Batteries and a strap for a vintage Zenith hearing aid
 

Ever have one of those projects that would probably take twenty minutes if you could just find the parts, but you can't get all your ducks in a row?

I'd like to take care of a few issues on my early 1950s Zenith hearing aid. This is one of those subminiature tube units. It's in pretty good shape, except for three issues-

- There's a worn label inside, maybe from battery leakage, so one decal is absent. I'm thinking of just contacting RadioDaze to see if they can make a repro based on some online images and a few measurements.

- The B battery is supposed to have a strap to help pull it out, but it's broken from the years of sitting (and possibly leaking batteries). I know battery straps are still a thing, so I'm trying to decide whether I can get a premade strap and install it, or if just buying some firm material would be best. Does anyone know what that thing is called? Looking up "battery tab" and "battery strap" just brings up those little disposable straps they stick in toys so the batteries don't leak on the shelf.

- On the subject of batteries, I'm having some trouble finding the correct batteries. I think I've found a source for the 22.5V B battery I need, but can anyone direct me to a matching A battery? There's no voltage marking on what I have, and no number on it. I need two of them.

Anyway, thanks in advance for any help. I'm including a few photos to help show what I'm looking for.

Okay, quick update - I'm pretty sure I've found the batteries. I've placed an order, so fingers crossed these are right.

So now I'm just looking to resolve the strap problem.

I *believe* the small battery is 1.5v. I've never seen one before, but I have an old Simpson battery tester meter that specifically has a setting for 'Hearing Aid' which is 1.5v. Incidentally, the 22.5v batteries are also used in older Simpson 260 meters. For the strap, I'm not sure how it was held in, but a piece of wide gift-wrapping ribbon would be just fine. That stuff's pretty strong, actually. And thin enough not to interfere with the position of the batteries.

Also... cool hearing aid.

That matches what I ordered. I was able to find a site that listed the battery numbers, and it looks like the A battery is an RM-1, which is actually still available online. It looks like there's also a company that's making reproduction 22.5V batteries, so fingers crossed those two will give me what I'm looking for.

You know, I had actually considered that same solution. I'd be able to color match it, and it would preserve the little ridges on it. I should probably open it up and see how it's mounted underneath, first, in case that ends up being more complicated than I'm expecting, but I think I'll give that a try.

You may want to contact this cat. I would say he is a serious
collector.
https://www.flickr.com/photos/517645...7631802145670/

BTW my grandmother always had Zenith hearing aids.

73 Zeno:smoke:
LFOD !

Okay, so the batteries are in, and I finally got a chance to try a power up. As far as I can tell, I'm not getting any life out of it. No amps across the power switch when I turn it on, and the tubes aren't heating.

My first inclination is to test whether any of the tube filaments are open. It uses two CK549DX tubes, and one CK546DX. I've managed to find the diagrams here: (https://www.radiomuseum.org/tubes/tube_ck549dx.html, https://www.radiomuseum.org/tubes/tube_ck546dx.html) but I'm having a little trouble reading them. I think those may be European style schematics, rather than American. Can anyone tell me how to read subminiature tube pins, and, based on those diagrams, which I should be checking?

Barring that, I'll be reaching out to that fellow Zeno pointed me to, to see if he has any leads on a schematic. This this uses a lot of couplates, so if any of those are bad, that may be game over for now. I'm not sure I have the skill and tools to reproduce complicated couplates in a size that would fit the small profile. I'm not sure that's possible at all, to be honest, but I'd have to see what each one contains first. There isn't a listing of couplate schematics based on the part numbers somewhere, is there? I at least have those.

I've done some more research on that band, and I'm thinking I'm going to reach out to strapworks (https://www.strapworks.com/default.asp) to see about having it reproduced. There's a little bump on the end of the strap that helps keep it in place once the front plate is on, that I'd ideally like to include in the new one. Fingers crossed they can set me up with something, they sound like a good source.

As always, any advice is appreciated.

the tube its self is drawn in a standard way for a battery tube look at something like a 3V4. Fil is center and right, G3 is also tied to the heater as in most penthodes and Beam power tubes. The dot on the schematic should correspond to a dot on one side of the base of the tube...Similar to the notch on the end of a DIP IC.

The amp schematic is definitely european, but if you read the component values and look at it with some care it should make sense...It is a hell of a lot clearer than some 1920's American radio schematics.

Thanks for the tip about the battery availability, mine works fine with new batteries. I am really surprised that the microphone works as well as it does, as most crystal phono cartridges of the era are quite dead. the hearing aid has tons of gain.

https://farm8.staticflickr.com/7828/...25dd67_z_d.jpg

jr

I bought one of the same model at a garage sale about 35 years ago and still have it.

I have no idea what kind of earphones are compatible with it.

The earphone that comes with it measures less than 40 ohms (dc). It has no problem driving inexpensive ear buds, such as Jlab J-5s, and works quite well driving Sony MDR-7506 headphones.

jr

I ended up with a couple spares, if you want one.

I need to get back into this. Last part I got to involved realizing that one of the wires to the button battery terminals had corroded from battery leakage and broken the lead off. I need to run a new length and splice them. Tube filaments tested fine once I got the note on how to read the schematics, so I'm pretty sure repairing that lead is gonna get me back in business.