Some hearing aids with tubes

Philips KL5000 WE Interior Western Electric type134 Amplivox pre-WWII

Click to get a bigger picture of the Amplivox

Brand and type: Upper row on the left is the Philips KL5000 Major, the one right is a Western Electric type 134. In the center you see a part of the interior of the WE with the tiny tubes, only a bit thicker than a pencil.
The Philips tubes are the same size.
The black device below is an English Amplivox.

Produced: Both Philips and WE in the first half of the fifties.
I have a strong feeling that the Amplivox is at least 15 years older, maybe it is pre-WWII.

Cabinet: The Philips has a chrome plated matal cabinet, the WE is flesh coloured plastic. The Philips is 100x60x20 mm, the WE is 105x57x20 mm and slightly bended
The WE has rather strong spring steel clamps at each side, but for what purpose? The Philips has one clip at the back to clamp it to your shirt pocket.
For the Amplivox you need huge shirt- or coat-pockets: one for the device, one for the high-tension Siemens battery. See the match in front of it for reference.
It has a steel plate case covered with black linen, the upper microphone part has a bakelite grill.

Tubes: Three pentodes for the Philips: 2x DF97 and a DL67 is the output. Probably the equivalent US-tubes for the WE: 2x CK505AX and a CK507AX. Be carefull with the filaments: the D-types are battery tubes and normally take 1.5V supply. But these mini tubes work with 0.625V on the filaments, and 2 are connected in series to a single 1.5V cell. The output tube has a filament for 1.25V. All filaments consume 15 mA.
For the anode circuits a 22.5V batery is used.
Philips says: switch it off when not in use, and take several filament batteries with you when used daily or for longer times. Exchange these more times a day when performance decreases. This will extend lifetime of each filament battery!

The Amplivox has the following tubes: 2 pcs. XSG, HIVAC brand, having a topcap, and X.. (not readable). The B+-battery is 45V, for the filaments you need a flat 4.5V battery which fits inside. The XSG tubes each take 2V for the filament. If you know the type-no. of the third tube, please inform me!

Controls: The Philips has tone and volume controls, on/off and a switch to select between mike and pickup coil. The WE has a switch and a volume control, as has the Amplivox oldie.

Obtained: All were found at ordinary flea markets. The Amplivox was in a carton box, addressed to the owner and came with the B+ battery and the earphone piece.

Working: The Philips has a built in microphone and also a pickup coil. The latter was used in theatres and churches equiped with a special audio frequency transmitter for hearing aids. It is all explained in the little booklet which came with the device, not telling how it works in detail. Though I don't understand how this works as the coil is enclosed in the all metal cabinet. The speaker of course is a crystal type earpiece.
It also has a so called "adjustment block" which was adapted to the individual using the device. It sets the maximum audio level and maybe the frequency response curve. I don't know what it contains. Probably one or more resistors.
In fact it is beyond repair, as all components are poured in a block of synthetic stuff.
The battery clamps are partly gone, oxidated by a leaking battery.

As for the WE, I know zero about it. Any information is welcome of course.

Finally the Amplivox, this one is OK. It must have been a big relieve to switch from a giant horn to a modern amplifying device, with the parts hidden under your clothes, and a hardly visible tiny earpiece avoiding people to scream at you....