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Croozer · 12th Oct 2019, 3:53 pm

It is difficult to make sense of some of the voltages in your last post.

For this exercise we are interested in the voltage between the two heater pins (1 & 8)rather than their relationship with the chassis. My previous calculations working this out using voltage taken wrt chassis appear to have confused matters,so for the moment we want to focus on what voltage exists between the start and end of each heater.

To measure this directly one probe of the meter goes to
pin 8 and the other to pin 1 on each valve

From the datasheet the following results should be expected:

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

But from the measurements you have already taken wrt chassis and the sums i have done, i would expect the results to be significantly too high (eg the UBL 21 65V instead of 55V)

For each of the four valves measure,on AC volts range, voltage between pin 1 and 8 and let us know the results.

Remember also that all of the pins are at a mains voltage at some point above earth, so touching some of them with your fingers will be a shock hazard depending on where they are in the heater chain. Do not touch the chassis when taking the readings as,again this puts you at risk of shock.

12th Oct 2019, 3:53 pm	#95
Croozer Pentode Join Date: Jul 2016 Location: Edinburgh, Scotland, UK. Posts: 110	Re: Philips BX281U20 valve radio It is difficult to make sense of some of the voltages in your last post. For this exercise we are interested in the voltage between the two heater pins (1 & 8)rather than their relationship with the chassis. My previous calculations working this out using voltage taken wrt chassis appear to have confused matters,so for the moment we want to focus on what voltage exists between the start and end of each heater. To measure this directly one probe of the meter goes to pin 8 and the other to pin 1 on each valve From the datasheet the following results should be expected: Uy1n -50v Uch21 -20V Ubl2- 55V But from the measurements you have already taken wrt chassis and the sums i have done, i would expect the results to be significantly too high (eg the UBL 21 65V instead of 55V) For each of the four valves measure,on AC volts range, voltage between pin 1 and 8 and let us know the results. Remember also that all of the pins are at a mains voltage at some point above earth, so touching some of them with your fingers will be a shock hazard depending on where they are in the heater chain. Do not touch the chassis when taking the readings as,again this puts you at risk of shock.