# How to identify a low voltage transformer

Not 100% sure this is the correct forum for this question. If not, I apologise.

I am trying to identify this transformer. It comes out of a Paradigm PDR-10 subwoofer amp. I believe it is bad as even when disconnected from the circuit board, it keeps blowing fuses. I am trying to find a replacement but there are no other labels on the xfmr. From the label presented, can anyone tell me how to read this label? Is there enough information on the label to find a suitable replacement? Thanks

• Other than contacting the manufacturer and ordering the same part number, no. The amp's schematic/service manual may have the information you need though. – Brian Drummond Apr 19 at 22:07
• It’s a long stretch but you may be experiencing remanence in the transformer if you say you blow fuses without anything connected on the secondary. Some other fault like some short is more likely but if you’re not afraid to experiment, try injecting some DC current and see if the situation improves. Link: electrical-engineering.academy/posts/the-secret-of-remanence – winny Apr 19 at 22:40
• So excuse my ignorance as smaller electronics is not my strong suit. The output of the xfmr is connected to 2 x 80vDC capacitors. So assuming whatever xfmr I get, as long as it is <160vDC, then I should be good to test with? – user2533368 Apr 20 at 21:14

So excuse my ignorance as smaller electronics is not my strong suit. The output of the xfmr is connected to 2 x 80 V DC capacitors. So assuming whatever xfmr I get, as long as it is < 160 V DC, then I should be good to test with?

Transformers are AC, not DC.

simulate this circuit – Schematic created using CircuitLab

Figure 1. Centre-tapped transformer, bridge rectifier and smoothing capacitors.

• The transformer is centre-tapped to provide a symmetrical power supply with a positive voltage rail and a negative power rail.
• When AC voltage is rectified and smoothed the DC voltage can reach $$\ \sqrt 2 \$$ times the transformer voltage.
• The 80 V rating of the capacitors may be just the next standard voltage above the DC output voltage.

I would be surprised if the voltage was much more than ±50 V. If that was the case the transformer would be something like 35 - 0 - 35 V.

I hope you can see that your idea of a 160 V transformer would have been disastrous. You haven't given the power rating of the amplifier, the ratings label or the impedance of the loadspeaker so it is not possible to estimate the likely current requirement.

• Thanks for the quick answer and education. Makes more sense now. I guess at this point, I am SOL to repair this. Just hurts that a $700 subwoofer is not working because of a <$30 part. – user2533368 Apr 20 at 21:40