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 Post subject: Mystery Twin-Chassis Radio
PostPosted: Jul Wed 21, 2021 2:14 am 
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I recently picked up this enigma from a fellow PSARA club member, and I'm trying to work out what it is and if any information exists on it or anything similar.

Photo dump time!

I apologize that the cabinets are empty, as I already dug into the set as soon as I got home with it.

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The set's construction, while unusual, does seem fairly well laid out and assembled. From the Girard-Hopkins resistors that dominate the radio chassis, and the fact that there are part numbers and wire labels on the (IF?) cans, I am guessing that this was either a kit or something built from magazine plans (possibly supplied by a company like Allied? There is a little sailing vessel on the dial).

The radio chassis has the following tubes: 56, 57, 58, 58, 55, 2A5. The left knob is a four position wafer switch, and I'm not sure what it does yet. I'm fairly confident that the switch and all the extra coils are for multiple bands in a superhet design, rather than a TRF. The power supply / speaker chassis is fairly mundane, one 80 rectifier and a field coil speaker that plugs in with a repurposed UX-226 tube base. The weird thing is the extra tube on the right, which I THINK is a 57...label is toast. The tube is connected to the tip jack and switch on the rear, and has a shielded connection to the grid cap. Pretty sure this is a phono input, albeit with only one connection (it does actually work). The weird thing is that the jack appears to be connected to the plate of the tube...and then there's the two mystery coil cans on the power supply chassis; one connects the power transformer to the plates of the 80, and the other is hooked up to the mystery tube and has a knob on the top. Still working on a schematic for this thing.

I just wanted to document this interesting piece of technology in case another appears in the future. Wil update as I move towards getting it working.

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 Post subject: Re: Mystery Twin-Chassis Radio
PostPosted: Jul Wed 21, 2021 3:01 am 
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That is a very interesting receiver. With shortwave and what appears to be a BFO on the power supply chassis the set appears to be intended for communications receiver market. I strongly suspect it is a west coast set, perhaps an EM Sargent product prior to their Model 8-34.

Norman

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 Post subject: Re: Mystery Twin-Chassis Radio
PostPosted: Jul Wed 21, 2021 5:15 am 
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My guess is that that's a homebrew that was based closely, if not exactly, to some plans from a radio magazine.

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 Post subject: Re: Mystery Twin-Chassis Radio
PostPosted: Jul Wed 21, 2021 12:42 pm 
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The riveted tube sockets lead me to believe that it is a factory made radio. Early 1930s for sure.

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 Post subject: Re: Mystery Twin-Chassis Radio
PostPosted: Jul Wed 21, 2021 12:57 pm 
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I also noticed that the tube sockets are riveted. I noticed that the female power supply socket was screwed in place and the hole for it is not smooth around it's edges but somewhat jagged, almost as if it was cut open free hand and not with a hole punch.

If that's an adjustable beat oscillator on that power supply, it would be awfully strange for a manufacturer to be placing it there. I've never seen that done before.

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 Post subject: Re: Mystery Twin-Chassis Radio
PostPosted: Jul Wed 21, 2021 4:02 pm 
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Maybe you're both right. Maybe the two chassis were originally hard wired together in a larger cabinet?

Someone re-packaged them and added the power plug and socket?


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 Post subject: Re: Mystery Twin-Chassis Radio
PostPosted: Jul Wed 21, 2021 9:31 pm 
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The styling of the cabinets does fit in with the era of the tubes and components.

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 Post subject: Re: Mystery Twin-Chassis Radio
PostPosted: Jul Wed 21, 2021 11:11 pm 
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Is it me or is there only one groove on the left hand side of the cabinet, picture 9?
Could be a hint that the chassis was later fitted to too narrow a cabinet..

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 Post subject: Re: Mystery Twin-Chassis Radio
PostPosted: Jul Thu 22, 2021 2:29 am 
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There are two grooves in the speaker cabinet, the photo just doesn't show it. The fit is fine, although the radio chassis just squeezes into place if the screws are installed on the sides to hold on the bottom cover.

I wondered if maybe this set was a kit, perhaps since the tube sockets are riveted in, and assuming a company would supply the chassis partially preassembled. The ugly hole for the socket on the power supply chassis does look extremely amateurish, but the rest of the set just seems too nicely laid out and put together....

I have a partial schematic for the set worked up, and after a few capacitor replacements, the set came to life! Good AM reception with a 2 foot antenna; picked up an LA station last night.

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 Post subject: Re: Mystery Twin-Chassis Radio
PostPosted: Jul Thu 22, 2021 3:27 am 
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It's amazing how an extra stage of tuned IF does wonders to a radios reception performance.

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 Post subject: Re: Mystery Twin-Chassis Radio
PostPosted: Jul Thu 22, 2021 4:40 pm 
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It is possible the socket/plug combination became broken and was replaced with one that required enlarging the hole. That makes more sense to me given that that socket is held in with screws while the rest of the construction is riveted.


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 Post subject: Re: Mystery Twin-Chassis Radio
PostPosted: Jul Thu 22, 2021 7:47 pm 
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That's an interesting audio circuit, with the AVC supplying bias to the triode section of the 55, and the volume control in the grid of the output stage.

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 Post subject: Re: Mystery Twin-Chassis Radio
PostPosted: Jul Thu 22, 2021 11:10 pm 
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I wonder if this could have been a JW Miller offering? They did offer limited numbers of coil kits in the early 30s and even knock-down larger kit offerings. For instance, I have a Miller model 302 preselector from them. At the least, I'd guess that all of the open coils and IF's are Miller.

Chris


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 Post subject: Re: Mystery Twin-Chassis Radio
PostPosted: Jul Fri 23, 2021 4:09 am 
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startgroove wrote:
It is possible the socket/plug combination became broken and was replaced with one that required enlarging the hole. That makes more sense to me given that that socket is held in with screws while the rest of the construction is riveted.


I haven't actually considered this, but its possible. The male end of the cable is actually damaged, as its just a repurposed tube base filled with tar. While researching the EM Sargent company on Radiomuseum, I found a photo of one of their models that uses the same IF transformers, which I though could be more than coincidental. Going to flesh out the BFO on the schematic tonight.

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 Post subject: Re: Mystery Twin-Chassis Radio
PostPosted: Jul Fri 23, 2021 4:12 am 
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Tim Tress wrote:
That's an interesting audio circuit, with the AVC supplying bias to the triode section of the 55, and the volume control in the grid of the output stage.


While I'm quite sure that's how its hooked up, I need to pull that IF can open and confirm it. There were multiple black wires running out of it and they all ohmed out to each other, from the diode section back towards the triode section.

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 Post subject: Re: Mystery Twin-Chassis Radio
PostPosted: Jul Sat 24, 2021 2:04 am 
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A better close up of the dial face graphics might help.


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 Post subject: Re: Mystery Twin-Chassis Radio
PostPosted: Jul Sat 24, 2021 3:19 pm 
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KJ6OFC wrote:
I wonder if this could have been a JW Miller offering? They did offer limited numbers of coil kits in the early 30s and even knock-down larger kit offerings.


I doubt Miller had anything to do with that unit since I don't see any Miller components used. That set does not follow any design that Miller has ever published.

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