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Old 14th Oct 2021, 5:48 am   #1
Jan Zodiac
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Default Restoration of a Neutrofon Guldsegl 5308

Hello.

This thread will be about the restoration of a danish high end (large) table radio from 1953/54.

First a small introduction to the few danish "ultimate luxury" receivers that were produced in small numbers between approx. 1949 and 1954.
Since I wasn't around at that time, and only limited information is found on these special receivers, I can't really give a specific reason why the five largest/finest radio manufacturing companies, some time after WW2 started a challenge of producing the best and most advanced receiver possible.
It was probably a project of prestige and manifestation. All these recievers were produced in very limited numbers, and they were only produced after an order was placed. They were assembled by hand, off the usual assembly/production line.
This also made them very expensive to produce, and I heard from several older technicians, that they lost money on producing them, which makes sense, since these "ultimate" receivers were only around a few years, and then completely dropped out of the product listings.

The five manufacturers and their respective supermodels are as follows:

Eltra Skymaster 919 - produced from around 1949/50 and a few years into the 50's. First it was an AM only, but later a FM unit was offered as an option. Was offered as a radiogram also (Skymaster 929).

TO-R Imperial C8U - I think this was only produced in 1950 and maybe in 1951 also. AM only, and no later FM options. Was offered as a radiogram also (VERY rare).

Linnet & Laursen Primas 501 and 512 (1950 and 1951). Started as an AM only, and was later offered with optional FM unit. As for the Eltra Skymaster, the FM unit could be mounted in previous AM only models also. Offered as a table radio only. A very large one though. Primas 512 with FM unit had 21 valves!

Bang & Olufsen Grandessa 506, 507, 508 and 509 (1951 to 1954). 506/7 is the first introduced and 508/9 the "second generation". Big, bulky and heavy. All of them could be ordered with an FM unit, which more or less was an integrated part of the main chassis. The first generation (506/7) was offered as a console and radiogram also. The 508/9 as table radio only.

Neutrofon Guldsegl 5308 - This was produced in a very limited number, introduced in 1953 and then probably gone already by 1954. It was offered in 2 radiogram versions also. It is a fully integrated AM-FM receiver.

I will later on make a description on each individual model and their special features, but to limit the space a bit, I will focus on the Neutrofon Guldsegl 5308 in this thread.

The 5308 was probably the most well engineered of all the "big ones". On AM it features a tuned RF amp. stage, and two IF stages with additional windings for a 3 stage IF bandwith control. FM with two IF stages + discriminator, and AVC controlled RF amp. The complete tuner section has its own power supply. The secon PS feeds the AF section. This is an AC/DC set (here they were called "universal"), as most radios was around that time, given the fact that we had a lot of local DC power plants.
The AF section has input for xtal cartridge, or upon request, a transformer could be fitted for 1,5 and 50 Ohm magnetic cartridges (Fonofilm/Ortofon and Bang & Olufsen). Mine has the optional transformer.
The tone controls uses selectors instead of potentiometers. In fact that was very common here. Both bass and treble features two individual controls. One for boost/attenuation and one for crossover frequency (bass control) or sharp roll off (treble control).
The treble roll off control is attached to the bandwith selector as well, and also a steep slope record noise filter for worn records is operated by this.

The output stage features two UL41 in push-pull, with a large section wound "high fidelity" output transformer. I measured the output power to 9 watts right before clipping. It is indeed a nice amplifier section.

There are two 8" Peerless bass speakers and a 4" Peerless "tweeter" (probably a bit large to be called a tweeter). Crossover frequency is around 1kHz. These speakers are very sensitive and the radio is capable of playing very loud.

The extremely beautiful cabinet consists of so many individual parts, that it must have cost a fortune to produce. It was quite a challenge to take it all apart for polishing. Resonances are supressed by soft fibreboard, glued to the inside walls of the cabinet. I have never seen this on any radio before.

It was in general a challenge to restore, because of all the paper in oil capacitors used, as well as a few regular paper caps. All the electrolytics in both power supplies were fine though. The two selenium rectifiers are only kept for display. I use silicon diodes and a larger series resistor to keep the correct voltages.
I aligned both AM and FM section completely. The AM sensitivity was specified to 1uV (bandwith in "narrow" position of course), which was quite good for a domestic radio. I can confirm that it is indeed very sensitive.
FM section is quite sensitive for its time. It has low noise and it sounds clear and crisp.
There is actually some noise/hiss from the amplifier section itself, which is especially noticable on low volume, or if volume is turned all the way down. There is no hum though, even if it is an AC/DC set.

/Jan
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Old 14th Oct 2021, 7:57 am   #2
red-duck
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Default Re: Restoration of a Neutrofon Guldsegl 5308

Interesting set. The design of the cabinet and the layout of the tuning scales gives it quite a unique look. Similar but very different from the Grundig/Telefunken/Saba sets of that period.
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Old 14th Oct 2021, 11:36 am   #3
Jan Zodiac
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Default Re: Restoration of a Neutrofon Guldsegl 5308

You are right Nigel. Actually this type of dial was not typical Danish styling in those years. A lot had a flip-up dial on top of the cabinet, or else the dial was mounted with a small distance to the front of the cabinet, giving it a "floating" appearance. So this Neutrofon has a quite unique styling. The pictures doesn't really show it, but the set is rather large. It is 65cm wide. The two small "windows" seen on each lower side on the dial, shows the tone control settings.

Regards,

Jan
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Old 14th Oct 2021, 1:54 pm   #4
turretslug
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Default Re: Restoration of a Neutrofon Guldsegl 5308

Hi Jan, thanks for the post on this unusual radio. What a lovely set, it must sound superb with good quality broadcasts. That looks to have been a challenging overhaul with all those suspect capacitors and resistors, I imagine the AF amp section with all its tone circuitry must have been quite awkward. It's always interesting to see some Continental luxury sets as a comparison to what was produced by the UK makers. Also interesting to see that they used a UCH81 (?) as VHF/FM mixer/oscillator as well as in the AM section, there seems to have been something of a transition period in early VHF/FM sets where various approaches were tried.

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Old 14th Oct 2021, 2:09 pm   #5
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Default Re: Restoration of a Neutrofon Guldsegl 5308

Fantastic! You guys seemed to be well ahead of the Brits with regard to broadcast FM reception ......
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Old 16th Oct 2021, 10:19 pm   #6
Jan Zodiac
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Default Re: Restoration of a Neutrofon Guldsegl 5308

It was indeed a bit of a challenge, replacing all the bad capacitors and resistors. Even if the chassis is quite large, it is still pretty cramped underneath.

I'm not aware of when FM was introduced in the UK, but here it was along the introduction of tv. From '51 or '52, experimental broadcasts (I think 1 hour a few evenings of the week) was carried out in the capitol city until '55 where "real" broadcasting was introduced. It's the same with FM. FM experiments were made already in the early 40's but on a lower frequency, I think around 40MHz. Neutrofon actually build a complete prototype chassis of an FM receiver along those experiments. I think because of the war it was all laid to rest. But this has surely helped the company gain some knowledge on the technology, which again helped them become one of the companies to first introduce FM on their early 50's models.
And yes, the mixer/osc is an UCH81 on both AM and FM section.

In my part of the country, near the German border, it was possible to receive German broadcasts, both tv and FM. So in this part of the country more sets was fitted with FM units, as was the case in and around the capitol city. Same goes for the sale of tv sets, although only occasionally it was possible to receive German tv. I think the transmitter was in Hamburg, which made it difficult to receive with proper signal.

I find it fascinating that still relatively many early TV sets were sold, although it was not until 1957 a local transmitter was build, both here in the southern part of Jutland and in Flensburg, North Germany. By that time the early sets were more or less outdated, compared to 1957 models. And most of the early sets were only 14" as well. This led to the early sets often did not see a lot of use, and was widely replaced with larger models when the new transmitter was in operation. On these old 14" sets, I have often found that the CRT's measured almost like new because of this.

Regards,

Jan
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Old 19th Oct 2021, 3:08 pm   #7
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Default Re: Restoration of a Neutrofon Guldsegl 5308

Great write-up!
I have many old TV set from Denmark.
Denmark is a very interesting country because they had more than 20 companies building TV sets in the 50s/60s!
Just that for a so small country with no export interests.

I love their style, just my unusual rare 1952 console TV set from Ruhe is great in style.
Very rare is my 1958 Derby from a very smal company.

I just read "Guldsegl", like my "oven"-TV set (17"), so I was very interested in your lines.

Regards,
German Dalek
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Old 19th Oct 2021, 4:44 pm   #8
Jan Zodiac
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Default Re: Restoration of a Neutrofon Guldsegl 5308

Thanks Dalek,

Interesting that you have danish sets, and especially Derby and Ruhe! And yes, it is quite impressive we had so many manufacurers in the radio industry, for such a small country.

I had two of the Derby tv's, one is sold to a collector of Derby scooter. These tv's are extremely rare, and only a very few was ever produced. Derby was a company that build motor scooters, and very shortly they produced a small batch of tv's. I still have one of them left, though unrestored.

The name "Guldsegl" which would be translated into something like "Golden Seal", was also used for their tv sets, as the one you have. Those small oven shaped sets are quite handsome.
The model name was introduced the 30's, where their top of the line radio sets where given the name Guldsegl.
Before WW2, Neutrofon probably made the best receivers of all here in Denmark. I have a 1938 Guldsegl also, and that is a great performer with a beautiful copper coloured chassis.

Best regards,

Jan
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Old 20th Oct 2021, 5:41 am   #9
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Default Re: Restoration of a Neutrofon Guldsegl 5308

Hi!
Many thanks for the informations about Derby, I didn`t know that!
I have from closeby all denish companies vintage TVs!
I own one of only a few made B&O consoles of 1953!

The Neutrofon radios are very impressive because of their quality and style!
I have a beautiful Neutrofon FM-converter in a brown bakelite cabinet.

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Old 20th Oct 2021, 5:24 pm   #10
Jan Zodiac
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Default Re: Restoration of a Neutrofon Guldsegl 5308

Hello.

You are welcome. The history of Derby is quite interesting. The founder and owner, Willy Johannsen, was a spontaneous person, which meant that a lot of their products never really came past their "childhood diseases", before they were discontinued in favor of the next new thing.
He made transistor radios as well "Derby Calypso". If they where made by others and then just re-branded as Derby, I don't know. Their later tv's where not manufactured by Derby, I know that for sure. I just don't remember who made them. Maybe Herofon/Arena from Horsens.
So the only "real" Derby tv, is the type 571. I guess 1000 where made, since I never saw a serial number exceeding this. I think the one I sold had serial number 922 or something like that. The unrestored one has a much lower number.

I have one of the small FM add on's from Neutrofon also. It is called Neutrofon FM Jack. It is very well build, and I like the fact that it has a low impedance output (cathode follower + signal transformer).

Best regards,

Jan
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