Safe use of an old valve radio

[joolsmy]

Apologies if I'm posting this question in the wrong forum. I have an old valve radio that has been rewired internally so is basically sound. The problem is it has no provision for a protective earth, the internal chassis is wired to neutral (was live before rewiring!) and it is far from double insulated. The control knobs are on brass rods which obviously protrude from the wooden case, so pose a risk (they are mostly concealed by the bakelite knobs but you could slide a nail file behind them and contact the rods). The grub screws in the bakelite knobs are recessed and have been covered with a non-conducting wax-like substance but a determined poke with a sewing needle would probably break through to contact them.

Given all the above plus the ventilation holes in the back cover, would a permanently wired RCD plug provide sufficient protection?

 

[telectrix]

it was common for the chassis to be connected to the neutral and only a 2 core flex on the radio. this was prevalent even up to the early 80's on TVs also. had many a shock from touching a chassis when the plug was wired the wrong way round. i would say that if this radio is for your own use, then fine as long as there's RCD protection, either a RCD plug or RCD supplying the sockets ( which there should be anyway). think of a toaster. those elements are live and it's easy to touch them with a metal knife etc. same with an electric fire element.

 

[freddo]

As above, do not attempt to earth a live chassis radio! If it uses an external aerial connection, it is a good idea to replace the aerial isolation capacitor(s) with a modern Class Y type if this was not already done when it was 're wired'. The capacitor connected to the grid of the output valve should also be replaced as a bare minimum to prevent expensive damage to the output valve and output transformer. Any capacitor connected across the mains input should be a modern Class X type, the old waxed paper capacitor often employed in this position will soon explode (if it hasn't already).
I have over 40 valve radios, and most of them work very well when they have been properly serviced, most faults are caused by ageing paper capacitors, they were never expected to last 50-80 years many often become electrically leaky as the paper dielectric absorbs moisture from the air. Fortunately modern plastic film caps will last many many years as they don't suffer this problem.

Ensure the back cover is fitted properly as well as all knobs, the grub screw holes should also be filled with wax to stop things being poked in.

What make and model is it?

 

[Specialist]

Apologies if I'm posting this question in the wrong forum. I have an old valve radio that has been rewired internally so is basically sound. The problem is it has no provision for a protective earth, the internal chassis is wired to neutral (was live before rewiring!) and it is far from double insulated. The control knobs are on brass rods which obviously protrude from the wooden case, so pose a risk (they are mostly concealed by the bakelite knobs but you could slide a nail file behind them and contact the rods). The grub screws in the bakelite knobs are recessed and have been covered with a non-conducting wax-like substance but a determined poke with a sewing needle would probably break through to contact them.

Given all the above plus the ventilation holes in the back cover, would a permanently wired RCD plug provide sufficient protection?

The chassis does not need to be Earthed, nor does anything else. To be honest I think your being rather paranoid over this. The grub screw holes didn't need to be filled, but can be filled with wax, between the knobs and case there is usually a felt washer. If you can't find or make one then you could use a 3/4" tap washer, but it shouldn't be necessary. The air holes in the rear cover are too small for even a baby to access, if you have children & your worried about them poking things into the radio then just make sure the radio is out of reach.
There are still a lot of vintage radios being used by enthusiasts daily, without problem.

 

[joolsmy]

As above, do not attempt to earth a live chassis radio! If it uses an external aerial connection, it is a good idea to replace the aerial isolation capacitor(s) with a modern Class Y type if this was not already done when it was 're wired'. The capacitor connected to the grid of the output valve should also be replaced as a bare minimum to prevent expensive damage to the output valve and output transformer. Any capacitor connected across the mains input should be a modern Class X type, the old waxed paper capacitor often employed in this position will soon explode (if it hasn't already).
I have over 40 valve radios, and most of them work very well when they have been properly serviced, most faults are caused by ageing paper capacitors, they were never expected to last 50-80 years many often become electrically leaky as the paper dielectric absorbs moisture from the air. Fortunately modern plastic film caps will last many many years as they don't suffer this problem.

Ensure the back cover is fitted properly as well as all knobs, the grub screw holes should also be filled with wax to stop things being poked in.

What make and model is it?

It's a Cameo, don't know the model, originally purchased in 1946-7. I think a lot of the caps were replaced. It's also been converted such that it will no longer work on 240v DC, a wire-wound resistor was removed and a washing-machine cap added. It runs a bit cooler than in its original configuration. I'm pretty sure there's no output transformer but I could be wrong.

So, given my dwelling's wiring is RCD protected, would it be a waste of time adding an RCD plug?

 

[telectrix]

i have a funny feeling that there's now the chance to buy radios without valves. they seem to work OK with some new-fangled invention called a transistor. main advantage, as i see it, is that the radio itself is now bigger than the batteries that run it. these batteries can now be purchased over the counter at places like aldi, teso, and the like, without the need for a trolley to carry them home.progress, eh.

 

[joolsmy]

i have a funny feeling that there's now the chance to buy radios without valves. they seem to work OK with some new-fangled invention called a transistor. main advantage, as i see it, is that the radio itself is now bigger than the batteries that run it. these batteries can now be purchased over the counter at places like aldi, teso, and the like, without the need for a trolley to carry them home.progress, eh.

Where's the fun it that?

 

[telectrix]

It's a Cameo, don't know the model, originally purchased in 1946-7. I think a lot of the caps were replaced. It's also been converted such that it will no longer work on 240v DC, a wire-wound resistor was removed and a washing-machine cap added. It runs a bit cooler than in its original configuration. I'm pretty sure there's no output transformer but I could be wrong.

So, given my dwelling's wiring is RCD protected, would it be a waste of time adding an RCD plug?

YES

 

[Specialist]

Aaw Tel, you know those transfer resistor things don't sound as good as the thermionics

 

[telectrix]

Aaw Tel, you know those transfer resistor things don't sound as good as the thermionics

i know. can't beat a good pentode for realistic sound. still i suppose semiconductors are OK for justin beaver and little mix. they will always sound crap whatever.

 

[Specialist]

I'd pick a valve radio over transistor any day, love the sound quality & they're much more fun to restore.

 

[telectrix]

hang 5 just putting pink floyd on over bloody semiconductors. get it real loud.then it's OK.

 

[telectrix]

now playing "wish you were here"

 

[Specialist]

Nice, played ZZ top on a vintage Danny the other day

 

[sparkdog]

Good to see there are a few valve radio enthusiasts around. I have over 40 of them myself. OP could probably use a mains isolation transformer.