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Ebay prices, 7D15
I've been watching auctions for 7D15s for a while because I have few I'd like to sell. The closing prices (not including shipping) have been around $10-$25, with some not selling for even less. Some of these are known good with a return policy. (I'd like to get $65 each for mine)
Suddenly, I find 370090549165, which has past $100. It's not been tested, and has nothing particularly interesting about it except that it looks new. What about this item is generating the bids? The fact that it's in Canada? -Dave |
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Re: Calibrating a 7704A
Craig Sawyers
Does the -02 work for slower scopes like the 7704A? If I bought one IAn -02 will work perfectly with any Tek scope up to 1GHz B/W. With the exception of the 7854, 7612 and 11xxx series with require -10. Craig |
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Re: 7603 filter caps
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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7603 capacitors
Thanks all for the discussion.
I have ordered new caps as well as an ESR meter. I expect the new caps will help, but am also curious as to the condition of the old ones. By the way, the comment about using several smaller caps in parallel helps explain why the TV I am working on has two 10,000uf in parallel. Bob |
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Re: 7603 filter caps
---- 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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Re: Calibrating a 7704A
David C. Partridge
The 067-0587-02 (or -10) version is good far ANY 7000 series 'scope. The
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-10 version is also good for 113xx and 114xx 'scopes as well (I think). Dave -----Original Message-----
From: TekScopes@... [mailto:TekScopes@...] On Behalf Of Neil Gruending Sent: 02 October 2008 16:00 To: TekScopes@... Subject: Re: [TekScopes] Calibrating a 7704A ... Does the -02 work for slower scopes like the 7704A? |
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Re: 7603 filter caps
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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Re: Calibrating a 7704A
Ok, I'm starting to understand a bit better. I'm in the processor of
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repairing the scope and have been trying to be careful to not turn pots that don't need it. But I'm getting to the point where the vertical amp needs to set properly and it would be nice to also test the horizontal properly. Does the -02 work for slower scopes like the 7704A? If I bought one I might as well get one that can do as many scopes as possible. Does anyone have one for sale or if you live within an hour drive from Sphere here in BC I can borrow it? Thanks, Neil On Wed, Oct 1, 2008 at 9:31 PM, <d.seiter@...> wrote:
This reminds me that I need to do a "group cal" on all my gear. I have both |
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DM44
Jordan Kersten
Can anyone explain to me EXACTLY what a DM44 does? I assume it takes voltage measurements, but does it take it from the scope? It's own probes? Can anyone talk me into/out of getting a 465 with one attached? Does interface with the scope or is it independent? Can you add a DM44 to a 465 that originally didn't have one?
~Jordan~ |
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Re: 7603 filter caps
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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Re: 7603 filter caps
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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Re: Tek DM44
Didier Juges
Ignacio,
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I believe that if you ask AA4DF, he will let you share the lower resolution scan of his manuals. I have bought the Tek 494P manual a year or 2 ago, and he let me post the low res version (which is perfectly usable, even though you won't be able to make paper copies as good as the original or as you would with the hi res version) of the manual on my web site. You may want to ask him for confirmation. On the other hand, his scans are of very high quality and his prices are very reasonable, so I can only recommend him, as well as ARTEK Media, for your manuals needs. We need people and businesses like those and it is our interest to keep them in business. Didier KO4BB ---- EB4APL <eb4apl@...> wrote: Jordan, |
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Re: Tek DM44
EB4APL
Jordan,
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I found the origin of this manual. I bought it from AA4DF site . Since they carefully scanned and sell this hi quality manual (I paid $10 but I think now it is just $4.99), I think it is no fair to them to make copies, so I???m sorry but I can???t send it to you. You can obtain your own copy from <>. I???m not related to AA4DF in any way, just a satisfied cutomer. Regards, Ignacio ---------------------------------------------------------------------------------- EB4APL wrote:
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Re: Tek DM44
EB4APL
Jordan,
I have the service manual in pdf. It???s about 12 Mb. It is a hi quality scan that I downloaded some time ago, I don???t rememeber the source so I can???t give them the due credit, sorry. If your mailbox is able to cope with a 12 Mb file, I can send it directly to you. Regards, Ignacio ................................................................................................................................................... Jordan Kersten wrote: Anyone got a manual for a DM44? Owners and/or service. ~Jordan~ |
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Re: 067-0587-02 (was Calibrating a 7704A)
d.seiter@... escribi???:
Does anyone know if the -02 has an achillies heel of any kind, Mmmm... let me see... yes, the exoticc elastomeric switch! Well, it has also quite a lot of exotic hybrids :)like maybe the strange elastomeric switch? Regards, Javier -- ------------------------------------------------------------------------ Javier Herrero EMAIL: jherrero@... HV Sistemas S.L. PHONE: +34 949 336 806 Los Charcones, 17A FAX: +34 949 336 792 19170 El Casar - Guadalajara - Spain WEB: |
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Re: 067-0587-02 (was Calibrating a 7704A)
Craig Sawyers
Does anyone know if the -02 has an achillies heel of anyOne of my two was DOA through this. Inside the switch ("do not open" says the manual. Ha!), the cunningly shaped elastomer had a tear in it, and was failing to operate two of the contacts. A bit of careful use of superglue later, and it has not missed a beat in four years. Craig |
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Re: 7603 filter caps
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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