One valve c.1923 radio

This one I found on-line along with another old radio, a 2 valve British General radio that I will restore soon. This one was in the worst state, all the rubber had fallen away form the wiring and the mounting arrangement inside the box was badly laid-out. So I removed all components, cleaned checked and repaired them, found a similar circuit on-line and re assembled all components on the rear of the Bakelite front, this way it's easier to service. The 2 coil assembly socket was fitted on the side and I fitted that between the aerial and earth terminals and used the fixing bots to hold the valve base on the rear.

Seen above as 'R' the grid leak resistor was open circuit, so as a fix I soldered a 1.5 megaohm resistor out-of-sight on it's rear. The tuning capacitor read 660 pf fully closed and the veins took quite a while to free-up from shorting out using bolts on the side. The valve, a Mullard PM1 was working fine to my suppose and the two tuning coils were missing. I found a pair for £5 on-line (had to repair them too) All nuts and bolts on components were cleaned with a modelers drill/polish kit (I inherited from my Pops, he make model galleons with it).
L1 is the aerial receiving coil, L2 is the feedback of reactance coil. C2 is 220pf and C3 is  fitted to remove any carrier signal from the output, but most headphone cables have the same effect, around 200pf will do (0.0002 uF in old money. Headphones can be any around 1-2k ohms. The HT battery is 6 x PP3's in series, giving around 55 volt and 2 x 1.5v batteries in series with a 100 ohm pot to reduce it to 2 volts. The reason the pot was used is so when the original accumulator battery was going flat you could turn up the voltage a little. Be careful though because 3v+ can quickly destroy a 2v heater winding, and on a 100 year old valve you don't need to do that, so keep a test meter to hand.

I mounted the valve base horizontally as the valve would have hit the bottom of the box using a 'L' shaped brass bracket bolted to the above (outside) coil socket assembly. The bolt holding the 200pf capacitor was also part of the above fixing, this way saves the need for unsightly bolts on the front panel. The Grid leak tubular type component has it's own fixing fitted to the capacitor. The wiring was done with 18 SWG gauge silver coated copper wire, it bends easily into shape and looks from the period.

After touching-up holes and a couple of coats of varnish

I filled the holes left in the side (after removing coil socket) with quick drying wood filler and sanded smooth, then with special wood touch-up felt tip pens of made the holes the same colour as the cabinet, taking care to highlight wood grain where needed with a pencil. This was then varnished along with a repair I did with removed hinges and lock fitting, as you can see it's hard to see the old holes. I didn't over polish cabinet otherwise it starts to look new.

I fitted the LT (or heater batteries B1) to the side of the tuning capacitor using one of the fixing bolts through the holder base. The HT battery (B2) was made by cutting a box to the size of the batteries when they were clipped into each other by their own terminals, no need to buy expensive clip kits when they have their own. I cut a PP3 terminal in 1/2 and attached that to the two free battery terminals. The card box was then stuck to the rear of the top with two sided tape, when it is fitted in the box it is held more Secure.

6 x PP3 batteries in a home made card box and glued inside lid. The triode valves of the 1920's will work as low as 30 volts to the anode and will draw about 15 mA, so last a long time. The heater battery no so good, 20's vales drew around 1/4 amp from them and the very early ones was around 3/4 amp. The run down home build radio radios can be found for very little money, as repairmen want the circuit, most of these kit ones were made using magazine articles and blue prints from the day. I have collected quite a few of them and period books, they all help with the constructors feel at the time, it's great to re-tred the footpath of an enthusiast of a hundred years ago. Go on you know you'll enjoy it like me. (email me if you need help)