MTFCA Forum

I realize this is off topic but needed as many people as I could muster to ID it.
It has a microphone and earpiece, is battery powered and in a nice wooden box. I've tried to ID it, Burgess battery to date it without any luck. Might need to see whats under he black plate

Looks like a closed circuit telephone, (i.e. intercom). Move the microphone so we can see the whole interior.

I added some more pictures. Not sure if the battery box belongs There was a battery case in the box dated SEP 1944, which could be misleading. The brass clip looks like it was to retain two D cell a batteries. There were no additional markings on the tube.

Sylvania or at least Sylvania branded tube is that a marking in the glass I see on the transformer side or just dust/reflection? some tube sites can help identify the year of the tube might help somewhat although I suppose an older tube could have been put in at some point or of course a newer tube. I have a feeling that tube may have been a military spec tube for whatever that's worth.

Tokyo Rose.

The tube should have a number on the glass portion in a dull black ink. That style tube was in common use around 1950. That one looks like a triode. A tube of that sort requires a dual power supply, with one voltage source for the tube's heater element, typically 6, 12, 35, or 50 volts DC and another for the plate circuit, typically upwards of 80 volts DC and often up to 200 volts DC. I don't think 2 D zinc carbon batteries would power even a one-tube device for more than a very short time. Battery powered home radios that used vacuuum tubes typically had an "A" battery that supplied the heater circuit with anywhere from 1 to 6 volts, and a larger "B" battery that supplied the plate circuit, typically 70 volts or more. The "B" battery would consist of around 50 dry cells in series. A mobile device with tubes usually ran off a storage battery and required a vibrator power supply and a power transformer with multiple windings, a rectifier tube, and assorted other devices to filter the power to a clean DC.

I agree with Jerry; the object in the OP is almost exactly the same shape and color as the intercoms that we had in a Ford dealer where I worked in the early 1960's.

The cylindrical tan colored object is a resistor. It is marked with a long-obsolete color code, known as the BED code. (Body, End, Dot) That suggests that the device is probably pre-1950. The Burgess battery should have a voltage imprinted on it.

A mobile device would have probably had a metal encased tube or a "Loctal" type tube.

One terminal is marked "GND" and the other one is marked "B+AMP"

TXGOAT2 wrote: ↑

Sat Dec 11, 2021 9:50 am

The tube should have a number on the glass portion in a dull black ink. That style tube was in common use around 1950. That one looks like a triode. A tube of that sort requires a dual power supply, with one voltage source for the tube's heater element, typically 6, 12, 35, or 50 volts DC and another for the plate circuit, typically upwards of 80 volts DC and often up to 200 volts AC. I don't think 2 D zinc carbon batteries would power even a one-tube device for more than a very short time. Battery powered home radios that used vacuum tubes typically had an "A" battery that supplied the heater circuit with anywhere from 1 to 6 volts, and a larger "B" battery that supplied the plate circuit, typically 70 volts or more. The "B" battery would consist of around 50 dry cells in series. A mobile device with tubes usually ran off a storage battery and required a vibrator power supply and a power transformer with multiple windings, a rectifier tube, and assorted other devices to filter the power to a clean DC.

Some of the voltage description sort of fits. The Burgess Battery Box is empty but one end has a -- +45 markings and a date to install before SEP 1944. What puzzles me is the ear piece, doesn't make sense for some kind of a loudspeaker system or radio broadcast. Thought it might be linemen's or phone repairman's hand set - before rotary phones. Thinking that being in the wood box would exclude field usage.
The wire on the ear piece doesn't match the rest of the set, BUT is very flexible as it would need to be for that purpose. I will see if there are marking on the top of the glass tube. And hook things up so to see if that earpiece has a place to plug into. This unit was in the first house we purchased in 1971 - there were other things indicating that the owner had dabbled in electronics.

The Burgess would have been the "B" battery to operate the plate circuit. The tube would have needed a filament supply also. I think the tube was used as an amplifier, perhaps permit two of the devices to be used with a long hardwire connection between them. The headset would operate at a much lower power than even a very small loudspeaker. The number on the tube, if it's still there, could be anywhere on the glass portion. That tube is probably a replacement, and looks newer than the rest of the device. Most likely, if that's a portable device, it would have used an equivalent tube with a metal casing. The metal type tubes functioned the same as the glass ones, but were more vibration resistant. The tube number might look something like 6L5, or 6L50, or 6L5 GT.

Last thought. There are no markings on the top of the glass tube or anywhere I can see. I connected things up and the earpiece has no place to be connected. The AMP nut loosens but has a stop. One last thing. When I said the previous house owner dabbled in electronics, I still have numerous Heath Kit manuals somewhere. Is it possible that this is some sort of DIY microphone preamp? The more I look at the box, lots of DIY, may have been repurposed. Thanks for all the input

Play Things Of Past
Medina, Ohio
330-558-0247
mailto:gbsptop@aol.com

He knows about every type of phone or intercom system ever made and can probably identify what you have.

The tube is likely a rectifier to produce a pulsed DC voltage to charge the battery.

There should also be a capacitor to smooth out the pulses and avoid 60 cycle hum in the earpiece.

The tube may have a 115 AC volt heater circuit for the cathode to operate, as they were common for early record players.

The transformer may have only reduced the charge voltage to the battery.

Remove the tube and tell me the number on it and I'll tell you for sure.

Dry cell batteries cannot be recharged, and a house current device would have no need of batteries. A battery powered device would have no need of a rectifier or filters. There is a paper capacitor in the device, but it's too small to be a power supply filter. The tube appears to have a barrel-type plate and at least one screen grid within it. A rectifier tube would not have any grids, being essentially a diode. The thing may have been some kind of field telephone with both a speaker and earphone. The earphone would make less demand on the battery than a speaker, but the tube would quickly run down anything but a large battery. The tube could be switched off to save the battery, but the device would then be inoperative and would require about 8 seconds for the tube to warm up when switched on, assuming the filament battery was in good shape. A carbon microphone and a battery might do to make a telephone that could operate on very low current draw when used with a headset, but I don't think it could be used over any significant distance without some amplification. A piezoelectric mike and headset might operate over some minimal distance without any outside power source, but this device does appear to have a rudimentary audio amplifier and battery power supply.

Interesting thread, it's been years since I looked at anything with valves (er, 'tubes'!), takes me back to my first radio, a R1155A.

At least these things were easy to understand how they worked, modern stuff relies much more on magic... anyway Pat raises an interesting question - is the mic a carbon or crystal unit?

A common dynamic speaker with a permanent field magnet can function as a microphone. If you connect a PM dynamic speaker to another speaker in the next room, talking into either one should provide some audio output at the other end. The signal produced by the microphonic speaker would be low voltage, high current, and so would not travel very far without considerable loss. The second, or receiving speaker would probably not be very efficient at turning the signal back into sound, but fidelity would probably be pretty good.

TXGOAT2 wrote: ↑

Sun Dec 12, 2021 4:35 pm

A common dynamic speaker with a permanent field magnet can function as a microphone.

Pat, thanks, you've brought up another memory associated with the age of Frank's mystery here; speakers that required power for the large electromagnet coil

They didn't have good permanent magnets prior to WWII. Most large radios and some table tops used an electromagnet for a field magnet. The field magnet was usually supplied with filtered DC at high voltage by the plate supply. They usually included a hum-bucking coil on the same core as the large field magnet winding. The hum bucker was much smaller with far fewer turns of heavier wire and was in placed series with the speaker voice coil. The field magnet winding doubled as an iron core choke to smooth out the plate supply. Somehow, the humbucker coil prevented an objectionable 60 cycle audio overtone. Most big radio sets had some background powerline hum. A good battery powered set out in a rural area would be hum-free and free of most interference in an area with no utility power. Some of those sets had TRF amplification stages and were very sensitive and selective. With a good outdoor antenna and a good earth ground and some patience, you could often capture some very distant stations. ALNICO permanent magnets began replacing the field coils in the post WWII era, and the little 5-tube AC-DC clock radios became the norm. Most of them featured a plastic case and a "four-inch speaker with powerful Alnico magnet for rich, room-filling sound". They were OK for news and weather, but no match for audio quality with the large pre-war console sets.