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Croozer · 11th Oct 2019, 4:31 pm

You need to measure the voltage between pins 1 and 8 on each valve

Uy1n -50v
Uch21 -20V
Ubl2- 55V

By doing a quick sum and working out the differences between pins 1 and 8 from chassis as i am assuming that these are the readings you posted, i believe you have (170-115) = 55V on the UY1N and (89-24)= 65v across the UBL21 heaters

But you should measure directly across those valves (pin 1 and 8) to be sure - and take the same measurements for the uch21s

I believe that if you do this, and add all of the overvoltages together you will arive at a figure close to the difference between 220V and your own mains supply .

This figure is the one which will require to be dropped -and will likely be 20-25V -just as in Lawrence's post.

To have the set running as designed you should also consider the HT circuit,which will also be over voltage, and consider the HT (DC)current in your calculation- in reality something ballpark 200-250 ohms would be expected, but it is worth doing the measurements and the sums.

Please dont go changing resistors for the sake of it as this is unlikely to yield improvement. The overvoltage measurements show the set is performing as expected in this respect because you are using a 220V set on 245V mains. Likewise there are many other possible causes of the intermittency you describe than a resistor. Proper diagnosis is required.

The additional dropper would go in after the mains switch.

11th Oct 2019, 4:31 pm	#91
Croozer Pentode Join Date: Jul 2016 Location: Edinburgh, Scotland, UK. Posts: 110	Re: Philips BX281U20 valve radio You need to measure the voltage between pins 1 and 8 on each valve Uy1n -50v Uch21 -20V Ubl2- 55V By doing a quick sum and working out the differences between pins 1 and 8 from chassis as i am assuming that these are the readings you posted, i believe you have (170-115) = 55V on the UY1N and (89-24)= 65v across the UBL21 heaters But you should measure directly across those valves (pin 1 and 8) to be sure - and take the same measurements for the uch21s I believe that if you do this, and add all of the overvoltages together you will arive at a figure close to the difference between 220V and your own mains supply . This figure is the one which will require to be dropped -and will likely be 20-25V -just as in Lawrence's post. To have the set running as designed you should also consider the HT circuit,which will also be over voltage, and consider the HT (DC)current in your calculation- in reality something ballpark 200-250 ohms would be expected, but it is worth doing the measurements and the sums. Please dont go changing resistors for the sake of it as this is unlikely to yield improvement. The overvoltage measurements show the set is performing as expected in this respect because you are using a 220V set on 245V mains. Likewise there are many other possible causes of the intermittency you describe than a resistor. Proper diagnosis is required. The additional dropper would go in after the mains switch.