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7603 filter caps
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DEANE KIDD
Hi All:
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The CRT's in the modern Tek scopes all have a problem with poor focus as compared to the the focus with the tubes as used in the 547, 546,545, 581,585, 561, 564 series of scopes. As the need for higher bandwidth became the norm much work was done to improve the CRT performance, but nothing seemed to help and a decision was made to add an element beyond the defection plates which is incorporated in all of the CRT's of modern design. This element is a doomed mesh screen thru which the beam is guided on its way to the phosphor. This allows the tube to have much lower deflection plate voltages which is required by the solid state amplifiers. There is a price to pay for this improved performance. Since the beam is guided thru the deflection system and then accellerated thru the doomed mesh, the beam is defocused and there are no other means of refocusing the beam and it appears defocused on the screen and this is the focusing problem that many of you are complaining about. This is the price we pay to have the gain/bandwidth of the modern oscilloscope. With the advent of flat-panel displays this problem is less apparent and the constant improvement in display technology is making it less of a problem. I started at Tek in August of '49 and retired in June of '91 and was on hand as these problems were addressed and decisions made. Deane E. Kidd ps: Add it all up and I have been around a long time. The ESR meter that everyone seems to believe is required piece of test gear in the service kit was never heard of until mid '90s when electrolytic caps of high values and low voltages became the norm. I have never used an ESR meter and my normal capacitors were 80 - 120 MFD at 350 - 450 volts. Deane ----- Original Message -----
From: tom jobe To: Paul Kraemer ; Tek Scopes ; Scott McGrath Sent: Wednesday, October 01, 2008 4:37 PM Subject: Re: [TekScopes] 7603 filter caps Hello Scott, Thanks for posting the link to the Anatek ESR comparison page. I have both the EVB from Portugal, and the CapAnalyzer 88A that are on the Anatek comparison page. The EVB is another modern version of the famous Bob Parker design, and it is my favorite everyday ESR meter. It is a very durable unit, as I have not been able to kill it yet, and I have done some very dumb things to it! It does not care about polarity, and it just works. I bought it directly from the fellow in Portugal who builds it, and he was a treat to deal with. I just followed the link on the Anatek ESR page to the EVB web site, and it still is just $79 $ US delivered, which is 56 Euros. This is not a kit, it is a finished ESR meter that you put a 9V battery in and use. The CapAnalyzer 88A is a full featured very nice ESR meter, but you will have at least $200 US in it by the time it arrives. The downside to the 88A is that it has a nice set of tweezers permanently attached (Pomona brand on my 88A) but that limits what you can check, as the tweezer only open up a little. The EVB does not come with any leads, so you supply (or make) some test leads, and then you can check anything with two separate leads that can be very far apart. The 88A also requires that you have the polarity correct. Working on this old equipment without an ESR meter of some kind, is very foolish in my opinion. Bad electrolytic capacitors are the number one failure in much of this old gear, and the ESR meter will identify the bad caps in a few seconds. tom jobe... ----- Original Message ----- From: "Scott McGrath" <mcgrath@...> To: "Paul Kraemer" <elespe@...>; "Tek Scopes" <TekScopes@...> Sent: Wednesday, October 01, 2008 12:40 PM Subject: Re: [TekScopes] 7603 filter caps > > See this web page > > > > - There is what is known as the 'Bob Parker' design this is a cheap > accurate ESR meter upon which countless commercial implementations have > been built upon. I use the BLUE meter myself it is more than accurate > enough for service work. > > But read the information and decide for yourself > > Paul Kraemer wrote: > > ESR meter > > Do you have a recommendation? Works well, cost effective. > > Thanks > > Paul > > > > ----- Original Message ----- > > *From:* Scott McGrath <mailto:mcgrath@...> > > *To:* go_boating_fast@... <mailto:go_boating_fast@...> > > *Cc:* Tek Scopes <mailto:TekScopes@...> > > *Sent:* Wednesday, October 01, 2008 1:24 PM > > *Subject:* Re: [TekScopes] 7603 filter caps > > > > Using higher Voltage/Capacitance ratings usually is not a problem > > especially since many of the old can type electrolytics were rated > > -20/+40% of nominal rating. > > > > Higher voltage is usually ok as long as the voltage differential > > is not > > extreme anything less than 3:1 is probably ok more than that and the > > capacitor will not work effciently > > > > Pay attention to temperature ratings and a ESR meter would be a good > > investment > > > > - Scott > > > > Robert Simpson wrote: > > > Hi folks, > > > Thanks for all the tips in this forum. I am just stating to work > > on a used 7603 with three plug-ins (7A18A, 7D15, 7B70) I acquired > > cheap as a second scope with a 442 I got also got cheap (neither > > working, both for $50, 442 now works) > > > Thanks for the article on washing scopes as the 7603 really > > needed it. With the plug-ins removed so they could be washed > > separately, I used the siphon spray wand for my air hose with a > > bucket of water with dish soap (avoiding the front panel). Rinsed > > it off with the garden hose, blew it mostly dry with the air hose, > > and then let it sit in the sun all afternoon. Then let it sit > > inside overnight. > > > > > > It now turns on. And with no plug-ins installed gets a spot beam > > in the center using the beam finder button. Most of the voltages > > are within spec except for +5 which is 4.4V. All voltages except > > 130V have too much ripple; I am guessing filter cap problems. > > > > > > So, since exact replacement caps are hard to find and incredibly > > expensive, I am thinking of using substitutes. For example, in > > place of the 1800uf 75V caps I could get 2000uf 100V caps. Would > > slightly larger specs work being they are used as filter caps? > > > > > > > > > > > > > > > > > > > > > ------------------------------------ > > > > > > Yahoo! Groups Links > > > > > > > > > > > > > > > > > > ------------------------------------ > > Yahoo! Groups Links > > > ------------------------------------------------------------------------------ No virus found in this incoming message. Checked by AVG - Version: 8.0.173 / Virus Database: 270.7.5/1702 - Release Date: 10/1/2008 9:05 AM |
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Hi folks,
Thanks for all the tips in this forum. I am just stating to work on a used 7603 with three plug-ins (7A18A, 7D15, 7B70) I acquired cheap as a second scope with a 442 I got also got cheap (neither working, both for $50, 442 now works) Thanks for the article on washing scopes as the 7603 really needed it. With the plug-ins removed so they could be washed separately, I used the siphon spray wand for my air hose with a bucket of water with dish soap (avoiding the front panel). Rinsed it off with the garden hose, blew it mostly dry with the air hose, and then let it sit in the sun all afternoon. Then let it sit inside overnight. It now turns on. And with no plug-ins installed gets a spot beam in the center using the beam finder button. Most of the voltages are within spec except for +5 which is 4.4V. All voltages except 130V have too much ripple; I am guessing filter cap problems. So, since exact replacement caps are hard to find and incredibly expensive, I am thinking of using substitutes. For example, in place of the 1800uf 75V caps I could get 2000uf 100V caps. Would slightly larger specs work being they are used as filter caps? |
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Scott McGrath
Using higher Voltage/Capacitance ratings usually is not a problem especially since many of the old can type electrolytics were rated -20/+40% of nominal rating.
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Higher voltage is usually ok as long as the voltage differential is not extreme anything less than 3:1 is probably ok more than that and the capacitor will not work effciently Pay attention to temperature ratings and a ESR meter would be a good investment - Scott Robert Simpson wrote: Hi folks, Thanks for all the tips in this forum. I am just stating to work on a used 7603 with three plug-ins (7A18A, 7D15, 7B70) I acquired cheap as a second scope with a 442 I got also got cheap (neither working, both for $50, 442 now works) Thanks for the article on washing scopes as the 7603 really needed it. With the plug-ins removed so they could be washed separately, I used the siphon spray wand for my air hose with a bucket of water with dish soap (avoiding the front panel). Rinsed it off with the garden hose, blew it mostly dry with the air hose, and then let it sit in the sun all afternoon. Then let it sit inside overnight. |
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Scott McGrath
See this web page
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- There is what is known as the 'Bob Parker' design this is a cheap accurate ESR meter upon which countless commercial implementations have been built upon. I use the BLUE meter myself it is more than accurate enough for service work. But read the information and decide for yourself Paul Kraemer wrote: ESR meter |
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tom jobe
Hello Scott,
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Thanks for posting the link to the Anatek ESR comparison page. I have both the EVB from Portugal, and the CapAnalyzer 88A that are on the Anatek comparison page. The EVB is another modern version of the famous Bob Parker design, and it is my favorite everyday ESR meter. It is a very durable unit, as I have not been able to kill it yet, and I have done some very dumb things to it! It does not care about polarity, and it just works. I bought it directly from the fellow in Portugal who builds it, and he was a treat to deal with. I just followed the link on the Anatek ESR page to the EVB web site, and it still is just $79 $ US delivered, which is 56 Euros. This is not a kit, it is a finished ESR meter that you put a 9V battery in and use. The CapAnalyzer 88A is a full featured very nice ESR meter, but you will have at least $200 US in it by the time it arrives. The downside to the 88A is that it has a nice set of tweezers permanently attached (Pomona brand on my 88A) but that limits what you can check, as the tweezer only open up a little. The EVB does not come with any leads, so you supply (or make) some test leads, and then you can check anything with two separate leads that can be very far apart. The 88A also requires that you have the polarity correct. Working on this old equipment without an ESR meter of some kind, is very foolish in my opinion. Bad electrolytic capacitors are the number one failure in much of this old gear, and the ESR meter will identify the bad caps in a few seconds. tom jobe... ----- Original Message -----
From: "Scott McGrath" <mcgrath@...> To: "Paul Kraemer" <elespe@...>; "Tek Scopes" <TekScopes@...> Sent: Wednesday, October 01, 2008 12:40 PM Subject: Re: [TekScopes] 7603 filter caps
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Stefan Trethan
That may be so, but when repairing relatively modern equipment with many
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many caps that need to have low ESR for the circuit to work (e.g. switching voltage converters) it is absolutely great to be able to test all caps in circuit in a matter of seconds. Sure, one could add a good cap in parallel and try the circuit, but that takes much longer. OTOH i have no need for it when designing new equipment (power supplies). But for industrial gear of say 5-10 years or more and consumer gear of 2 years of more the electrolytic cap has been the primary failure for me. I have repaired a OS254P-U (which is very similar to a 7603) and found one major fault with the esr meter, so i'd say it's definitely been useful there. Sure i could have found the fault some other way. ST On Wed, Oct 1, 2008 at 6:39 PM, DEANE KIDD <dektyr@...> wrote:
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I wouldn't say that the ESR meter is "required", but it sure makes life easier! Plus, it's a cool kit to build (if you happen to go that route...;-))
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-Dave -------------- Original message ----------------------
From: "Stefan Trethan" <stefan_trethan@...> That may be so, but when repairing relatively modern equipment with many |
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Craig Sawyers
TheDeane is quite right. Think about it this way - when the bridge diode turns on, the capacitor charges up through the secondary resistance of the power transformer and the reflected primary resistance, plus the series resistance of the bridge diode. For high voltages that is generally many tens of ohms. Even then, the effect of an ESR even equal to the charging resistance is pretty minimal - the charging time simply doubles. The effect on discharge when the diode is turned off and the capacitor is supplying current to the circuit is even less dependent on ESR, since the current is less than during the charging cycle (by roughly the charge/discharge duty cycle). The main significance of ESR, or an ESR that is rising as the years pass, is that the capacitor runs hotter - since the ESR is a real dissipative component. Look at a modern cap's spec sheet - say a good power electrolytic from RIFA - and you will see the main consideration for reducing ESR to the milliohm level in high value low voltage electrolytics is entirely to do with power dissipation and maximum operating temperature. The effect on ripple is mininmal. The main failure mode for Tek electrolytics, as we have discussed many times on the forum, is the Sprague twist-lock caps. The failure mode is that the internal negative tab connection corrodes through inside the can just where it goes into the can crimp - so the capacitance falls to zero, more or less instantly. Then you can see the ripple for sure! Craig |
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Jerry Massengale
The ESR is critical to ripple.
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--- On Thu, 10/2/08, Craig Sawyers <c.sawyers@...> wrote:
From: Craig Sawyers <c.sawyers@...> Subject: RE: [TekScopes] 7603 filter caps To: "'Tek Scopes'" <TekScopes@...> Date: Thursday, October 2, 2008, 3:52 AM TheDeane is quite right. Think about it this way - when the bridge diode turns on, the capacitor charges up through the secondary resistance of the power transformer and the reflected primary resistance, plus the series resistance of the bridge diode. For high voltages that is generally many tens of ohms. Even then, the effect of an ESR even equal to the charging resistance is pretty minimal - the charging time simply doubles. The effect on discharge when the diode is turned off and the capacitor is supplying current to the circuit is even less dependent on ESR, since the current is less than during the charging cycle (by roughly the charge/discharge duty cycle). The main significance of ESR, or an ESR that is rising as the years pass, is that the capacitor runs hotter - since the ESR is a real dissipative component. Look at a modern cap's spec sheet - say a good power electrolytic from RIFA - and you will see the main consideration for reducing ESR to the milliohm level in high value low voltage electrolytics is entirely to do with power dissipation and maximum operating temperature. The effect on ripple is mininmal. The main failure mode for Tek electrolytics, as we have discussed many times on the forum, is the Sprague twist-lock caps. The failure mode is that the internal negative tab connection corrodes through inside the can just where it goes into the can crimp - so the capacitance falls to zero, more or less instantly. Then you can see the ripple for sure! Craig [Non-text portions of this message have been removed] |
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Scott McGrath
Primary use for a ESR meter for me is testing all caps in a circuit because frequently I purchase a piece of equipment which has been out of service for a LONG time and the electrolytics in many cases have failed or dried out due to leakage.
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Tek is (in)famous for switch mode power supplies which require low ESR caps to operate. Prior to ESR meter I would just replace all electrolytics and call it a day now i can replace only those which have failed so it's a moneysaver as well. For HV low capacitance circuits it's pretty obvious when a cap has exceeded its useful life although ESR becomes critical again in HV high capacitance circuits like those found in RF amplifiers where a high ESR usually manifests itself with a bang and a flash of light and electrolyte sprayed all over the amp chassis. Stefan Trethan wrote: That may be so, but when repairing relatively modern equipment with many |
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Bernice Loui
Hello,
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It's also dependent on frequency.. If the 'lytic cap in question is used in a good old fashioned line frequency copper/iron power transformer, the ESR requirement is not very high since ripple frequency for a full wave rectifier is 120 Hz in the US and 100 Hz in other parts of the world. Most any garden variety cap should be good for this. Not true for high frequency switching power supply capacitors. As the Equivalent Series Resistance goes up, the losses per cycle goes up too which causes internal heating inside the capacitor and shortens it's life. This is why capacitors have a ripple current rating on top of the ESR spec. Many of the current generation low ERS capacitors are designed for use in switching power supplies and one look should examine the ESR vs Frequency curve to decide if this part will work for it's intended application. Ripple current vs frequency is another consideration along with max temperature which is usually +85 or +125 degrees C. There is also a life rating in hours based on temperature and ripple current. Be aware that while the new generation of smaller 'lytics pack a lot of capacitance and performance in a small package, they can be short lived. Hour ratings of 2,000 hours at it rated ripple current and temperature. Expected capacitor life is quite dependent on operating temperature and circuit conditions. They are a wear out part in just about every electronic device :( Bernice ~~~~~~~~~~~~~~~~~~~~~~~~~ --- On Thu, 10/2/08, Jerry Massengale <jmassen418@...> wrote:
The ESR is critical to ripple. |
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---- Bernice Loui <rupunzels_window@...> wrote:
Hello,Case in point / preaching to the choir. You often see cases where, for example, instead of using one 500 MFD capacitor the designer has elected to use five 100 MFD capacitors in parallel. This is often seen on PC MBs for example. The use of multiple caps in parallel lowers the esr and the lead inductance as compared to a smaller number of larger caps and this lowers the temperature and ripple and, as implied above, will increase the service life FWIW I have built the esr meter and can recommend it but keep in mind that it will show a very low ESR on a shorted cap : ) Actual capacity and leakage at the working voltage a important also. Bert |
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Craig Sawyers
The ESR is critical to ripple.Like all these things, the devil is in the detail. Lets assume that we are talking about a smoothing capacitor conventional 50/60Hz system, and not a switcher. Provided the ESR is significantly less than the total driving impedance (Tx secondary, reflected primary, diode R etc) there is no significant effect. Here are some numbers for a supply with a 220uF capacitor fed by 1N4007 diodes from a 333V secondary with a total series resistance of 31 ohms (typical for valved/tubed applications in classic Tek gear). The current draw is 100mA. ESR ripple p-p 0.1 3.7V 1 3.9V 3 4.8V 10 8.9V So in order to double the p-p ripple you need to have an ESR that is about 30% of the total series resistance feeding it. *For this particular example*. Note that the waveform becomes much more "spikey" at higher ESR, and hence the RMS value is much less effected. Craig |
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Jerry Massengale
Greetings,
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? Very good point. For high impedence gear, the ESR most likely is too low to be a factor. ? Jerry --- On Thu, 10/2/08, Craig Sawyers <c.sawyers@...> wrote:
From: Craig Sawyers <c.sawyers@...> Subject: RE: [TekScopes] 7603 filter caps To: "'Tek Scopes'" <TekScopes@...> Date: Thursday, October 2, 2008, 3:03 PM The ESR is critical to ripple.Like all these things, the devil is in the detail. Lets assume that we are talking about a smoothing capacitor conventional 50/60Hz system, and not a switcher. Provided the ESR is significantly less than the total driving impedance (Tx secondary, reflected primary, diode R etc) there is no significant effect. Here are some numbers for a supply with a 220uF capacitor fed by 1N4007 diodes from a 333V secondary with a total series resistance of 31 ohms (typical for valved/tubed applications in classic Tek gear). The current draw is 100mA. ESR ripple p-p 0.1 3.7V 1 3.9V 3 4.8V 10 8.9V So in order to double the p-p ripple you need to have an ESR that is about 30% of the total series resistance feeding it. *For this particular example*. Note that the waveform becomes much more "spikey" at higher ESR, and hence the RMS value is much less effected. Craig |
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Michael J Wallace
I hope this goes thru ok and helps some people ...
TDS Screen Capture via the RS-232 option This screen image was captured from a TDS oscilloscope over the RS-232 port using the Windows Hyperterminal program. To transfer the screen image follow the procedure outlined below. 1. Start Hyperterminal 2. From the TDS Utility IO menu set the port to RS-232. Harware Setup: 9600,1,none,on. Software Setup: Soft Flagging Off. 3. Set the hard copy format. ( This image was produced using PCX ) 4. Set the communications settings in Hyperterminal to match those of the oscilloscope. 9600,8,1,None, Hardware. 5. In the Hyperterminal program, select File Properties click on the settings tab. Click on the ASCII Setup button and un-select Wrap lines that exceed terminal width. This will enable the Hyperterminal program to save binary screen images. 6. Go to Transfer menu, Capture Text, and select a file name and location. 7. Once you have the image you want on the oscilloscope display, press the HARD COPY button. |
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Didier Juges
Or use this software:
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Which now also includes the option of downloading the entire 2500 record (worth 10 divisions in height) and plot it on the screen (I need to upload that version, later today). Didier KO4BB -----Original Message----- |
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Dave_s
TekScopes@... wrote:
Re: 7603 filter caps FWIW I have built theHi, I am trying to see that ESR Meter circuit referred to in this mailnote. I'm very interested in building this circuit. Please help me by providing a usable URL. On this site, searching for ESR produces no hits. Thank you. 73, W6MIK, Dave |
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I've got one of these:-
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very good it is, too. www.peakelec.co.uk/acatalog/jz_esr60.html --- On Fri, 3/10/08, Dave_s <group78@...> wrote:
From: Dave_s <group78@...> Subject: [TekScopes] Re: 7603 filter caps To: TekScopes@... Date: Friday, 3 October, 2008, 3:07 PM TekScopes@yahoogrou ps.com wrote: Re: 7603 filter caps FWIW I have built the oone.com/ links.php < oone.com/ links.php> esr meter and can recommend it but keep in mind that it will show a very low ESR on a shorted cap : ) Hi, I am trying to see that ESR Meter circuit referred to in this mailnote. I'm very interested in building this circuit. Please help me by providing a usable URL. On this site, searching for ESR produces no hits.. Thank you. 73, W6MIK, Dave [Non-text portions of this message have been removed] |
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Garey Barrell
Dave -
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Try here. <> 73, Garey - K4OAH Glen Allen, VA Drake 2-B, 4-B, C-Line & TR-4/C Service Supplement CDs <www.k4oah.com> Dave_s wrote: TekScopes@... wrote: |
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Lawrence Glaister
If you have a few spare parts, you can build a capacitor ESR meter
quite easily. Below is a prototype I built. I just added the spice model to the web page in case you want to explore how it operates. cheers -- ===================================================================== Lawrence Glaister VE7IT mailto:ve7it@... 1462 Madrona Drive Nanoose Bay, B.C. Canada V9P 9C9 ===================================================================== |
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