[davemc]

I am restoring a Philco 37-624. This is a 6 volt DC set.

http://www.nostalgiaair.org/PagesByModel...013214.pdf

The filter capacitor, #34 is non-polarized, 2+8uf at 200 volts. Is this because the B+ will be negative if the 6 volt source is connected backward? It uses a synchronous vibrator.

If I wish to restuff this can capacitor, what would I use? I have seen 2.2uf film caps, but they are large. I have never seen an 8uf film capacitor. I suppose I could just use normal electrolytics, such as a 4 and a 10uf at 250 volts and just make sure to connect the radio to 6 volts correctly. Any other recommendations?

I have restored many 6 volt sets, but this is the first one I have seen that used non-polarized filters.

[Chuck Schwark]

If you read the parts listing description for cap #34 it reads; electrolytic.
The schematic symbol shows the (+) side to B+ and the negative (-) to ground.

It is polarized. An electrolytic cap is, by definition, polarized.

A 10 uF. cap will be fine for a replacement at same or greater voltage.

Chuck

[davemc]

On the part itself (on the can) it reads NON-POLARIZED.

[Ron Ramirez]

I was going to look up the part number but can't find it in the 1941 or 1946 Philco parts catalogs. I have 1937 and 38 catalogs but they are in storage.

Chuck, can you look this part number up? 30-2171

That should solve the mystery.

FWIW, looking at the schematic, I can't see why it would be non-polarized... Dave, is this the original Philco part, and does it have 30-2171 stamped on it?

[davemc]

Looks original, and since it's on the RF subchassis, it is unlikely it has been changed (if you know what I mean)!

Marked Philco 30-2171-X

[Steve D]

Higher value film capacitors are available from many sources such as ASC capacitors:

http://www.ascapacitor.com/Products/x663f.htm

Steve D

[davemc]

Higher value film capacitors are available from many sources such as ASC capacitors:

http://www.ascapacitor.com/Products/x663f.htm

Steve D

Thanks. It really irks me that my favorite vendor (Mouser) no longer stocks ASC capacitors. It appears that JustRadios in Canada stocks a few. The high voltage ones are needed for restoring TV sets, such as the 7" ones using electrostatic deflection. Allied has them, but they have a high minimum order. I have not checked DigiKey and other sources.

Good tip. I still would like to know IF I need to use non-polarized capacitors for filters in this radio, and WHY! I just looked at another 6 volt set in my collection (37-34) and it does NOT use non-polarized caps.

Dave

[davemc]

The parts lists says 30-2171, but the part itself is labeled 30-2171-X and definitely says NON POLARIZED - maybe Philco made a change. It functions as the RF/converter screen bypass and oscillator filter cap. The main filter cap in the power supply says electrolytic.

I see no reason why it has to be non-polarized, and will restuff with standard electrolytics. Maybe they wanted a paper type cap in the application, vs. an electrolytic. I might cheat and install a .1uf film cap across the electrolytics just in case (if there's room in the can).

[Ron Ramirez]

Dave

I've looked at the schematic, and I also do not see any reason why Philco would have used non-polarized caps in these two locations. ??? Obviously the original part was non-polarized, for whatever reason.

[davemc]

I just noticed that the MAIN filter capacitor (metal box) C64, which is a 4+8uf/200 volt unit, IS ALSO NON-POLARIZED! Part number is 30-2160S.

I rebuilt it using normal polarized capacitors.

Again, my theory is that since this radio uses a synchronous vibrator supply, if the 6 volt source is connected backward, the B+ will ALSO be backward, which would mean the filter caps would be subjected to reverse polarity. I suppose since the power leads were just large alligator clips, it would be easy to connect them to the wrong post on the battery.

Perhaps Philco made the change after customers complained.

I wonder how long a polarized cap could stand full B+ at reversed polarity?

[Ron Ramirez]

How long will a polarized cap stand full B+ at reversed polarity?

Only a few seconds at best.

I learned that the hard way some years ago...I had recapped a Philco Model 15X, and accidentally connected one of the main electrolytics backwards. Turned it on and POW!!! Sounded like a gunshot. Immediately unplugged the set and looked underneath. It didn't make a big mess, fortunately, but it was a goner nonetheless. Replaced with another, making sure the polarity was correct...Lesson learned.

[harley92]

Here is a suggestion for these radios that use non-polarized caps and there is the possibility of reversing the battery leads. It may be a tight squeeze in some of these sets, but install a full-wave bridge rectifier in the set so no matter which way the battery is connected, positive goes to the vibrator p/s and negative goes to ground. Just make sure to use one of high enough amp rating. You may have to install a second on for the filament string. Not sure the radio would work correctly with the B+ to the filaments being reversed polarity. You could also install it before the switch, byt may want to do an inline fuse in case the bridge goes bad. I ordered some non polarized caps from Justradios.com in Canada. When they arrive, I will post on the re-stuffing results.

My 37-624 restore is a challenge at every turn, but will be worth it.
Gerald D.

[Arran]

You can get non polarized capacitors from Mouser, just not of the ASC brand, and are not in the 8 kv range. They stock a bunch of Panasonic capacitors that are large value film capacitors, and they are fused to in case something goes wrong. Sorry but I don't have a listing for them, use Mouser's search engine, I was thinking of picking up some to use in some early AC radios I have that originally had big paper caps as filter caps.
Regards
Arran

[harley92]

Hi all,

I too am restoring one of these 37-624 sets. Mine still has the original Philco cap. The part number on it is 30-1271-X. It is marked non-polorized and is 8uf and 2uf at 200VDC. This is just in case the battery is connected backwards. I just purchased some 8.2uf & 2.2 uf film caps for use in this restoration. They are quite large, however if you have an old electrolytic can that is tall enough, you could restuff it with these caps. they are available from AES. Part number for the 8.2uf is C-FS8D2-630 and for the 2.2uf is C-FS2D2-630. I also purchased a 4.7uf for part number C-FS4D7-630 to use with the 8.2uf to restuff the filter cap next to the vibrator p/s. It was a tight fit, but I slightly modified the metal case to get all to fit and stacked them end to end. I just finished repairing and restoring the vibrator power supply and these film caps work great. It puts out 155volts DC with no ripple observed on my scope. These are film caps so polarity is not a problem. I did need to unsolder and pull the end cap off the vibrator and clean the contacts. I used some alcohol and a relay contact burnishing tool to clean the contacts. I then had to slightly tweek one of the contacts to get the square wave equal height and duration. And yes I did restuff the three metal can caps in that p/s as well as the buffer cap. It should now last a long time.
Feel free to email me with any questions.
Gerald D.

[tbone]

The use of film caps is a good idea. In the case of this receiver and its quick warmup tubes, you would be able to use the 400 volt version of the AES caps mentioned. This would make it easier for restuffing. I wouldn’t expect to see anything over 200 DC and the film caps would handle the ripple ok.

630 V film caps a great in AC transformer sets where the startup voltage can exceed 500 volts.

Just a thought.