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 Post subject: Battery eliminator for A, B, C batteries.
PostPosted: May Sun 02, 2021 6:24 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1524
Location: Auburn, AL
Does anyone have any good plans for battery elsewhere eliminator for a,b,c supplies?

I’ve got a friend who has an old radio with 3 O1a tubes in it, and I’d like to build a battery eliminator for him, and make one for me while I’m at it.

For the filaments, easy enough to get a 5v regulator IC. But I’m thinking it might be smart to make this adjustable so that different tubes can be accommodated with voltages from 1.4 to 6.3 or maybe even 12v?

C supply, looks like we need 0-15v or so.

B supply would need 22, 45, 90 and maybe 120v. Since it’s low current draw, I’m guessing it would be easy enough to make a simple unregulated supply that is 120v with an isolation transformer, and then make a voltage divider with taps for the various voltages? Use an old VTVM transformer for the B+ , and make voltage doubler/trippler for the c supply with the filament winding and regulate with LM317?

Separate 12.6v or 6.3v 2A transformer for the filaments.

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 Post subject: Re: Battery eliminator for A, B, C batteries.
PostPosted: May Sun 02, 2021 6:42 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 16333
Location: S. Dartmouth MA 02748-1225 USA
The recently introduced ABC unit from the AWA may be the answer:

https://www.antiquewireless.org/homepage/pcb-item-5/

Designed by the engineering staff a vetted parts list is included...

Fair warning: Do not set the main "A" voltage to the set at 5 volts, (for 201a's) this will starve the thoriated filaments and result in a more rapid depletion of surface thorium rendering the tubes as "paralyzed" non functional. Always set for 6.3 to 6.6, the internal "A" rheostat add/or series dropping resistors will drop the voltage and provide an initial bias. Plus give a range of volume through control of emission.

Chas

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 Post subject: Re: Battery eliminator for A, B, C batteries.
PostPosted: May Sun 02, 2021 6:46 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1524
Location: Auburn, AL
There are some big rheostats in the set, I was thinking they’re for dropping the battery voltage down. Thanks for confirmation on that.

I’ll check out the AWA plans so as not to reinvent the wheel!

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 Post subject: Re: Battery eliminator for A, B, C batteries.
PostPosted: May Sun 02, 2021 11:24 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: S. Dartmouth MA 02748-1225 USA
anchorman wrote:
There are some big rheostats in the set, I was thinking they’re for dropping the battery voltage down. Thanks for confirmation on that.
I’ll check out the AWA plans so as not to reinvent the wheel!
Good for you! The care and feeding of 20's battery sets is very simple but taking short cuts does not work like one would think it would.
Here is more about thoriated tubes:
http://www.nostalgiaair.org/References/ ... lash08.htm
I used to repeat this information all too many times, but N/A has it there and as long as their remaining hard drive does not fail it will be there...
Note there is a chart of tube voltages it has an obvious error...
In many home brew and even manufactured sets from the 20's provision was made for a sensitive detector tube. In some radios all of the important factors are adjustable in others not so. The clues are a vernier rheostat for the filament of the detector tube. Four or more to 1 ratio of 1st audio transformer and easy access to the grid leak or even a panel adjustable grid leak (carbon pile). When a detector tube is exploited for its sensitivity the filament voltage, grid leak and plate voltage become critical.
There is a difference between sensitivity and volume. the detector can create good amplification at lower grid leak values and 22-1/2 volts. The sensitivity to weak signals will be lacking. Turning up the AF amp will not help. When the detector is critically set either a vacuum or a gas detector the curve in the tubes characteristics is exploited. The output volume will fall off but the ability to detect weak signals will improve. Lowering the plate voltage and changing grid leak values usually raising them then selecting a critical filament voltage will allow for detection down to the noise level. The amplification is made up by the use of a 4 to as much as a 10 to 1 first audio transformer. The overall gain of the AF amp usually controlled by one or more filament rheostats is adjusted ft o bring up the volume of these detected stations...

This is not my theory. Most any radio magazine or handbook from the 20's explains how to manage a sensitive detector. Some articles are more complete than others.

Note all of the circuits including the ARBE-III, the AES and the Schneider do not make the detector voltage variable. The vintage Majestic and many other vintage "B" supplies do provide an adjustable detector voltage.

All of the modern power supplies can have a 10k or so linear pot across the detector "B" and the "B-" then the wiper of the pot becomes an adjustable "B" adding a 1 mf shunt cap to ground will isolate the new tap..

There is nothing worse than a shaky "B" supply insufficient "A" supply except neglecting the radio and not re-soldering all soldered connections, loosening and re-tightening all mechanical connections, cleaning tube pins including the tips of the pins.

GL Chas

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