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I'm a bit of a newbie so please bear with me.

I'm looking to build a DIY phono pre-amp kit that comes with its own additional PSU board (search for EAR834p clones on ebay) and components. All I'm required to source myself is the tubes and power transformer (and also any other additional components e.g. a chassis, etc.).

I have a good vintage transformer that could possibly meet all of its criteria in theory, but the PSU circuit calls for up to 280V AC and the HT secondary on this transformer is 280V - 0 - 280V @ 100mA, so 560V AC when measured between both ends of the secondary winding. Is it possible to just use one side of the two 280V windings along with the centre tap for a 280V AC source? I'm assuming at the very least that I'd only have half of the current available to me which is still enough for the circuit I have in mind, but I'm just not sure if this is a possible use-case for this type of transformers, or if it could damage the unit in any way. The transformer is a Partridge 1597 from around the 60s, if that helps.

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    \$\begingroup\$ I’m assuming the AC will be rectified at some point, in which case the ‘usual’ configuration would be a dual diode valve or two semiconductor diodes (selenium if you’re old school!) to form a full wave rectifier. The centre tap goes to 0V/gnd. \$\endgroup\$
    – Kartman
    Commented Aug 1, 2022 at 22:34
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    \$\begingroup\$ You're wrong about the current, it'll still be 100mA. Just the voltage will be halved if you only use half the secondary. \$\endgroup\$
    – Finbarr
    Commented Aug 1, 2022 at 22:43
  • \$\begingroup\$ One needs to study the power supply schematic, furnished by the kit supplier, to confirm suitability or otherwise of the Partridge 1597 transformer. Please provide the same. \$\endgroup\$
    – vu2nan
    Commented Aug 2, 2022 at 10:09

3 Answers 3

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The correct way to use this transformer would be a center-tap full-wave setup with two rectifier elements, common when the only rectifiers available were valves with forward voltage drops in the 10s of volts. You should be able to re-create this using diodes since your circuit can take 280VAC. If not, you might get acceptable performance only using half of the winding and putting it through a semiconductor rectifier but I would look around for a transformer with an appropriate whole-secondary voltage. A dedicated tube amp site might be able to suggest a workaround.

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Yes, you can only use one side of the transformer, if its current is sufficient for your circuit. Leave the other side of the transformer disconnected.

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Are there four connections/wires out of the transformer or only three? If there are four, you’ll get more current from the transformer if you parallel the two windings - but the polarity has to be matched or it will burn out almost instantly(!).

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