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In the Forum: Off Air Audio
In the Thread: A tube tuner? REL Precedent 646C
Post Subject: A small step and the giant leap.Posted by Romy the Cat on: 8/1/2008

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.

The Cat

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