Thread: Antique? not!
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Old 10-24-2003, 07:43 PM
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Jeffhs Jeffhs is offline
<----Zenith C845
 
Join Date: Feb 2003
Location: Fairport Harbor, Ohio (near Lake Erie)
Posts: 4,035
More info on my Zenith K731. It works well, controls operate quietly, tuner works perfectly [no problems with the dial cord], sounds great (like all Zeniths) and looks fantastic atop the refrigerator in my apartment. One of the main reasons I bid on this radio in the first place was I noticed the color of the cabinet would probably match the rest of the furniture in my apartment. I was right.

This set has incredibly good sound for a table radio, but that is directly attributable to the large wood cabinet (they don't make them like that anymore, which is yet another reason I bid on it) and the oversized speaker (I believe it's a 6x9 oval, but I could be wrong), not to mention the 35C5 output stage and the tone compensation circuitry. This set has incredible bass; turn the tone control to the full bass position and you might damage the speaker. How much output is a 35C5 good for? I think this was the 35-volt equivalent of the 50C5, so the two tubes, if they are in fact identical except for the filament voltage, ought to have the same output rating.

I can't help but wonder, however, why Zenith designed the power supply of this radio to use a selenium rectifier, rather than a tube such as a 35W4. I remember reading somewhere (I think it was on an antique/vintage radio website) that when seleniums go bad they emit a gas which smells like rotten eggs, and under certain conditions they can pose a shock or fire hazard. Has anyone here on AK heard of this? If so, is there any truth to it? Is there any real advantage to replacing a selenium rectifier with solid-state diodes? I don't intend to leave my set plugged in when I'm not using it, but I'd just like to know.

Now all I have to do is get a schematic for it (even though it works very well now, there is no telling when a radio of that vintage will develop problems such as bad filter capacitors, open filaments in tubes, etc). I ordered the Sams Photofact for my Zenith H511 from Radio Era Archives; I wonder if they would have the Sams for my K731? The 731 is not yet an antique (it was made in either 1959 or 1960--I've seen both estimates on ebay), so I'm not sure if Radio Era Archives would even have the diagram for it. At what point does Radio Era Archives draw the line, i. e. what is the newest schematic in their files? Do they even bother with filing Sams folders from 45-50 years ago, or do their files stop with the late '40s?

Thanks, good luck and very kind regards.
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Jeff, WB8NHV

Collecting, restoring and enjoying vintage Zenith radios since 2002

Zenith. Gone, but not forgotten.
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