Old US test equipment use in UK

[Mike Watterson]

The saturation problem happens at zero load just as much as at full load. Both iron and copper losses rise as the core saturates and the transformer can get too hot even at no load. Obviously under full load there are additional copper losses.

It's even a problem for some marginally spec'd transformers for 220V 50 Hz mainland Europe, even where the secondary HT & LT is still reasonable at 230V or 240. A series resistor is needed.

Some USA domestic gear might have marginal transformers. So 50Hz at 120V might be an issue but at 110V it might be OK.

Use a stepdown transformer to 110V and see is the transformer cool with no load.

[ppppenguin]

A resistor is cheap and simple but gets hot. A buck transformer is a better solution for dropping 20V or so. A tiny 10VA transformer will suffice to buck 20V for up to a 120W load.

[Murphyv310]

Hi.
Indeed the series resistor works but of course wasteful and far from elegant.
Interestingly the Russian Rekord TV I have is for 220v, it uses electrolytic caps off the 110v tap as a doubler to give the HT, an odd arrangement indeed. If you use a power resistor to drop the 20v odd mains volts the transformer buzzes madly but using the variac or buck transformer it's fine with no such buzz.

[Mike Watterson]

A resistor is cheap and simple but gets hot. A buck transformer is a better solution for dropping 20V or so. A tiny 10VA transformer will suffice to buck 20V for up to a 120W load.

Yes, it depends on the load (30W vs 60W set) and the supply voltage (230V here vs 240 to 245V in UK). I'd certainly normally use a 20V transformer in the UK and check AC Polarity to avoid having 260V! Here I've been able to use 3W resistors on some German sets. The Battery/Mains sets seem to use more marginal transformers than the larger mains only sets. One mains set with an EL95 o/p was marginal; maybe a compact Opus LW-MW-SW-VHF set.