19 Set restoration - Part 2: Initial Radio checks

As I mentioned previously, my 19 Set is a British MKIII one that had that had been rebuilt by REME sometime after WW2, probably in the 1950s.

These rebuilt examples are not to the original spec, having been rebuilt without the VHF 'B' set, but they do have the advantage of having been re-wired with pvc insulated wire. Original WW2 sets may have multiple faults due to crumbing rubber insulation.

My 19 Set as received..note grey colour paint

Everything on the front panel was present and correct, apart from a missing handle on the right hand side. Once the case was off, a quick inspection showed that chassis was complete and as it should be, apart from a high wattage wirewound resistor above the chassis that was obviously not original; I'll come back to this later.

On top of the chassis, adjacent to the PA valve there is a small paxolin board bolted to the chassis with a number of capacitors and resistors on. At this point I hadn't studied the manuals and the purpose of this board was not clear to me, but I did notice that one of the wires (actually the centre conductor of a bit of coax) had broken off one of the tags. It was obvious where it should go, so I soldered it back on. The mica capacitor in the photo looks like it is broken, but is actually OK.

'Broken' capacitor and detatched wire.

The 19 Set has a large number of decoupling capacitors, mostly 100nF. These appeared to be military quality (metalised foil possibly)  types.  With the older type wax paper capacitors my usual approach is to replace all on sight, but the number of capacitors in the 19 Set would have made this a very big job. Instead I just removed three of four for testing on my AVO component bridge. All were very close to their intended value with no leakage indicated, so I just popped them back in. There is a slight risk in doing this, and I may yet have to replace some if they prove to be leaky later on

I did however replace the one on the audio amplifier grid (usually referred to by restorers as 'that capacitor') and those decoupling the AGC line as these are areas where even a small amount of leakage could seriously upset things.  I also replaced all of the small number of electrolytic capacitors, which fortunately were easy to get at... which most things in a 19 set are not!

Checking resistors is easy and in most cases can be done in circuit. Some of the higher value ones had gone up in value, but most were still in tolerance. I did end up changing a few, like the 470K visible in the photo below. The green screw head is the adjusting slug of the BFO coil, which I'll come back to later.

Replaced capacitor and resistor

So far, so good; everything looked ready for a power up test.