UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - My first valve radio project

Lucien Nunes · 27th Dec 2016, 7:29 pm

This all sounds a little peculiar. How confident are you about the accuracy and reliability of your meter on its various AC voltage ranges?

To clarify the expectations, transformer voltages are inter-related by the number of turns of each winding and only catastrophic damage to the transformer will cause them to vary much with respect to one another. As Tony mentions there is a certain amount of voltage drop as load is applied - the ratio between maximum and minimum is called the regulation and it's worse on small transformers than large ones - but you should be seeing results within perhaps 10% of stated figures provided you are feeding in the correct voltage as selected on the dial.

Of course, if there is a mismatch between the supplied voltage and the setting, everything else will be out by approximately the same ratio. E.g. if what is actually reaching the set through the limiter is 3/4 of the selection (say 184V on the 245V setting) then you would expect all the secondary voltages to be roughly 3/4 of their proper voltages. If you feed in 245 on the 245V setting, then a 4V rectifier heater supply should be pretty well on 4V and getting 3V definitely indicates a problem.

Usually, it would be shorted turns or one of the other secondaries overloaded, and hence the thing would be getting toasty or the lamp limiter would be ablaze, which is why it seems odd. However if your measurement is out by 1V, then we might all be looking in the wrong direction, so a double-check of the meter might be worthwhile.

27th Dec 2016, 7:29 pm	#122
Lucien Nunes Rest in Peace Join Date: Apr 2008 Location: London, UK. Posts: 2,508	Re: My first valve radio project - Philips 462A This all sounds a little peculiar. How confident are you about the accuracy and reliability of your meter on its various AC voltage ranges? To clarify the expectations, transformer voltages are inter-related by the number of turns of each winding and only catastrophic damage to the transformer will cause them to vary much with respect to one another. As Tony mentions there is a certain amount of voltage drop as load is applied - the ratio between maximum and minimum is called the regulation and it's worse on small transformers than large ones - but you should be seeing results within perhaps 10% of stated figures provided you are feeding in the correct voltage as selected on the dial. Of course, if there is a mismatch between the supplied voltage and the setting, everything else will be out by approximately the same ratio. E.g. if what is actually reaching the set through the limiter is 3/4 of the selection (say 184V on the 245V setting) then you would expect all the secondary voltages to be roughly 3/4 of their proper voltages. If you feed in 245 on the 245V setting, then a 4V rectifier heater supply should be pretty well on 4V and getting 3V definitely indicates a problem. Usually, it would be shorted turns or one of the other secondaries overloaded, and hence the thing would be getting toasty or the lamp limiter would be ablaze, which is why it seems odd. However if your measurement is out by 1V, then we might all be looking in the wrong direction, so a double-check of the meter might be worthwhile.