Thanks, I came across that article earlier this year, but somehow managed to misplace the link :-( In any case, my own intention right now is to make a fully passive device. Best regards, Rob. Electronics and Books schreef: > Look at : > www.metrology.pg.gda.pl/full/2009/M&MS_2009_183.pdf > > These are temperature regulated resistor compared to a standard. > > Met vriendelijke groeten > Regards > > ElectronicsAndBooks@Yahoo.com > http://www.ElectronicsAndBooks.tk > TEL +31-(0)6-36024590 > >

feedthrough capacitors of low capacitance. After mounting the resistors
and a thorough cleaning, the whole thing will be baked at ~85°C
overnight to get rid of any moisture, then filled with oil and soldered

Johnson's baby oil has fragrance in it. Not a good thing. Probably somewhat conductive.. Regards, John K1AE John Allen - PC Support Solutions www.pcsupportsolutions.com PC On Site Service and Training - Computer HW/SW/Network debugging, installation and upgrades. -----Original Message----- From: volt-nuts-bounces@febo.com [mailto:volt-nuts-bounces@febo.com] On Behalf Of Brent Gordon Sent: Tuesday, December 15, 2009 2:54 AM To: Discussion of precise voltage measurement Subject: Re: [volt-nuts] Resistance standard Rob Klein wrote: > feedthrough capacitors of low capacitance. After mounting the resistors > and a thorough cleaning, the whole thing will be baked at ~85°C > overnight to get rid of any moisture, then filled with oil and soldered shut. I tried something similar to this about 15 years ago. I needed a 10 KW dummy load so I bought a bunch of 300 W air-cooled dummy loads, removed the resistors, and connected them together in a series-parallel combination to get 50 Ohms. I measured the value just to make sure. I then got a small drum and filled it with baby oil and put the resistor assembly in. The next day the resistance had changed by more than 50% ( I don't remember if it increased or decreased.). The value continued to drift and every time the resistor heated up the value changed even more. Tried cleaning, washing in solvent, and baking at high temperatures in various combinations but I could never get the value of any of the resistors even close to 50 Ohms. Ended up throwing the whole mess away. The resistors were uncoated, tubular types so this warning probably does not apply to your molded resistors. Another post in this topic mentions baby oil. Even though I had problems with my dummy load, it wasn't because of the baby oil. I also tried some lab-grade mineral oil and had the same problem. I recall reading on a mailing list somewhere (probably Time Nuts) that at Los Alamos National Lab a group had to buy baby oil because mineral oil was considered a hazardous material. Brent _______________________________________________ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.

Rob, I want to apologize for making a snap judgement of your background and capabilities. In all honesty that was the way it came across to me. In my opinion, I think you may have wasted your money on the lead compensator. You would be better served obtaining a Fluke 750A Reference Divider. It is an extremely good, stable fixed division divider. There is a non-destructive modification that was done at the Navy’s Primary Standards Lab to make the comparison section use a 10 volt reference instead of the standard cell as was originally envisioned. The way the metrology world maintained the Volt for decades was through tons of measurements, cross-measurements and statistical evaluation of Standard Cells. The standard cells used would not permit any current to be drawn. It was always done in a null configuration, i.e., a source compared against many standards cells through a null meter; no current drawn. These standard cells were used in large groups and constantly inter-compared to 1.) determine the bank mean and 2.) To guard against errant cells that misbehave and, obviously, inter-compared between other labs both nationally and internationally. My comment about the oil is depending upon the oil used, it could affect the non-hermetic resistor’s composition. Fluke’s resistors were sealed with a shellac compound of some sort, so no, the Fluke 720A resistors are not just some resistive material open to the elements as such. The same goes for the Fluke 750A. They could be, but then an awful lot would have to be known about the oil and it's affects. The same problem with a potting material of some sort, particularly with regard to leakage paths. Regarding binding posts and such, many manufacturers specify a temperature that a component can withstand before destruction. Does that really say the stability of the plastic (or whatever material) binding post is going to retain its insulation abilities ? Many binding posts, with regard to leakage, are literally junk even without heating. Before you select a binding post get a sample, mount it to a panel and apply a kilovolt (you do have a Fluke 335D ?) through a 10 meg Ohm resistor between the post and the panel monitoring the current flow. There shouldn’t be any but that is obviously unrealistic. At least you can measure it. Again, I apologize for my snap judgement. Bill....WB6BNQ Rob Klein wrote: > Bill, > > Thanks for your comments, they are appreciated. > > WB6BNQ schreef: > > Rob, > > > > Fluke has over 60 years of real experience correctly make highly accurate stable > > resistors. Actually they figured it out in the very beginning of their > > business. Without a serious metallurgic background, plus a few more disciplines, > > I doubt seriously you would even come close. However, there is nothing wrong > > with trying. > > > But I am not going to try to actually make a resistor, I 'merely' want > to build several resistance standards, out of > commercially available ones. And I certainly do not have any intention > of beating Fluke at their own game. > > First off, what is your purpose for such accuracy ? What do you intend to do > > with these ? > > > Purpose? This is the volt-nuts group, isn't it? :-) > I'm a self-employed electronics engineer with 'a thing' for precision > measurements. I have, over the years, built > up a nice collection of multimeters, calibrators, etc. and a resistance > standard is going to make a welcome > addition to that. > > I see a number of problems that need to be addressed. First, it does no good to > > have the highest possible quality resistor if you do not have the proper means to > > compare it to other items. To maintain that level of quality, for that given > > resistor, you would need to duplicate its’ measurement environment precisely, > > i.e., temperature, humidity, etc. > > > While my workshop isn't a cal-lab, it is nonetheless pretty stable, > environmentally. It has to be, in order to keep > my pick-and-place machine happy. > As I'm not aiming for sub-ppm precision, it will more than likely suffice. > > Having a resistor, in of itself, serves no purpose without the proper equipment > > to compare it against other items or to use it in a measurement process. Items > > like a highly accurate voltage/current source and a very good null meter (Fluke > > 845A/B) are but a few things needed. > > > Let's see: > - Fluke 720 KVD, check > - Fluke 845, check > - Various high stability voltage sources, check > Add a recently aquired lead compensator (bought "as is" and not yet > tested, so maybe not) and I think I'm > reasonably well set-up. > > Nonetheless, some of your intended construction ideas need to be reviewed. You > > talk about wanting to equal or beat Fluke, yet you only intend to buy 0.01% > > instead of 0.001% resistors. What’s up with that ? > The VHP202's I'm buying *are* 0.001%, as I stated. > > Those are not considered standards by any means. > Really? Then kindly explain how the metrological world was able to > succesfully maintain the Volt for decades, > using standards that deviated almost 2%. > As long as the value is known and stable to within the required > uncertainty limits, I'd almost say that anything > could be considered a "standard". > > Just series/paralleling a bunch of resistors is not > > going to help you unless you know, precisely, the temperature coefficients are > > for each resistor. In order to play that game you would need to buy a whole lot > > (like thousands) of them, not just a couple. Then you spend an inordinate amount > > of time testing the temperature coefficient for each and then mixing and matching > > in trying to achieve a zero temperature coefficient. Or at the least the > > smallest variation of resistance verse temperature change. > > > The RTC of Vishay's Z-foil resistors is as low as it gets, not by > selection, but by design! The series/paralleling > is mainly to increase the long term stability > > On the one hand you talk about buying expensive resistors then decide to get the > > non-hermetically sealed models because they are cheaper. > I intend to use *both*, so that I can build several different types, in > order to compare their long term behaviour. > It will be interesting to see just how good these non-hermetic types > behave over time. > > Using an oil filled container is not going to help if the resistor is not hermetically sealed. > But the point is to use an oil filled *hermetically sealed* container to > hold the non-sealed resistors. Fluke did this for the > main resistors of the first decade of their 720 KVD, Tegam, formerly > ESI, do it for their SR104, widely considered to be one > of the best, if not the best, standard resistor there is. So it appears > this idea might not be as daft as you make it seem. > > The > > same goes for using any other kind of fill material. It is going to impact the > > non-hermetically sealed resistor and its going to impact the leakage. > > > How, exactly, is it going to impact the resistor? > > The biggest > > point for leakage is the connection post insulation material; most are junk ! > > > Hmm, this got me curious enough to dig out my insulation resistance > tester. Unfortunately it seems the batteries > are flat :-( To be continued ... > > The second biggest point will be dirt between the connection posts. > > > I am well aware of the neccesity of keeping a clean shop. > > However, it is not so simple as just pouring in some oil. Oil has a multitude of > > properties and the selection is not going to be an easy one. > Eh, yeah, that's one of the main reasons I came here for advice :-) > > You talk of baking the resistor/can combination. What are the limits of the > > resistors relative to heat ? Heating it to 85c is going to change its > > characteristics and would require you to re-test the resistor all over again. > > > I have already 'pre-cooked' the first batch of 9 Z201's for three weeks > at around 60 °C and found a > downward shift of maybe a few ppm, as compared to a 1kOhm reference; a > 20 year old VHA412, from Vishay. > The TCR of this older resistor is, at around 2 ppm/°C, a lot higher than > that of the resistors under test and > may have had a considerable influence on the measurement. > > I have not been able to find any references to changes in TCR, caused by > temperature cycling, in these devices. > > The baking may also help relieving some of the stresses that might built > up during soldering. > > What about that low emf connector ? You need to consider what that material > > (insulation) will do when you “bake” it at 85c. Most likely will ruin it. > > > The binding posts are rated at 115 °C max. operating temperature and are > not going to be baked anyway. > > Best regards, > Rob. > > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there.

Bill, I want to apologize for making a snap judgement of your background and capabilit ies. In all honesty that was the way it came across to me. No worries, cause no offence taken. Perhaps I should have given more information about my background in that first post. In my opinion, I think you may have wasted your money on the lead compensator. Nah, I picked it up for $25. Combined shipping with a HP3457A, so it's no great loss in any case. You would be better served obtaining a Fluke 750A Reference Divider. It is an extremely good, stabl e fixed division divider. There is a non-destructive modification that was done at the Navy's Pr imary Standards Lab to make the comparison section use a 10 volt reference instead of the standard c ell as was originally envisioned. Interesting! Do you have any more information about this mod? A link to a paper or something? The way the metrology world maintained the Volt [...] Well, yes, I know how it was done. It was a rhetorical question in reply to your comment about 0.01% not "being considered a standard". My comment about the oil is depending upon the oil used, it could affect the non -hermetic resistor's composition. Fluke's resistors were sealed with a shellac compound of some sort , so no, the Fluke 720A resistors are not just some resistive material open to the elements as such . The same goes for the Fluke 750A. They could be, but then an awful lot would have to be known abo ut the oil and it's affects. The same problem with a potting material of some sort, particularly wi th regard to leakage paths. I highly suspect that the resistors Fluke used are the card wound, shellac sealed types we all know and love. Not going to open the tank to take a look, though :-) The resistors I'm using are not "just some resistive material open to the elements" either, they are molded in epoxy. Using a good, pure oil, I see little reason why they would be affected. I'm thinking about dropping the resin potting idea completely and just have one ensemble as is. That way I can compare the behaviour of the canned ensemble agains a 'naked' version, which is more meaningful. Regarding binding posts and such, many manufacturers specify a temperature that a component can withstand before destruction. Does that really say the stability of the plastic (or whatever material) binding post is going to retain its insulation abilities ? Many bindi ng posts, with regard to leakage, are literally junk even without heating. Before you select a binding post get a sample, mount it to a panel and apply a kilovolt (you do have a Fluke 335D ?) th rough a 10 meg Ohm resistor between the post and the panel monitoring the current flow. There shou ldn't be any but that is obviously unrealistic. At least you can measure it. The ones I got are [1]Pomona 3770's. Their insulation is polycarbonate. I'm going to dig out my GenRad megohmmeter this afternoon and make some measurements. I'll post the results later. Regards, Rob. References 1. http://www.pomonaelectronics.com/pdf/d3750-3760-3770_101.pdf

Rob Klein schreef: > I'm going to dig out my GenRad megohmmeter this afternoon > and make some measurements. I'll post the results later. I just couldn't contain my curiosity and dug it out a bit earlier. Literally dug out, 'cause it was in the basement between a lot of boxes. Fortunately, the mice didn't do any damage to it. As I have already made a front panel for my proposed standard, with binding posts for measurement and guard in place, it should be relatively easy to measure how the insulation holds up with regard to leakage. The meter is a GenRad 1644 <http://www.tequipment.net/pdf/IET/IET_GR1644.pdf>, which I saved from the scrapheap at one of my former employers. It is a Wheatstone bridge based instrument, with bridge voltage settable from 10 to 1000V and a highest range multiplier of 1TOhm (1E12), enabling measurements of up to 1E15. Basic checks on the instrument were made by first connecting it to the voltage input of a handheld multimeter and observing the bridge balance at 10MOhm. Lead wires were then removed and bridge balance was checked to be at infinity at the highest range multiplier and 1000V. Silicone insulated test leads were then attached to the instrument, taking care not to let them touch each other. The banana plugs on the far end of the leads were placed with their insulation on the edge of a plastic sheet, so that the metal parts were not in contact with anything but the surrounding air (which should be pretty dry, as it is freezing outside). Bridge balance, still at 1000V, was obtained at around 300 TOhm. Next, the '-' terminal was connected to the guard connection on the panel (which is electrically connected to the panel) and the '+' was connected to the nearest binding post; 15mm heart to heart. At the same dial setting, the bridge was still pretty much balanced, just ever so slightly lower. This suggests a very high insulation resistance indeed. Certainly well over 1E15. It will be interesting to repeat these measurements in the summer, when the humidity is up and the binding posts have aged a little. For my next trick, I shall endeavour to repeat the above for the feedthrough capacitors, albeit at a lower voltage. Regards, Rob.

Bill,

No worries, cause no offence taken. Perhaps I should have given more
information about my background in that first post.

Nah, I picked it up for $25. Combined shipping with a HP3457A, so it's
no great loss in any case.

Interesting! Do you have any more information about this mod? A link to
a paper or something?

Well, yes, I know how it was done. It was a rhetorical question in
reply to your comment about 0.01% not "being considered a standard".

I highly suspect that the resistors Fluke used are the card wound,
shellac sealed types we all know and love. Not going to open the
tank to take a look, though :-)
The resistors I'm using are not "just some resistive material open to
the elements" either, they are molded in epoxy. Using a good,
pure oil, I see little reason why they would be affected.
I'm thinking about dropping the resin potting idea completely and just
have one ensemble as is. That way I can compare the behaviour
of the canned ensemble agains a 'naked' version, which is more
meaningful.

The ones I got are [1]Pomona 3770's. Their insulation is polycarbonate.
I'm going to dig out my GenRad megohmmeter this afternoon
and make some measurements. I'll post the results later.
Regards,
Rob.

1. http://www.pomonaelectronics.com/pdf/d3750-3760-3770_101.pdf

Hi Rod, The modification in the 750A is not terribly involved. My friend, who was responsible for the Navy’s primary voltage standard made the mod, but I do not remember the exact details. It involved disconnecting the standard cell R string and jumping some other point I think. I will pin him down on the particulars. He also was responsible for a number of improvements to the Fluke 731 series. He modified the 750 after he characterized a large number of 731 units and kept the best four for his use. One of his ideas was to parallel the four 731's so the output was a voted value. So the four he kept had equal but opposite temperature coefficients such that the error was basically cancelled. I believe that Fluke used that, among his other ideas, in one of their later units. Yes, the Fluke resistors were of the card variety. The oil comment regarding the Vishays was aimed at the non-hermetically seal units that you were considering. I would be interested in your findings on the Pomona posts. Bill....WB6BNQ Rob Klein wrote: > Bill, > > I want to apologize for making a snap judgement of your background and capabilit > ies. In all honesty > that was the way it came across to me. > > No worries, cause no offence taken. Perhaps I should have given more > information about my background in that first post. > > In my opinion, I think you may have wasted your money on the lead compensator. > > Nah, I picked it up for $25. Combined shipping with a HP3457A, so it's > no great loss in any case. > > You would be better > served obtaining a Fluke 750A Reference Divider. It is an extremely good, stabl > e fixed division > divider. There is a non-destructive modification that was done at the Navy's Pr > imary Standards Lab > to make the comparison section use a 10 volt reference instead of the standard c > ell as was > originally envisioned. > > Interesting! Do you have any more information about this mod? A link to > a paper or something? > > The way the metrology world maintained the Volt [...] > > Well, yes, I know how it was done. It was a rhetorical question in > reply to your comment about 0.01% not "being considered a standard". > > My comment about the oil is depending upon the oil used, it could affect the non > -hermetic resistor's > composition. Fluke's resistors were sealed with a shellac compound of some sort > , so no, the Fluke > 720A resistors are not just some resistive material open to the elements as such > . The same goes for > the Fluke 750A. They could be, but then an awful lot would have to be known abo > ut the oil and it's > affects. The same problem with a potting material of some sort, particularly wi > th regard to leakage > paths. > > I highly suspect that the resistors Fluke used are the card wound, > shellac sealed types we all know and love. Not going to open the > tank to take a look, though :-) > The resistors I'm using are not "just some resistive material open to > the elements" either, they are molded in epoxy. Using a good, > pure oil, I see little reason why they would be affected. > I'm thinking about dropping the resin potting idea completely and just > have one ensemble as is. That way I can compare the behaviour > of the canned ensemble agains a 'naked' version, which is more > meaningful. > > Regarding binding posts and such, many manufacturers specify a temperature that > a component can > withstand before destruction. Does that really say the stability of the plastic > (or whatever > material) binding post is going to retain its insulation abilities ? Many bindi > ng posts, with > regard to leakage, are literally junk even without heating. Before you select a > binding post get a > sample, mount it to a panel and apply a kilovolt (you do have a Fluke 335D ?) th > rough a 10 meg Ohm > resistor between the post and the panel monitoring the current flow. There shou > ldn't be any but > that is obviously unrealistic. At least you can measure it. > > The ones I got are [1]Pomona 3770's. Their insulation is polycarbonate. > I'm going to dig out my GenRad megohmmeter this afternoon > and make some measurements. I'll post the results later. > Regards, > Rob. > > References > > 1. http://www.pomonaelectronics.com/pdf/d3750-3760-3770_101.pdf > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there.

On the oil question, you really do need a sealed system, with provisions for expansion, or the oil will "breathe" with temperature and atmospheric pressure fluctuations and absorb water. As to potting, the resistive elements must NOT be strained or the values will certainly shift. Just think how strain guages are made. IMO, vacuum would be a bad idea. It is the antithesis of an isothermal resistor. Any dissipation would lead to heating and value shifts. Best, -John ===========

In message <1180.12.6.201.35.1260974407.squirrel@popaccts.quik.com>, "J. Forste r" writes: >On the oil question, you really do need a sealed system, with provisions >for expansion, or the oil will "breathe" with temperature and atmospheric >pressure fluctuations and absorb water. I would go for the copperblock and use thermal paste to improve the resistors thermal contact with the block, rather than start experimenting with oils. The only reason oils got used in the first place, was lack of anything better under the constraints back then. Today most cal-labs try to avoid it if at all possible. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.

Bill,

No worries, cause no offence taken. Perhaps I should have given more
information about my background in that first post.

Nah, I picked it up for $25. Combined shipping with a HP3457A, so it's
no great loss in any case.

Interesting! Do you have any more information about this mod? A link 

Well, yes, I know how it was done. It was a rhetorical question in
reply to your comment about 0.01% not "being considered a standard".

I highly suspect that the resistors Fluke used are the card wound,
shellac sealed types we all know and love. Not going to open the
tank to take a look, though :-)
The resistors I'm using are not "just some resistive material open to
the elements" either, they are molded in epoxy. Using a good,
pure oil, I see little reason why they would be affected.
I'm thinking about dropping the resin potting idea completely and just
have one ensemble as is. That way I can compare the behaviour
of the canned ensemble agains a 'naked' version, which is more
meaningful.

The ones I got are [1]Pomona 3770's. Their insulation is 

1. http://www.pomonaelectronics.com/pdf/d3750-3760-3770_101.pdf

Bill It would be very interesting to have the details of his "improvements" to the Fluke 731's, if this is possible. Roy -------------------------------------------------- From: "WB6BNQ" <wb6bnq@cox.net> Sent: Wednesday, December 16, 2009 12:03 PM To: "Discussion of precise voltage measurement" <volt-nuts@febo.com> Subject: Re: [volt-nuts] Resistance standard > Hi Rod, > > The modification in the 750A is not terribly involved. My friend, who was > responsible for the Navy's primary voltage standard made the mod, but I do > not > remember the exact details. It involved disconnecting the standard cell R > string > and jumping some other point I think. I will pin him down on the > particulars. > > He also was responsible for a number of improvements to the Fluke 731 > series. He > modified the 750 after he characterized a large number of 731 units and > kept the > best four for his use. One of his ideas was to parallel the four 731's so > the > output was a voted value. So the four he kept had equal but opposite > temperature > coefficients such that the error was basically cancelled. I believe that > Fluke used > that, among his other ideas, in one of their later units. > > Yes, the Fluke resistors were of the card variety. The oil comment > regarding the > Vishays was aimed at the non-hermetically seal units that you were > considering. I > would be interested in your findings on the Pomona posts. > > Bill....WB6BNQ > > > Rob Klein wrote: > >> Bill, >> >> I want to apologize for making a snap judgement of your background and >> capabilit >> ies. In all honesty >> that was the way it came across to me. >> >> No worries, cause no offence taken. Perhaps I should have given more >> information about my background in that first post. >> >> In my opinion, I think you may have wasted your money on the lead >> compensator. >> >> Nah, I picked it up for $25. Combined shipping with a HP3457A, so it's >> no great loss in any case. >> >> You would be better >> served obtaining a Fluke 750A Reference Divider. It is an extremely >> good, stabl >> e fixed division >> divider. There is a non-destructive modification that was done at the >> Navy's Pr >> imary Standards Lab >> to make the comparison section use a 10 volt reference instead of the >> standard c >> ell as was >> originally envisioned. >> >> Interesting! Do you have any more information about this mod? A link >> to >> a paper or something? >> >> The way the metrology world maintained the Volt [...] >> >> Well, yes, I know how it was done. It was a rhetorical question in >> reply to your comment about 0.01% not "being considered a standard". >> >> My comment about the oil is depending upon the oil used, it could affect >> the non >> -hermetic resistor's >> composition. Fluke's resistors were sealed with a shellac compound of >> some sort >> , so no, the Fluke >> 720A resistors are not just some resistive material open to the elements >> as such >> . The same goes for >> the Fluke 750A. They could be, but then an awful lot would have to be >> known abo >> ut the oil and it's >> affects. The same problem with a potting material of some sort, >> particularly wi >> th regard to leakage >> paths. >> >> I highly suspect that the resistors Fluke used are the card wound, >> shellac sealed types we all know and love. Not going to open the >> tank to take a look, though :-) >> The resistors I'm using are not "just some resistive material open to >> the elements" either, they are molded in epoxy. Using a good, >> pure oil, I see little reason why they would be affected. >> I'm thinking about dropping the resin potting idea completely and just >> have one ensemble as is. That way I can compare the behaviour >> of the canned ensemble agains a 'naked' version, which is more >> meaningful. >> >> Regarding binding posts and such, many manufacturers specify a >> temperature that >> a component can >> withstand before destruction. Does that really say the stability of the >> plastic >> (or whatever >> material) binding post is going to retain its insulation abilities ? >> Many bindi >> ng posts, with >> regard to leakage, are literally junk even without heating. Before you >> select a >> binding post get a >> sample, mount it to a panel and apply a kilovolt (you do have a Fluke >> 335D ?) th >> rough a 10 meg Ohm >> resistor between the post and the panel monitoring the current flow. >> There shou >> ldn't be any but >> that is obviously unrealistic. At least you can measure it. >> >> The ones I got are [1]Pomona 3770's. Their insulation is >> polycarbonate. >> I'm going to dig out my GenRad megohmmeter this afternoon >> and make some measurements. I'll post the results later. >> Regards, >> Rob. >> >> References >> >> 1. http://www.pomonaelectronics.com/pdf/d3750-3760-3770_101.pdf >> _______________________________________________ >> volt-nuts mailing list -- volt-nuts@febo.com >> To unsubscribe, go to >> https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts >> and follow the instructions there. > > > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. >

I think it could be hard to get a strain free mount arrangement that way. If you don't like oil (a reasonable dislike) there are some high MW Freons. However they are very expensive and maybe (wrongly, IMO) highly regulated because of the Global Warming alarmists. -John ============ > In message <1180.12.6.201.35.1260974407.squirrel@popaccts.quik.com>, "J. > Forste > r" writes: > >>On the oil question, you really do need a sealed system, with provisions >>for expansion, or the oil will "breathe" with temperature and atmospheric >>pressure fluctuations and absorb water. > > I would go for the copperblock and use thermal paste to improve the > resistors thermal contact with the block, rather than start > experimenting with oils. > > The only reason oils got used in the first place, was lack of anything > better under the constraints back then. Today most cal-labs try to > avoid it if at all possible. > > -- > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > phk@FreeBSD.ORG | TCP/IP since RFC 956 > FreeBSD committer | BSD since 4.3-tahoe > Never attribute to malice what can adequately be explained by > incompetence. > >