[TechAssist] Re: Radio designed for B and A batteries: want to convert to ac
- From: "J Silverman" <greentron@xxxxxxxxxxxxxxxx>
- To: <techassist@xxxxxxxxxxxxx>
- Date: Fri, 20 Dec 2002 20:03:00 -0500
Dont forget the double layer caps. You can get 5 or 10 Farads in a single
part as long as the voltage is less than 6 volts. Also a nicad battery makes
a good filter cap.
Jerry Silverman
Greentron Inc
4 Newland Ave
Greenville SC 29609
864 232 3889
Fax 271 2080
mailto:greentron@xxxxxxx
----- Original Message -----
From: "Damon" <DAMON101@xxxxxxxxxxxxxx>
To: <techassist@xxxxxxxxxxxxx>
Sent: Thursday, December 19, 2002 8:07 AM
Subject: [TechAssist] Re: Radio designed for B and A batteries: want to
convert to ac
>
> How much capacitance??? Try 4700uf, yeah I know it's a lot......but these
> old DC Filament radios must have absolutely NO AC on it .
> Could also try a Series regulator to smooth out AC Ripple, but where to
find
> one that regulates at 3 volts is a big question, maybe a "build your own"
> using a 3.6 V zener. Obviously if your bench supply can give you a smooth
> humless output, you can look at it's design and try to replicate it as a
> last ditch effort.
>
> Oops....almost forgot. There's a thing called "impedance matching". What
> that means is that you want your power supply to not just put out 3 Volts,
> you also want that unit to supply enough current too. If you're using a 5
V
> supply loaded heavily.....and it drops down to 3V, well that won't cut it.
>
> Damon Brunger
> damon101@xxxxxxxxxxxxxx
> Telrad Electronic Services
> Ft Wayne, IN 46815
>
> ----- Original Message -----
> From: <wjstv@xxxxxxxxxxxxxx>
> To: <techassist@xxxxxxxxxxxxx>
> Sent: Wednesday, December 18, 2002 3:27 PM
> Subject: [TechAssist] Radio designed for B and A batteries: want to
convert
> to ac
>
>
> >
> > 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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