27-07-2011, 07:40 PM
On the assumption that what you have is a simple primary winding on the transformer (perhaps via a switch and fuse), with no other connections on the primary side, it doesn't matter which way around the primary is connected.
The same applies to an AC only radio.
However, it becomes an issue with 'live chassis' equipment such as DAC90As because the chassis is connected directly to one side of the mains. Taking the DAC90A as an example, although, as we know, the set will work fine with the reversible mains plug (actually being female it's a socket - the plug is the two male pins on the rear apron) either way around, one way will connect the chassis to the line, so all the metalwork will be live, but the other way around, neutral will be connected to the chassis.
There are no such issies with the Hunts CRB (Capacitance Resistance Bridge'). The circuit on page 13 of the 115-page manual of the Hunts CRB is a bit sketchy, but simple shows a straighforward single winding on the primary. Not only is the mains isolated from the case, the manual states: "This instrument has been tested at 2000 V DC from mains lead to case. It is recommended however that it is earthed at the terminal provided". I think you're doing the wise thing by earthing it via a three-core mains lead Rob.
We might wonder why it didn't have a three-core mains lead to earth he case from the outset but standards change over the years, and I think it behoves us to rank safety higher than originality when renovating equipment that is now almost 70 years old.
The manual I'm referring to is 'CRB-2' dated 1945, which I asssume is the relevant one, which - in case you or anyone else needs it, I've attached to this post
Hope that helps.
Best of luck with the restoration Rob!
David
The same applies to an AC only radio.
However, it becomes an issue with 'live chassis' equipment such as DAC90As because the chassis is connected directly to one side of the mains. Taking the DAC90A as an example, although, as we know, the set will work fine with the reversible mains plug (actually being female it's a socket - the plug is the two male pins on the rear apron) either way around, one way will connect the chassis to the line, so all the metalwork will be live, but the other way around, neutral will be connected to the chassis.
There are no such issies with the Hunts CRB (Capacitance Resistance Bridge'). The circuit on page 13 of the 115-page manual of the Hunts CRB is a bit sketchy, but simple shows a straighforward single winding on the primary. Not only is the mains isolated from the case, the manual states: "This instrument has been tested at 2000 V DC from mains lead to case. It is recommended however that it is earthed at the terminal provided". I think you're doing the wise thing by earthing it via a three-core mains lead Rob.
We might wonder why it didn't have a three-core mains lead to earth he case from the outset but standards change over the years, and I think it behoves us to rank safety higher than originality when renovating equipment that is now almost 70 years old.
The manual I'm referring to is 'CRB-2' dated 1945, which I asssume is the relevant one, which - in case you or anyone else needs it, I've attached to this post
Hope that helps.
Best of luck with the restoration Rob!
David
