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 Bias batteries in mains-powered radios?
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 Return to top of page · Post #: 1 · Written at 5:11:42 PM on 11 May 2020.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 1910

I was looking at some Canadian radios recently and I noticed that, in the 1930s, it was common practice, particularly by Rogers, to fit C batteries, even in mains powered radios with indirectly heated valves.

Strange! They had special long-shelf-life batteries for the purpose. Air cells??

In restorations, lithium coin cells are commonly used.

Anyone seen C batteries in mains radios here?

 Return to top of page · Post #: 2 · Written at 7:32:58 PM on 11 May 2020.
Brad's avatar
 Location: Greenwich, NSW
 Member since 15 November 2005
 Member #: 1
 Postcount: 6352

I've never once seen a cell or battery inside any radio that runs on the mains. I've largely confined my collecting to Australian receivers and that's probably why.

A valve a day keeps the transistor away...

 Return to top of page · Post #: 3 · Written at 10:30:13 AM on 12 May 2020.
Ian Robertson's Gravatar
 Location: Belrose, NSW
 Member since 31 December 2015
 Member #: 1844
 Postcount: 1910

I guess if their lifetime was roughly equal to that of wet electros it might have been a viable option.

Still, it was surprising....

 Return to top of page · Post #: 4 · Written at 10:49:24 AM on 11 June 2020.
Keith Walters's avatar
 Location: Sydney, NSW
 Member since 16 January 2008
 Member #: 219
 Postcount: 55

I think the reason might have been that it allowed proper grid biasing without needing to lose several volts across a back-bias resistor.
That wouldn't matter so much if the radio had a mains transformer, but if it was an AC/DC type, it could be required to operate with a DC mains voltage of under 100 Volts, and after passing through the rectifier and speaker field winding, there would be likely less than 90 Volts left to play with.
Some early car radio radios also used bias batteries.

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