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    The Zenith Transoceanic R-520 (and all other transoceanics for that matter) was designed to run on 3-way power: AC current, DC current, and batteries. We'll look at all the options here.

AC/DC CURRENT

    Sometime in the late 30's, radio companies like zenith designed a new way to power radios without having to use the large, bulky, and expensive power transformers. This is now known as an AC/DC radio. The radio was powered directly from the AC line, and the current was converted to DC via a single wave rectifier (either a tube, or as in the R-520, a selenium diode). There were several advantages to this method: it allowed the radio to run off of 110 volts DC (I haven't found any information to show if this was ever really used by the public), made the radio lighter, and most importantly, reduced manufacturing costs. On the negative side, it made the chassis dangerous, as it could have 120 volts on it, so proper shielding, plastic knobs, and enclosed cabinets were required to prevent people from getting a nasty shock.

    The R-520 was designed to use 110 volts AC/DC power. Since this radio was meant for army use both at home and overseas, Zenith supplied a power adapter and several different line cord adapters with the radio, enabling it to be used in countries with 220 volt power grids.

Z1 Power Adapter

    The Z1 power adapter (known as the ballast adapter in the H500 operating guide) allowed the radio to be used in 220 volt AC, 220 volt DC, and 110 volt AC/DC environments simply by changing the position of the switch on the adapter. Original Zenith part number is S-15715.

Line cord adapters

    This radio included 4 line cord adapters, mounted on a metal bracket above the chassis inside the cabinet. The picture below shows only 3 of the 4 line cord adapters. Pictures courtesy of Mark P.

BATTERY OPTIONS

    There are four options for powering the R-520 off of batteries. The first one is universal to all the transoceanics, the other three are unique to the R-520 and R-520a, but can be used on the other transoceanics as well.

Option 1: Zenith battery pack Z985 (and other manufacturers)

    The Zenith Transoceanic radios used a special battery, providing a 9v "A" supply for the filaments, and a 90v "B" supply for the plate supply. This battery sat under the radio chassis inside the cabinet. According to zenith, if the radio was used on battery about 30 hours per week (3-4 hours per day), these batteries would last approximately 150 hours (5 weeks). See the table to the right for a list of common battery types used in the transoceanic radios, and below for some pictures.

        Unfortunately these battery packs are no longer available. With a little ingenuity you can build a working solution using 6 D-cell batteries for the filament supply, and either 10 9v batteries or 60 AA-cell batteries for the plate supply. If you can't build one, there are other alternatives.

    The first solution is Jim Poitivient's AB battery pack. This well made pack uses 9 1.5V D-cell batteries to provide regulated power to both the filament and plate circuits. Jim donated this battery pack specifically for this restoration. Please contact Jim abbattery@aol.com for more information and prices on his excellent product. It is shown inside my parts H500. I have used it in my R-520 for about 30 hours so far, and it works really well, no background hum or other noise at all. Many thanks Jim!!

    Here is Jim's quote about his product:

"This battery pack uses only 9 D cells to operate ALL tube model Zenith Trans-Oceanics including the 7G605, 8G005, G500, H500, the complete 600 series, Universals 5G500R, 6G501, 6G505, 6G601, 6G001, 6G004, Hallicrafters TW1000, TW2000, and the RCA Stratoworld. It replaces the Zenith Z985, Eveready 752, RCA VS047, Burgess G6B60, or any other equivalent battery. In addition, a tenth internal D cell holder with matching female connector provides dial light operation for the 600 series Trans-Oceanics. (Other packs require an external add-on battery holder for this feature). Both A and B voltages are current protected and voltage regulated. Voltage regulation assures optimum shortwave performance and longer tube life by providing a constant, non-drifting, pure DC voltage well within tube specifications. Other unprotected and unregulated battery packs utilizing 6 D alkaline cells for the "A" supply subject the tube filaments to an over voltage condition until the D cells have lost sufficient voltage with use. That can't happen with this battery pack because voltage regulation assures the filament voltage will NEVER rise above the recommended 8.5 volts. The battery life expectancy is about 70 hours normal use. It can be re-supplied with batteries for less than $8.00 (US funds) with batteries purchased locally or rechargeable batteries may be used to make battery cost negligible. Like the original battery, the connector pins are recessed to prevent damage and there are no hanging wires to break. Just install nine or ten batteries, plug in the battery connector, and your receiver will be portable again with no AC line hum or other AC line interference."

    Another solution is Bob Graff's Reuseable A/B battery pack.

    Special thanks to R. Bob Graff who allowed me to use this picture on my site. Please visit www.batpack.com for more information.

Option 2: Yellow harness W5 with battery tube

    This option used 6 type BA-30/U 1.5 volt batteries in a study cardboard tube with removable endcaps for the filament supply, and 3 type BA-423/U 30 volt batteries for the plate supply. The wire harness is permanently attached to the battery tube. The tube is 15- 3/4 inches long and 1-3/4 inches in diameter. See picture below. Picture courtesy of Phil V.

Option 3: Red wiring harness W4

    This option allowed the use of multiple combinations of various widely available military batteries, and still have the batteries stored inside the radio cabinet. One such combination used a type BA-423/U 90 volt battery for the plate supply and 3 type BA-407 3 volt batteries for the filament supply. When not in use, this option was stored in a cloth bag in the battery compartment. Picture courtesy of Mark P.

Option 4: Black wiring harness W6

    This option was used for larger batteries that would not fit in the battery compartment of the radio. Any combination of batteries could be used to provide a 9 volt filament supply and a 90 volt plate supply. All documentation I have read on this adapter recommends attaching the 9 volt supply first, to prevent someone from accidentally putting 90 volts across the tube filaments, and burning out the tubes. This harness was also stored in a cloth bag in the battery compartment when not in use. Picture courtesy of Mark P.

I received a note from Jim P. about this option:

"According to my documentation the battery pack that you are referring to was considered to be a farm pack since many farms didn't have electricity. It was the Zenith 990. It's dimensions were 14 X 7 5/16 X 4 1/2. It weighed 24 lbs., almost three times as much as the Z985. In 1949 it's price was $8.50. Given the increase in the cost of other batteries over the years the price for an alkaline version of this battery pack today would be well over $300.00. It was connected by a battery extension cable # S-9598 which cost $1.20 in 1949. " Thanks for the info Jim!!

Storage bag

    When the additional battery cables were not in use, they were stored in a small cloth bag and kept in the battery compartment. The bag was made out of a lightweight, olive drab colored canvas, 4 3/4" by 6 3/4", and had a draw string on top.

NOTE: With all of these battery options, the filament and plate supply batteries were placed in series so that the plate circuit had a total of 99 volts.