Philco 49-1611 restoration - Printable Version
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Philco 49-1611 restoration - Texasrocker - 01-08-2012 06:25 AM
If any techs here ever get the opportunity to electronically restore a Philco 49-1611 chassis, " pass"!! just kidding!! Here are some tips on the power supply section. This later model Philco chassis has a half wave selenium voltage doubler on back of the chassis. When replacing the old selenium back-to back units, the forward B+ voltages goes way "high"! To bring down the B+ voltage at the first filter capacitor, you will need to add a resistor that most of us restorers do not keep on hand. To drop the extra modern day a.c. line B+ voltage on these sets, requires adding a 18K to 20K (20 watt) wirewound resistor across the 1st filter cap to bring the B+ voltage back to reality. The double 1N-4007 diodes can be mounted under chassis on a added terminal strip. The new resistor can be mounted on a terminal strip on rear of chassis under the original heat cage that housed the original selenium units. This particular model Philco is a AC/DC filament string set that has a AM/FM chassis, and new filter caps won't fit in original cans unless using the new style "pencil" capacitors. Extra space under these particular chassis to add anything is very minimum indeed!
Just another tip from ol' Tex at http://www.texasvintageaudio.com Keep all those old Philco's sets working like new!
Re: Philco 49-1611 restoration - Ron Ramirez - 01-08-2012 02:12 PM
Tex - excellent tips, thanks for sharing. I have yet to purchase any of those new "pencil" electrolytics but once I get around to working on any more postwar equipment, I'm sure I will be ordering some.
Re: Philco 49-1611 restoration - Texasrocker - 01-09-2012 05:25 AM
Glad to share Ron. I also shaved off a few more forward volts from the 1N-4007 voltage doubler today. And it reduced heat in the added 20 watt resistor also getting rid of about 40 volts ac. If you look at the schematic for the Philco 49-1611, one one side of the ac line is tapped, goes through a original 40 uf / 200 v electrolytic that intersects between the old diodes in the selenium voltage-doubler recitifier. After replacing the old selenium units with 1N-4007s, replacing that particular electrolytic on the ac line with less microfarads brings down the B+ voltage to a even more comfortable current draw. I replaced the original 40 uf electrolytic called for in the schematic with a 22uf @ 250 v. rating, and further dropped the B+ voltage by another 10 volts to a very comfortable operating range for the B+ in these particular sets, and the 20 watt bleeder resistor across 1st filter cap cooled down even more. I remembered this trick from a old WW2 Radio tech that taught me many years ago.
This info isn't available in any of the books we all learned from, this is trial & error, using ohms law also. If you ever work on on 49-1611, you will want to remember these tips. The forward voltage of using 1N-4007s in these particular sets goes way way high, and dropping 40 volts ac is a head scratcher for sure.