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Castley GA-30 need help converting from 220 to 120

Started by Zappacat, May 07, 2010, 02:17:14 PM

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Zappacat

I thought it had to have dual secondaries?

Quote from: bry melvin on May 13, 2010, 03:10:27 PM
Personally I would try to go a little higher on the VA rating and check to see if transistor and cap voltages were not exceeded but...

using your criteria the closest I see in Digikey is the Hammond 166J36 @36VA single primary 36 V single secondary center tapped

unless I'm missing something that should work.

I didn't check Physical size and fit though

There are other ballpark ones LISTED but not stocked.
I put my pants on just like the rest of you - one leg at a time. Except, once my pants are on, I make gold records.

J M Fahey

#16
Hi zappacat. That measurement you made was *very* useful.
The transformer is smaller than I think.
The (approximate ) Math: rectangle 6 x 2.7 cm; compatible with a core of 1.9 x 2.54 cm (3/4" x 1")= 4.826 cm square ; good for about the square of that in V.A.= 23.3 VA.
So, earlier guesses of 30 or 35 VA ratings were quite on the spot.
It would mean a 18+18V or 36V c.t. @ 1 ampere.
Any current or VA rating above that is not a waste, but a security margin.
After rectification and filtering it provides around +/-24V DC.
A real world amplifier will provide around 14V RMS (tops) into an 8 ohm load, around 24W RMS. Call it 20W RMS and we are set.
Some suggestions:
http://www.mouser.com/ProductDetail/Hammond/164J36/?qs=sGAEpiMZZMv4oUrzpPKU3G%2fRTSrPlrIuSG7DBMfNh7M%3d
http://www.mouser.com/ProductDetail/Hammond/162J36/?qs=sGAEpiMZZMv4oUrzpPKU3Gl9uzeWkd1%252bV%252bIZXWKOO%252b4%3d
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=185D36-ND
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=A41-43-36L-ND
I think that's enough.
Good luck.
EDIT: Bry Melvin's suggestion is just on spot; I suggestewd a slightly larger trasnsformer to play it even safer, you de$ide.