Hi there
I am in the process of restoring a JBL 6290 amplifier, and in that process I've stumbled upon something i can't really explain and I hope someone of you might be able to share knowledge i don't have.
The amplifier doesn't have voltage trough the output transistors and in the preliminary checking of the amp module I work from the power supply and towards the amp boards.
The mains transformers (one for each channel) supplies the correct current on the 2 secondary windings when running at 220V, but the amplifier draws almost 2A at Idle
So I unhooked the power transformers and have made some measurements of current draw at different supply voltages.
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The transformer is labeled as a 220V unit, however the current here in Denmark is 230 from the wall - but that is another issue. What I suspect is that the transformer is actually winded for 60hz and not the 50hz, the european net provides.
At first I thought the transformer was bad, but it seems odd that two identical transformers from the same product, should have a short at the exact same place, as my measurements are exactly the same!

The target value for the entire system is 120W idle consumption at 220V as per the user manual.

Right now the system draws 330W at idle (If supplied with 220V). at this is just from the mains transformers.

If the transformer was winded for 60hz operation, the power draw at 220V 60Hz would be the same as the power draw at 180V 50hz (220V/60) * 50 = 180.
Here I see my transformer drawing 0,251A - which would translate into roughly 110W at 220V both transformers driven.
Ie. very close to the specified 120W operation at idle (we also have to account for the bias of the transistors which are not included right now)

So my question is - could it be that the 220V UREI transformer was actually winded for 60hz operation and not 50hz as I would expect from a unit with a 220V transformer?