Hi Guys,
I have started organising new caps for what we assume is my 1954 Aeradio radiogram, see my Member Introduction post (Hi from Briz Vegas) for photos, but am now a bit confused by of all things the power lead.

On closer inspection it has no ground/earth wired into the earth terminal of the plug. Said Bakelite plug has been checked and will be reused by the way. My limited understanding was that if an appliance was not grounded back to the wall socket it was supposed to be 'double insulated' to prevent nasty surprises. This is obviously not double insulated, or could the timber surrounds of the radiogram be called that? The radio unit on its own is obviously not.

My main question is about the process of adding the earth connection to the unit when I do replace the 2 core power lead with a 3 core? Where should the earth wire be connected to on the chassis?

Cheers

The earth wire should be bolted to the inside surface of the chassis via a crimp lug (eyelet type). To be legal it will require its own bolt and nut and the surface of the chassis adjacent to the crimp lug should be sanded to make sure bare metal is exposed.

Avoid soldering as it is not always reliable and definitely do not share a connection with components. If such a connection broke away from the chassis then high tension would be pumped down the earth wire into the household wiring.

Old radios are definitely not double insulated. Timber is a fair insulator if it is dry but it is only a single barrier. If you reuse the Bakelite plug make sure it is a type with two halves that need to be screwed together. The earlier type with the exposed wiring on the face with the pins can bring trouble if strands of wire pop out to the side or the thin Bakelite just decides to give way as it is inserted into the power point. If you were to sell the radio you would need to fit a clear modern plug such as a Clipsal 439S to comply with recent standards on plug and socket safety.

If you are not overly concerned about original, you can use a gland (often installed backwards) as a decent cable clamp. Often I will buy a plug & cable which is molded & often cheaper than a plug & cable separate (Middy's); It will have an eye terminal on it. I use those on commercial fixes.

I have seen the bolts come loose, never a solder one. You cannot tie a knot in the cable these days & the cable has to "anchored" The latter being one of the failures with a knot, as it allowed the cable to move & it could then flex off.

Marc

I have sent you the schematics. Had forgotten who requested them.

First of all thanks to GTC for the schematic.

Secondly, yes the original bakelite plug is one that splits in 2 and is screwed. It looks in very good condition with no discolouration, no cracks and will be happy to reuse it. The cable however fails all criteria...no earth, cracking rubber 'stuff' and knotted within the chassis to 'prevent' movement.

Thanks for the info re how best to ground. It will be the first thing fixed.

Tony

The knot may prevent it pulling, but in many cases it will not stop twisting & that's what breaks wires off terminals. That can be interesting.

Old rubber wire is a curse in radios & houses. I was astounded recently when a radio came in with hum: Normal cause. What was so astonishing is how it had managed not to kill someone, or burn down the house.

The set was a 1950's Wedding present, still in service & virtually original (cap) right down to the rubber two wire mains cable, featuring mass cracking and some bits missing as it exited its original Bakelite plug. I think I got that one in the nick of time.

Marc

That clear insulation would have looked quite modern at the time and it was also often used in 'drops' between ceiling roses and cord-grip lamp holders. The problem with it is that it is not UV stable and will be the first to break down and expose the conductors.

The insulation Marc speaks of is VIR rubber - used a lot by Kriesler and a few others and is pretty much a disaster waiting to take place. This stuff can crumble in your hands if it hasn't already done so in someone else's hands. When a radio arrives I usually just automatically cut the cord off about 50mm out from the cabinet. This removes the danger and the temptation to fire it up in an un-inspected state.

My preferred way to anchor power leads now is to use a traditional grommet and cotton-covered three core flex but instead of the knot use a nylon cable clamp similar to Jaycar Cat #: HP0752 with a nut and bolt. As Marc said, nuts and bolts can work loose though including a spring washer next to the nut will sort this out. If you are pressed for time a cable gland would work too, though this doesn't look as authentic even when reversed. That said, the back of the radio isn't normally visible so as long as the cable's movement outside cannot affect the joins it doesn't matter which method is used.

Sometimes you just have to bight the bullet & compromise authenticity in the interest of safety & if its a commercial fix, compliance with regulations, on the mains side.

Marc

I purchased a radio last week that had been 'restored'
The mains cable is a flat 3 core ribbon where all three cores are grey. No way to identify what goes where. It is only single insulated too.
It would be up there with one of the more dodgy things I've seen.
240 v bites a bit too hard to stuff around like that.

I have a portable Gulbransen with something similar - a sort of 3-core figure-8 cable. It awaits restoration to this day because it's not a burning priority though when it does take its turn on the operating table that cable will definitely go.

While I was in the shed I had a look at the next project. It looks the same as the radiogram but the Bakelite plug looks pretty horrid. Sounds like this is pretty standard then.

I didn't think to reverse one of Jaycar's metal cable glands.
You could soak the metal parts in vinegar for a few days or tin the whole thing with leaded solder to sort it out.

Glands such as Jaycar HP-0724 can be reversed if there is room in the pan, and on consoles, some will also allow the cable to exit via the side. Do note though that these are not suited to all chasses.

Often you can also tap the hole into the box that the gland is going into. A cable tie can also assist in preventing the cable from being pulled through a clamp, or gland and stop the cable from rotating, by leaving a tail.

Plan the move: Some cable exit points are just crazy & just have to be changed.

Marc

To be on the safe side, I always install one of these from Bobs Tube Audio;

http://www.ebay.com.au/itm/3-PIN-REPRO-CORD-SET-CLOTH-COVERED-MOULDED-BROWN-PLUG-AS-NZS-3112-2000....

Agree, these are good & essential if you want it to look more original, but to buy one is pricy. Where it is not critical the same in plastic would be in the order of $5.