Sensitivity Kolster Brandes FB10-15

[ChristianFletcher]

I have been working on a FB10 although it could be a FB15 as it has different internal serial numbers and doesn’t quite match any service sheet. The set has some form of wound rod antenna but I don’t think it’s a ferrite road just a paper tube. It is pulling in about three or four stations on MW not very loud, but really comes alive with a full medium wave band very active if I plug in an external antenna. I would say it performs less well than a DAC10 on its internal antenna but amazing on the external long wire.

Can anyone confirm the performance of their FB10 for me. I have restored quite a few radios now, but I always have this dilemma of not knowing whether or not a set is actually faulty or if it’s working as well as they did back in the day. I think my FB10 is a bit deaf but gaining improvement is often a diminishing return on time and money invested.

I was wondering what yard stick people employ for gauging a radio sensitive. I do have loop antennas and signal generator but it’s still not easy to maintain repeatable results. It could just be I need more practice with receiving station in my local area and there received signal strengths.

Thanks Regards Chris

[Sideband]

The FB10 is OK sensitivity-wise but it was never designed as a 'serious' radio....just a second set. I have one with a ferrite rod which is reasonably good but no better than the version with a frame aerial. I think you have to consider that there are fewer stations on MW now and it largely depends on the area you are in and what is available. It is nothing special as a design but should be able to pull in quite a lot of stations.

If yours is an FB15, it is a continental version and I have no idea how it is supposed to perform. Are you sure the ferrite rod is not missing? How about a photo or two?

[Gabe001]

David wrote a success story about this radio and also remarked that it sounds much better with an aerial plugged in.

[ChristianFletcher]

Ok I thought the Rods in these were just a paper tube ? I called my antenna a frame antenna but for clarity I think it’s a cardboard tube, however I am not certain on my alternative facts ?

Ok I will search for David post as they are always excellent.

Thanks regards Chris

[ChristianFletcher]

I have to say I’m a bit confused if this is a FB10 or 15 as i now believe that Kolster used to change design and parts almost as frequently as I change my socks. The reason I thought it was a 15 is because the plastic alignment indicator has FB15 printed on it and the chassis design doesn’t quite match either of the two service sheet. The serial number does have FB10 stamp on it.

Perhaps someone can confirm if it is a ferrite rod it doesn’t feel like a ferrite rod more like a piece of wood. The service sheet calls it a frame antenna. But it’s not a frame. I’m now preparing to believe it’s an early ferrite rod thats been mummified

The service information mentions some trimmer capacitor mounted on the tuning gang which look like two stuck up matches C20 and C22 “see picture” but my set has an additional larger trimmer capacitor but this isn’t shown in the service picture chassis layout. I think it could be C20 as it connects to S1 of the tuning selector so I’m not sure what the two match stick things are for as the service sheet identifies them as C20 and C22.

The alignment Instuctor all mentioned L13 and show this on the chassis layout. My set just has a hole where L13 should be.

I’m a bit confused! Anyone had one like this or is it another Kolster brand theory of evolution ?

[Mr 1936]

Hi

I assume the internal aerial is the horizontal cylindrical thing that at casual glance looks like a tapped wirewound dropper resistor ?

If it really is a simple air cored inductor it won't be very efficient as an aerial, as it's cross sectional area is just too small, maybe less than 1 square inch. A true frame aerial would be square or round with an area of let's say 20 square inches or more.

Alternatively, if you incorporate a ferrite rod, it concentrates the magnetic flux within the winding and considerably increases pickup. My rule of thumb is that a ferrite rod is about as effective as a frame aerial with a diameter equal to the rod's length. Ferrite rods are convenient for packaging within a radio case, and less liable to detuning by nearby metalwork, but frame aerials can work just as well.

It seems to me as though either the designers weren't too fussed about sensitivity, or someone has nicked the ferrite from inside the coil !

[ChristianFletcher]

For clarification it not just a tube former but it doesn’t feel like a solid ferrite rod so I’m not sure. I would love to know when the first ferrite rod antennas were used etc.

[ms660]

From the photo's, at first glance it could be the modified FB10, the schematic that's headed up FB10 Modified Circuit Diagram Jan 1954, R8 seems to fit the bill as regards value, size and location, the extra capacitors across the tuning gang could be because the trimmers were changed to suit the new internal antenna setup and the extra capacitors are there to increase min and max trimmer capacitance.

Lawrence.

[ChristianFletcher]

Thanks Lawrence it hadn’t really occurred to me to look for different versions of the service data but that’s a good tip.

Thanks regards Chris

[ms660]

Originally Posted by ChristianFletcher

Thanks Lawrence it hadn’t really occurred to me to look for different versions of the service data but that’s a good tip.

Thanks regards Chris

It's in the manufactures FB10 Service Data Supplement which is dated Jan 1954.

Lawrence.

[Sideband]

I have not seen that version before. Mine has a conventional ferrite rod. Another I had was fitted with a frame aerial but the performance was about the same. You are right about these sets though....KB used whatever parts were available so there are lots of variations although the basic circuit remains the same.

[ChristianFletcher]

Ok I think I have figured it out it’s a FB10/2 from 1955. I found the information on the KB website. Has a lot of great information and an interesting read. I have to say I could be looking for more of these quirky sets in the future

http://kbmuseum.org.uk/kb_service_ma..._FB10-2_kb.pdf

[ChristianFletcher]

Thanks for helpful comments from you all much appreciated

Chris

[Leon Crampin]

Neglecting valve types, which don't materially affect performance, I would group the FB10s into 3 generations: Mk 1 - frame aerial with LW loading coil; Mk 2 - fat short ferrite rod aerial as illustrated above; Mk 3 - long thin ferrite rod.

Each iteration improved performance and I have recently restored a Mk 3. I would rate the set as being above average in sensitivity after careful alignment, although the tracking and LW dial accuracy is rather poor. It out-performs a DAC90A on sensitivity but the Bush set has better audio and will track almost perfectly.

The FB10 scores well however by having a separate winding on the rod for the external aerial input. Unlike the idiotic bottom coupled arrangement used by Bush on their later sets (eg. VHF61), the external aerial input works really well on this set and the centrally positioned winding for it on the rod provides a really useful result.

My FB10 was a basket case with a snapped rod and an IF transformer with broken cores and stripped adjuster threads. I'm very pleased with its performance after restoration.

Leon.

If you have any doubts about the presence of ferrite in the heavily waxed aerial coil, apply a magnet. All the dial backing sheets I have seen are marked FB15 for some reason. This is even shown on the KB service sheet. Mine was missing, but a plastic 4 pint milk container made a perfect substitute.

[ChristianFletcher]

Thanks Leon

I think I started the tread by saying I thought my set is a bit deaf on its internal ferrite rod but when I plug in my long wire it really comes alive and the MW band is full. This radio is for a friend and I will be sorry to give it back. But I think I will be searching ebay for one of my own in the near future. Thanks regards Chris

[crackle]

Just to clarify, if there was a KB FB15 model then it would have been an AC/DC type with dropper resistors instead of the auto transformer. After the war KB had a model numbering system that was pretty predictable.
I am not aware of a FB15 but there are FB15T models around and there is also a FB15TA model listed in the Radio Museum.

The FB15T models were for export mainly outside of Europe to places like the Far East and the Americas, they had no LW band, but were SW as well as the normal MW.

The dial backing will probably also be marked on its reverse with FB11T. The FB11T set was a battery only version and I have never seen one in the flesh. It was also intended for export having no LW but just SW and MW.

The FB10 came with the frame and fat stubby ferrite type aerials, whereas the FB10/2 is described in the service information as having a 5/16th inch ferrite rod which was a bit longer.
However as already noted KB did tend to change things during a models production run and the cut of for the new model was not always definite.

Going back to the original post, the FB10 should perform adequately in good signal areas using its built in frame or ferrite rod antennas.



Mike

[ChristianFletcher]

I have made a worthwhile increase in sensitivity regarding the IF alignment. I’m a bit uncertain about the alignment of the HF end of the band. It Uses Trimmer capacitors T2 and T3 for locals oscillator and tuning section. They look like match sticks stuck up from the gang of the tuning capacitor. Do these things have a name I may have called them something like Gimmick wires in the past ?

What’s the best way to adjust them. I’m considering leaving them well alone they look like the kind of thing that will break off as soon as look at them. I think the winding is meant to slide up and down the central wire shaft but nothing wants to move with gentle persuasion?

Thanks for the reply Mike. I think I probably need to spend a little bit more time finding out what is normal for me regards MW propagation in my locality


Thanks regards Chris

[crackle]

Those trimmers on the tuning gang comprise of a thin enabled wire wound round a thicker centre conductor. I would suggest leaving them alone.
Mike

[ChristianFletcher]

Thanks Mike

I will be follow your sage advice. The HF end was spot on the mark when I checked it so I’m guessing these are very stable.

Thanks Regards Chris

[ChristianFletcher]

https://youtu.be/4PvTBwzOsCg

Well this is how it turned out. I think I am going to leave myself the teacher comment "Could do better" C-

Thanks Regards Chris