K-B Toaster restoration

[kestrelmusic]

The kind gentleman who gave this set to me presented me with quite a challenge! I like these quirky little sets, though they are an exercise in getting a 4+R mains superhet into the smallest possible space.

In the first place, it was coated internally with the usual mixture of coal soot and tobacco tar. I stripped the whole of the top of the chassis, removing the frame aerial and the output Tx. To my surprise, both of the transformers were good. I tested the valves separately; I know the “received wisdom” is that you should test the valves in the set, but that does assume that everything else is probably OK. Chassis top cleaned, de-rusted and painted to match the original.

The smoothing caps were knackered, one with zero capacitance and one virtually a short circuit. Easily enough replaced, but you have to find one that fits in between the tuning gang and the LT/HT transformer.

The valves all tested good except the 6BA6 IF bottle. As I didn't have one of these available I replaced it with a Russian 6K4P which is pretty similar except that the cathode and G3 are connected internally. That needed slight rewiring of the base.

The tuning gang was very rough with some corrosion on the plates. The bearings were locked solid too. A delicate application of Plus-Gas and an overnight wait freed them enough to get them moving with a little gentle persuasion. A new drive cord was needed as the old one was knackered. These FB10s are devils to get a new drive cord fitted, but it’s much easier to do if the output Tx and frame aerial are removed first.

All the wax caps came out and were replaced, then the output Tx put back. The primary leads on these are incredibly fragile, so I put a tiny slip of Paxolin on top and soldered them to tags on that, so that if I needed to remove it again it would reduce the risk of breaking them. Rewinding transformers is not my favourite occupation!

One of the contact strips on the wavechange switch had come loose. Fortunately I had a spare. Changing that revealed that the LW padder was open circuit, so that also needed replacing.
The AF stages worked nicely the first time but as soon as I put in the IF valve it started getting unstable. In the end I tracked it down to excessive gain in the IF stage. Substitution of the 47R and 0.05uF cathode resistor and capacitor with 470R and 0.1uF fixed that. IF alignment (unusually, 422kc/s) was pretty close.

The speaker was very rough due to corrosion on the pole-piece and coil. I’ve had some success in the past by turning down the pole-piece on the lathe, but it obviously weakens the magnetic field. In this case I replaced it with a modern one. The problem with this was that the magnet was much larger than the original and collided with the HT capacitor. In the end I removed it and substituted two modern ones slotted in under the deck. Not authentic, but it works!

The dial was missing so I printed one on an acetate sheet, attached it to a piece of glass and fitted it. Also replaced the speaker cloth.
Finally, alignment. It was pretty close. Back into the case. Now onto the next one...

[vinrads]

Well done! another one back from the dead, is the case in original paint ? Mick.

[Sideband]

When you consider how simple these sets are (circuit-wise) they work remarkably well. Yours is the earlier version with the frame aerial. I have a slightly later version with the ferrite rod. There are other minor changes as well including a 6BW6 output valve rather than a 6V6

[Phil G4SPZ]

A thoroughly comprehensive restoration! I’m particularly impressed with the new dial, and this must have taken some time to make, yet you gloss over it in just a few words! I’d like to know how you did it - did you photograph a good dial? How did you achieve the clear apertures?

I restored my FB10 a decade ago and it has been used daily (in the kitchen) ever since. Great little radios.