[TechAssist] Radio designed for B and A batteries: want to convert to ac
- From: <wjstv@xxxxxxxxxxxxxx>
- To: <techassist@xxxxxxxxxxxxx>
- Date: Wed, 18 Dec 2002 15:27:00 -0500
Anyone less than 50 years old should probably delete now.
This is a Sears radio model 2541 using 4 tubes, 1A7, 1N5, 1A5, and 1H5 and
designed to operate off 2 "B" batteries @45v each (90v in series) to power
the B+ and an "A" battery @2v to operate the tube filaments. We have the
schematic.
Very good friend wants us to convert it to ac. Using two bench dc power
supplies we found that the radio works and sounds good. We made a 90v dc
supply out of a bridge rectifier and the power transformer from a circa 1977
Zenith tv which had lots of taps to choose from. (first use we've found for
these transformers other than two bolted together to make a boat anchor).
Problem is the 2v filament voltage. If we use a bench power supply or a 1.5v
battery to power the filaments, radio plays fine. If we use an ac-dc adaptor
or a little transformer and bridge rectifier to power the filaments we have
loud ac hum (with volume turned down). Adding additional filter capacitance
helps but not enough.
Any suggestions appreciated.
Smith TV Service
1930 Main St
Newberry, SC 29108
803/276-4946
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