I have two 1920's-vintage battery eliminators, both of which use BH-type tubes. I have heard that these are all pretty much useless now, as the helium has all been absorbed into the electrodes. Has anyone here successfully substituted another tube for the BH-types? I'd like to get these vintage eliminators working with a minimum of (preferably ZERO) alterations to the circuitry...

Rich

There are a lot of usable BH tubes out there.

You can make a BH sub using an 0Z4 rectifier. Either use the 0Z4 with adapter or remove inside glass tube and solder wires into a 4 pin base. They look nice in operation, glowing purple.

Most of the OZ4 tubes I have seen for sale are metal ones. Are the glass ones rare?

0Z4G?
Don't know, I have a few. As Norm says, there is a glass envelope inside the metal can of the 0Z4.

I tried 0Z4's in '65 when I got my first estate of battery radios and eliminators. I'll admit I tried used 0Z4's, I could not get them to strike in a Majestic "B". I never tried a new one, limited funds for radio back then. I did try diodes, but no series limiting resistor, the test shorted on of the chokes to ground.

I suspect that the used 0Z4's were defective. I didn't have a tube tester at that time...

FWIK now, changing out the paper filter capacitors is very important as the heavy load placed on the chokes and any rectifier in these old "B" eliminators from leaky caps will result in what I had experienced 47 years ago. Consider that much more time has past for deterioration...

I did rebuild one Majestic "B", rather simple, all caps are in a tar block. Open up, clean out and install a bus wire to support the new caps. I used all tubular Mylars back then. Should still be a viable repair, I did not use any electrolytics...

YMMV

Chas

My Majestic Super-B is missing its top cover, and one of the carbon pile rheostats is broken, but i got it for cheap so I'm not complaining too much. The one I REALLY want to get working is apparently an A-B-C eliminator. According to the tag, it is a "Modern Electrical & Radio Products Type C1-A", and was made in Toledo, Ohio. It has three fixed cartridge-type resistances, two unmarked and one marked "50,000 Ohms" (50K). The binding post terminals are marked:

C AMP
C PWR
FIL
FIL
B-
DET
AMP
PWR

The filament terminals are not, apparently, marked for polarity. The wiring is rubber-coated, and the insulation is crumbling. There is also an A/C socket mounted on the top cover (maybe for a trickle charger?

It's a mystery, for certain!

Could the filament not have polarity because it's AC? When AC tubes were first available people would convert over their battery radios.

Good 0Z4's will work in place of BH tubes. Might also look for CK1005. These show up surplus, new. If you want to try building a BH sub send your mailing address.

PM sent!

Got it..

If I can get the A-B-C eliminator working, and it turns out the filament power is A/C, I may see if I can find a vintage trickle charger to plug into the socket and get a sealed 6-volt lead-acid battery, and somehow try to disguise it as a vintage battery (if possible).

Why don't you open it up and see what is going on. If there is an "A" supply there should be some sort of low voltage rectifier. Tungars, copper oxide or wet tantalum. If you find a relay and its coil is wired in to those "FIL" terminals then what you have is "B &"C" supply with a current relay to transfer an external trickle charger and turn on the "BC". If that is so, a suitable LA battery must be used with one of the LA battery leads wired to the "FIL" terminal and the other "FIL" terminal going to the radio. When the filaments of the radio are turned on the radio, the relay turns "OFF" the trickle charge and "ON" the "BC" supply.

The rubber wiring can be replaced with 18 ga stranded machine tool wire 300 volt, known as "MTW" available at most electrical supply houses...

Chas

Ought to be interesting, to say the least - most of the components are potted in tar that will have to be melted out before I will be able to tell what is what. I think there may possibly be a copper oxide rectifier in there - at least, there is a cylinder bolted to the inside, painted black, that has two leads attached to it and which looks like it is made up of stacked disks.

I found an article titled "A New Rectifier Tube for 'A-B-C' Power Units" from "Radio News for October, 1926", detailing the BH tube. The article showed an A-B-C eliminator circuit similar, though not identical, to mine (mine, for example, does not have any variable resistors, but rather uses three cartridge-type resistors and what appears to possibly be a heavy-duty tapped wire-wound resistor), but it shows both an A+ terminal, and a pair of terminals marked "A.C. Filament Supply for Power Amplifier Tube". Mine does not have an A+ terminal, however. I might have a line on a cheap Rectigon-type battery charger, and if I can get that AND get the eliminator working, I'll just plug the charger into the 115-volt socket in the top cover of the eliminator and use a sealed 6-volt L/A battery for my "A" supply.

I've read that old HeNe soft seal laser tubes can "rejuvenated" by placing them in a bag with helium or a simple chamber made of PVC pipe and fittings. Since it took 80+ years for the helium to defuse through the hard glass seals it might take longer than any of us oldtimers have left for the helium to defuse back in but it might be worth a try?

Should be able to force helium in under pressure. That's the way we did leak testing. Insert a part into helium under pressure then remove the part. Draw a vacuum and detect any helium coming out of a part.

I'll just go with re-basing an 0z4 tube. Seems like the simplest route.

Hi Rich -

I just found your other thread. If I were you and felt driven to restore this so it can be used to power any battery radio, I'd add a line fuse before powering up again.

And that stacked disk thing is most likely a copper oxide LV rectifier.

All that said, here's what I use to get battery radios working:

Interesting P/S unit, but I'm a bit confused about the "2 X 7805" on there. Are there two 7805 regulators in parallel, or what? If so, why?

7805 is 1.5a,, two would be 3a...

Filament supply for battery radios using 5 volt tubes should be 6 volts,up to 6.6 volts, a full charge on a lead/acid battery. The radio's rheostats will provide the voltage drop and the difference generates the proper bias for the tube(s) being controlled. Therefore, 7806 would be a better choice. Sure, the radio will work with 5 volts too... Sensitivity and volume may be reduced. An issue you have because of the location...

Caution is advised with a power source that is not completely isolated from the power line ground for a A-K 35 and similar designed radios...



If an adapter is made from a 4-pin tube base that has the bayonet pin using a ring mount octal socket, any 0Z4 could be used should one fail in the future...

YMMV

Chas

Something else I am a bit confused about is the grounding system on that s/s power supply. I notice the ground coming off pin 2 on the 7805 has a different symbol than all the other "ground" connections. Why is this? I'm guessing all the others connect to mains ground, but what about this one?

Also, could two separate 12-volt transformers with their secondaries connected together as per the schematic work? Seems a pair of Radio Shack 12-volt transformers would be less expensive than the listed one.

One symbol represents a common chassis connection, the one shared by the ground connection to the power source. The other symbol represents earth, however, in this instance it appears to represent a common heat sink, which, should not be connected to the power ground...

Yes, two transformers could be used, so long as the secondaries are at least 1.5a each. IF paired the MUST be identical transformers. Note the the bias is achieved via a reference through the power source and is not isolated... Bias could also be achieved via voltage drop in the B+ string or a separate transformer.

Did I understand that you have an ARBE-III? That has isolated power supplies with no reference to earth or ground. That is a connection that the user makes if it is needed. The chassis/cover is connected to the AC ground via the 3-wire plug...

You will probably discover that the capacitors in the ABC supply you are repairing are of very low value. Filtering is accomplished by the choke iron... If you can measure the caps they are probably no more than 2mf for each wrapped package and could be as low as .5mf. With that in mind 630 volt metalized caps could be used in pairs or however grouped to replace the papers. There would be no polarity issue and the caps would last practically forever...

If you want to try out the power transformer be sure you know what leads are what and energize the primary with 12 volts you should see appropriately reduced voltages on all the other leads, simply multiply by 10... Once that is know re-energize with 120 volts on the primary via a 60 watt lamp in series. The lamp should glow dimly, allow the transformer to remain energized for a 1/2 hour there should be virtually NO heating. The transformer will be good. If the transformer is bad, heating will begin in just a few minutes and the bulb will glow rather brightly. This indicates the transformer has a short.

YMMV

Chas