...> Date: 5/29/20 10:09 AM (GMT-08:00) To: [email protected] Subject: Re: [TekScopes] Advice about buying a 7904 Hi Reg-What y'all need to solve the fan noise problem on the 7904 is a Type 555 mainframe!? Just turn it on for a little while and when you turn it back off you won't even realize the 7904 is on!? <laughing>The 555 is my favorite scope, but it does have two very serious fans!73Tom AE5I
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Hi Raymond,
Old fashioned electrolytic capacitors have a fairly reactive,
(to aluminum) highly conductive, water based electrolyte.
The capacitor's leakage current creates an electrolytic cell
with the aluminum plates, and removes the oxide layer from the
cathode plate, and builds an oxide layer on the anode plate...
The oxide layer on the anode plate is the dielectric (insulator)
for the capacitor.
This reaction is the "reforming" process that lives on in
electrolytic capacitor lore... Even today. It is also a process
known colloquially as anodizing aluminum.
The aluminum oxide dielectric layer has competing issues:
As the oxide grows thicker, it became a better insulator, and works
to stop the leakage current necessary to grow the oxide layer thicker.
As the oxide layer ceases growing, the electrolyte dissolves the
oxide layer, allowing the leakage currents to increase... growing the
oxide layer thicker.
In normal operation, a balance is reached between leakage current
and growing the oxide layer.... A "working voltage" rating results.
The only way to increase the thickness of the oxide layer once
it reaches equilibrium, is to increase the voltage across the
electrolytic cell, making the cell's current increase, and in turn,
the oxide grow thicker... creating a new higher voltage equilibrium,
and a new "working voltage".
As long as the heat created by the leakage current doesn't raise
the temperature of the electrolyte to a point where the it boils,
the capacitor is fairly happy.
This means that higher than working voltage surges will start to
heat the electrolyte, but as long as the surge goes away before the
electrolyte boils, the capacitor will live to see another day.
One other factor needs mentioning:
The thinner the oxide dielectric layer, the higher the capacitance,
and the lower the working voltage.
The thicker the oxide dielectric layer, the lower the capacitance,
and the higher the working voltage.
The manufacturer had to balance all of these conditions when they
wrote the specifications for their old style electrolytic capacitors.
If you used these old electrolytic capacitors at a lower than working
voltage, their capacitance would increase, and their ability to
operate safely at their specified working voltage would diminish.
Unless you reformed the capacitor... safely limiting the current
until the oxide layer thickened...
Modern electrolytic capacitors use a nonreactive (to aluminum)
electrolyte and as a result, reforming is no longer necessary.
Modern electrolytic capacitors have their oxide layer created, and
their voltage rating determined, before the capacitor is even
assembled.
-Chuck Harris
Raymond Domp Frank wrote:
toggle quoted message
Show quoted text
On Fri, May 29, 2020 at 04:07 PM, Eric wrote:
There are 2 fundamental differences that need to be taken in to account when
replacing “vintage” caps. And I use the term vintage loosely. One is
tolerance. In the worst case I can remember a capacitors value was +150% -%100
tolerance. The means that for a 1 uF the measured value of anything between
2.5 uF to .1 uF would be considered “in spec” old radios still amaze me
they ever worked. Now a days +-20% is the normal. The service manual will tell
you the tolerance of the filters. From memory I am guessing it is going to be
+100% to -20 % so pretty wide design tolerance on the filters.
The other important spec is the voltage rating of the cap. And here vintage
caps and modern caps differ greatly. Vintage caps were very tolerant of over
voltage especially given how tube gear warms up before the tube’s comes in
to operation the B+ will spike some times as high as 200 to 250 volts higher
then when the device is operating and can hang there for about 15-30 seconds.
This is not an issue in your 475 as it is solid state. However modern caps are
completely intolerant of over voltage so if you have the physical space it is
always good to bump up the voltage rating of the cap it wont effect anything
to replace a 63V cap with a 400V cap excepta little cost in $ maybe one or 2
and physical space it will be slightly bigger then it’s modern lower voltage
counterpart. However both are usually smaller then their vintage counter part
even doubling the voltage the modern can will be smaller physically.
I don't think anyone would have accepted caps with +150/-100% tolerance, not even electrolytics...
Any information on the inability of modern caps to withstand overvoltage more than vintage caps used to? Maybe WV was just very conservatively spec'ed?
I'd rather have known the actual max.
For (wet) Al electrolytics, choosing a spec-voltage very much higher than it's ever going to experience, has a deformation effect, so is not recommended.
Raymond
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Re: Mystery part Type 576 Curve tracer.
Michael,
Yes, used on all, my B36xxxx instruments have them as well.
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Re: Mystery part Type 576 Curve tracer.
Bob,
Excellent! Thank you.
Were these used on the much later model 576? I also have a 576 that dates from the mid 1980’s and I do not recall seeing these in that unit.
--
Michael Lynch
Dardanelle, AR
|
Hi Eric,
I think in the case of the +150% - 100% rated capacitor,
they were using the "-" as a hyphen, not a minus sign.
I think they meant to convey that the capacitor could range
in value from 150% of the marked value to 100% of the marked
value... otherwise it makes no sense to me.
In most cases, the range is as you would suppose.
-Chuck Harris
Eric wrote:
toggle quoted message
Show quoted text
Bruce,
There are 2 fundamental differences that need to be taken in to account when
replacing “vintage” caps. And I use the term vintage loosely. One is tolerance. In
the worst case I can remember a capacitors value was +150% -%100 tolerance. The means
<snip>
|
Re: Advice about buying a 7904
Hi Reg-
What y'all need to solve the fan noise problem on the 7904 is a Type 555 mainframe! Just turn it on for a little while and when you turn it back off you won't even realize the 7904 is on! <laughing>
The 555 is my favorite scope, but it does have two very serious fans!
73
Tom AE5I
|
Re: I missed some messages due to SPAM Filter Issues
On Fri, May 29, 2020 at 06:31 PM, Dennis Tillman W7pF wrote:
My apologies if I missed something important because my daily SPAM reports
stopped coming over a week ago.
No need to apologize, Dennis. On the contrary, it all stems from the work you do for us. Raymond
|
I missed some messages due to SPAM Filter Issues
Last night I noticed it had been over a week since I got the last daily list
of possible SPAM emails my ISP was holding up. I go through every one of
these daily SPAM reports I get and unblock the legitimate emails and mark
the sender as trusted. It can sometimes be a tedious job if there was a lot
of potential SPAM in that day's daily catch.
Quite a few TekScopes messages were waiting for my OK in the SPAM filter for
me to release them but I had no idea they were there since my daily notices
stopped coming over a week ago.
My ISP just reset my SPAM Filter settings and sent me a list of what has
been waiting for over a week for me to check. It was a very long list. I
just finished going through it. There were about 50 legitimate emails that I
release as legitimate.
My apologies if I missed something important because my daily SPAM reports
stopped coming over a week ago.
Dennis Tillman W7pF
|
For the life of me I cant remember the peace of gear that cap was it but it was a filter and VERY old and I cant forget the cap cause I was shocked at the tolerance spread as well. But even in the 576 some of the filter tolerances is +100% -10% and some of the ceramics is +80% -20%
toggle quoted message
Show quoted text
On 5/29/2020 11:23 AM, Raymond Domp Frank wrote: On Fri, May 29, 2020 at 04:07 PM, Eric wrote:
There are 2 fundamental differences that need to be taken in to account when
replacing “vintage” caps. And I use the term vintage loosely. One is
tolerance. In the worst case I can remember a capacitors value was +150% -%100
tolerance. The means that for a 1 uF the measured value of anything between
2.5 uF to .1 uF would be considered “in spec” old radios still amaze me
they ever worked. Now a days +-20% is the normal. The service manual will tell
you the tolerance of the filters. From memory I am guessing it is going to be
+100% to -20 % so pretty wide design tolerance on the filters.
The other important spec is the voltage rating of the cap. And here vintage
caps and modern caps differ greatly. Vintage caps were very tolerant of over
voltage especially given how tube gear warms up before the tube’s comes in
to operation the B+ will spike some times as high as 200 to 250 volts higher
then when the device is operating and can hang there for about 15-30 seconds.
This is not an issue in your 475 as it is solid state. However modern caps are
completely intolerant of over voltage so if you have the physical space it is
always good to bump up the voltage rating of the cap it wont effect anything
to replace a 63V cap with a 400V cap excepta little cost in $ maybe one or 2
and physical space it will be slightly bigger then it’s modern lower voltage
counterpart. However both are usually smaller then their vintage counter part
even doubling the voltage the modern can will be smaller physically.
I don't think anyone would have accepted caps with +150/-100% tolerance, not even electrolytics...
Any information on the inability of modern caps to withstand overvoltage more than vintage caps used to? Maybe WV was just very conservatively spec'ed?
I'd rather have known the actual max.
For (wet) Al electrolytics, choosing a spec-voltage very much higher than it's ever going to experience, has a deformation effect, so is not recommended.
Raymond
|
Re: Advice about buying a 7904
On Fri, May 29, 2020 at 05:13 PM, Roger Evans wrote:
If you are concerned about the pulse response for very fast risetimes I would
recommend the 7A29 over the 7A19. I have two 7A19s and they are very difficult
to set up for clean pulse response, you need an extender (which I don't have)
and decent non metallic tools to adjust the hairpin inductors which work
harden slightly after several attempts to adjust them. The 7A29 has a much
cleaner step response but may be getting hard to find.
The 7A29 was a much better (and newer) amplifier than the 7A19 altogether. Much has been written about that and can be found on TekWiki and other sources. Raymond
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On Fri, May 29, 2020 at 04:07 PM, Eric wrote:
There are 2 fundamental differences that need to be taken in to account when
replacing “vintage” caps. And I use the term vintage loosely. One is
tolerance. In the worst case I can remember a capacitors value was +150% -%100
tolerance. The means that for a 1 uF the measured value of anything between
2.5 uF to .1 uF would be considered “in spec” old radios still amaze me
they ever worked. Now a days +-20% is the normal. The service manual will tell
you the tolerance of the filters. From memory I am guessing it is going to be
+100% to -20 % so pretty wide design tolerance on the filters.
The other important spec is the voltage rating of the cap. And here vintage
caps and modern caps differ greatly. Vintage caps were very tolerant of over
voltage especially given how tube gear warms up before the tube’s comes in
to operation the B+ will spike some times as high as 200 to 250 volts higher
then when the device is operating and can hang there for about 15-30 seconds.
This is not an issue in your 475 as it is solid state. However modern caps are
completely intolerant of over voltage so if you have the physical space it is
always good to bump up the voltage rating of the cap it wont effect anything
to replace a 63V cap with a 400V cap excepta little cost in $ maybe one or 2
and physical space it will be slightly bigger then it’s modern lower voltage
counterpart. However both are usually smaller then their vintage counter part
even doubling the voltage the modern can will be smaller physically.
I don't think anyone would have accepted caps with +150/-100% tolerance, not even electrolytics... Any information on the inability of modern caps to withstand overvoltage more than vintage caps used to? Maybe WV was just very conservatively spec'ed? I'd rather have known the actual max. For (wet) Al electrolytics, choosing a spec-voltage very much higher than it's ever going to experience, has a deformation effect, so is not recommended. Raymond
|
Re: Advice about buying a 7904
If anyone in Southern Arizona is interested, I have a 7904A with two 7A26, 7B92A and 7B70 Plug-Ins. Contact me off list to discuss. Motivated Seller. 73, Dick, W1KSZ ________________________________ From: [email protected] < [email protected]> on behalf of Roger Evans via groups.io <very_fuzzy_logic@...> Sent: Friday, May 29, 2020 8:13 AM To: [email protected] < [email protected]> Subject: Re: [TekScopes] Advice about buying a 7904 I have a 7904 and a 7934 (obviously different but I believe the PSU is very similar to the 7904A). I find the fan noise of the 7934 becomes a distraction after a while when you are trying to concentrate on something else, but I agree, if you find a nice scope of either the 7904 or 4A then you should be happy with it. If you are concerned about the pulse response for very fast risetimes I would recommend the 7A29 over the 7A19. I have two 7A19s and they are very difficult to set up for clean pulse response, you need an extender (which I don't have) and decent non metallic tools to adjust the hairpin inductors which work harden slightly after several attempts to adjust them. The 7A29 has a much cleaner step response but may be getting hard to find. Regards, Roger
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Re: Advice about buying a 7904
I have a 7904 and a 7934 (obviously different but I believe the PSU is very similar to the 7904A). I find the fan noise of the 7934 becomes a distraction after a while when you are trying to concentrate on something else, but I agree, if you find a nice scope of either the 7904 or 4A then you should be happy with it. If you are concerned about the pulse response for very fast risetimes I would recommend the 7A29 over the 7A19. I have two 7A19s and they are very difficult to set up for clean pulse response, you need an extender (which I don't have) and decent non metallic tools to adjust the hairpin inductors which work harden slightly after several attempts to adjust them. The 7A29 has a much cleaner step response but may be getting hard to find.
Regards,
Roger
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Mlynch001
Raymond Domp Frank