Zenith 15U270 - Printable Version
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+--- Thread: Zenith 15U270 (/showthread.php?tid=21378)
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RE: Zenith 15U270 - Phlogiston - 06-06-2020
Probably a good idea. You can always decide to fix it later.
RE: Zenith 15U270 - rfeenstra - 06-09-2020
So I put this radio back on the bench. I played with the dial lamp - it was all the way in. I found a different 47 lamp that was slightly longer and had the filament way out at the end. It improved the dial lighting a bit.
I hooked the IF section up to the spectrum analyzer to see what I could do with the response curve. Here are the results:
IF peaked per alignment instructions. At 6 db down the bandwidth is about +-3.5k.
I looked at doing this. At 6db down, bandwidth would be about+- 7K but the sensitivity is down a lot.
I settled in on this. At 6db down, bandwidth is about +- 6k.
At the loss of quite a bit of sensitivity, I gained a fair amount of bandwidth. Still not as good as the Philco 37-116. The radio does sound better with my HiFi transmitter, though. That's the way I usually use my AM sets. If I listen to real broadcasts, it's usually talk radio so the high frequencies are not needed.
Kind of fun to play with!
RE: Zenith 15U270 - PhilcoJohn - 06-10-2020
That Radio is just beautiful, I love the wood on the cabinet. A Zenith radio like that is hard to come by I bet. Enjoy it! I wish I had one just like it. I bet it plays beautifully.
RE: Zenith 15U270 - Phlogiston - 06-11-2020
Yes, and they are not a "dime/dozen" - if you could find a dozen.
I was just dealing with a rare radio, so rare that it has not been properly identified, anywhere. It has a crack in the arc on the right side. Not large, but you can see it if you look - and I do. It was caused by poor construction. It looks like they left a gap along that whole arc making the bent plywood unstable. I could have fixed it. It would have required the replacement of the front/sides along with the veneer - so probably about half the cabinet or about 3/4 of what a person sees. If these were common, it would have been OK to fix, but, on a rare radio it was better to make it look as good as possible and try to look elsewhere as I walk by.
More to come on Parmak 525.
Russ
RE: Zenith 15U270 - rfeenstra - 06-11-2020
To every change there are consequences! By broadening out the IF response curve, I reduced the sensitivity. Now, with a very strong signal, I get a lot of distortion. I presume the strong signal is over driving the RF stage since the AVC is not shutting the RF and Detector amps down enough. I'll have to take some AVC voltage measurements with the IF peaked and compare it with the broadened IF AVC voltages. Perhaps changing one resistor will bring it in line again. It's fun to fiddle!