Premier Radio Earthing question

[Radio Surfer]

Morning from the windy Hebrides,

I have a Premier valve radio from I guess the 1950's in a bakelite case that my father brought back from the "machine workshop" years ago. I've now had this for 40 odd years and have just removed the inner workings to vacuum out the cobwebs and give the case a general clean.

I have noticed that there is no earthing connection. The live cable goes to the on/off/volume control with the neutral to a tab which is attaching the speaker to the metal frame as per the picture below. There is a wire linking this to the volume control. Hopefully, the picture makes this clear.

All looks original apart form the power cable and wires connecting the speaker tab to the volume control. Surely that can't be right even for the 1950's? Someone's clearly messed with it in the past. How would it have been wired/should it be wired?

Kind Regards, Richard

[Graham G3ZVT]

Welcome to the world of "live chassis"!
The technique avoided the use of a heavy and expensive mains transformer and was used on domestic radios and TV sets into the 1980s

[dave walsh]

You mentioned that you got this radio working [a long time ago] in your very first post Richard. I'm assuming it has no transformer and is an AC/DC set, in which case the chassis functions as mains negative. If the wires are reversed at the plug end the chassis is positive and live This isn't a problem if the metalwork isn't exposed but it now is, so caution is advised. This type of set never had an an earth lead to the chassis as, if the plug was wired the wrong way round, it would just blow the fuse. This is why the mains lead may not be colour coded as it still worked either way. The mains wiring doesn't look original but I can't see that it's incorrect. If it's otherwise ok, I don't think you have a problem-unless the metal IS live and someone can get at it. Even if it has an auto-transformer [tapping a voltage off] that is no safer. Others will know more!

Dave

PS Looks like Graham agrees!
We are not lacking wind, rain or freezing cold here on the South Coast at the moment!

[Hartley118]

Judging by my examples of the 'Premier Radio' kit radios, they often just used a 6.3V heater transformer mounted on top of the chassis. That supplied the paralleled valve heaters and the HT was direct from the mains via a selenium rectifier (which may or may not still be working).

As long as you make sure that it's the neutral side of the mains that's connected to chassis, that's reasonably safe when the chassis is in its cabinet.

Martin

[Station X]

Originally Posted by dave walsh

You mentioned that you got this radio working [a long time ago] in your very first post Richard. I'm assuming it has no transformer and is an AC/DC set, in which case the chassis functions as mains negative. If the wires are reversed at the plug end the chassis is positive and live T

Sorry to be a pedant, but when it comes to AC supplies there's no positive and negative. It's live and neutral or line and neutral.

[dave walsh]

Nothing wrong with being accurate Graham. I'm probably thinking batteries.
I was once convinced on here that a certain plug was called a "wanderer" rather than the correct wander but I was wrong!

[I'm a bit pedantic about people who can't pronounce "t" eg Tatt Ooh!] I like the song of that name by the Who but it wouldn't be the same].

Dave

[mickm3for]

Hi i have just got a hallicrafters s38 also ac/dc 110v radio the single pole on off switch is in the neutral side of the mains. So in the on position neutral chasis no /low voltage to earth
however in the OFF position the chasis is live via the valve heater chain and could be lethal
Mick

[turretslug]

As said, this is fairly typical and as intended- it's brought back memories of dismantling a UY85 etc. domestic set donated by one of my grandmother's friends when I was about nine and being slightly alarmed about the direct mains connection to chassis! An education that stuck in the mind. At least this set doesn't do what some similar PSU sets did- in order to minimise hum pick-up by the adjacent volume control, the neutral wire was switched with the less-than-charming result that when the correctly wired supply was switched off, the whole shebang floated up live including chassis. That must have caught a few uninformed repairers in its time.

Crossed with Mick! Colin

[Radio Surfer]

Hello,

Thank you to everyone for the prompt responses and good to learn all is as expected. I don't tend to work with mains stuff of this vintage, so I'm not familiar with the "live" chassis concepts and the surprises that can bring.

Dave, you mentioned my first post, that was actually referring to another radio - a much safer battery Hacker. I must do an update on that as I've got it working at last and am listening to it now. So much better than "Alexa", it doesn't keep turning off unexpectedly and suddenly saying "sorry I didn't understand that" ! This Premier radio has always worked, but it's the first time I've taken it out it out of the case. Now I've vacuumed the cobwebs and dust away and polished up the bakelite I'll put it all safely back together where I can forget about the internal wiring. Pity there's not much left on medium and long wave, the dial certainly brings back memories of long lost stations.

Kind regards,

Richard

[Sideband]

...in short (no pun intended) it isn't designed to have an earth, it MUST NOT be earthed. It is perfectly safe if mains neutral is wired to chassis and the plug is connected correctly. Also there should be no exposed metalwork including screws securing the chassis.

This was a very common technique used for radio's and incidentally most B/W TV up until the 70's.

[Radio Surfer]

Thanks Sideband,

All now safely back in its case, plug checked and all securing screws recessed out of harms way. I'm now listening to it for the first time in years, not much on MW up here; 5-Live on BBC Home, Talksport Scotland on Midland Region and a "non stop hits" independent (not sure what) on Scottish Region. Nothing on LW. Still sounds surprisingly good though.

Regards, Richard

[dave walsh]

Hello again Richard. You did mention a Hacker in your introductory post [15/4/19] but also the Premier valve radio Maybe it's just me being pedantic now. Anyway, the "main" thing is you are out of harms way!
The biggest problem is that [these days] people sometimes turn up who confirm a lack of knowledge by plunging in ill advisedly and this can be a bit alarming with things like live metalwork. They fail to do the sensible thing and ask first [as you did]. AC/DC circuits are often discussed on the Forum. Despite being a [contemporary Health] and Safety nightmare, there are no reports of death or injury within the general population but perhaps a few shocks in the Workshop? I think the no transformer aspect, may have brought more consumer goods to the masses as prices could be reduced.

Dave W

[Radio Surfer]

Hello Dave,

Yes, indeed you are correct. I was thinking of the post I made about the Hacker which wasn't my first as you point out. Must make a note to think more, or maybe less would be safer!

At least I've learnt something today, which is good.

Kind regards Richard

[dave walsh]

Further to Micks comment re the Hallicrafter radio Richard [p7], you might want to check out the "Neon Tester Screwdrivers" thread which is back with Gezza's comments [post 29*] and a link to a "Death Trap" warning article re the S38! There seem to have been more fatalities in the US! Mind you this is a very early comms set with totally exposed metal and not in an insulated case, as with the UK domestic products!

Cheers,

Dave

The author even points out that the AC/DC approach was adopted to lower the sale price! Later models were modified!

[TrevorG3VLF]

I buit a couple of Premier radio kits in the 50s, one TRF and the next superhet. The knobs were fixed with grub screws which were recessed but it could still be exciting if your fingers were wet. The recesses should be filled with wax.

Later knobs were held with hidden spring clips.

[unitelex]

If the set has an old 2 pin mains plug (many did), I would always advocate replacing that with a modern 3 pin plug ensuring that the chassis is neutral.

Chris