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Philco 38-7CS...I think - Printable Version

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Philco 38-7CS...I think - neali - 06-02-2014

Hello all,

First post. I recently - Sunday - acquired a Philco 38-7CS. It is in original untouched shape and the finish is ok, not great. Some finish loss along the base from careless feet and the usual fleabites but no hacks and the veneer is tight. I came across Bob Anderson's terrific videos and I am torn between keeping it original and refreshing it but I will probably keep it the way it is.

I have been googling away and I came across pictures at radiomuseum of the 38-22CS which looks identical but is apparently an AC/DC set with a 93 volt string so I assume it came with a curtain burner. Suprised it sold for $5 more in 1938.

I hope I have the 38-7CS and not the 38-22CS but it is still in the back seat of my car until it can be cleared with she who must be obeyed. Icon_mrgreen

I'll post pictures soon.

RE: Philco 38-7CS...I think - Arran - 06-02-2014

The 38-22CS didn't use a curtain burner, as a matter of fact I don't think that any Philco AC/DC set ever had a line dropper built into the power cord. The 38-22CS would have used a plug in ballast tube on top of the chassis, so it's really not a big deal to deal with. Most sets that used a line dropping power cord were really cheap sets with a compact chassis, the 38-22CS would have used the same chassis as a 38-7CS but without a power transformer, so if you don't want a ballast resistor there is room to use a capacitive dropper.
Regards
Arran

RE: Philco 38-7CS...I think - OldRestorer - 06-03-2014

WELCOME!

Kirk

RE: Philco 38-7CS...I think - neali - 06-03-2014

Hi Arran,

Thanks for the informative post. I am not familiar with capacitive ballast but I am figuring on 125AC from the wall yields a cap that needs to drop 32 volts @ 300 mA. I get 106 ohms which means an ~ 25 uF non polarized AC cap or a DC cap of at least 400V. Did I do that right? Might be a moot point.

Hiya Kirk from a fellow Long Islander way East in Suffolk. You have amazed me with your cabinet restorations from kindling. Let me know if you take on projects for others - paying of course. PM.

Rich

RE: Philco 38-7CS...I think - Bob Andersen - 06-03-2014

I get about 10uF (9.53uF to be exact) for a 32 volt drop using the spreadsheet at the bottom on this page: http://www.vintage-radio.com/repair-restore-information/valve_dropper-calcs.html

I like to use polypropylene motor run capacitors which are designed to have AC current running through them.

Here's one from Digi-key
http://www.digikey.com/product-detail/en/B33364A3106J050/495-4323-ND/2330457

RE: Philco 38-7CS...I think - neali - 06-03-2014

Hi Bob,

Great videos!

I got much the same entering 125 volts, 60 Hz, 93 Volts, 0.30 Amps and 10 volts gave me 11.24uF. I see the Brits are also assuming a surge limiting resistor of 33 ohms 3W which is probably a good idea. That would reduce the required reactance from a pure capacitive dropper but I still think I goofed in my calculation. I like the idea of using a motor run capacitor and the spread sheet is useful. They calculated 107 ohms also. (106 - close enough)

How is your 38-7CS chassis coming along?

RE: Philco 38-7CS...I think - Bob Andersen - 06-03-2014

When I did my calculation, I left out the surge limiter. I haven't touched my chassis yet but I did pick up a spare in case I need any parts. I have a more demanding job these days and free time is hard to come by.