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| DaOld Man:
--- Quote from: Robbbert on April 23, 2021, 08:51:52 pm ---You've poked me in my favourite hobby damn you. If that schematic is correct, then you have a TRF radio, which means a whole bunch of tuning knobs to adjust whenever you choose another station (it's AM band only). Some really expensive TRF radios had the adjustments linked up with a chain or some other means. If you're planning on powering it up, make sure you replace all the capacitors with modern equivalents with suitable voltage ratings. Then check the values of all the resistors and replace as needed. The radio is so old that even the insulation on the wires could have rotted away, so then you'll have to replace all of them too. Don't forget the power cord - the insulation is probably rubber which will have perished ages ago. If you just plug it in without checking, you'll either destroy all the irreplaceable parts, or you'll start a fire. Be very careful with the valves (tubes). If you break one, then you're unlikely to find a replacement any time soon. The schematic doesn't show the power supply - I'm assuming it's mains powered, but perhaps it runs on unobtanium batteries. AS for its worth - it would have been pricey back in the day, but whether that excites anyone today is another matter. Good luck? EDIT: I see the photo only shows 3 knobs (which appear to be missing). So I'm not at all sure the schematic matches this radio. Perhaps you could look inside and see what valves are there, and how many. --- End quote --- I found a video on you tube showing this radio does have a tuning coil actuated by a lever rod that is attached to a knob, not sure where though, maybe one of the missing knobs on the front? The power supply is a very heavy box. May have batteries in it I dont know. I figured it contains an old heavy transformer. I havent done anything at all to it yet, but I have taken more pictures of the inside. Will post them soon. |
| DaOld Man:
More pics. This is the speaker and to the right of it is the power supply. Here is a shot of the receiver. Not sure what the box is in front of the tubes. 2 tubes (valves) or maybe three. Looks like there may be a tube socket int the front (of pic, actually facing back of cabinet), that may have had a tube in it. If so at least one tube is missing. Another shot of the speaker. Not sure what that thing is mounted to the wall, to left of speaker. Maybe a line filter??? And finally, a shot of the tuning cap, enclosed in a metal box. (Im pretty sure it is the tuning cap.) |
| bobbyb13:
That is such a cool unit (and I have no idea what the hell I am looking at in there really either.) Makes you wonder exactly what its history is. Appears in great shape for something probably quickky approaching a hundred years old! |
| Robbbert:
Thanks for the photos. Firstly, I had another look at the schematic (assuming it's the right one). There's 5x type 27 tube, which you can still buy online for about $15 each. The first 4 are straight RF amps, and the last is what I believe is called the anode-bend detector (it's really ancient technology that soon fell out of favour). The last 2 tubes are type 45 which are rather more expensive, $70 or more (or a lot more), wired as a push-pull audio output stage. The speaker transformer (probably part of the speaker assembly) converts the valve's high voltage low current to the speaker's need for low voltage high current. Every valve radio has a speaker transformer, although the rest of the technology evolved over time. As for the power supply, if it's an AC type (plugs into the wall socket), there will be a transformer, a rectifier valve (most likely type 80), some smoothing capacitors (which will need replacing), and perhaps a choke. Most radios of that age didn't have a choke, but instead used a winding on the speaker for that purpose. That's because magnet technology wasn't up to speed back then, and the magnetic field of the choke winding did the job instead. If the power supply is a battery type, then all that's in there will be various batteries, all gone flat or leaking by now. However, if we once again depend on the schematic, voltages exceeding 300 volts are mentioned, and these would only come from an AC supply. You can imagine what 300 volts would do to old dud capacitors. That's why you should replace all of them before even thinking about applying power. |
| Robbbert:
Now to your photos. The speaker unit looks quite complex, but in fact is fairly standard for that time. There will be the field winding (the choke winding mentioned above), the speaker transformer and the voice coil winding. Today's speakers only have the voice coil, the rest no longer needed. So, don't ruin the speaker unit, it's irreplaceable. But does it work? You'll need your multimeter set to ohms, and make sure the field coil is intact (should measure several hundred ohms or so). The primary of the speaker transformer must conduct between all 3 pins (being a push-pull unit). And lastly the secondary, which joins to the voice coil, must conduct as well. The most likely failures are the field coil and the primary winding, both of which are fatal to your radio, I'm afraid. As to the cylindrical unit near the speaker, I couldn't really say, it could be anything. Given the age, it might even be a baretter, another lost piece of technology. A baretter looks like a fancy light globe, and performs the task of a current regulator. Like any light globe it has a filament that can blow. Further analysis can only be performed by removing the receiver chassis, turning it over and seeing what lies underneath (but be careful with those valves). |
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