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Old 08-18-2017, 02:14 PM
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Tim R. Tim R. is offline
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Sound Quality

Hey all,

Having finished the restoration of my Philco 43B, I've been listening to it a lot lately and am really happy with it...but I feel like something is not quite right. The tone control gives me two options - really tinny sound or really muffled sound. No middle ground, just two extremes. Even though it was designed to make the best of the broadcasts of the day, I believe a set this nice is surely capable of sounding better!

I understand that the early Philco cathedrals, like the 70 and 90, didn't sound all that great due to an overly stiff spider. However, by the time my set was built, that problem had been corrected and the speakers sounded much better.

Due to a mouse using the radio as its home the speaker had to be reconed, so I have no idea if that changed the characteristics of the speaker, creating a problem where previously there was none.

Would anyone who has a similar vintage Philco radio be able to chime in? Does your set sound anything like mine? Has your speaker been reconed?


Thanks!

Tim
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Old 08-18-2017, 02:33 PM
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compucat compucat is offline
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I have a Philco 37-610 tombstone table model that has a three position tone switch. In the low position it sounds muffled, the high position sounds tinny and the mid position is the only one that sounds good overall. I think it is just the way these tone controls work. My speaker is original and not reconed. You might try different values of capacitors in the tone circuit to get both switch positions to produce acceptable results.
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Old 08-18-2017, 03:16 PM
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Tim R. Tim R. is offline
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Quote:
Originally Posted by compucat View Post
I have a Philco 37-610 tombstone table model that has a three position tone switch. In the low position it sounds muffled, the high position sounds tinny and the mid position is the only one that sounds good overall. I think it is just the way these tone controls work. My speaker is original and not reconed. You might try different values of capacitors in the tone circuit to get both switch positions to produce acceptable results.
Thanks for your input! I don't have another Philco cathedral to compare mine to, so I'm not sure how they are supposed to sound. I'm no expert on speakers, but based on what you're saying, the reconing probably didn't affect things that much.

Good idea on subbing caps around. The 42 has a .01 from its plate to ground, and IIRC the tone control switches in a .1. So maybe a .047 is what I need to find that "sweet spot."


Thanks,

Tim
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Old 08-18-2017, 03:26 PM
old_coot88 old_coot88 is offline
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If it's a 2-position switch, it's a simple treble-cut circuit using a single cap that's switched in or out (i.e., on/off). You can reduce the value of that cap till you find one that gives the tone you like best.

The cap usually goes to the plate of the output tube.

OOPs didn't see your last post. A .1 will definitely muffle it. A .01 or thereabouts would be more in the ball park.

Last edited by old_coot88; 08-18-2017 at 03:32 PM.
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Old 08-18-2017, 03:55 PM
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Tim R. Tim R. is offline
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Originally Posted by old_coot88 View Post
If it's a 2-position switch, it's a simple treble-cut circuit using a single cap that's switched in or out (i.e., on/off). You can reduce the value of that cap till you find one that gives the tone you like best.

The cap usually goes to the plate of the output tube.

OOPs didn't see your last post. A .1 will definitely muffle it. A .01 or thereabouts would be more in the ball park.
Yep, I think you're spot on about it being a treble cut switch. Although that wouldn't affect the low end, though, would it? It seems like the radio has excessive treble but lacks bass, so I wonder if there is something else "out of whack" in the preamp or final amp circuits?

I'll definitely swap capacitors around. And also verify that I put the correct value of cap in the tone switch when I restuffed it. Philco made things unnecessarily complex by leaving the part values off the schematics back then!


Thanks,

Tim
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Old 08-18-2017, 05:24 PM
old_coot88 old_coot88 is offline
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The treble-cut cap will affect the bass end very little.

You mentioned that the speaker had been reconed. Does the cone move in and out easily with no rubbing? If the new cone were too stiff, it could impair the bass.

If the coupling cap feeding the grid of the output tube were too low in value, it could reduce the bass without affecting treble. (A misplaced decimal point will change a value 10X.)
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Old 08-18-2017, 08:48 PM
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Quote:
Originally Posted by old_coot88 View Post
The treble-cut cap will affect the bass end very little.

You mentioned that the speaker had been reconed. Does the cone move in and out easily with no rubbing? If the new cone were too stiff, it could impair the bass.

If the coupling cap feeding the grid of the output tube were too low in value, it could reduce the bass without affecting treble. (A misplaced decimal point will change a value 10X.)
Seems to be moving freely and properly, as far as I can tell. Is there a break-in period for speakers, like with a new car?

I'll check the coupling cap as well. That value was actually marked on the schematic (penciled in), but I'll double check to make sure the anonymous repairman wrote in the correct value.

Thanks,

Tim
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