[GarySP]

OK guys.  Forgive my electronics ignorance, but are you saying that if I install line filters on my 20 I can eliminate the need for a dedicated ground wire?  I had been looking for cloth braided three wire line cord to satisfy the need for a ground path.  Also, with the y caps in place would there be any advantage to also installing an X cap across the lines?  I have a donor chassis for a bakelite block and it seems the Y cap filters would be the easier way to go.  I never stop learning from you gurus on this site!  Take care, Gary

[Steve Davis]

If you add line capacitors, a ground connection to the chassis is no longer needed. Before adding the capacitors to my Philco 20, with no ground wire, only the strongest stations would come in. When I would connect a ground, many weak stations would suddenly come in and the strong ones would boom in very loud. After adding the line caps, the radio works equally well with or without a separate ground connection. I have another Philco 20 that I plan to add the line caps. I also intend to modify the interstage transformer circuit.

Steve

[Ron Ramirez]

How do you intend to modify the interstage circuit, Steve?

...or maybe I'll just stay tuned and read about how you do this as you progress with this set.

[Steve Davis]

Ron, I wasn't very clear, I already did the interstage transformer circuit mod on ths radio (see post number 5) as shown in the tech section   http://www.philcoradio.com/phorum/showth...?tid=14984      I have another Philco 20 that I restored a few years ago, that I plan to do the  line cap mod and the interstage mod.

I would recommend both of these modifications to anyone that has a Philco 20
 

Steve

[Ron Ramirez]

Ah, I see. Thanks!

And...that is a great idea about adding the line bypass caps!

[GarySP]

Hello Steve. A couple more questions. Which modification did you do on your interstage transformer? The tech section shows three different procedures. Also, where did you get your new cone and spider for your speaker? Mine is begging for a re-cone. And, do you see any advantage to also installing an X cap across the lines for the line filter adaption? take care, Gary

[Steve Davis]

Gary, My interstage transformer was still good so I did modification "A".

This is the speaker cone that I used   http://www.electronix.com/speaker-replac...13892.html     Here is a spider that should work    https://www.ebay.com/itm/A-pair-Best-Sub...1438.l2649    I should mention, because of the way the wires inter the speaker, I had to cut out a small section of the spider for clearance.





There is no need for an across the line capacitor. I used .01uf safety capacitors. When there is a .01 cap connecting each side of the line to chassis ground, you have in effect, .005uf across the line.

Steve

[GarySP]

Thanks for the info, Steve.  Take care, gary

[GarySP]

Steve, since you are not adverse to applying modifications I thought you might find these two articles I found interesting.  Popular Science has all of their issues online to read.  In the July 1933 issue, pages 51-53, there are two articles I found curious.  One was a simple way to add a tone control to a radio (model 20?), and the other was modifications to use more advanced output tubes.  The only concern I had was if the tube conversions would overtax the capability of the power transformer.  If nothing else, interesting reading.  Take care, Gary.

[Steve Davis]

A tone control might be useful with a modified speaker like this 20. One would need to use a pot with a switch, so as to not drill an extra hole in the front panel.

That is a neat to be able to look at the back issues of Popular Science. Just the other day, I was looking a the magazine rack at Walmart.There was not a single magazine the interested me. I thought about all the old magazines I used to subscribe to that are no longer published. We have some really neat things available to us today, but we have lost a lot of good things too.

Steve

[mg34.42]

Steve where are you getting the parts for the speaker
benny

[Radioroslyn]

Hi Benny,
I don't know of those parts are still available. Over the last few yrs they have been a hit or miss. It's much easier to send the spkr out and have it reconed. Sound Remedy in NJ does a good job at replacing the cone, spider, and voice coil. They convert it to use spider that attaches to the basket rather than the old style w/the screw in the center to center the vc (very stiff). This will give you much better sound as the vc is much freer to move. It's qbt $40+ the ride.

[Ron Ramirez]

...Popular Science has all of their issues online to read. In the July 1933 issue, pages 51-53...

https://books.google.com/books?id=AygDAA...e&q&f=true

[Radioroslyn]

Gary
For the most part changing out the 71A in the model 20 for another type of tube is problematic.
There are few output tubes that require 5v to power the filament. 112A were used in the old skool battery sets from the 20's so it was designed to have a low filament current consumption 5v @ 1/4A = 1 1/4watts. But in order for any tube to make a noticeable improvement the total need to be higher as the filament is the part that generates the electrons that flow inside the tube. In short the bigger the filament the more current the plate can draw. And conversely a small filament the less total current the tube can draw.
Now the 45 tube would seem to  be a likely candidate but there are two issues. The 45 tube require 2.5v for the filament. So not a big problem you wire the two 2.5v filament in series so now you need 5v to power them perfect!! The the filament requirement for the 45 is 1 1/4 A. This poses a problem as the filament winding on the 20's is 5v@ 1/2amp so the 45's would draw more than twice as much @abt 3watts. The 45s require more grid bias. Think I remember Ron posting that he had swapped the power transformer from a newer set using 45s,24A, and 27. THis would give the proper voltages and current to support such a tube swap. The other 2.5v tubes (47, 2A5, 59, ect) are worst as they require more filament current.

Ron
Tnx for posting good read. Lots of cleaver bits throughout even a National Co. SW-3 sunken into a table top!

[GarySP]

Yes Ron, thanks! I had forgotten all about this thread. Take care, Gary