KB 286 "Kolstar", 1932 superhet radio

[crackle]

This radio has been lurking in my garage for a couple of years now, it is a fairly substantial 7 valve, very early superhet radio from 1932, and it came complete with 2 plug in SW coils.

Valvebloke very kindly dragged it across London on public transport and foot, and delivered it to Pppenguins get-together for me back in, I think, 2013.

Now I have it on the work bench it is obvious that somebody has had a go at it and abandoned their efforts half way through, probably because they found the speaker energising coil was open circuit. (oh no not another one ) Well I am pretty certain the duff Rola speaker which came with the radio would not have been fitted by KB anyway.

Tests made so far;
Speaker energising coil is open circuit.
The mains transformer seems to test OK, 2x 4 volt windings and is giving a very healthy 380 volts on each half the HT winding.
The choke also has a continuous winding.\
The OP transformer windings test as continuous.
The inter-valve AF transformer windings also test continuous.
The 4v dial lamp filament is OK.
And all 7 valve heaters are continuous.

The capacitor block, I assume to be electrolytic, is a 4 x 4 x 3 inch lump, it has had some wires cropped and various other capacitors have been half heartedly fitted around it. It is marked as 12.1MF Working 250 VDC and has I believe 2x 4uF 2x 2uF and a 0.1uF.

I am going to have to cut the bottom off this block to replace the contents. But something which puzzles me is, it is marked as only 250vDC, and I would have thought this was rather low considering the HT windings are giving 380 volts.

There is also another 8uF capacitor with a screw thread base (missing, been replaced with a smaller one from the 50's) which fits onto the shelf for mounting the speaker,

which I would like to source a replacement for, so I can re-stuff it. I an pretty certain that the missing capacitor should look like one of these.

The Bakelite on/off switch mounted on the side of the radio has had a whack at sometime in the past and has half the front missing.

There is a ganged potentiometer listed as 500k and 15k it seems to be working of a sort but is measuring 1M and somewhere between 100k and 25k, so it looks like the rivets will need to be drilled out and the insides given a service.

The underside of the chassis looks a lot more original and untouched.

I will put a post in the wanted section for the screw base 8uF cap and Bakelite on/off switch.

Mike

[Cathovisor]

That is going to be a very interesting restoration, Mike; I rather like early superhets and this one seems a cut above the usual, and unusual too with its plug-in coils.

I look forward to reading more. By the way, I would imagine the caps in that block are actually all paper types. It would explain the low working voltages; there are large (2µF?) paper caps inside the infamous EMI block used on the 262/440 and similar models.

[crackle]

Mike, I think you are right about the capacitor block.
Yes, when I got this radio I put it to one side as I felt it was rather historically important as an early superhet. But looking at it closely now there has been a fair bit, of what looks like to me, bodging around the PSU. I hope to get this corrected and the radio working again.

The radio does have some interesting features though;
Many of the original resistors are still very close to tolerance, I have not checked the rest of the "stand up" metal can type paper caps as yet, but suspect they will probably need changing/stuffing.
The double potentiometer has one track to control the aerial input and the other track controls the input to the last IF amp stage.
It has the usual safety cut out that KB fitted during this period, so when the back is removed the radio chassis is isolated from the mains. It is reconnected by fitting an standard un-wired 5 amp plug into the socket, simple yet effective. The back is missing from this radio, but the little 2 pin plug is there fitted in the socket. I will have to make a new back.
I can see no identification marking on the radio, not even on the dial, they must have all been on the Back panel. But the SW coils are marked Kolster Brandes.
The radio is fitted with 2 speaker "telephone" jacks, one disconnects the internal speaker and the other enables both internal and external to work together.
There is also a jack for gramophone input, although this is after the last IF stage and hence there is no volume control as far as I can see, great for those wild parties of the 30's. Inserting a jack disconnects the radio signal from the AF stages.
The tuning dial is calibrated with the normal ranges for medium and long waves but in kilohertz.
The IF frequency is very low at 114 kHz.
Reading through the service notes ( available on Paul Stennings web site and CD) for this radio, they refer to "Parker Kalon" screws, I assume this was a term for the early type of self tapping screw used.
Tomorrow I am going to try and gain access to the capacitor block. It would appear that it is soldered together, but I dont fancy the idea of trying to unsolder all the sides, it will destroy the painted finish, so the plan is to use a disc cutter to cut around the inside of the bottom, leaving the mounting flanges still soldered to the top and sides.
I will then plan to mount the new capacitors on tag strips fitted to the chassis and use the old capacitor block case just as a cover. That way anyone can easily get to the capacitors should they need to in the future..
Mike

[Cathovisor]

Interesting - I always thought of P-K screws as being a post-war thing: evidently not!

[crackle]

Yesterday I was sure I counted 2x 4uF and 2x 2uF capacitors together with the missing 8uF one.
But today I cant see a second 4uF one on the circuit.
Anyway I have ordered a quantity of 2.2 and 4.7 uf 630 volt polyester capacitors to fit in the big capacitor block.

Today I opened up the capacitor block. I used a blow lamp in the end, concentrated on the base where it did not matter scorching the paint. Finely I managed to prise it off, along with a large quantity of molten black pitch.
I screwed a couple of 3 inch screws into the insides of the block so I could pull on these with pliers.
I then used a hear gun carefully around the sides and on the inside to soften the pitch just enough to get the contents out, which were paper caps by the way.

Next job is test/repair the rest of the paper caps and the pentode bias electrolytic, 6 of them in all.
The rest of the caps look like mica types so I will trust them as being good, for now.
I may also start on polishing the cabinet.
Mike

[Katie Bush]

Hi Mike,

Is that the set I collected from the guy in Driffield? The one with the plug in coils.....

If it is, I never saw it whilst it was here, but I know it was a heavy old beast, and VB took it from here on its Southern jaunt.. If it is indeed that set, then it looks like and interesting, even if daunting, set to tangle with.

Marion

[crackle]

Do you know Marion I think you are correct, I do apologise for forgetting. Thanks very much for collecting it and helping it on its way to me. I have a note to say it was bought on 29/11/13. I normally make a better note of who helps me collect a set, mainly because sometimes I actually forget all about them, then suddenly get a reminder that they will be meeting me at Harpenden or something.

I had a bit of a minor disaster today. I decided to take the plunge and remove the torn speaker cloth to see if it could be cleaned and repositioned to hide the tears. It came off the baffle easily enough when I dabbed it with a wet cloth. Then I decided to see if the brown stain could be removed so sprayed it with kitchen cleaner and gently wafted it around in a sink of warm water.
Quite a lot of brown stain came of but so did the gold coloured threads where the brown muck had been.

I only decided to do this as a last resort to see it it would clean up because I had one more piece of the dark gold/bronze coloured vintage cloth to use as a replacement, just as well. I dont know why I think I can clean up old speaker cloth, it never seems to work, unless it is Tygan weave.

I have been formulating a plan for making a new TCC "wet" electrolytic should my wanted thread produce no results. More about that when I have got all the bits assembled.

Here is the new circuit / tag board for the capacitors (back left), the original capacitor block case (front left) will sit neatly over the board.

Mike

[crackle]

While I was waiting for the replacement capacitors to arrive, I started to think about fabricating a replacement "wet" electrolytic.
How difficult can it be, if they can do it in 1932 I am sure I can come up with a suitable replacement.

First get hold of a 10mm pipe compression coupling.
Some stout copper wire.
A length of threaded 2BA brass rod, washers and nuts.

Drill a hole in the side of the compression fitting, and a hole in the end of the threaded rod. Solder the copper support wires into each of these.
A length of scrap 30mm plastic pipe, the outside diameter of this is about 35mm.
Epoxy filler, (car filler may do, but not as strong)

Wax the inside of the 30mm pipe so the epoxy fill er does not stick to it.
Make a jig to support the brass fitting and the plastic pipe. Carefully and slowly drizzle the epoxy filler into the bottom of the plastic pipe so it runs around the brass fitting and allowing air to escape..

The lid of a CIF bathroom mousse spray.

Cut out a circle from the centre of the Cif cap and sand/file to fit the tube then glue with superglue.
Make a new Label.

tcc cap label.jpg (33.29 KiB) Viewed 4609 times

Paint the tube silver, and stain the label to suit with a wet tea bag.

The label seen in this photo is a temporary one, I will reprint it on a laser printer as inkjet ink runs.

Also here are the new insides of the main capacitor block.

Bought from EBay seller Ecl80, they arrived the next day.

Mike

[Michael Watterson]

Gorgeous replication!

[Terrykc]

Excellent work, Mike!

The label seen in this photo is a temporary one, I will reprint it on a laser printer as inkjet ink runs.

Good - you can correct the typo at the same time! (CONDESER)

[Cathovisor]

I have to echo Michael's comment - that is an excellent repro of the condenser.

[crackle]

Oh what a wally, I will have to steam the label off now, good job I only used Pritt stick.
The recap has been done, only the metal can waxed paper ones have been "modernised". What a messy job,
I am not sure if it is better to chip bitumen out cold or heat it to let it run out, both methods are about as messy as each other. I have little black specks all over the vinyl floor in the workshop where tiny chips have dropped.
Now waiting for a couple of wirewound resistors to go in the PSU shelf.

I bought a HP Laserjet MFP printer fax scanner thing on Sunday for a bargain £8. The printer has a web page interface for configuration and management and it shows it has only printed just over 200 pages in total. It claims to be "wireless" but as far as I can see it is only wireless once it is connected by cable to the wireless router. At least Gill can now print from her iphone.
Off to print another label with an extra "n" in it.
The scan interface on the MFP is even worse than my old 15 year old HP scanner and it is twice as slow.

Mike

[crackle]

Here is the new label, and condenser fitted to the oak speaker shelf, ready to go back into the radio. The print on this label is now nice and sharp after its bath in a hot saucer of tea.

The speaker transformer on the left of this photo is really on its last legs. It is working with a sensible resistance showing on the primary but one of the stranded wires has frayed where it enters the Bakelite bobbin, and is hanging on by a single strand, no chance of soldering it. I have immobilise it with a blob of glue over the broken strands to hold it tight to the Bakelite. Fingers crossed.

Mike

p.s. thanks for noticing and letting me know about my bob boo Terry.

[crackle]

Out of the 5 valves with external screening on the envelopes only 1 had any continuity to the cathode pin.
One appeared to have had no screen wire fitted even though 2 more identical ones did.
Repairing the screen connection on the valves was easy with most of them, gently scrape the screening coating to get a good contact then paint on silver loaded conducting paint over the screen wire and the screen coating.

The connection of the screen wire with the screen coating had been broken, here the old tarred tape was cut away to expose the original joint and conducting paint used to remake the joint.

But the valve with no screen wire it was more of a problem.
Normally I would have just run a wire wrapped around the base of the valve, externally across the valve base and soldered onto the centre pin. However in this case the valve base sits flush onto the metal chassis and any exposed wire would risk the cathode being shorted to chassis.

Here the valve can be seen resting on the chassis.

My solution was to drill a small hole through the valve base to take the wire in close to the centre pin, this making it impossible for it to touch the chassis.

A new screen wire was fitted so that it bypassed the corner of the valve base where it could have shorted to chassis.

Mike

[crackle]

I got fed up with looking at the very obvious repair to the metalising on the absolutely filthy MSG/HA valves and I wanted to disguise the silver repairs to the metallising connections. I tried unsuccessfully to match the colour. But when I removed another "Cossor" label I found that the original colour was a grey metallic finish. I had some Humbrol silver which had large silver flakes and added a few drips of brown, green and black till it looked the correct shade. Oddly, when the paint dried it went a much lighter colour, but it still looks and feels fairly authentic with that rough gritty feel of the metallising.
I am happy with it any way.

Here are some photos of the "more or less" finished chassis. I say more or less because I am still waiting for the 10W 33k Welwyn resistor I bought for the PSU. The underside looks roughly original, all the capacitor blocks have been restuffed with new caps and sealed up again with a layer of bitumen. (the dog bone resistor in the top left of the chassis does not look original, I suspect an replacement at sometime)

the left hand half of the chassis

the right hand half of the chassis

The worst of the rust spots were scraped and treated and then the top of the chassis was hand painted by brush to match the original.
Because the metal capacitor box got a bit stained and dirty during my attempts to melt the interior muck, I resprayed it green like the original. Then I realised I didn't really need to because it is hidden under the PSU cover anyway, but at least it looks like a new capacitor block now..

The "new" capacitor block in the top left of the chassis

The PSU cover was given a good rub down to remove the rust and a spray with silver coloured paint to try and match the original.

Here is the chassis complete with top cover of the PSU

I made a slight alteration to the way the PSU cover was fitted. Originally the PSU top cover was bolted together with the bottom shelf to the main chassis through 2 oak spacers, requiring the whole heavy PSU assembly to be removed to get at the components inside. I simply bolted the metal PSU tray to the spacers and main chassis, and then drilled 2 holes through the top cover flange to fit 2 self tapping screws to fix it to the bottom tray. Now the cover can be taken off by just undoing 2 screws.
Not original but I thought a worthwhile improvement, which is not noticeable.
I suspect there was a cover to go over over the rectangular hole in the front of the PSU. but I will not make one to replace the lost one, so the ventilation is improved.

Mike

p.s. When did dog bone resistors come out?

[Michael Watterson]

Gosh, it looks new!

[crackle]

I am Disappointed with water based wood stain.
After 4 days work rubbing down and patching up the chips and scratches on the cabinet using water based wood stain, I have now found that it wrinkles and comes off when a top coat of a spirit based varnish is applied. I have now rubbed off all the stain with a cloth dampened with white spirit ready to start again.
The mouldings around the arch and down the corners and sides of the cabinet are made from beech wood, the side panels of the cabinet are also beech ply so are naturally a very light colour. The top and front have a decorative veneer, I cant decide if it is mahogany or not.
There are 2 problems as I see it with water based stain. (1.) it raises the grain again once you have carefully finally rubbed down with 600 grit. (2.) it dissolves when dry, and it does not rub down very easily, Oh that's three then.
I will have to go back to making my own stained lacquer, using diluted varnish (up to 1:1 depending on the amount of wood dye), spirit based wood dye, and black and brown paint to get the amount of opaqueness right for the non decorative wood and ply to disguise the poor grain. It seemed to work well on some other cabinets.
The trouble is spirit based dye is almost impossible to get now.
Looking around the web it appears that Liberon describe their product as Spirit based, but they do give a warning that it is not compatible with spirit based products.

Maybe it is wrong to look for "spirit" based dyes, what I am after is white spirit based dyes.
Mike

[Cathovisor]

It was once recommended to me that I use 'aniline' dyes (as supplied for stage use) for this purpose as their intensity means very little need be used once dissolved in meths.

See https://www.brodies.net/index.php/sceni ... e-dye.html

[Terrykc]

What an excellent job you've done there, Mike.

... When did dog bone resistors come out?

I would suspect at the same time as colour coding as they seem ideal for the original body-tip-spot method.

Assuming that the clay/carbon mix (or what ever it was) could be controlled to keep variations within one decade, measure each unit to find out what the first digit is, then dip in appropriate pot of paint to give the body colour and hang out to dry.

Separate the brown ones for further testing to separate 10 and 15 values - assuming an E6 range, there are no other values having the same leading digit - then dip one end into appropriate paint pot and leave to dry.

Finally, add the decade spot by hand.

Would it be unreasonable for the increasing demand for components as the wireless became a 'must have' item to have inspired mass production component methods like this by 1932?

[crackle]

I had been thinking of trying to repair the broken on/off switch with epoxy. Then Michael W suggested a method which seemed a good idea.
The photos will probably speak for themselves. But basically first I gave the broken edge of the switch a good scrub with meths and a toothbrush. I filled the space with wax, being very careful to not get wax on the broken edge. Then shaped it to what I thought would be the inside shape of the epoxy. Then coated with epoxy, the epoxy I use is very slow curing and it tended to drip, so for the next 3 hours whilst I watched TV. I had to turn and rotate the switch to get the epoxy to sink back to a decent shape.
When the epoxy had become stable but still soft I pressed a nut which I had cut in half into the edge to help make a bit of thread that was missing.
This morning it was hard enough to stick the soldering iron tip into the bottom of the switch to melt out the wax, and file the epoxy into shape. It didn't go exactly to plan as the new epoxy piece came away cleanly from the switch so the majority of the filing had to be done carefully whilst I held the tiny piece in my fingers. it took quite a bit of shaping the outside curves and slot to get it to a stage where the switch lever could be operated.
When that was finished I cleaned it all again in white spirit and then meths, and used superglue to fix the little piece bock on.

[sideband]

...some people are able to do things like that.......

Great job Mike. Incidentally that old switch has actually got European approval marks on it.....

[BriancuffRest In Peace]

That's really super Mike. The job overall is a credit to your patience and skill.

[Refugee]

That is a fiddly job. It reminds me of a Bakelite hinge repair I did a couple of years ago.

[crackle]

The radio saw some mains today, probably the first time for 30 or 50 years, judging by the 5 amp 2 pin plug that was still attached to the cloth mains lead.
I started of with the variac at about 150v and lamp limiter switched in. Every thing looked good and the HT was building nicely to 200 volts. Switched out the lamp limiter and turned up the variac. Loads of HT but an absolutely dead radio. Ah, plug an aerial in I thought, still nothing, the OP valve heaters looked very dark.
Then I realised I had not tightened up all the screws on the connecting block to the PSU, it was still temporally held on with just the 2 end screws, soon resolved.
Switched on again and was soon greeted with a deafening and rather distorted BBC Essex. I turned the volume down and it was very good quality sound.
I need to look at the volume control, it tends to be rather all or nothing, and the wave change switch, as MW works better with the switch in mid position. LW works fine with quite a few foreign stations and R4.

On with the cabinet restoration.

Mike

[crackle]

It looks as if the volume pot is kaput. I will have to look for an alternative, and I will need to get 2 identical ganged pots one 500k and one 15k, although that one will probably have to be a 22k pot, then hopefully they can be used to make up the unique one required for this radio.
The voltages all look reasonable, all are just slightly higher than expected, possibly because I have used polyester caps to replace all the paper and wax ones and even the main smoothing electrolytic. But V5 is down on anode voltage, not yet discovered why.

I cant see anything wrong with the wave change switch, so not sure yet why it works better midway between MW & LW, all contacts are operating correctly.

Mike