1930 Philco 20B Cathedrals - Printable Version

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1930 Philco 20B Cathedrals - PhilcoPhan1936 - 02-07-2018

Last September, I picked up an empty but otherwise in excellent condition, Philco 20B early version Cathedral cabinet. I have since completed it with a chassis and speaker.

If all goes as planned, this coming Thursday, I have a fellow collector and Facebook friend dropping off a late version 20B Cathedral for me to restore for him.

I was contemplating working on them side by side.

I looked over the schematics briefly for both that Ron posted here at the Phorum, and downloaded them.

One question I have: The Capacitors in the Capacitor Block (27). Since they are marked with polarity, I assume electrolytics are called for. Are 450v caps sufficient?

Also, If I have problems find the exact value, are 2uF or 2.2uF substitutes OK?

My primary experience is in mid to late 1930s Philcos, so I'm wandering into somewhat unfamiliar territory with these 1930 models.

Any tips, advice and help are welcome and appreciated.

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RE: 1930 Philco 20B Cathedrals - Ron Ramirez - 02-07-2018

Jeff

Use film rather than electrolytic. There's plenty of room inside the can, and they will last much longer than electrolytics. I would use 600/630 WVDC but others will chime in with their opinions.

2.2 uF is a good sub for 1.5 uF. You can get 1 uF to replace the original 1 uF units.

I posted those schematics before film substitutes were known to me.

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RE: 1930 Philco 20B Cathedrals - PhilcoPhan1936 - 02-07-2018

Thanks Ron.

Based on your recommendation, it looks like I will need to put an order in. I don't think I have all those values in stock.

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RE: 1930 Philco 20B Cathedrals - Steve Davis - 02-07-2018

Just my 2 cents, fairly large value film capacitors are available at a reasonable price. I would go with 1mf for terminals 1-2, 4.7 for terminals 1-3, 4.7 for terminals 1-4  and omit the capacitor on terminals 2-6

Steve

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RE: 1930 Philco 20B Cathedrals - Ron Ramirez - 02-07-2018

Steve is right, especially about omitting the capacitor across terminals 2 and 6.

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RE: 1930 Philco 20B Cathedrals - PhilcoPhan1936 - 06-03-2018

(02-07-2018, 11:45 AM)Ron Ramirez Wrote:  Steve is right, especially about omitting the capacitor across terminals 2 and 6.

So, please help out a relative newbie- what function does the cap between 2-6 do, and why omit it?

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RE: 1930 Philco 20B Cathedrals - morzh - 06-03-2018

Cap in this position is supposedly improves the ripple by producing the opposite-directed ripple +90 degrees vs -90 degrees, so they cancel each other.
Its kinda counter intuitive.
The inductor alone is sufficient plus the cap in position 4-1 can be increased quite a bit without fear of damaging the 80 tube to have much better effect on the ripple.

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RE: 1930 Philco 20B Cathedrals - PhilcoPhan1936 - 06-06-2018

(06-03-2018, 08:08 PM)morzh Wrote:  Cap in this position is supposedly improves the ripple by producing the opposite-directed ripple +90 degrees vs -90 degrees, so they cancel each other.
Its kinda counter intuitive.
The inductor alone is sufficient plus the cap in position 4-1 can be increased quite a bit without fear of damaging the 80 tube to have much better effect on the ripple.

Thanks!

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RE: 1930 Philco 20B Cathedrals - PhilcoPhan1936 - 06-06-2018

I'm ordering parts and doing preliminary checks on both chassis. On mine, it looks like the 1st section, between pins 1-2 on the candohm is dead . What wattage should I look for to replace this section?

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RE: 1930 Philco 20B Cathedrals - PhilcoPhan1936 - 06-06-2018

I'm getting a Philco 66S from radiowilbur, so I'm hoping he can round up a replacement part, but just in case, knowing the wattage for a replacement would be helpful, thanks.

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RE: 1930 Philco 20B Cathedrals - PhilcoPhan1936 - 06-07-2018

Bump. Anyone know the needed wattage for the candohm? I can't find any documentation on this part. Thanks.

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RE: 1930 Philco 20B Cathedrals - Radioroslyn - 06-08-2018

Total dissipation is 2 1/4 watts would use a 5 or 10w unit.

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RE: 1930 Philco 20B Cathedrals - PhilcoPhan1936 - 06-08-2018

Thanks Terry.  

I'm working on the bakelite blocks. I've done many of these, and it's going smoothly. While working, I'm also checking resistors. I had to disconnect one end of the lower of the 2 dark gray dog bone resistors in this pic in order to flip the block over. It checked out at 800K, and should be 500K, so it needs to be replaced. My question is, what wattage is it? My experience tells me a 1W will replace it, but I wanted to confirm. Thanks.

[Image: https://farm2.staticflickr.com/1743/40873811610_32d59e73dd_k.jpg]

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RE: 1930 Philco 20B Cathedrals - Radioroslyn - 06-08-2018

1/2w is fine for both of the 500,000 ohm resistors.

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RE: 1930 Philco 20B Cathedrals - Ron Ramirez - 06-08-2018

+1 what Terry said.

For what it's worth, all of the dogbone resistors in Model 20 are 1 watt. Some, such as the 500K, are overkill. Philco simply did not have anything smaller in wattage at the time.

1/2 watt resistors did not start to appear in Philco sets until 1931.

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