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Just opened up a fairly nice bakelite 53-566 tonight. It has BC and what looks like the old police band on it. Lots of loud buzz/hum so caps need replacing. It has a 4-section filter cap: 40, 40, 40, 25. I'm trying to decide whether to replace the 40s with 33 or 47 mfd. Which do you think would be better? Of course a 22 will take care of the 25.
Planning to re-stuff the original container just because of space.
Thanks for your ideas.
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Ooops. Got this in the wrong folder. Move it if you want to Ron.
Art
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I think either value will work fine.
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I would use the 47 uf if you have them laying around, or a combo of those and the 33 uf, and stuff them inside the old filter cap tube just for neatness. Interesting how the set has a cathode capacitor on the power output tube, the last few late 40s early 50s Philcos I worked on didn't have one, they had the resistor but not that small electrolytic included.
Regards
Arran
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Using a cathode bypass cap on the output tube was an engineering design decision, not necessarily dependent on the cost of the extra part.
Including the cap increases the voltage gain of the output stage at the expense of added distortion. Eliminating the cap has the effect of providing negative feedback, thereby reducing distortion. In this case, the loss of gain must be made up elsewhere in the audio section, otherwise the radio will not play as loud as it otherwise would.
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It is also frequency-dependent increasing gain on higher frequencies.
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I have lots of 47s Aaran.
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I was under the impression that you can always go a bit higher in the capacitance value (i.e - replace a 40uf cap with a 47 uf cap), but NEVER should you go lower? Is that wrong?
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Why not use 40s? I always keep plenty on hand. I like to replace all caps with the same value when possible.
Eric
The Villages, FL
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On a lower end set like five tuber in the Transitone series i think that leaving the cathode capacitor out may have been a cost saving measure given the market, it's also possible that when this 53-566 was built Philco got a deal on four section caps with the cathode cap included. I have noticed that adding one tends to improve the bass response, sometimes it increases the gain substantially, sometimes not as much, I haven't noticed any more distortion though. I have found that it's more beneficial when the set has a larger diameter speaker, like a 5'' inch or larger, otherwise it gets a little too boomy.
Regards
Arran
P.S Art, if you have lots of 47 uf caps, use them, the pi filtered power supplies in these AC/DC sets are so crude they can use all the filtering they can get, especially on the output filter cap.
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Does anybody have a clear copy of the schematic (Riders Philco page 23-45) and chassis layout (page 23-44) scans they can email to me? Nostalgia Air stuff is a little fuzzy on my end. Email is artdrhs at yahoo dot com
Thank you.
Art
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