Turn on the radio, Marantz 20B FM Tuner

Introduction

Sitting in front of a great tuner late in the evening, when all the daily trouble is gone and listening to some of the very good broadcasters here in Berlin, like Deutschlandradio and Deutschlandradio Kultur or Radio 1 is something very special.

Those broadcasters are not private stations, they are financed by a sort of tax, we listeners have to pay here in Germany (Rundfunkgebühren) – so they are not overblown with advertisement programs and could search their content which they bring on air more freely.

That means that you are able to listen after 8 O clock pm. on Deutschlandradio some live concerts they recorded themselves with their own very, very fine recording equipment, and you will listen to music never sold on a media like cd or vinyl. You get access to artists, who are not widely known or just the opposite – well known super star conductors and their orchestras, which play for you some music seldom heard. Sometimes they broadcast jazz festivals live or they invite the artists into their studios and record them live which results in very intimate music – in short – you have the chance to listen to very, very good special interest program.

Getting an FM Tuner

The only chance to listen to such program in proper quality, is to use a very good FM tuner. As you might guess, I am not a big fan of internet radio – and I hate commercial radio which broadcasts such an extremely processed sound, that there is less than 4db dynamic range left at the end. Very good radio in Germany means dealing with the small stations and mostly no private broadcasters.

Germany has a very narrow FM bandwith were all the different stations are located on – so a proper FM tuner must have the ability of a high station separation, to get rid of all that noise of little birdies singing behind the broadcasted program. A lot of separation means very steep filter design – and steep filter design often generates a sharp synthetic sound – so a good tuner is not something you will find around the corner.

Tubes or transistors?

Vintage tube tuners have an amazing warm and detailed sound, but most of them were made in the USA, which do not have the same bandwith – situation we face here in Germany, so the ability to get a strong reception and good separation is a task most of the vintage tube tuners could not achieve. And, if you think about one of the most popular vintage tube tuners – in may opinion the pinnacle of tube tuner design – the Marantz 10B, you need 22 tubes , most of them very, very rare. So a tube tuner is a nice thing to have – but if you judge the complete package it is mostly the second best way to achieve a fine radio tone into your listening room. On the other hand we have the modern synthsizer tuners, some late models with digital converters on board to feed digital amplification systems – these generation of tuners lack the classic, warm radio tone. This kind of presentation, the quality how radio should sound, was formed in my childhood. My dad drove an old Mercedes/8 – and in that car there was a radio installed – a Becker Mexico – which fed a huge oval fullrange speaker mounted on top of the dashboard. This radio sound was intoxicating! Voices sounded warm and deep with all that colourful proximity effect realised via a close up microphone position – music sounded big and bolt with a special wet treble sound – it was amazing. The other event, which formed my view how radio should sound was the purchase of an old Loewe Opta mono tube radio, I found one day at a shop dealing with vintage electronics.

How can I get exactly that tone with the ability to get a little bit more detail in the sound, more resolution – but without a synthetic attitude so often detectable with modern radio sound??

The Marantz 20B

I had to get one of the famous first generation transistor tuners from Mcintosh or Marantz. And I opted for the successor of the famous Marantz 10b, the Model 20.

The Model 20 was made right after the 10b, which nearly ruined the Marantz company, because they made it in such an expensive way, that with every single unit they sold , the company made no revenue – instead they had to spent money.

As the famous Marantz 10b, also the Model 20 was constructed by Sid Smith and Richard Sequerra – both legends in the history of high end audio!

There are two variations of the Model 20 in existence – the Model 20 and the Model 20b, the latter is much more scarce that the Model 20. The difference between both is a modificated front end on the Model 20b and a slightly better output stage!

To find such a 20b is like winning the lottery – most of the examples you will see, are not working anymore – or they are “upgraded” with “nice” things like LED lamps or the circuits were modified. If you want to hunt such a rare piece of audio history, you need time and patience, and not indulging in illusion – these things have to be overhauled and restored to their original specs – you can do that by your own, if you have enough skills in working with some solder iron and in reading circuit diagrams – or you have to find someone who will do that for you. My example I eventually found,  was in a very poor state as I bought it – the front plate was bent, not a single lamp was working anymore, the stereo lamp circuit was defect, corrosion had done its work on the chassis and some internal parts, a couple of cpacitors were leaking….you get the picture. But it was love at first sight!

Restoring the blue eyed lady

I had to bring this thing to its specs and back to a much more beautiful condition as it was, when we first met each other.

I needed 6 months of research were to get the parts, getting the circuit diagrams, service manuals and a lot of soldering work. I tried in most cases to repair the unit with its original parts, which is not an easy task, because most of the so called NOS (New Old Stock) Parts of that time might be as much out of their specs as those found in the unit itself. But after 6 months there was a sign of hope – one evening I heard the first sound coming out of that classic tuner. Maybe you can imagine how I felt, as I listened to the first transmitter noise coming out of that old Marantz FM tuner – it was like me, the little Dr Frankenstein made his a dead believed monster to breath again. I am a happy man – because my wife (the most understanding girl in the world!!!) had to face weeks of a half occupied kitchen table with soldering iron, solder, small and large parts and an mazing amount of dirt on it – and she did not  protest nor was she annoyed.

Later I got in contact of an expert who was able to do the alignment of the tuner because I have not the special equipment needed for that job nor do I have any experience with such things. After the alignment was done, there was the first contact with our house antenna and the stereo system!

The tone is back

There it was!!!!

This specific classic warm radio tone, which left its mark on me since my childhood, the old Becker Mexico installed in my dad´s Mercedes / 8 which I never could forget during all that years – a sound I adored so much!

The Marantz 20b has an amazing quality in its low end – it is one of the most satisfying tuners in this regard – bass impulses broadcasted not with too much compression are nearly as full bodied as I can reach that with my turntable. The sheer impact is amazing, and till today, I found no other FM tuner capable to produce this quality of bass. The treble is completely open and detailed – not the typical rolled off sound so many FM tuners share – there is a sort of presence and light at the treble region, which is fantastic. Keeping in mind, that broadcasted program is cut at 15Khz, the treble performance made me to doubt for that fact.

In the midband the tuner has this classic warm and realistic touch, I do miss so much with more modern equipment. The whole gestalt of the sound is bold with the ability to create a huge soundstage garnished with a sparkling treble wich is smooth as silk. If you like the sound of vinyl, than this old Marantz FM tuner is not so far away from that aesthetic direction.

My biggest problem was to find the lamps, which Marantz used at this time – 6V/5Watt. You get everything in the 6V category, but not 5 watt…..this type of bajonet socket lamps vanished from the market.

One day I found a shop which sells parts for vintage motorcycles – and BINGO – this ebay shop had exactly what the doctor ordered – and my Marantz 20b struck again its sexy blue eyes.

Last things I had to do was dealing with the poor cosmetics of the device. The front plate has do be fixed, which needs a lot of gentle violence – but I succeeded. One of the biggest problems was the rusty original laquer at the steel chassis. A full repaint would mean to loose all the original stickers which were used on this piece of gear instead of some engravings. I decided to use a very tricky coating technique to obtain all the glued on signs once the Marantz factory had put on that tuner.

At the end the tuner got a new rope driving the needle which shows you the FM frequency, a new Telefunken oscilloscope tube and a complete cleaning.

To give you a short description of the operation, let me explain the features of that old audio classic.

The Marantz 20b has 2 pairs of adjustable RCA output sockets at its rear side. Beneath those you will find two spindle potentiometers to adjust the output level, as also the output balance of both pairs – their maximum output level will be 1V. Also at the rear side you will find two RCA input sockets, which lets you feed a signal into the tuner to have the possibility to use its scope, measuring that given signal. This comes on handy, if you adjust the azimuth of your phono cartridge for example. To activate any external signal fed to the scope, you have to turn the diyplay switch to its “ext.”(external) position.

Also at the rear side there is a pair of sockets for test purposes and we will find a strange locking pedestal which takes the 3 antenna inputs as also a switch on its backside wich adjust signal damping on the antenna signal. Last but not least we will find at the back a fixed power cable, my unit was officially imported to Germany, which means it is a 220V unit with a proper Schuko plug at the end of the umbilical. The European distributer for Marantz gear at this time was the Swiss company Bolex, who also built some of the most famous film cameras of that day (Bolex 8mm or 16mm cameras).

At the front we face on the left side two small potentiometers which are used to center the focus of the oscilloscope tube. If the tube is cold, after you switched the unit on, the scope will not match with the engraved cross marking at the screen – so you are able to correct that at the beginning of any adjustments done with the other switches or the tuning wheel – because the scope shows you everything you have to know regarding signal strength and multipath performance. So it is a good idea to begin with adjusting the scope. To do that you need to switch the knob called “display” to the point were it hits the “ext” marking (external). The scope shows now a small point, which has to be centered with the two potentiometers on the horizontal plane as also at the vertical plane – both are lettered accordingly.

The display switch has 4 more positions. “Audio” will show you the phase relationship between the two channels of your program on the scope. If you listen to a true mono signal, as it will be the case with speech, there is a 30° stroke displayed. If you have a strong stereo modulation the scope will show you more or less a circle with a lot of movement accordingly to the modulation of the music.

The next mode is off – that is self explaining – but I need to ad – off is a very good mode ;-))), because if you are not dialing in a station or observe the phase relationship between both stereo channels – it is a good idea to switch the scope off – because the tube will live much, much longer and to get a new one gets more and more complicated today.

The next two modi of the display switch, show you the signal strength on the scope or the multipath performance!

Next to the display switch we will find the knob for the different muting modes. The Marantz 20b has an adjustable (internal) muting threshold at which the signal will drop in volume, which is a nice feature, if you want to get rid of all that noise between two stations. But you can turn of that mode – and for that purpose exists the bespoke muting switch.

On the right hand side we will find the on and off switch and a knob  labeled with “mode”. Here you can decide if you want to listen in stereo or mono – but there is more…. If you listen to a weak stereo station, the noise you will receive is annoying – so there is a position between stereo and mono called “high blend”. Sid Smith used therefor a special trick in his circuit – it is a high frequency blend which uses phase cancelation of the noise – not a traditional high frequency cut. With that “filter” you will miss on weak stereo stations no treble! – That was a sensation at the time were the Marantz 20b hit the market. What you will loose is some spaciousness, the signal gets more into the mono direction – but is still a stereo signal!

All in all such a fantastic vintage FM tuner is a nice addition to a very good vinyl playback system – and at night, when I am listening to some rare music performance broadcasted in high quality, the wish comes up to record all that great stuff – but that is another story for another day.

My biggest respect goes to Richard Sequerra and Sid Smith, the inventors of the Marantz 20B, may Sid rest in peace, as he died in the year 2000…

Thank you for the music, you two genies….

 

E. Strauss