06-06-2014, 09:30 AM
I now have the Figaro up and running. From a mains i/p of 240vac, I get 180vac at the junction of the 100 ohm resistor and 1N4007 anode. DC at the cathode is 205v, and at the smoothing cap is 174v. The series resistor (R17) is 1k2, whch gives a calculated HT Current of ca. 26mA. I replaced the original 300 ohm ECL82 cathode resistor (R16) with a 330 ohm 1 watt type, the terminal having pulled off the original. After having run the set, out of it's cabinet for about 2 hours
the above readings were still the same, with no sign of any overheating, increased hum or other distress, so I now only have to repair the w/c switch 'fork', and all should be well. My only query relates to the 2 watt 100 ohm resistor I fitted in series with the 1N4007 rectifier diode, and it is that, from the above measurements (made with a M3800 DMM incidentally) 35 volts is being dropped acroos the 100 ohm resistor, i.e. 350mA is being drawn, which is 12.25 watts, meaning I should use a lower value series resistor, which would raise the HT ( No voltage readings are given on the service sheet, but I would have expected the HT to be nearer, say, 230v than 200v) I'll check the curren drain through the 400mA mains fuse later just to confirm. ( I've just realised that, by measuring the drop from the mains input to the rectifier, I'm including the heater & bulb current in the reading, whereas only the HT current flows through the rectifier and it's series resistor. This would be no more than about 50mA, drawn from a tap on the autotransformer, so maybe I'l leave the 100 ohm 2 watt resistor in place! (Only been doing this job for 44 years!!!)
the above readings were still the same, with no sign of any overheating, increased hum or other distress, so I now only have to repair the w/c switch 'fork', and all should be well. My only query relates to the 2 watt 100 ohm resistor I fitted in series with the 1N4007 rectifier diode, and it is that, from the above measurements (made with a M3800 DMM incidentally) 35 volts is being dropped acroos the 100 ohm resistor, i.e. 350mA is being drawn, which is 12.25 watts, meaning I should use a lower value series resistor, which would raise the HT ( No voltage readings are given on the service sheet, but I would have expected the HT to be nearer, say, 230v than 200v) I'll check the curren drain through the 400mA mains fuse later just to confirm. ( I've just realised that, by measuring the drop from the mains input to the rectifier, I'm including the heater & bulb current in the reading, whereas only the HT current flows through the rectifier and it's series resistor. This would be no more than about 50mA, drawn from a tap on the autotransformer, so maybe I'l leave the 100 ohm 2 watt resistor in place! (Only been doing this job for 44 years!!!)
