Potentiometer - UK Vintage Radio Repair and Restoration Discussion Forum

Bigears · 21st Nov 2019, 4:02 pm

Anyone know which of the four lugs are for at the back of this Potentiometer

John10b · 21st Nov 2019, 4:09 pm

If I understand you correctly they are used as an On/off switch.
Cheers
John

Kentode · 21st Nov 2019, 4:24 pm

Stick your multimeter across the contacts and switch the pot on and off until you find continuity/ infinite resistance .

Four contacts probably means DPST, or double pole single throw.

AC/HL · 21st Nov 2019, 6:44 pm

It looks quite deep, it could be rotary or push-pull. Try both.

Bigears · 22nd Nov 2019, 6:46 pm

Yes you're right John it's an on/off switch. On the existing Potentiometer, it has two lugs, it has a two-cord mains cable (Brown and Blue) the Brown"Live" goes to one lug of the existing Pot and the Blue goes to the big transformer then from the second lug a red wire goes to the transformer.

My question is it possible just to use one set of lugs as each pair is an on/off switch
which lug would I use for the live ?

julie_m · 22nd Nov 2019, 8:26 pm

Use a multimeter to work out which switch contacts are connected together when the switch is ON, and use one pair for the live. If you are not switching the neutral (there's no reason to, in the UK, and it's actually very slightly safer not to; although it makes about as much difference in real life as crossing the road to avoid breathing in the smoke from someone else's cigarette) just use either of the two pairs which are connected together when the switch is ON.

David G4EBT · 22nd Nov 2019, 8:26 pm

It doesn't matter which pair of tags you use for line or neutral.

There are two independent single throw switches which operate simultaneously when you switch the potentiometer on or off. All that matters, is that whichever pole you chose for either line or neutral, must be correctly matched to line and neutral on the output side. IE, to make sure that you don't have one polarity on the input tag, and the other polarity on the output tag.

At risk of stating the obvious, see pic below.

Hope that helps.

Bigears · 23rd Nov 2019, 1:27 pm

Thanks, Julie and Dave

21st Nov 2019, 4:02 pm	#1
Bigears Pentode Join Date: Nov 2017 Location: Durham, County Durham, UK. Posts: 144	Potentiometer Anyone know which of the four lugs are for at the back of this Potentiometer Attached Thumbnails

21st Nov 2019, 4:09 pm	#2
John10b Nonode Join Date: Nov 2016 Location: Aberaeron, Ceredigion, Wales, UK. Posts: 2,883	Re: Potentiometer If I understand you correctly they are used as an On/off switch. Cheers John

21st Nov 2019, 4:24 pm	#3
Kentode Octode Join Date: Mar 2015 Location: Yorkshire, England. Posts: 1,301	Re: Potentiometer Stick your multimeter across the contacts and switch the pot on and off until you find continuity/ infinite resistance . Four contacts probably means DPST, or double pole single throw. __________________ Regards, Ken. BVWS member

21st Nov 2019, 6:44 pm	#4
AC/HL Dekatron Join Date: Nov 2003 Location: Heckmondwike, West Yorkshire, UK. Posts: 9,642	Re: Potentiometer It looks quite deep, it could be rotary or push-pull. Try both.

22nd Nov 2019, 6:46 pm	#5
Bigears Pentode Join Date: Nov 2017 Location: Durham, County Durham, UK. Posts: 144	Re: Potentiometer Yes you're right John it's an on/off switch. On the existing Potentiometer, it has two lugs, it has a two-cord mains cable (Brown and Blue) the Brown"Live" goes to one lug of the existing Pot and the Blue goes to the big transformer then from the second lug a red wire goes to the transformer. My question is it possible just to use one set of lugs as each pair is an on/off switch which lug would I use for the live ? Attached Thumbnails

22nd Nov 2019, 8:26 pm	#6
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Potentiometer Use a multimeter to work out which switch contacts are connected together when the switch is ON, and use one pair for the live. If you are not switching the neutral (there's no reason to, in the UK, and it's actually very slightly safer not to; although it makes about as much difference in real life as crossing the road to avoid breathing in the smoke from someone else's cigarette) just use either of the two pairs which are connected together when the switch is ON. __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

22nd Nov 2019, 8:26 pm	#7
David G4EBT Dekatron Join Date: Feb 2003 Location: Cottingham, East Yorkshire, UK. Posts: 5,761	Re: Potentiometer It doesn't matter which pair of tags you use for line or neutral. There are two independent single throw switches which operate simultaneously when you switch the potentiometer on or off. All that matters, is that whichever pole you chose for either line or neutral, must be correctly matched to line and neutral on the output side. IE, to make sure that you don't have one polarity on the input tag, and the other polarity on the output tag. At risk of stating the obvious, see pic below. Hope that helps. Attached Thumbnails __________________ David. BVWS Member. G-QRP Club member 1339.

23rd Nov 2019, 1:27 pm	#8
Bigears Pentode Join Date: Nov 2017 Location: Durham, County Durham, UK. Posts: 144	Re: Potentiometer Thanks, Julie and Dave