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 Post subject: Flea market rescue, mutt or pure bred?
PostPosted: Oct Sun 25, 2020 10:07 pm 
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Location: Amherst, Massachusetts
Back in the early nineties my mother bought this radio for me at a flea market. It had been repaired fairly well by someone back then and the crack along one side of the Bakelite cabinet was well camouflaged. It is a nice looking radio painted in matte black and it worked for many years though I have not used it in a long time.

Inside one can see a couple of spots where the paper capacitors have melted over the years and a crudely attached plastic/celluloid dial that might not belong on this radio. Though hard to see in the pictures, you can see brown and green Bakelite beneath the black paint. The buttons were originally white and were painted black.

Does anyone recognize this radio such that I might get schematics? It seems unlikely it is a true McMurdo but I'm no connoisseur.


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File comment: Front view: Incorrect dial?
McMurdo_Silver_front_small.jpg
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McMurdo_Silver _Chassis_small.jpg
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McMurdo_Silver_Under_Chassis_small.jpg
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File comment: Notice the way the cracked dial is attached to the cabinet.
McMurdo_Silver_Inside_Cabinet.jpg
McMurdo_Silver_Inside_Cabinet.jpg [ 713.98 KiB | Viewed 1243 times ]
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 Post subject: Re: Flea market rescue, mutt or pure bred?
PostPosted: Oct Sun 25, 2020 10:37 pm 
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It uses the logo of McMurdo Silver's last business venture which was in the test equipment realm after WWII.

He sold the high-end radio business to Scott about 1938.

I didn't know he sold any radios during this time, but it is possible. A simple AA5, I can't imagine it has any special value, even with his name on it.

-Steve

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 Post subject: Re: Flea market rescue, mutt or pure bred?
PostPosted: Oct Sun 25, 2020 10:38 pm 
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Nothing more then a rebadged Crosley 9-120.

Image

Schematic: http://www.nostalgiaair.org/pagesbymode ... 003665.pdf

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 Post subject: Re: Flea market rescue, mutt or pure bred?
PostPosted: Oct Mon 26, 2020 1:01 am 
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Location: Amherst, Massachusetts
Yes, it has to be a Crosley!

Thank you both for such helpful information and the schematic.


Last edited by ElectricDream5 on Oct Tue 27, 2020 12:52 am, edited 1 time in total.

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 Post subject: Re: Flea market rescue, mutt or pure bred?
PostPosted: Oct Mon 26, 2020 1:08 am 
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That's a keeper, since you have the history, just needs all new caps. 8)

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 Post subject: Re: Flea market rescue, mutt or pure bred?
PostPosted: Oct Mon 26, 2020 1:25 am 
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The old repairs were rather crudely done; you should be able to do better. Also, this radio has been modified; there is a silicon diode in the upper right corner of the under-chassis photo. So don't expect it to match any schematic you find.

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 Post subject: Re: Flea market rescue, mutt or pure bred?
PostPosted: Oct Mon 26, 2020 2:18 am 
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I would rip it all out and start over, wiring it per the Crosley schematic.

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 Post subject: Re: Flea market rescue, mutt or pure bred?
PostPosted: Oct Mon 26, 2020 2:31 am 
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Highly unlikely that it's a rebadged Crosley as they weren't really into building radios for others. I'd be more likely to suspect that a very small company built their own chassis using surplus Crosley cabinets a year or two after Crosley discontinued that model.

Since AA5 schematics are really generic, you probably can't go wrong by rewiring it to follow the Crosley schematic. Note that the set is currently wired with one side of the AC line tied to the chassis through the power switch, while the Crosley schematic shows a safer design with floating B- which is bypassed to the chassis with a capacitor.

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 Post subject: Re: Flea market rescue, mutt or pure bred?
PostPosted: Oct Mon 26, 2020 3:08 am 
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Image
Chassis of Crosley R-120

Link to another Crosley R-120 chassis: https://www.icollector.com/Radio_i33098334

Link to a Mulby radio which uses the same Crosley R-120 cabinet and chassis: viewtopic.php?f=1&t=297823

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 Post subject: Re: Flea market rescue, mutt or pure bred?
PostPosted: Oct Mon 26, 2020 3:15 am 
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Both of the Crosley R-120 chassis photos which have been shown, as well as the Crosley R-120 schematic from Rider, show a set with a very unusual design featuring only one IF transformer and the schematic has R-C coupling from the IF stage to the detector.

The butchered chassis shown in the photos from the McMurdo Silver set clearly has two IF transformers. There's no way it could ever have been a Crosley R-120 chassis, as those aren't even punched for a second IF transformer.

I thought we had already determined that the only identifiable part of the Mulby set that we previously discussed which resembled anything Crosley was the cabinet itself. The chassis certainly isn't Crosley.

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 Post subject: Re: Flea market rescue, mutt or pure bred?
PostPosted: Oct Mon 26, 2020 3:38 am 
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Your right, one version of the chassis has 2 IF transformers and the other has only one IF transformer. Small variances but the overall layout of the components is basically the same on very similar looking chassis. Where does it say that Crosley HAD to produce the EXACT same chassis for other customers?

The Mulby chassis has 2 IF transformer punch-out's but only one is used. Another variant.

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 Post subject: Re: Flea market rescue, mutt or pure bred?
PostPosted: Oct Mon 26, 2020 12:34 pm 
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Just pick any AA5 schematic from the 1950s with a floating ground, and you will be OK. Make a sketch of the oscillator coil wiring, so it can be rewired the same way. Be aware that those IF transformers are the ones that can develop SMD, so look out for potential problems there.

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 Post subject: Re: Flea market rescue, mutt or pure bred?
PostPosted: Oct Mon 26, 2020 8:57 pm 
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Joined: Aug Thu 27, 2020 10:47 pm
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Location: Amherst, Massachusetts
Thank you all for your input.

Clearly I have a mutt here. Haven't had a chance yet to trace the wires against the schematic but at a quick glance I see the differences mentioned. Same with the Mulby chassis.

This being only my second radio to work on, I am inclined to start by recapping gradually rather than a full reconstruction but I need to study the layout before deciding. I like the idea of making it safer as suggested by Tim and Mr. Detrola and it could be a good learning experience.

If I do rebuild it per the Crosley schematic, is it OK to leave both IF cans?


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 Post subject: Re: Flea market rescue, mutt or pure bred?
PostPosted: Oct Mon 26, 2020 9:10 pm 
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Almost all AA5 sets have two IF transformers. Only the cheapest ones left the second transformer out.

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 Post subject: Re: Flea market rescue, mutt or pure bred?
PostPosted: Oct Tue 27, 2020 12:04 am 
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Location: Detroit, MI suburbs
I expect that this radio was never a Crosley, but just like the Mulby, whoever made it used surplus cabinets left over from the Crosley production or perhaps new cabinets made with the same mold which was used for the Crosley. I would try to keep it as close to possible as it was if I could. That was what I did with the Mulby.

Larry


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 Post subject: Re: Flea market rescue, mutt or pure bred?
PostPosted: Oct Tue 27, 2020 1:02 am 
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Crosley did make radios for United Motors (Delco) pre WWII.

Post WWII I don't know. It was owned by Avco by then.

-Steve

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 Post subject: Re: Flea market rescue, mutt or pure bred?
PostPosted: Oct Tue 27, 2020 1:15 am 
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It would be interesting to know whether or not there were sets built for other brands during the AVCO years of Crosley.

As Steve pointed out the only older ones I was aware of were a few Delco sets before WW2 and there weren't all that many of those.

There's a rather interesting story on how the current iteration of Crosley branded appliances came to be, and how little monetary value AVCO seemed to place on the Crosley name's reputation at the time they sold the rights to the name to the current owners.

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 Post subject: Re: Flea market rescue, mutt or pure bred?
PostPosted: Oct Wed 28, 2020 1:47 am 
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How odd. I've got a Crosley 58TK that looks very much like it. Who ever made the bakelite cabinet appears to have also made it for your radio too. https://www.radiomuseum.org/r/crosley_58tk.html

However, like the other Crosley mentioned, it only has one IF transformer and uses an RC network in place of the 2nd IF transformer.


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Crosley 58TK.jpg
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 Post subject: Re: Flea market rescue, mutt or pure bred?
PostPosted: Nov Mon 02, 2020 5:51 pm 
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Had a little time this morning to trace the Crosley 9-120W/9-119 schematic and compare with my radio. Besides the differences mentioned above, the tubes on mine are slightly different:

___________________ McMurdo / Crosley
Rectifier____________ 35B5 / 35W4
AF Power Output____ 50C5 / 50B5
Detector AVC AF amp_12AV6 / 12AT6
IF amplifier__________12BA6 / 12BA6
Converter __________12BE6 / 12BE6

There seem to be differences in resistor values but it may be that mine are out of spec. Not sure how significant these differences are.

I am putting together a parts order but I am unsure of the resistor connecting the Rectifier/35B5 the AF Power output/50C5 in this image. Is this the 1200 Ohms (brown-red-red) resistor labeled as 12 on the Crosley schematic? The colors are washed out.


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File comment: What is the value of this resistor?
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 Post subject: Re: Flea market rescue, mutt or pure bred?
PostPosted: Nov Mon 02, 2020 6:54 pm 
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Yes, I'd say that is the brown-red-red resistor.

Your rectifier, check it again, the glass 7-pin mini tube needs to be a 35W4.
35B5 is a power tube. It could be someone swapped in the wrong tube way back when.

There is a wiring difference between 50C5 in your radio and 50B5 in the Crosley schematic. Confirm with whatever the schematic shows and the actual wiring to your socket.

12AV6 is a successor to the 12AT6, so no problem there.

In the tube diagram shown in this link you can see that the plate of the 50C5 is connected to pin 7. Confirm that your socket has that connection to pin 7 and not to pin 5 and you are good to use the 50C5.

https://www.radiomuseum.org/tubes/tube_50c5.html

I'm only mentioning this because the presence of a 35B5 raises doubt about your tube string. If this seems complicated and unclear, just ask for clarification. Cheers.

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Burl Ives, RIP, oldtimer.
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