Whenever you see a set number suffixed by 'U' as in 445U, it signifies that it's an AC/DC set ('U' meaning 'universal').
I'd have thought it highly unlikely that all sections of R25 and R24 are open circuit. If you check each section with an Ohmmeter to see which if any are open circuit, you can simply solder a high wattage ceramic wirewound resistor of the nearest preferred value across that section. (That was standard workshop practice back in the days when TVs and radios extensively used droppers). R25 is a total of 1,330R, tapped at 130, 1130, and 1230. Hence, the sections consists of 130R, then 1K, (130+1,000 = 1130) then 100, (1130+100 = 1230), then another 100 (1230+100 = 1330). 1K and 100R are present day standard values, but 130 is not, so if you used 150R for that section (assuming it's duff) the total would be 1350R, which is +1.5% - well within the original tolerance of +/- 5%.
For R24, that is 750R tapped at 300R, so consists of two sections, so the second section is 450R. The nearest preferred values would be 270R + 470R = 730R, which is - 4% - again, within the 5% tolerance.
If you haven't done so already, you should clip out C45, which is across the mains input before it goes bang. The set will work fine without it, but it should be replaced with a .01 'X Class' capacitor designed to be used in that situation. Also, you should replace 'that cap' - the .05uF cap which feeds the grid of the output valve because if it is leaky (in the electrical sense), it will allow DC to pass to the valve, which risks overdriving it, and damaging the value and the output transformer.
I've attached a diagram of R25 to make things a bit clearer.
Hope that helps.
Good luck with the set!
I'd have thought it highly unlikely that all sections of R25 and R24 are open circuit. If you check each section with an Ohmmeter to see which if any are open circuit, you can simply solder a high wattage ceramic wirewound resistor of the nearest preferred value across that section. (That was standard workshop practice back in the days when TVs and radios extensively used droppers). R25 is a total of 1,330R, tapped at 130, 1130, and 1230. Hence, the sections consists of 130R, then 1K, (130+1,000 = 1130) then 100, (1130+100 = 1230), then another 100 (1230+100 = 1330). 1K and 100R are present day standard values, but 130 is not, so if you used 150R for that section (assuming it's duff) the total would be 1350R, which is +1.5% - well within the original tolerance of +/- 5%.
For R24, that is 750R tapped at 300R, so consists of two sections, so the second section is 450R. The nearest preferred values would be 270R + 470R = 730R, which is - 4% - again, within the 5% tolerance.
If you haven't done so already, you should clip out C45, which is across the mains input before it goes bang. The set will work fine without it, but it should be replaced with a .01 'X Class' capacitor designed to be used in that situation. Also, you should replace 'that cap' - the .05uF cap which feeds the grid of the output valve because if it is leaky (in the electrical sense), it will allow DC to pass to the valve, which risks overdriving it, and damaging the value and the output transformer.
I've attached a diagram of R25 to make things a bit clearer.
Hope that helps.
Good luck with the set!
Regards, David.
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
