Hi All

Well I'm back restoring Valve Radios after a few years AWAy.

I have an AWA 565MA / Hotpoint P65ME that has a burnt out Antenna Coil.

Someone has tried a "Restore" on this set before me as can be seen in the photos (Thanks Brad)

Has anyone got a wrecked set that I can score this coil from?

Thanks

Flakes

Welcome back, Flakes. It has indeed been a long time.

I will have a look at work tomorrow and see what is there - I do keep a stash of radios and spares there as I have no room at home for everything. AWA did have a habit of making these tar-dipped nightmares.

Looks like one photo was included twice.

Good pickup - all fixed now.

Is it reallly fried? It looks to have been encapsulated in black wax, but there are no signs of burning. But maybe your nose tells you. How is the continuity?

The aerial coil part number is 30768 and was used in many AWA models.

If you have a wrecked chassis, compare the model number with the AWA service manuals on Kevin Chants site.

Yes its totally fried. have a close look at the bottom part of the coil its copper and burnt black. Also look at the chassis and its a brown burnt colour with splatter of black wax/tar.

I dont have any wrecked chassis and thats why I was asking if anyone had one.

The set needs a full go over as most of the wire insulation is cracked and falling off.

Yes its totally fried. have a close look at the bottom part of the coil its copper and burnt black.

Odd. I've never come across that situation. Did this set maybe suffer a lightning hit via its aerial?

If this is cooked, rather than the tar fall off that is bizarre. If it is the primary winding the only thing that can burn it out in normal operation is lightning. There are no circuits hooked to it that could do that unless it got hit by lightning and that's rare. But I have had two and that only wiped out caps & resistors.

The secondary might burn on a shorted grid, however, I am not buying it. The second and scariest way that coil would burn(if it has) is an earth leakage fault on the mains side. If the set only had a ground via the antenna primary and the mains went to ground with that two wire cable that has to go, that might fry it. Not convinced.

So, there needs to be a "Tag & Test" like procedure on the primary side of the transformer to ensure the wiring, switch, or the transformer primary has not gone to ground. Rubbish wire as noted may extend to the transformer and I have been obliged to repair more than one of them.

Most coil breakages are on the outside and caused principally by rodents. Really need to see a close up of the damaged area: Mark it, or where the not damaged coil is connected & measure its resistance for reference later,. When you remove it for further analysis.

I agree, the situation is quite bizarre. I'd like to see resistance readings on each winding, as well as from one to the other, before condemning it.

What's more concerning is the nearby wiring is all rubber and breaking up, needs replacing.

As to the cause of the burn, apart from a lightning strike or some other kind of incredibly unusual event, I don't know.

Hi Guys

I will have to investigate a bit more with the Power transformer as I haven't even got that far yet. I used the service manual figures for the DC resistance of all the other coils and they check out. Didn't even think of the O/P and Power Transformer.

the Antenna coil seems to have taken a huge hit. but its only the primary winding, secondary is good. the set had the caps and resistors changes as shown in the photo. I have not had a hot iron near it yet.....

all IFTs and OSC coil are spot on.

Ill put it back on the bench and pull out the Megga and Low Ohms meters and give it another once over.

Will be a day or so as I have flu at the moment.

I have an AWA WW2 vintage Army Amenities receiver that runs on 6 volts.

Its antenna primary was cooked just like that one. Burnt through the former and all.

I have always assumed that the uninsulated antenna wire fell out of the tree and onto the battery terminals.

Lightning hit damage (and I have seen many examples) don't look like that. They don't have time to cook, they just vaporise all the metal and leave the insulation pretty much intact.

That's a slow burn, perhaps due to a 2 core mains lead, a grounded antenna wire and power transformer leakage at a dangerous level.
Or maybe an outside antenna came down onto power wires in a storm or vice versa.

At least you don't have to change the caps!

I know this is bizarre BUT.

I did come across a species of valve set that actually had A CAPACITOR FITTED BY THE FACTORY THAT CONNECTED THE MAINS INPUT TO THE AERIAL TERMINAL!!!!
If the cap shorted the antenna coil would fry up.
The bloody cap was tucked away right at the back of the chassis and you would not know it was there until a real close look.
Got a feeling it was a 'Philips' set but cannot remember the details.
Agree with the other guys that chassis wants a very close leakage and insulation check before taking 240 volt anywhere near it!

Fred.

Snap! it was a Philips 100 I repaired, look in special projects in 2020.

Fred.

AWA did use a capacitor from the mains input to the antenna terminal as an internal antenna, an example is the model 520M.
It used a 500pF (I think) rated at 2000V Test.
If it fails and the chassis is earthed, depending on the active/neutral wiring, BOOM!
Harold

Interesting. Got half way through the post & the internet died & the site would not reload?
America seemed to have an obsession with “Line caps” not done well and on lots of sets, be they Transformer od hot chassis and earthed cable on transformer sets, not common. Noting that a “hot chassis” cannot be grounded.

So, in most cases where there was not a dedicated utility earth /ground wire the chassis was tied to neutral as it was at ground potential and that gave RF a ground. The fall down here was their NEMA two pin plug tops were, unlike ours: Reversable. That meant that there was a 50/50 change of the chassis being active.

Now: If there is a Waxed Paper cap, which I have seen, of a non-approved type, they leak like sieves and it on active (never uncommon) and leaking like a sieve. That has a remote, but cannot be ruled out, chance of frying an antenna primary.
Now, if that is actually. The non resonant primary that’s open, that’s not such an issue. A method I have used on an STC that rodent damage was to remove the coil, noting in detail & photos what went where. I connected an insulation tester to it, in the hope that I had a surface break.
Using dim light, a couple of pulses presented an arc, where it was open and close to the surface.That turned out to be a double break, presenting three sections and a swine of a fix: Hair fine wire.

Function generator, Oscilloscope, Ohm meter, scalpel, magnifier etc.

Where a grounding is suspected on a transformer, pulling out the rectifier normally isolates the HV secondary but disconnect the centre tap, from ground. The same for heater winding. With tubes & lamps removed & make sure their sockets are not shorting. some do with the globe is removed B+ has to be removed from an #80 / 5Y3.

I will then test, per regs at 500VDC between all windings & ground: Then between windings in case one Is shorting to the other.