KN Products 1930s Radio - Car Boot find

[Electronpusher0]

Attached are some photos of a recent car boot find.
It looks like a battery portable radio of 1930s vintage.

It has a 5 valve line up, most of the markings are rubbed out but this what I can read.
Left to right looking from the front
1 ?
2 Mullard 204A
3 Osram May 1964
4 U14 - Made and Patented in England
5 ? - The bottom of the glass has been taped to the bakelite base.

The two knobs are marked Tuner and Volume and are both geared multiturn (the inner turns rapidly and the graduated outer turns slowly).

There is a label holder screwed in the centre that has a label handwritten on a Card No8 for logging stations received. The handwriting says "KN Radio Supply Co, 49A Park Rd, W Dulwich."

The lid seems to contain a speaker with a central knob, not sure what for, I have not investigated yet. There is a switch in the lid marked Long, Off, Short.
There are 3 wires between the lid and the valve compartment on each side. On the right hand side one of the wires is loose, I will have to determine where it goes.
There seem to be 2 sockets in the lid also, probably aerial and earth?

There are marked leads with plugs in the rear of the base in what I assume is the battery compartment under a removable lid.
They are marked:
HT+1
HT+2 (The number 2 has been scratched out)
Bias -1
Bias -2
Bias +
LT+
plus two other leads without plugs and unmarked. (HT- and LT-?)
The wires are all extremely fragile as the rubber has hardened.

The hinges catches and metal corners are rusty and will need blasting and re-plating or replacing, the fabric is in pretty good nick.

I am putting it aside at the moment until time permits me to do a proper restoration.

Peter

[Electronpusher0]

Attached is a few more photos
Peter

[vinrads]

Nice find Peter, do you intend to make a mains power supply? When you get round to restoring it the first thing I would check is the speaker continuity, also the inter stage transformer if it has one. Good luck with it, if you are not sure regarding the connections and voltages ask on here.

Mick.

[Electronpusher0]

Hi Mick,
Ultimately I would like to run it on batteries but will almost certainly run it on a combination of power supplies while testing.
Any help with the likely voltages would be appreciated.
Also does anyone know what the plating on the hinges, catches and corners would have been? Chrome, Nickel?

Peter

Peter

[Nickthedentist]

69A Park Road is just round the corner from Gerry's!

[crackle]

Most of these radios will work on a 120v dry HT battery with various tappings, and a wet 2v accumulator, with a variety of grid bias voltages..
You can probably compare with any of the other many suitcase portables from that time.
Here is a circuit for the KB 146 portable which I have marked up with the various voltages.
http://www.kbmuseum.org.uk/kb_servic.../KB_156_ME.pdf

Mike

[Electronpusher0]

Thanks Mike, that gives a good starting point.
I intend tracing the circuit diagram first and the circuit you posted gives me a good idea what to expect.

Peter

[G6Tanuki]

The knob in the centre of the speaker suggests it is one of the old 'reed' type speakers (like an overgrown earpiece!) rather than a moving-coil. The knob is used to adjust the position/tension of the reed with respect to the coils/pole-pieces.

[Ian B]

I would say the metal fittings would almost certainly have been nickel plated.

Ian Blackbourn

[Paul_RK]

A nice find indeed. Its general appearance and the numerical rather than wavelength markings on the controls have me guessing it to be a late '20s rather than '30s set. I don't think U14 has been used for anything other than a full-wave rectifier, which wouldn't of course belong there and makes me wonder how many of the present valves are whatever came to hand to fill the sockets. It looks the type of set that may just have used four similar HF triodes followed by an LF one.

Paul

[PJL]

Agreed, looks like a random selection of valves. I would expect it to use the typical 2V valves of the period (Mullard PM series) unless someone has made circuit changes.

[Electronpusher0]

Oh dear, when I got it I was congratulating myself on the fact that the valves were all there.
Taking another look I am sure that you are right, in at least one case the socket is 4 pin but a 5 pin valve has been fitted with the centre pin just loose in the hole in the middle of the socket.
I will have to trace the circuit and come back to the forum for suggestions as to which valves to try and get and fit.

Peter

[Paul_RK]

If I'm on the right track, four Mullard PM1HF and a PM2 would fit the bill, as in my 1927 Pye 555:

https://www.vintage-radio.net/forum/...0&d=1187011203

And probably quite similar supply arrangements, except that set has three GB- connections.

A great many 2 volt battery triodes used in such sets are fairly closely equivalent, it was fully expected that valves from different manufacturers might be used, and they were available from a good few smaller companies as well as from the leading ones.

Paul

[PJL]

This looks like an all triode set so it would need a valve line up of something like this https://www.radiomuseum.org/r/aeonic...ortable_v.html

[deliverance]

A nice find the restoration will be interesting .

[Electronpusher0]

Originally Posted by PJL

This looks like an all triode set so it would need a valve line up of something like this https://www.radiomuseum.org/r/aeonic...ortable_v.html

Thanks for the link, my set looks very similar indeed to that one.
I said in my initial post that I would be putting it aside until time permits a restoration but I feel it moving up the priority list...........

Peter

[julie_m]

You can make up a HT battery using 9V smoke alarm batteries wired in series (7 for 63V, 10 for 90V or 13 for 117V) and a grid bias battery using six 1.5V AAA or AA cells in series, with the junctions between each pair of cells brought out to a terminal to give options of 1.5, 3, 4.5, 6, 7.5 or 9V.

If you can't get hold of a suitable 2V lead-acid cell and charger, you could use a pair of D cells with a series resistor to drop the excess voltage. You would need to know the filament currents of the valves to calculate the value. Add up the total current, call this I, and use R=V/I to work out the value of resistor that would pass this many amps with one volt (= the difference between the 3V from the battery and the 2V wanted by the valves) across it. Then multiply I by the voltage across it (= 1 in this case, so the multiplication is easy) to get the power dissipated in the resistor, and choose the nearest preferred value at the next power rating up.

[Electronpusher0]

Thanks Julie,
I have built replacement batteries type AD35 and B126 for my Vidor Lady Anne before but have never needed a grid bias battery so your advice is useful.

I am hoping to find an old glass 2v accumulator to rebuild. I have found a Varley sealed lead acid battery type V-60 on ebay type which looks like it could be opened and re-stuffed with a 2V cell but this dates from the late 40s or 50s so is not the right period.

Who knows, maybe my local car boot will come up trumps again....

Peter

[crackle]

You still get Cyclon cells:-

https://www.ebay.co.uk/itm/223020024899?

https://www.ebay.co.uk/itm/223214435039?

Mike

[TonyDuell]

RS also stock Cyclon cells. They're not much more than the Ebay prices and I would rather get them from a supplier I trust.