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 Post subject: Curious little radio
PostPosted: Apr Sat 28, 2012 1:52 am 
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A co-worker gave this to me. It is a homemade 1920s battery set. Not sure if it follows any particular circuit or plans. maybe even hodge-podged together, but it is a bit more interesting than a typical 5 tube 3 dialer.

This uses three UV199 tubes. The filaments are intact and have no shorts. Two Remler clamshell type variable capacitors. Three audio transformers. Two All American Mohawks and one Jefferson. The Jefferson and second AAM have open primaries, of course. The three tube sockets are springy Benjamin brand.

What is very curious is the ERLA fixed crystal detector suspended in mid air.

I surmise this must be a reflex circuit, though the one basket weave coil looks thrown in as an afterthought.

I suppose I will trace out the circuit sometime and post it.

-Steve


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 Post subject: Re: Curious little radio
PostPosted: Apr Sat 28, 2012 2:06 am 
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I think you're right about its being a reflex, given the detector and extra audio transformer.


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 Post subject: Re: Curious little radio
PostPosted: Apr Sat 28, 2012 2:29 am 
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Cool! I love early homebrews...


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 Post subject: Re: Curious little radio
PostPosted: Apr Sat 28, 2012 5:49 pm 
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It looks like you have three or more upgrades changing the original circuit into something else over the years.
When You work on the schematic mark the obvious changes somehow. I use colored pencils usually.
You may be able to find original articles the owner used for the upgrades and changes in old Radio News or other magazines at the local library.
Looking at the layout I think you will have problems with unwanted feedback because the components are too cramped and laid out poorly. You do not normally run into audio feedback problems on sets of that age but I'm sure you will on this one. Motorboating put put oscillations are usually easy to fix, just move the audio components away from the RF circuits.
Too negative..I hope you have few problems on this one. I love the ones that are obviously daily drivers and were upgraded several times over a lot of years. The fixed xtal hanging there is common, and a selling point as the panel and chassis did not have to be drilled or modified for the upgrade.


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 Post subject: Re: Curious little radio
PostPosted: Apr Sat 28, 2012 6:46 pm 
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Would be interesting to trace that out and recreate the schematic, all right. Those tuning caps make collectors go ga-ga and they bring a pretty hefty price just by themselves.


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 Post subject: Re: Curious little radio
PostPosted: Apr Sat 28, 2012 10:58 pm 
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Thanks for sharing :D


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 Post subject: Re: Curious little radio
PostPosted: Apr Sun 29, 2012 12:35 am 
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And it looks like the original "C" battery is still there, ready to be restuffed.

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 Post subject: Re: Curious little radio
PostPosted: Apr Sun 29, 2012 12:51 pm 
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Pull the battery and look for a manufactured or expiration date. That will give you a good idea of the last date used. It looks like the label used by Burgess in the early 50's and maybe into the 60's.


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 Post subject: Re: Curious little radio
PostPosted: Apr Sun 29, 2012 2:59 pm 
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Homebrew, I couldn't find any dates on the battery other than patent dates. Last one being 1927. The battery is in very poor condition as the photo shows.

I also quickly and roughly traced out the circuit. It is presented here exactly as it is hooked up. There are a couple anomalies such as the rheostat in line with the C battery and the ungrounded detector circuit, but I didn't wire the thing. :wink:

Yes, it very much is a reflex circuit. RF amplifier, xtal detector and two stages of AF amplification.

It probably is worth more in parts, but I'll keep it intact as it is a piece of 1920s history. Whether it worked very well or not. Probably not. :?

-Steve


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 Post subject: Re: Curious little radio
PostPosted: Apr Sun 29, 2012 3:41 pm 
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Is the Jefferson a RF transformer? You can sub a later small Miller RF coil to get the set working.
Both types of transformer used in your set have the same design problem. The fine wire from the transformer breaks at the solder connection where the fine xformer wire is connected to the interconnect wire going to the outside terminals. The solder joint is usually just under the paper wrap on the coil. The bad audio xformer can be temporarily bypassed by setting the stage up as a resistor coupled amp. You will lose some volume but gain fidelity.
Around three out of ten homebrew and kit radios that I run across have wiring errors that would have made the radio inoperative originally.
The design should be a good DX radio, worth fixing.
The earliest Burgess battery I've found with a date code is 1951 so yours is probably earlier. The shield shape goes back to at least 1926.


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 Post subject: Re: Curious little radio
PostPosted: Apr Sun 29, 2012 4:00 pm 
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The Jefferson is an audio transformer.
I have had some success zapping open audio windings with a high voltage. many years ago (early 80s?) IHRS member Walt Sanders had a small article in the club Bulletin describing this procedure. The success rate is low, but sometimes it brings an otherwise dead audio transformer back.

I even had success reviving a flyback transformer on an RCA projection TV with this procedure, allowing the customer to use their TV until the backordered replacement arrived. :D

-Steve

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 Post subject: Re: Curious little radio
PostPosted: Apr Sun 29, 2012 4:32 pm 
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Generally the transformer where the Jefferson is would be a RF type, the secondary looking like a short to the audio and passing it thru. Seems like a audio xformer would load the RF portion way too much? I'll have to pull some older kit parts lists to see if I can find one with a audio in that position.


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 Post subject: Re: Curious little radio
PostPosted: Apr Sun 29, 2012 4:39 pm 
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Well, it is a reflex circuit.
The Jefferson transformer is feeding the detected audio back into the RF amplifier making it an audio amplifier as well.

-Steve

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