[TechAssist] Re: Radio designed for B and A batteries: want to convert to ac
- From: gulftech@xxxxxxxx
- To: techassist@xxxxxxxxxxxxx
- Date: Wed, 18 Dec 2002 19:43:31 -0800
I think you will find you problem to be the filament current is too high
for the transformer you are using or the filter caps. I don't have a
clue how much those filaments draw, but look at that voltage with your
scope and will be easy to see.
Good luck,
Ken Smith
Gulf Technical Services
3034 Gulf Breeze Parkway
Gulf Breeze, FL 32563
850-934-8324 (Voice) 850-932-0819 (Fax)
On Wed, 18 Dec 2002 15:27:00 -0500 <wjstv@xxxxxxxxxxxxxx> writes:
>
> 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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