[TechAssist] Re: Radio designed for B and A batteries: want to convert to ac
- From: "Damon" <DAMON101@xxxxxxxxxxxxxx>
- To: <techassist@xxxxxxxxxxxxx>
- Date: Thu, 19 Dec 2002 08:07:05 -0500
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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