Repro AD65, earthing point or not? - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

julie_m · 7th Jul 2008, 2:39 pm

If it's an AC/DC radio, the chassis will be connected to mains neutral (hopefully!) which is connected to Earth at the substation, and -- if you live in a town -- again in your house where the cable comes up from the street.

Boom · 7th Jul 2008, 2:55 pm

Quote:

Originally Posted by Robbie99

Hi Guys

The two wander sockets mentioned are both aerial sockets. One VHF, one MW. The other wires to the back board are for the quarter inch headphone socket I asked to be added.

Cheers

'Headphone socket'? This can't possibly be a live chassis!

julie_m · 7th Jul 2008, 4:14 pm

Quote:

Originally Posted by David Tilley

'Headphone socket'? This can't possibly be a live chassis!

Oh yes it can, because a loudspeaker (or headphones) is almost invariably coupled to the anode of the output pentode through a transformer; and, unless you are trying to build a really hi-fi amp -- by which I mean rather higher "fi" than medium- or long-wave radio could aspire to -- there is no need to take negative feedback from the far side of the transformer. (I do actually have an amplifier that is built that way; but I also happen to know that both its HT and LT supplies are derived from a transformer.) So the connection to the speaker / 'phones will not be live.

Boom · 7th Jul 2008, 4:36 pm

Quote:

Originally Posted by ajs_derby

Oh yes it can, because a loudspeaker (or headphones) is almost invariably coupled to the anode of the output pentode through a transformer
.

You'd trust the insulation on a loudspeaker transformer alone to keep the mains from direct contact with your head? You are a braver man than me!

Steve_P · 7th Jul 2008, 6:04 pm

I agree. How do you know the mains hasn't developed a fault! Happens....

There was a guy in a US prison who tried to wire headphones to a mains radio while sat on a matal bog. That's where they found him - DEAD!

Cheers,

Steve P.

Ian B · 11th Jul 2008, 5:59 pm

I have one of Gerry's repros too, I'm sure it has a mains transformer. There's a separate transformer under the chassis to supply the vhf tuner board which has its own separate power supply. However, the tuner board on mine is also under the chassis - I guess different batches were modified in the light of experience building them.

Ian Blackbourn

7th Jul 2008, 2:39 pm	#21
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Repro AD65, earthing point or not? If it's an AC/DC radio, the chassis will be connected to mains neutral (hopefully!) which is connected to Earth at the substation, and -- if you live in a town -- again in your house where the cable comes up from the street. __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

7th Jul 2008, 6:04 pm	#25
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Repro AD65, earthing point or not? I agree. How do you know the mains hasn't developed a fault! Happens.... There was a guy in a US prison who tried to wire headphones to a mains radio while sat on a matal bog. That's where they found him - DEAD! Cheers, Steve P. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

11th Jul 2008, 5:59 pm	#26
Ian B Hexode Join Date: May 2006 Location: Arlesey, Bedfordshire, UK. Posts: 401	Re: Repro AD65, earthing point or not? I have one of Gerry's repros too, I'm sure it has a mains transformer. There's a separate transformer under the chassis to supply the vhf tuner board which has its own separate power supply. However, the tuner board on mine is also under the chassis - I guess different batches were modified in the light of experience building them. Ian Blackbourn