dewald: DeWald B-504 Battery/115 volt AC

Ok, I pretty much a nubie here folks. I did a search on the forum and I did not see a hit, so I started here. I hope this is correct.

I have a few questions on this 1948 DeWald B-504. I know to replace all the capacitors. I laughed when I Googled the two batteries. I got nothing and it said pretty much that.

I just came across this gem and the 4 1/2 volt battery still read 3.5 vdc. Geeze after some 70 years! I believe these two batteries are original. Im sure no one has been in this radio since it was sold in 1948 best I can tell.

First question, should I replace the selenium rectifier? If so, this is done with a diode and a resistor? What values are these? I read somewhere that these gismos can catch fire?

Secondly, I supose I could come up with a power supply to test the batterys that are not available?

Any hints or kinks that anyone may have would be greatly appriciated.

Thanks.....Justin-

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Three Alkaline AA, or C cells, or D cells in a holder for 4.5V, depending on space. Likely the D cells fit.

The 67.5 V was probably 45 off layer cells. Using 7 or 8 small rectangular 9V pack with the spring tops will work, they can daisy-chain so only one connector cut in half is needed. Obviously 45 AA or AAA cells will last better, but may not fit. The 67.5 V pack would have been about 72V before use if fresh and the radio would stop suddenly at between 46V and 40V on the discharge. The IR5 stops oscillating. The volume fades more slowly as the 4.5V pack fades towards  3V.

You'll find downloadable replica lables for DIY working battery packs. The notes don't say exactly which models the two packs are. Presumably the 1R5, IT4 and 1U5 filaments are in series for nominal 4.5V pack and the 3V4 must have ballast resistor on the filament to drop 4.5V to 3V. The target voltages for a PSU would be 4.0V +/- 5% and 60V +/- 10% Using 3.9V and 55V would be fine.  However the set is also designed to be run off mains.

The risk with the selenium rectifier is that it gradually leaks more AC and the main smoothing capacitor explodes. They also stink of rotten fish as they die. Likely a 1N4007 and a 220 Ohm 2.5W wire wound resister will do. The filament voltage on the 1R5 should be between 1.3V and 1.4V when on mains (line) operation. The radio is probably not be isolated when on line AC, so take care or use a 1:1 isolation transformer when measuring line operation.

 

 

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Michael,

Wonderful, yep I think the D cells would work and fit. I will do some searching for a holder. I did consider the 9 VDC batteries I had the same thought. I love your thoughts on the voltages that is what I was wondering, I will start with the 72 Volts.

I tried to operate this guy on line voltage and I just got a hum and no signals. I did test all the tubes an tested just fine. Hey at least I did not make any smoke!

I will start slowly with the electrolitic, then the rest of the Caps and lastly the solinium rectifier and test as I go. In the mean time I will try and work on this battery configuration for my battery operation. Those 9V batteries as of late are not cheep.

You make it sound like you have one of these radios in your collection or have worked on one.

Thanks again Michael. Love this site

 

j-

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No, I have not a model like yours, but do have many battery tube models and made battery packs for many. I do have some USA models. This is part of my collection.

In general the HT voltage is not very critical, but a 10% increase in filament voltage can halve the life of the direct filament battery tubes.

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