[Chris55000]

Hi!

In my experience with vintage radios the worst horror, not so far mentioned on this thread, has to be "line cord".

This dreadful stuff consisted of a very fine, and very long nichrome element
as one of its leads, sold as "x ohms per foot", and makers of "midget" sets (Pilot was fond of this stuff) used it instead of droppers or barretters for the series heater circuits. The idea was simple in theory - you calculated length required by dividing the total series resistance needed by the "ohms per foot" specified to give the length in feet needed - trouble is our 200-250V supplies needed yards of the wretched stuff, and fires were not unknown because unwitting householders tried to shorten the "long wire from the set." The other lead was invariably vulcanised rubber, used for the neutral connection.

I would strongly advise anyone not to attempt to try and get a set working with this stuff under any circumstances! Inevitably there's no room in the cabinet for any type of dropping component, so the only safe way of *using*
a set of this type is either a specially-made or several transformers to give the heater-chain voltage, and you'd need 4-way mains-cable!

Apart from the fact that line cord invariably crumbled to dust with heat and age, you had to use special "three-way" line cord in order to get enough HT in UK sets which needed 170V at least as a rule, which meant only single-pole on/off switching was possible, another safety hazard.

The only safe way of dealing with a "line-cord" set is to restore it as a display item only.

Mains transformers:-

In my experience I has always found sets as far back as 1952 when minature valves started to be used to have perfectly safe transformers, assuming of course these were the "isolated type" with a HT half-wave or full wave winding, not just a heater transformer! As long as the mains switch and cable in still safe there should be no problem, but one all too common practice was to knot mains leads at the chassis entry point as proper clamps were very very rare in those days! The dangers of this were obvious - the lead would inevitably harden and crack at the knot resunting in a blue flash, bang and a black sooty inlet hole!

Transformers usually remain safe if they're not overheated due to electrolytic failures, leaky anode-to-grid couplers or shorts on dial lights! Once wax or other impregnation has stared to ooze from a mains transformer, *it is no longer safe* even if it is still running the set apparently normally.

Dropping resistors:- If the cement coating has started to flake off a heater dropper in the AC/DC type set exposing the elements, again the set should be considered no longer safe to test or attempt to use.

Aerial sockets - Before ferrite rods were introduced in the late 50s, most receivers needed external aerials with a two-pin Aerial/earth socket panel, and unless the set is *known* to have a double-wound HT transformer - don't guess! - use a series capacitor of 4700p max of the 250V Class Y type in series with each terminal, and a 2M2 VR37 resistor across the AE/E terminals to prevent static build-up, and one 4M7 VR37 between the E terminal and chassis/HT-.

Finally I mentioned earlier "barretters" - these glorified light-bulb-like devices consisted of a long tungsten filament in a glass bulb filled with hydrogen gas, and they had a marked PTC characteristic which rendered a mains voltage-tapping panel unnecessary. The problem with 'em is that they were fragile, any bump or dropping the set invariably fractured the filament! More to the point, they're totally extinct today - again, a set using one probably wouldn't have room for anything else!

"Capacitor droppers" - *DON'T!!!* I don't believe there's any type of paper/polyester capacitor on the market that will withstand a 150mA-250mA sustained current flow to run heaters in an old radio.

Again, I would agree with other chap's postings that it isn't safe to use a PAT tester on an old radio - you *can't* use one on a "universal set" and the winding insulation (primary to core) of even isolated transformers may not withstand the test voltage.

HT battery replacement for All-Dry sets - the Kit Radio Company's product is really the only feasable and safe way to do it if you want to make the set truly "portable". Whilst you can try stringing 10 PP3s in series, those from car-boot sales may not last very long, even with only 10mA drain. *Don't* try and make one with Alkaline or NiCd or NiMH cells - the short circuit current from even the PP3 size is tremendous and accidental shorts from untidy workmanship could easily cause a dangerous explosion that could put your eyes at risk! It is safe to use one single "D" size alkaline cell in a proper holder
for filament/LT supplies.

Grub screws - many receivers used these for securing their knobs with a beeswax type of stuff to insulate them from the user. I think you can still get
beeswax, but don't try candle grease - it just makes a mess everywhere! Later sets used push-on knobs - this was a BS415 revision at some tiime in the 50s.

Chris Williams