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reduce voltage - Printable Version

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reduce voltage - denver - 03-17-2010

Any way i can reduce transformer voltage to my electrolytic caps ? Maybe with a power resistor ? have 125 volts receptical current i think this is problem .
tranformer rated at 750 volts . Idont have enough understanding of a bucking tranformer . Put some 4.7uf in and 10mfd at 450 volts they blew after awhile.
Or maybe i can do it at line cord. Icon_rolleyes Icon_redface Icon_idea
Thanks humbeled Denver.

Re: reduce voltage - rghines1 - 03-17-2010

Bucking transformer or variac is best. To do it with power robbing resistors is a poor way to go. Would need to know the details of your circuit starting with the make and model.

Re: reduce voltage - denver - 03-17-2010

Sorry thought i did philco model 111.

Re: reduce voltage - denver - 03-17-2010

http://www.nostalgiaair.org

Re: reduce voltage - rghines1 - 03-17-2010

Try a 1000 ohm 10 watt resistor between the cathode of the 80 rectifier and the first electrolytic cap and see if this is sufficient. May need to experiment some with the resistor value.

Edited: 3/19/2010

Re: reduce voltage - denver - 03-17-2010

Will do have to order some resisters . What do you think 100 to - And what size cap would be best.
Thanks alot Denver. Icon_biggrin

Re: reduce voltage - Ron Ramirez - 03-17-2010

Your new filter capacitors should not have blown even if your line voltage is 125 volts.

Are they connected correctly?

Are you sure?

You can't be too careful, you know... Icon_smile

Re: reduce voltage - denver - 03-17-2010

Pretty sure on big cap block terminals 10 and 9 for electrolytic caps to #3 negative end to #3.
THANKand thanks Denver Icon_rolleyes Icon_biggrin

Re: reduce voltage - Carl Travis - 03-17-2010

Ron has a clearer schematic on this site than the one on Nostalgia Air:
http://philcoradio.com/tech/images/111.jpg

Re: reduce voltage - rghines1 - 03-18-2010

Agree with Ron saying that those caps should not have blown to begin with. Take some voltage measurements of the power supply again.

Concerning using a resistor to drop voltage. Assuming the average B+ current is approximately 80 milliamps and with a 1000 ohm resistor would drop 80 volts. Wrote earlier 100 ohms but that would only drop 8 volts which is not much. A 1000 ohm resistor would need to be 10 watts.

The resistor solution is not perfect since during warmup the voltage can still surge quite high. Rectifiers tend to warmup first before the other tubes are warm enough to start drawing current.

Re: reduce voltage - denver - 03-18-2010

Thanks will do all great help. Icon_wink
Denver

Re: reduce voltage - rghines1 - 03-18-2010

Another thing to check is the negative bias going to the 45 tubes. If any of those resistors labeled 57 and 58 are open or increased dramatically it will also cause a large increase of voltage across the caps in the power supply. Resistor 59 in the cathode circuit of the 45 tubes is worth checking too. It could cause higher than normal B+. These resistors balance the loading of the power supply and should be within 20% tolerance.

Re: reduce voltage - denver - 03-18-2010

Will do . can,t check voltage waiting on caps & resisters. Icon_biggrin
Denver.

Re: reduce voltage - denver - 03-21-2010

WAS THINKING MAYBE A LITTLE TO MUCH . Would changing my 80 rectifier tube blow a cap . I was looking at the tubes the 80 had some blue in it so changed it thats when the
electrolytic cap blew. Or would the blue color be from to much voltage. Still havent recevied caps yet . Live in small town have to order everything Icon_mad
Thanks alot Denver Icon_rolleyes Icon_biggrin

Re: reduce voltage - denver - 04-06-2010

hi I figured out why voltage running high when i checked. Wasn,t hooking speaker up Icon_redface Hard set to work on big console big speaker.
Ihave it playing fine picks up good for about 20 min . Then fades out let cool off then plays 20 min again .
I replaced every cap resistors and bad tubes . Only things i did not are the micas what do you think.
If i did which ones .
Thanks Kent. Icon_rolleyes