UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post

Sideband · 19th Apr 2019, 5:29 pm

If there is an electrolytic across that 270 ohm resistor (cathode bypass), it's worth checking it since an O/C cathode resistor will make the cathode of the valve rise towards HT. As you were measuring 27V on the cathode with an O/C resistor, the capacitor (if fitted) may have been damaged and could now be acting as a low value resistor thus bringing the cathode voltage down. Most UL84's run with a cathode voltage of somewhere between 9 and 12 volts. What does the circuit voltage say?

19th Apr 2019, 5:29 pm	#127
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,567	Re: Ferguson 382U Firefly not playing ball If there is an electrolytic across that 270 ohm resistor (cathode bypass), it's worth checking it since an O/C cathode resistor will make the cathode of the valve rise towards HT. As you were measuring 27V on the cathode with an O/C resistor, the capacitor (if fitted) may have been damaged and could now be acting as a low value resistor thus bringing the cathode voltage down. Most UL84's run with a cathode voltage of somewhere between 9 and 12 volts. What does the circuit voltage say? __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....