Author Topic: Vintage Transformer Question  (Read 302 times)

Online Aqualung

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Vintage Transformer Question
« on: August 18, 2017, 07:24:01 PM »
Hi Guys,

I am looking at an old (big and very heavy) transformer, and have 3 questions:

1. The output side has 3 wires: Red / Blue / Red. In faded pen on the cover it says 50V / 0V / 50V and 5amp. The input side has 4 wires: Blue / Black / Red / Yellow. In faded pen on the cover it says 10V / 0V / 220V / 240V and 2 amp. The Blue and Yellow wires are taped up, and the Black and Red wires go to a connector block. There is a fuse in line with the Red wire. Question: is it really 10V, or more like 110V and the writing is just faded?

2. Should I use the 220V or the 240V input? In my house the AC almost always measure 237V.

3. On the output side the Blue wire is taped off, and the two Reds go to connector blocks. I measure 98 and 99V AC on the connector block when the transformer is plugged in. So what would this have been used for / what would it be good for?

All information and opinions appreciated.

Thanks,
Johan
I love music - analog and digital. Even listening to the Blues makes me happy. During the day I coach and counsel, after hours I indulge in my second passion - listening to vinyl and restoring turntables. Some I keep, some I sell...

Offline kubusi

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Re: Vintage Transformer Question
« Reply #1 on: August 18, 2017, 08:42:58 PM »
From the information you have given and the measurements made the 50-0-50 is obviously the secondary with a centre tap so with 2 nice sized diodes connected to the red wires you will get a nominal 50 volt input to the filter/smoothing caps and take the negative from the blue wire, if you ignore to blue centre tap and connect a bridge rectifier to the red wires you will get a nominal 100v.
On the primary side the 0v is used with either the 220 or 240 volt connected to the mains input, however if your mains supply is 230 or 250 volts instead of using the 0v connection you use the 10 volt input wire. If you use an ohmmeter and measure the resistance between the 0v  and the 10v you will find the resistance very low as it only consists of a few extra turns of wire on the transformer.
The 2 amps I would guess is the current available across the 50-0-50 ie at 100volts so at 50 volts as mentioned above you would be able to pull 4 amps from the transformer. Could be used for a nice solid state amplifier.
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Offline Steerpike

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Re: Vintage Transformer Question
« Reply #2 on: August 18, 2017, 11:36:55 PM »
50-0-50 AC is very high for a transistor audio amplifier, except one of really high output power, and then 4 amps isn't enough current.

(Using a single ended supply (0-50) is possible with modern transistor amp circuits, but not common or preferred because it requires a big output capacitor)

Using a voltage doubler type rectifier it could get you enough B+ for a small valve amplifier, but you'd need an additional transformer for the heaters, and 4A of B+ current is ridiculously overkill.

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Re: Vintage Transformer Question
« Reply #3 on: August 20, 2017, 05:22:08 PM »
Thanks guys, I appreciate the answers.
I will measure the resistance this week, and report back.

:thumbs:
I love music - analog and digital. Even listening to the Blues makes me happy. During the day I coach and counsel, after hours I indulge in my second passion - listening to vinyl and restoring turntables. Some I keep, some I sell...