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Old 31st Oct 2021, 6:41 am   #1
Jan Zodiac
Triode
 
Join Date: Sep 2021
Location: Aabenraa, South Jutland, Denmark.
Posts: 31
Default Eltra Skymaster 919

Hello,

I decided to make a thread on another one of the "big five" danish radio models from around 1950. There are a few more than five, but these were probably made in even lower numbers. They were also made a few years earlier.

This time I will cover the Eltra Skymaster 919 model. This model was the first of the big ones I got for my collection. It was maybe 15 years ago. I always loved the model for its appearance. I only ever saw a few of them by other collectors. Then one time I had the opportunity to buy not one, but TWO of that model. One in great condition, and one for parts. Both fitted with the FM unit.
Later on, I received more of these and have kept a few in storage. These are more or less untouched though.

The one I use in my livingroom, was actually never restored. I only replaced the critical papercaps, a few resistors and one of the electrolytics in the power supply. It even still runs on the original selenium radiator type rectifier.

The appearance of the radio is quite impressive, with its dial divided into three separate floating glass dials.

The AM and FM (optional) section are separate units, but operated through the same dial cord, as well as receiving power from the same power supply.
It is an AC/DC set, with no mains transformer. It has two filter chokes, and a lot of care was taken to prevent hum.
The AM section does not have an RF amplifier, instead it has two IF stages, and of course the detector stage. There are three bandwith settings, narrow - normal - wide, which is engaged on both IF stages.
The band selector is quite impressive. It is a revolving unit made in copper, like often seen on communication receivers. I will of course attach some pictures of the chassis, as well as of the complete radio.
A small tuning capacitor is used to match the antenna. This is a nice feature.

Near the bottom at the left side of the lower dial, a user guide is written, to help the (unexperienced...) owner get the best possible reception, using the bandwith selector and treble control in combination.
The "narrow" setting of the bandwith selector does give quite a lot of sensitivity, and is mainly used for long distance. The "normal" setting is... well normal The "wide" setting is actually VERY wide. Like 20kHz or so. So this is only for local reception. I use it for my own in-house transmitter, and on this setting it come very close to listening to FM.

The FM unit was not available as an option of the first models produced. It could later be fitted at the dealer, which also included the lower glass dial with the FM band printed on it (squeezed in between two other bands, and barely visible unless you really search for it). Later models could be fitted with the FM unit directly upon ordering. As far as I am informed, the model was introduced in early 1950, maybe late '49. In 1952 it was gone.
The FM unit itself is build by Eltra also. I was told (unconfirmed though), that these FM units were used at our danish broadcast company for monitoring. Keep in mind that it was all experimental until 1955 where FM and TV were introduced on a larger scale.
The FM unit is indeed a well working and very stable unit. I read somewhere long ago in a description of it, that it used "radar crystals" as detector
It was just normal germanium diodes of course, but these must have cost a fortune at that time, and was therefore not used in domestic radios, which made them a lot more mysterious.
What looks like a tuning capacitor on one side of the unit, is actually tuning coils. These were made by Eltra and fine tuned by adjusting the aluminium plates through the copper windings. Very nicely made.

It should be noted that this radio was very very expensive at that time, and it was not produced before it was ordered. None of them was displayed at dealer shops, in case they did not manage to sell them. So customers bought them through pictures and technical descriptions, without actually having seen one for real.

The AF section is quite different from what was the norm. It consists if a normal input selector, athough on the "phono" setting, it has an extra triode to compensate for gain. To match a given cartridge, different plug-in units were available. Several of these having transformers.
All this is fed into a volume control and a normal class A single ended output stage. The signal is then fed into a low Z tone control. There are settings with both steep and graduate roll offs for different frequencies in the HF region, as well as normal boost or steep boost in the bass region. All this gives a LOT of opportunities to match both radio reception, but especially for getting the best results of playing records. It is absolutely stunning for 78 records. Early vinyl is acceptable, but it is not easy to obtain curves that matches vinyl records well. On 78's is really where it shines. Even badly worn, early century mechanical recordnings can be played with astonishing clarity. Late 78's plays with full frequency response, especially if Ortofon or B&O cartridge is used (with proper plug-in unit of course).

The actual frequency response from the different tone settings is shown on the small back lit display at the mid bottom of the front.

After this tone control section, the signal is fed through a phase splitter transformer, and into a class AB push-pull output stage. A large output transformer is used for the main (bass) speaker, and a small transformer is coupled in parallel to it, though a capacitor as a high pass, to feed the smal HF speaker.
One might think, that with the audio signal passing such an amount of filters and transformers, the result would be really poor. I don't know how they managed to make this radio sound so great. I would say that out of the five big luxury models available at that time, the Skymaster wins the competition on sound quality. Voices and instruments sounds natural, and it is easy to get a lot of details especially from records.

Kind regards and a nice sunday to all of you!

Jan
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Old 31st Oct 2021, 6:48 am   #2
Jan Zodiac
Triode
 
Join Date: Sep 2021
Location: Aabenraa, South Jutland, Denmark.
Posts: 31
Default Re: Eltra Skymaster 919

Here are a few pictures of the quite large and heavy chassis. Note the FM unit is mounted over the revolving AM selector unit.
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Old 31st Oct 2021, 6:54 am   #3
Jan Zodiac
Triode
 
Join Date: Sep 2021
Location: Aabenraa, South Jutland, Denmark.
Posts: 31
Default Re: Eltra Skymaster 919

And finally the FM unit itself. Speakers were made here in Denmark by Peerless. One picture is showing an example of the cartridge matching unit. It is also large and heavy (well shielded). The Garrard headshell is for size comparison. It should be noted that Eltra made their own transformers, even the small ones for cartridge matching.
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Old 31st Oct 2021, 3:09 pm   #4
G6Tanuki
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Default Re: Eltra Skymaster 919

I am fascinated by these insights into Danish post-WWII radios you have. It really does seem that some manufacturers produced impressive radios, but as you point out they did not make many of them!

British manufacturers seemed more focused on making cheap and mid-range radios - I think that was because we had lots of bombing during WWII and people did not have spare money to spend on radios or televisions when they still had bomb damaged roofs and ceilings to replace.
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