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General Vintage Technology Discussions For general discussions about vintage radio and other vintage electronics etc. |
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16th Jun 2021, 11:07 pm | #1 |
Tetrode
Join Date: Jun 2012
Location: Cardiff, Wales, UK.
Posts: 79
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Step Down Transformer connections
I have recently bought a 60s Wurlitzer 2510 jukebox. It has an old step down transformer with it which after testing the continuity of both windings I am planning to wire in.
The UK end is already wired (neutral to 'com' and live to '220') I can't seem to work out which way around the US end (live/neutral) should go. The RHS (in this photo) is labelled '1' and the LHS labelled '2' so I assumed that 1 would be neutral - does anyone know if that makes sense? I've tried looking up the company and I think they still exist but I suspect my inexperience is showing and so I hope that someone on here will know and be kind enough to help me thanks |
16th Jun 2021, 11:40 pm | #2 |
Dekatron
Join Date: Jun 2009
Location: Staffordshire Moorlands, UK.
Posts: 5,271
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Re: Step Down Transformer connections
if it's an isolating transformer then I dont suppose it matters, if it's an auto then the easiest way is to power it up and measure each terminal voltage to earth.
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Kevin |
17th Jun 2021, 3:37 am | #3 |
Nonode
Join Date: Oct 2010
Location: Tintinara, South Australia, Australia
Posts: 2,340
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Re: Step Down Transformer connections
Wire it so that the secondary N is on the same side as the incoming mains N.
Theoretically, it shouldn't matter which way round it is wired if it is a fully isolating transformer. If it is an auto-transformer, then it matters. |
17th Jun 2021, 8:10 am | #4 |
Pentode
Join Date: Oct 2012
Location: Dorset, UK.
Posts: 240
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Re: Step Down Transformer connections
First thing is to ascertain whether this is an autotransformer or an isolating transformer. With the transformer disconnected from the mains, use the lowest ohms range on a multimeter to check whether all of the terminals, including 1 and 2 show continuity to the com terminal, or whether there is continuity between 1 and 2 but not to the com terminal
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17th Jun 2021, 9:04 am | #5 |
Dekatron
Join Date: Feb 2009
Location: Chesterfield, Derbyshire, UK.
Posts: 3,762
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Re: Step Down Transformer connections
The juke box will have an isolating transformer usually with wire coded black and white , for 115 volt mains so it matters not which way round you connect your auto transformer for 240 mains . better still get yourself a fully isolated step down . Mick.
Last edited by vinrads; 17th Jun 2021 at 9:19 am. |
17th Jun 2021, 4:22 pm | #6 |
Tetrode
Join Date: Jun 2012
Location: Cardiff, Wales, UK.
Posts: 79
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Re: Step Down Transformer connections
Thank you for your posts
There is continuity across the 2 sides. From the looks of it I am wondering whether it may just be better to buy a new fully isolated one Thanks you |
17th Jun 2021, 4:24 pm | #7 | |
Heptode
Join Date: Mar 2017
Location: Cedar Grove, Wisconsin, USA.
Posts: 823
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Re: Step Down Transformer connections
Quote:
On the primary side, reconnect the live side to the 240v terminal, as your mains voltage is nearer to 240v or more. Dave, USradcoll1 |
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17th Jun 2021, 5:08 pm | #8 |
Tetrode
Join Date: Jun 2012
Location: Cardiff, Wales, UK.
Posts: 79
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Re: Step Down Transformer connections
They seem to be a bit pricey so think I may be resurrecting this one after all…
So in terms of Kevin’s suggestion - seems like the only way to be sure. I usually avoid doing tests on AC mains like this for safety reasons. Presumably both prongs in one hand and one on the mains earth wire and the other on 1 and 2. The one with a result should be live? |
17th Jun 2021, 5:12 pm | #9 | ||
Tetrode
Join Date: Jun 2012
Location: Cardiff, Wales, UK.
Posts: 79
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Re: Step Down Transformer connections
Quote:
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17th Jun 2021, 6:36 pm | #10 |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,535
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Re: Step Down Transformer connections
FWIW single phase plug wiring in the US is coloured black (and/or bare copper core) for line and white (and/or tinned copper core) for neutral.
If the TX is an auto type, one or other of the output terminals will be short to COM and therefore neutral provided that COM is neutral as described. The other output terminal will then be the 120V line.
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17th Jun 2021, 7:40 pm | #11 |
Tetrode
Join Date: Jun 2012
Location: Cardiff, Wales, UK.
Posts: 79
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Re: Step Down Transformer connections
Thanks Chris - that’s very helpful.
I get 0.4 R between com and point 2. This is the same as I get when I touch my prongs together. I get 1.8 R between com and point 1. Between com and the 220v I get 3.8 R so am now fairly confident which way around it is. Thank you all so much - |
17th Jun 2021, 7:55 pm | #12 | |
Dekatron
Join Date: Sep 2007
Location: Oxfordshire, UK.
Posts: 4,311
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Re: Step Down Transformer connections
Quote:
EDIT: Crossed with Graham. Cheers, GJ
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17th Jun 2021, 7:56 pm | #13 | ||||
Dekatron
Join Date: May 2010
Location: Greater Manchester, UK.
Posts: 18,715
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Re: Step Down Transformer connections
Quote:
Quote:
Quote:
GJ, I deleted my post for a moment while I thought it through one last time
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18th Jun 2021, 12:12 am | #14 |
Nonode
Join Date: Jun 2007
Location: Coulsdon, London, UK.
Posts: 2,163
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Re: Step Down Transformer connections
What supply voltage was your 1960s Wurlitzer designed to work on?
Apparently American mains supply voltages have increased slightly over the years. When you first power up the amplifier, check the heater voltage getting to the valves. This is usually more important than the HT voltage. Adjust the transformer connections to get the best heater voltage. |
18th Jun 2021, 7:32 am | #15 |
Tetrode
Join Date: Jun 2012
Location: Cardiff, Wales, UK.
Posts: 79
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Re: Step Down Transformer connections
Thank you
I really appreciate that - I was thinking I needed to work it through as I may have it the wrong way around with regards to the input voltage. Thank you - very helpful I think the lower end of the voltage is generally preferred in order to take the pressure off of the fluorescent lighting as it is designed for 60hz. I will change to 240v and see how things go. |
18th Jun 2021, 10:11 am | #16 |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,535
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Re: Step Down Transformer connections
Interesting about the fluoros. Makes sense if they're using traditional inductor ballast gear.
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....__________ ....|____||__|__\_____ .=.| _---\__|__|_---_|. .........O..Chris....O |
19th Jun 2021, 10:51 am | #17 |
Dekatron
Join Date: Jun 2009
Location: Staffordshire Moorlands, UK.
Posts: 5,271
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Re: Step Down Transformer connections
the reason I suggest measuring the secondary voltages to earth is because it's easy doing it the resistance way and get it wrong, the right and wrong way only being an ohm or so apart. Quite easy on old dirty terminals to make a mistake, whereas measuring the voltage to earth will leave no doubt.
I'm just speaking from experience with autotransformers where I've had to recently repair a batch bought from China which had miswired primaries, meaning the 115V-supplied equipment had 115V across them but 240V to earth
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Kevin |