A couple months back I sent to Dima a link with a wonderful collection of audio articles from first part of the 20s century:

http://www.one-electron.com/Misc_Docs.html

In next couple days, talking with Dima he asked me: “Roma, what is REL Company all about?” I told that REL is a British company that makes subwoofers? “How good their tuners” Dima asked. I answered that I have no idea – “Most likely if should be nothing special if they do any”. Dima replied that it is very strange as at the link I sent his he came across a schematic of R.E.L. Precedent 646C FM tuner  (closer to the bottom) that was one of the very few schematics that he feel was describes a near perfect tuner. Dima, did pointed out to some simplifications as shortcoming of the schematic but he also told the it was the most properly made commercial circuit he even seen. Dima, pointed out: “This REL was designed by people who truly knew what they do and from point of tuners design it is almost as good as Rohde & Schwarz EU-6201 but made around tubes. Roma, juts because the tubes the REL might be even better then the Schwarz. Get it and try it.”

http://www.goodsoundclub.com/PDF/REL_Precedent_646c.pdf

Well, I have some aversion to tube tuners:

 http://www.GoodSoundClub.com/TreeItem.aspx?PostID=7892

Never was able to have them to sound right.  They have fine reception but no good sound to my ears. However, considering the in REL tuner there is not sound before output of detector and considering that I was not going to use anything after detectors I decided to try. I learned the REL stand from Radio Engendering Laboratory of Long Island NY. The company is long gone and the Precedent 646C was their flagman model. There was some chatter on line about REL Precedent but what I was able to read more indicated about the Moronity or Idiocy of the people who pass their comments then about providing any useful information about this tuner. Not to mention that I generally treat the comments of audio people about audio with no more esteem then blabbering of a 3-year old baddy about the Theory of special relativity.

Recently, I discover 4 REL tuners available for sale and I discovered that one of them was serviced and aligned by Charles King. I dealt with Charles around my Stellavox machine and was very pleased with his service, he is also one of the few who hears and recognized the heard. So, I decided to give it a try… I even drove 100 mile away as the tuner never was shipped after the Charles’ alignment – I would like to keep it this way…

The very first thing that I did was checking how different Morons told me that Precedent is “spectacular” mono tuner and that “it is so good in mono that you would not need stereo”.  Well, I was listening the Precedent in full mono. I was revolting. The tuner has fine reception, not super-sensitive but fine selectivity and low noise. However, the quality of the sound was not just revolting but truly laughable. The Sansui TU-1X goes 10 times better running AM of the stock antenna...

Then I disconnect the de-emphasis network from REL and run the composite signal to my external Multiplex decoder. It was also very bad. There was not good bass and not good tops. The sound was euphoric, lazy and truly tube-like in turns of very-very bad tubes design. Dynamic is not there and my system sounded more like 64dB sensitive electrostats driven by a 2A3 amp… It was clear that the REL’s output stage is garbage, what is very much visible and was predictable from the schematic. Taking the signal before the REL’s output stage, right after the detector changed situation a LOT. The sounds become listenable. It is still not as good as Sansui of the Schwarz. It is not even contestable at this point but I think it is a good first step. I would n to put a buffer after the REL detector to drive my multiple and make some minor change in the REL detector (change diodes to Shotky and the 2 mixing resistors to better resistor). I do not know if the REL will be able to sound at the level of TU-1X or Schwarz. I hope… From the positive side: REL it looks like has some elegance and grace. It has no balls, perhaps the week detector can’s drive my 1.5 meter cable to decoder. Charles is putting the MPX decoder right into the REL – but I did not hear the complete unit with a built in decoder. It does not make send for me to put decoder into the REL as then it would force me to use another decoder in Schwarz and to replaces the cables if I would like to record the FM feed (I have just two A/D processors).

So, so far the REL Precedent is very much NOT plug and play solution and it would take some efforts to make it sound good – of it ever can sound good. Now is a bigger question: what the hell I am trying to accomplish and why I am being a fool with 3 tuners. I admit that I do not need 3 tuners. I need one or max two that would be optimized for the specific reception condition (strong local vs. weak suburban from saturated local). With all equal I would stay with TU-1X with pain in ass manual attenuator. I do it for sake of sound – the untouchable, particularly this specific unit that I left for myself. The TU-1X  is also is extremely comfortable to use. I also stay with Rohde & Schwarz EU-6201 as the best SS tuner ever built. Schwarz kills TU-1X in reception and equal to TU-1X in sound BUT I still would like to have Schwarz with better decoder and be able to over-perform TU-1X. So, what REL doe in my room? The RELL is trying to do what TU-1X or Schwarz do or perhaps is trying to be better then they. The stupid debate about tube vs. SS is being played with my tuners again only now we do know that fro Radio Frequencies the tubes are questionably better. If REL is the most promising tube tuner ever made then now I need to learn how to get out if it a adequate sound. Will see what happen next…

One of the ways to drag the REL tuner in the realm of civilized sound is to get rid of any crap that it has after its detector. One of the first things is to replace the 60 years old Germanium diodes with contemporary ultra fast and ultra low capacitance Schottky detector diodes. However, it is a quandary that I have: why do not use the tube detector diodes? There were those sub-miniature vacuum tube diode that might do fine:

http://home.netcom.com/~compactron/tubes/5647.pdf

I took the REL’s output amps and the follower out and I have two filaments available to drive the tube detectors… So, another little battle of tube vs. SS, only now in the realm of detector diodes. The good part is the REL is made with extremely easy and very comfortable access to anything and to try different detectors is a matter of a few minutes. A pair of new detector diodes, a par of new RN60 resistor after the detector, perhaps a pair of 47pF mica caps to ground and the output buffer for composite signal – it is all that I am willing and able to do with this tuner to make it to sound better. It might be interesting to see how it goes…

Paul S wrote:

Of course you will give this Grande Dame ('54 - '55 ?) a fair shot with some new parts, apropos?  Especially new caps?

I would certainly would be very interested if someone with RF knowledge would rebuild the REL circuit from scratch, using better contemporary part and better building methods, perhaps with some minor improvement of the REL’s ideas; however I will not be the person who will touch anything in the REL as it is now. I trashed the REL output stage. Whatever in there before the detector diodes is not sound but radio frequency and I have absolutely no knowledge how the RF parts are responsible for sound. There are explanations how the RF solutions effect reception characteristics but not sound, at least it not know to me.

All that I intend to do if to put better contemporary end of the detector and build-in a good op-amp buffer for MPX signal to drive my external stereo decoder. It might be an elegant idea to use the sockets for tubes V14 and V15 to build my own output stage but I never was able to make a transparent enough tube buffer.  If you still deal with Mike Zuccaro then ask him what buffer he used, unless he built into the REL a very sensitive decoder chip.

BTW, I changed today the detector diodes to regular 4pF silicone and the mixing resistors and the sound did got better, much less cotton-like. I weigh when the Schottkyes and the ap-amps arrive…

A few days back I got rid of the 60-year old Germanium glass diodes in the REL detector and put in there the regular 1N4148 4pF low-signal diodes/ it was quite positive improvement. I need to be said that detector diodes are not the regulars diodes but a core of the tuner detector something that figuratively “converts” auditable frequencies from radio frequencies. So, it is much more than a pair of the diodes but they are THE diodes on the FM discriminators. Yesterdays, I received the special Schottky Diodes that were made for this application. It is 1N5711 diodes - low capacitance, low switching voltage and ultrafast. They were made specifically for use in the UHF/VHF and video detectors, frequency discriminators and wave shaping devises.

Since I am not a huge fan of all that “vintage paranoia” I decided right along with putting the right detecting diodes to redo the whole after-detector section.  Got rid the 600V after-detector shunting caps, putting in their small 100V/47pF silver mica. I got ring the super critical mixing resistors. The where dust-made and literally they dilapidated in my hands when I touched them.  I also, followed the Dima’s Instructions separated the End of the Detector Radio Frequencies ground with Audio Frequencies ground. The signal meter was also removed from output and decupled with own buffer.  All together it is not a huge revision worth $10.

Oh, boy what a result!!!! Dima, suggested the special detector Schottky shell be better but why would think that it would be like this? The cotton-like mumbling of the tuner is gone. The idiotic “vintage” upperbass is gone. The whole upper range is cleared up very significantly with an additional adding a lot of HF extortion. Dynamically it got much more enthusiastic with very nice “crisp” sound, in fact very pleasant sound. Else, believe me or not but the detector with new Schottky outs 6-8dB more voltage then with 60-year old Germanium glass diodes – only this worth the price of addition!

So, what my REL is now all about? It is actually a nice sounding tuner now, moderately sensitive and moderately selective. It is not as super selective as Rohde & Schwarz and it is not as insultingly sensitive as Sansui. It however handles the overload very nicely (I do not use a lot of REL’s signal attention and I have my own external attention).  The Schwarz still have much more sophistication to handle overload, despite the REL’s vacuum tube advantage.  Sonically REL is so far slightly on soft side. It has a genital touch to sound – but it might be my mental pretendectomy to the tube’s nature of REL. With all new HF and dynamic breakthrough REL still is losing to TU-1X in dynamic and slightly in HF. Not as laughably as it was initially but still auditable. The FH are “almost” there but the dynamic has quite a room for improvement. The lower region of the REL probably is the worst. It has no tubby bass anymore, but better REL bass juts made too visible how much TU-1X is deeper and more interning in lower region. I also have some problem with my T85 Multiplex Decoder to read the REL composite signal.  The T85’s decoder read Schwarz’s signal perfectly but it is finicky REL’s signal. I did not figure out yet hat is going on.

Anything is on a positive side? REL has a different type of background noise. I would not say that it is better but different – particularly when a station has own noise and the tuner own notice talks with the station’s noise.

There are few other things that I consider to do with REL. Buffer the output in order do not let the detector to drive the multiplex.  Change the 8 limiters Germanium glass diodes with the Schottky but I need to discover if it screws up the alignment of the tuner. I need to get an Equivalent Series Resistance Meter and to check out those 60-year old caps. Perhaps they are dead and replacing them would fine the bass. There are a few other minor things…  Anyhow, it is slowly but it is getting better. The question is: can it do at it’s best better Sound then TU-1X. The answer is pending.

Romy the Cat wrote:

I also have some problem with my T85 Multiplex Decoder to read the REL composite signal.  The T85’s decoder read Schwarz’s signal perfectly but it is finicky REL’s signal. I did not figure out yet hat is going on.

Then there is Stereo. My problem with Precedent’s stereo sound was why I went into people to see what others say. To me the SU-1X is the reference stereo. The T85 Multiplex Decoder driven by Schwarz has practically identical stereo quality, however when T85 is driven by REL the stereo imagine is very pure. It is not that T85 is bad MPX decoder – it is extremely good I presume that since the REL was made before the 1961 - when FCC announced stereo FM - the REL’s composite signal is not optimum to care MPX signal. I did not see anybody mention it about REL but the funny people say “juts attach a multiplex decoder to REL and you will have it”. Have what? Do those people have any remote sense who a proper FM stereo broadcast shell be presented? The Precedent’s stereo a juts a sad parody, at list in my case, how the FM stereo shell be. I was wondering why.

Upon further investigation, reading the technical articals like this:

http://transmitters.tripod.com/stereo.htm

and consultant with different people I come to the discovery that mono and stereo need different bandwidth from intermittent frequency stage. The REL IM section is fine for mono signal but when REL cares wider bandwidth of stereo signal then it truncates the side-band, introducing HF phase distortions – it is exactly how it sounds. I consulted with Dima and he was laughing saying that it is silly to expect the best sound while caring stereo with IM section that has mono-targeted 250kHz bandwidth. So, what REL need to be able to run any more or less civilized stereo is to widen the bandwidth of intermittent frequency stage to 400kHz.  Then, only then it would worth to look how the REL sounds in full stereo. Without it (if I am correct) the REL is good only for listing the NPR’s  “Wait Wait... Don't Tell Me!” but not good for the real musical broadcasts.

Figuring out how to switch REL Precedent’s IM bandwidth to more suitable for Stereo operation I was wondering about something else. The 250kHz window though which the REL Precedent looks to the FM band is might be fine for DXing or having good selectivity but from what I see in context of another tuners 250kHz is too narrow range for producing best sound quality. All modern tuners have IM filters tined from 430kHz to 150kHz. Sansui TU-X1 has Wide-400Hz and Narow-200Hz (in fact it sound VERY nice in Narrow). Yamaha 7000 has 430kHz - the widest and the Yamaha T85 has 150kHz – the narrowest. Sure, with shrinking the capture widow makes the selectively of a tuner go all the way up but also the sound quality goes all the way down.  The T85 in Ultra Narrow mode has a phenomenal selectivity but it sound like MP3 player. Tuning to a good station in the Super-wide on T85 mode adds a LOT to sound quality compare to more narrow modes….

 So, why to have in the REL Precedent the 250kHz capture window if wider ranghe would add more to sound quality? I do not need this tuner to catch the live transmission of Florida radio stations broadcasting the high-speed chase of local drag dealers. I needed it to get max sound quality from my very local stations. So, the REL Precedent will be converted to 400Hz IM bandwidth – and it might make it to have the Sansui’s sonic space and the Sansui’s bass. (Bass is dying first with shrinking of IM bandwidth as I can hear).

So, to recall everything g the 3 major modifications were done on REL tuner:

1) Change  of Detector diodes from 60 year old glass diodes to 1N5711– with huge advance to Sound

2) Change diodes that come to grids of the limiter stage to 1N5711. The effect not huge  but to sound positive – the LF harmonics got removed from noise and the noise become more uniformed

3) Increase the IM bandwidth from 250kHz to 400kHz - huge advance to Sound as well.

All of those advances in REL did not lead to better sound overall as in a few days the front-end on the REL when down (for own independent reasons). The funny part is that the REL is so good that it sucks signal from antenna… without the front end (the first tube is not there). This crates some noise that prevents to hear the tuner in the way how it might sound. It looks like I know what is the problem was and I can’t wait to get home and to fix it. I really would like to listen how the REL with all that injected adrenalin would sound.  It should not be worse and I do anticipate a very interesting push up sonically against the SU-X1 and Rohde & Schwarz

I'm strugling with dreaded Mcintosh Mr67 tuner . I borrowed one from a friend and it was very nice ;clear , crisp , dynamic so I went out and bought one for myself . It sounds like a mud and matches 100% of your description of average tube tuner sound -vintage POS. I don't know what kind of mods had unit I've borrowed . My friend already sold it.
Dima if you're around could you suggest some mods to improve performance of that unit ? It is not collectible (chrome is gone from chassis so I can hack it , use only front end etc. If that's to much to ask for thanks anyway for the hint with detector diodes and decoupling the meter.
Regards, W

Romy the Cat wrote:

I have no idea where this saga with REL leads me. Even though I do have substantial sonic improvement over the original REL version I still do not know if I like this tuner all together. The 50 years all tube tuner with 17 tubes is very freaky thing. I still have some tuner owned noise that I would like do not have. The damn thing sounds very deferent with the change of the few tubes (particularly oscillator and the last tube of limiter). The tube sockets all are garbage and twisting the tubes in their stockers do changes sound of the tuner to a degree. As now REL sounds more or less OK but kind of unstable. My SS tuner beat if with large degree. Perhaps the REL at this point need a recalibration and viewing by somebody who has more RF skills then I do? I am considering it. At this point REL is more pain in ass then results.

Well, what can I say? My SS turners turn out to be WAY more superior then REL, even after two alignments.  If to consider that REL is more sophisticated and more properly made tuner then all of those McIntoshs, Marantzs, Leaks, Scotts and Fishers then it was a good journey into SS vs. tube tuners debate.

It is sad in a way as I had a lot of expectations from REL, furthermore my REL had SS output stage and tube-made were only the RF stages. Still the R&S and Sansui beat it, primary in bass, dynamics and noise. With all sadness I decided to let REL to go. The legend did not prove itself….

Paul S wrote:

Do I recall that the REL had a fairly "unusual" tuning section - among its many features that were (and still are) novel for a "civilian" tuner - , and that many of those old parts were not only top, SOTA mil-spec back then but most of them were also "critical value", matched and trimmed to within a gnat's eyelash?  I can't imagine trying to work on that thing.