Ratio Transformer Gertsch RatioTran RT-18 - Page 1
Forum section: electronics / general

author: quarks
author_rank: Frequent Contributor
timestamp: January 28, 2013, 02:56:08 pm
content: A while ago I saw this really nice old Ratio Transformer and could not resist, because of the 0.00001% resolution/linearity.This is a very interesting piece of gear and seems to be, what the Fluke 720A KVD is for DC, just for AC. I do not know how accurate it really is, because my best meters are probably not nearly good enough to judge it. But at least they agree to about their lowest digits.The manual is dated 1/68, so this instrument can easily be 40+ years old. That is an amazing piece of (technical) art in my eyes.To bad this company is not existing anymore. But as far as I know TEGAM acquired Gertsch/Singer around 1990. So hopefully this great technology is not lost and maybe somewhere in the IET LABS INC. by now.For anyone more interested, here is a link with some good/interesting information about Gertsch Ratio Transformershttp://www.ciphersbyritter.com/RADELECT/RATIOTRN/RATIOTRA.HTMhave fun

author: saturation
author_rank: Super Contributor
timestamp: January 28, 2013, 03:37:49 pm
content: Where did you buy if from? I know those units well, more later!

author: JuiceKing
author_rank: Regular Contributor
timestamp: January 28, 2013, 04:02:30 pm
content: Quote from: quarks on January 28, 2013, 02:56:08 pmYes, that's a really nice one, with one more digit than most.What kind of switches does it use inside? Are they the big, heavy-duty ones?- Ken

author: quarks
author_rank: Frequent Contributor
timestamp: January 28, 2013, 04:20:06 pm
content: Quote from: saturation on January 28, 2013, 03:37:49 pmI bought it from ebay end of last year and picked it up from German custom this morning.Quote from: saturation on January 28, 2013, 03:37:49 pmThat sounds promising

author: quarks
author_rank: Frequent Contributor
timestamp: January 28, 2013, 04:31:26 pm
content: Quote from: JuiceKing on January 28, 2013, 04:02:30 pmThat was the first 8digit one I have ever seen. That is exactly why I could not resist.Quote from: JuiceKing on January 28, 2013, 04:02:30 pmI have not opened it, but the switches feel absolutely as big, heavy-duty ones.Because the second switch numbers are not perfectly aligned (slightly off to the left) I might open and align it.If I do that, I can make some pictures from the inside, if there is interest.

author: ElektroQuark
author_rank: Unknown
timestamp: January 28, 2013, 05:37:12 pm
content: Quote from: quarks on January 28, 2013, 04:31:26 pmDo it!

author: JuiceKing
author_rank: Regular Contributor
timestamp: January 28, 2013, 05:46:06 pm
content: Quote from: quarks on January 28, 2013, 04:31:26 pmSure. If it's like all the others, it's very easy to open--remove the face screws and lift out whole business from the aluminum sarcophagus. The ratio transformers themselves are potted, so there's not a whole lot to see, but what is there is a joy to behold.I will admit right here and now to having a fetish for ratio transformers. No home should be without one. The usual 6-digit versions can be had for $50 if you don't care about cosmetics. If the switches are OK--and they generally are--then there's not much to go wrong unless they've been abused with DC or overload.It's an interesting challenge to test one of these down to the least significant digit. I had trouble getting a stable signal--all my sources tended to drift down as the signal generator warmed up. I had to use a step-up transformer to get a big enough voltage at the input in order to have something recognizable at the output's finest resolution.I've found it handy when I've needed very small signals for testing circuits such as mic or phono pre-amps.It's also nice to see that an AC meter works as advertised, but none that I have are anything close to accurate enough to determine if the ratio trans is as good as it's supposed to be.I'm also eager to use one to build bridge circuits, but for that I believe I need a precision 1:1 transformer, and I've yet to find one at a cost that I can justify for that.I'm curious to learn of other applications. A fellow I met at an MIT Flea Market (where I bought my RT) told me that he had used them some 30 years ago in his dissertation. Later, he said, he did some joint research with Russians and was informed that they would have given their teeth for one of those RTs. Evidently, the Soviets didn't have ones that worked nearly as well. Making one that really works properly was not easy.

author: quarks
author_rank: Frequent Contributor
timestamp: January 28, 2013, 06:31:31 pm
content: ok, I opened it and aligned the number.The case and the build is very nice and rugged as expected. There is nothing spectacular to see inside.

author: PA4TIM
author_rank: Super Contributor
timestamp: January 28, 2013, 07:01:14 pm
content: Very nice. I have a ratiobridge but it is emedded in a GR-1620. But that can not be used separate (as far as I know)Until Ken told me about the ones he has, I did not know things like the Gretzsch even exist. Let alone what to use it for. But I think there is no way back, every house has to have one ;-)Just a few days ago i read about a interesting measurement that needed a ratiotransformer, that made me think, i need one too.It was in an old HP benchbrief about the HP463B I have. To test its gain they use a ratiodivider. Coupled to a generator they feed for instance 10V to a nuldetector and the top of the divider. 1V from the divider goes to the 463 amplifier and the output of the amplifier in the 10X position goes to the other post of the nuldetector. If the meter zeros, the ampification is 10X. By adjusting the ratio divider you can calculate the exact gain.That made me think, I have a Fluke 10V AC standard. I can use a divider and the 463 to get other voltages from a few uV to 100Vrms. Very cool !!Quarks, did you search a long time for it ? And did you find it in Europe ?

author: quarks
author_rank: Frequent Contributor
timestamp: January 28, 2013, 07:57:38 pm
content: Quote from: PA4TIM on January 28, 2013, 07:01:14 pmYour bridge app. sounds interesting. Please share the information.In the link in my first postishttp://www.ciphersbyritter.com/RADELECT/RATIOTRN/BRIDGUSE.GIFWhen I found this RT-18 one in US, I actually searched for quite a while for a totally different type (I cannot find the link to the details, but it was kind of like this ESI KVD (see picture) format but was a brand I unfortunately do not remember, it looked somehow olive green military style in a can and the top was square, maybe someone know what I mean and can refresh my memories).Today I saw a very close type (a ESI Dekatran DT1145, but only with 3 decades + pot) of what I originally wanted, on ebay and right away bought it. When I have it I will show some pictures.When you look for a similar 6/7/8 decade one, search for Gertsch RatioTran / ESI or Tegam DekaTran / Singer / GR Variac. There should be quite a few on the net, from really cheap to very pricey.Here is a link to some Tegam info'shttp://www.tegam.com/category.asp?categoryID=43&redirected=1

author: PA4TIM
author_rank: Super Contributor
timestamp: January 28, 2013, 09:55:06 pm
content: http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1967-05.pdfI was wrong, It was a HP journal but I found it again.I wonder if I can use my GR-1620 as a divider. Must look in the manual for that. It has an external standard connection and there is some switch to use the ratios. But I never studied that because I had no external standard. ( that is, only if I can do that without altering something to the 1620)

author: saturation
author_rank: Super Contributor
timestamp: January 30, 2013, 04:05:41 pm
content: Yes, that unit I was watching for a while. They are reference units that still sell for many hundreds of dollars despite being 40+ years old. I saw a very similar unit sold for a 'make an offer' that listed for $500 ;http://feedback.ebay.com/ws/eBayISAPI.dll?ViewFeedback2&userid=ateknia&&_trksid=p2047675.l2560&rt=nc&iid=271112515230&sspagename=VIP:feedback&ftab=FeedbackAsSeller... which is fairly easy to suggest it made it to this threadTerry Ritter's page is currently the best one for general technical information, but this eBay guide is most prolific too and provides a lot of data Ritter does not.http://reviews.ebay.com/ebaymotors/AC-Ratio-Transformers-Inductive-Voltage-Dividers?ugid=10000000001625986Quote from: quarks on January 28, 2013, 04:20:06 pm

author: saturation
author_rank: Super Contributor
timestamp: January 30, 2013, 04:30:25 pm
content: I use an RT-7 as a precision divider for ACV. An old working Gertsch is very cost effective, as the ratios are far more accurate that even an HP 3458a AC section would be hardpressed to confirm. I am still pondering the units higher ratios, as its indeed very difficult to confirm accuracy of the Ratio Trans as published, or confirm that a used unit is still working at the factory specifications.AFAIK, no one has been able to make an RT except Gertsch and later the companies that bought his original factory tools, see the link to the history. What few competitors that appeared did not last as long nor match its published specifications [ know the original design was patented too.] Thus most all RT today are traceable to the original Gertsch design, build and factories, I do not think they were made anywhere else in the world except the USA.One major benefit is once the unit has been confirmed working to spec, it is maintenance free and can last several lifetimes; its purely mechanical for electronic/electrical purpose. So its a reference AC divider that can be obtained for very low capital cost [ the lesser decade variants] and nearly no maintenance.Since its difficult to confirm the last few decades of the better Gertsch models, and given that an HP 3458a is only accurate to 70ppm in AC, at best, even the more limited decade Gertsch are practical for today's use.Quote from: JuiceKing on January 28, 2013, 05:46:06 pm

author: JuiceKing
author_rank: Regular Contributor
timestamp: January 30, 2013, 06:58:43 pm
content: Quote from: saturation on January 30, 2013, 04:05:41 pmYeah, my low-ball offer on this one was wisely refused. You never know. Glad to see that it ended up in good hands!

author: quarks
author_rank: Frequent Contributor
timestamp: January 30, 2013, 07:17:58 pm
content: Quote from: JuiceKing on January 30, 2013, 06:58:43 pmyes, that's the one

author: saturation
author_rank: Super Contributor
timestamp: January 30, 2013, 07:42:43 pm
content: Given than Gertsch RT are not as widely known [ hopefully prices do not increase much as eevblog discussions tend to alter eBay values], once cross referencing terms like MIT, flea market, Gertsch .. .. very wonderful photos and high resolution:http://www.flickr.com/photos/the-maestros/7793165676/#in/photostream... it seems like discussants there have also made it to this threadQuote from: JuiceKing on January 30, 2013, 06:58:43 pm

author: quarks
author_rank: Frequent Contributor
timestamp: January 30, 2013, 07:54:24 pm
content: Quote from: saturation on January 30, 2013, 04:05:41 pmSaturation thanks for the feedback and this link. Now my memory is back. On this side, the right picture "Gertsch - 3 decade + pot..." with the square top, is the one I was searching for.

author: quarks
author_rank: Frequent Contributor
timestamp: February 01, 2013, 03:37:23 pm
content: Quote from: quarks on January 28, 2013, 07:57:38 pmI received it yesterday but had no time because of my repair work on 540B. So here are the pictures I just made. It is really in almost new condition and is perfectly accurate down to the last digits of my TEK DMM 4050.These Ratio Transformers are just beautiful.

author: PA4TIM
author_rank: Super Contributor
timestamp: February 01, 2013, 03:49:17 pm
content: Nice, (where do you open it to fill it with fresh pepper(just kidding)) it is realy nice. I am curiuos how it will perform

author: saturation
author_rank: Super Contributor
timestamp: February 01, 2013, 03:51:11 pm
content: it does look in very good shape; clearly made with superior materials. The patent numbers are all easily visible, while expired for some time, no one has picked up making these except Tegam [ who has also taken all of the Gertsch-EDI-Singer etc., tools], and they are not cheap.

author: quarks
author_rank: Frequent Contributor
timestamp: February 01, 2013, 03:54:50 pm
content: Quote from: PA4TIM on February 01, 2013, 03:49:17 pmyes, it looks like a cup/can to drink from.Performance is great, my 6.5 digit meter is probably not nearly as linear as the RT.

author: JuiceKing
author_rank: Regular Contributor
timestamp: February 01, 2013, 06:12:43 pm
content: Quote from: quarks on February 01, 2013, 03:37:23 pmNice. It's great to see what these look like when they are in pristine shape. I have a variant of this one, too, with more than a few dimples and "beauty marks" but it still works fine. Because it's so small, it's the one I use the most.- Ken

author: quarks
author_rank: Frequent Contributor
timestamp: February 02, 2013, 07:45:49 am
content: Quote from: JuiceKing on February 01, 2013, 06:12:43 pmHello Ken,because I am new to RT's, it would be nice if you could share what for / how you use it.So far I only used it for precise voltage dividing (and the RT-18 also for multiplying) my Valhalla 2703 calibrator source. The Gertsch is ideal for better (digital) resolution on the source side and ESI because it is small/handy and the pot allows to perfectly trim the voltage, when I want only to (analog) adjust the meter reading to a value in between the digital steps the source gives me.Thxquarks

author: JuiceKing
author_rank: Regular Contributor
timestamp: February 02, 2013, 02:25:33 pm
content: Quote from: quarks on February 02, 2013, 07:45:49 amI use it mostly for messing around with low-noise amplifiers--audio mic/phono amps, impedance bridge detectors, my own test circuits. My signal generator's built-in attenuation goes down to 40mv, which is way too high for this situation. I can cut that by a factor of 10, 100, 1000, etc. very easily with the RT. I don't need it so often, and three orders of magnitude are plenty. The pot is handy for trimming to a baseline voltage, but since none of my signal sources are particularly stable (they all drift down over the first few hours of warm up) in practice the last few digits are meaningless to me. At some point I will build a Jim Williams' stable signal generator... See Linear Tech. AN 47 (kindly introduced to me by EEVBlog pa4tim).I've heard that RTs were once used for testing avionics, but that they are obsolete for that application today and that's why the RT-5 types are so plentiful and inexpensive. I don't actually know what tests were done, and am curious to know more, so do share what you discover.- Ken

author: quarks
author_rank: Frequent Contributor
timestamp: February 02, 2013, 03:29:33 pm
content: Quote from: JuiceKing on February 02, 2013, 02:25:33 pmHello Ken,thx for the information.I will have a look at the AN47 and PA4TIMs info.Just an idea, do you know, if it is possible (with all necessary safety precautions), to use the RTs on mains voltages?About your audio use. In my very early electronic days, I build audio amps (mainly inspired by ELEKTOR Magazine design), and even made (tried to) my own enclosures, with thick aluminum front, engravings, massive nobs and so on. I even made my own attenuator with crazy expensive ELMA switches measured each individual resistor to perfectly match both stereo channels. Very stupid all together, but back in the 80s I liked it and I was allowed to use top notch Rhode&Schwarz Audioanalyzer from my working place. I did also compare (metrology wise) my selfmade gear to a lot of big names back then (if I remember right Burmeister, Accuphase, Krell, Mark Levison and others) and my gear did quite well spec wise. Now my selfmade Audio stuff is unused sitting in my lab.With your hint about audio, I may try to reuse it. Maybe it makes (within its limits) a quite good ACV/ACI source. If this works, maybe it is a good idea for others here. In theory all you would need for a stable "selfmade" ACV/ACI "calibrator" is a good clean signal source (i.e. just a CD player with a good test CD, with sine wave for all audio frequencies from 20Hz to 20kHz) and an audio amp to get voltage/current up. And for best possible results maybe a Ratio Transformer for almost "perfect" linearity, when you voltage divide your signal.But with the spirit of Bill Bryson's great book "A Short History of Nearly Everything " really everything is interesting, when you look close enough to it, I am in big trouble, because I have no idea when I can do all the things I am interested in.byequarks

author: saturation
author_rank: Super Contributor
timestamp: February 02, 2013, 07:29:23 pm
content: A typical Gertsch, usually rated at 0.35 x frequency or < = 350V rms whichever is reached first, means on mains you'll need a variac to reduce the voltage. You'll find the limits on a label on the unit.

author: JuiceKing
author_rank: Regular Contributor
timestamp: February 02, 2013, 08:23:15 pm
content: Quote from: saturation on February 02, 2013, 07:29:23 pmYes, this is the usual rating.There are also high-voltage variants, with a 2.5 x frequency rating but I've never seen one in a standalone configuration. They are paired with the typical 0.35 x frequency rated RT inside the big 1000 and 1009 dual-RT boxes. Two RTs in one.Let me guess that two RTs will not be enough for you.I like your suggestion of seeking a stable signal source from a digital player, and I'll give it a try.

author: amspire
author_rank: Super Contributor
timestamp: February 02, 2013, 11:20:56 pm
content: Quote from: JuiceKing on February 02, 2013, 02:25:33 pmI Did a post on Sperry avionics servo calibrator containing a RT:https://www.eevblog.com/forum/reviews/sperry-ratio-potentiometer-teardown/msg74752/#msg74752.Richard

author: saturation
author_rank: Super Contributor
timestamp: February 06, 2013, 09:57:47 pm
content: That's a very good thread, and thanks for linking! I forgot all about it, and you also describe good purposes for using a Ratio Tran. The other thread is good additional information to anyone on this thread.There are several avionics calibrators on eBay that pop up now and then with embedded RTs; while they can come cheap, they tend to be true "boat anchors." Gertsch stand alone units are often ~ 10# and encased in sheet steel.If you find models that have external fuse mounts then unless its been abused, its unlikely to have been opened since sealed by the factory. One thing to ponder with its age is if prior owners could have contaminated or abused the unobtanium switches.Quote from: amspire on February 02, 2013, 11:20:56 pm

author: SilverSolder
author_rank: Super Contributor
timestamp: January 09, 2020, 04:01:33 am
content: Sorry to re-awaken a slumbering thread... but does anyone know where I might get hold of a manual and/or a spec sheet for a Gertsch RatioTran RT-18 ?

author: amspire
author_rank: Super Contributor
timestamp: January 11, 2020, 09:32:04 pm
content: I have the PDF manual for the RT-5. Do not have one for the RT-18.Richard