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

AndrewM · 25th Apr 2011, 8:54 am

As mentioned above, with a low boost voltage I would be concerned about the Line Output stage operating conditions.

Check that the screen, grid and cathode voltages are within spec for the 6CM5 output valve. If they are close to correct then you can safely leave the set running for more in depth troubleshooting on the CRT.
It is most important that the 0.14 volts on the cathode not be much above 0.18 or so volts (measured with an analogue multimeter) or the Line Output transformer will be overly stressed. If voltages are near correct, the Horizontal Oscillator may be running off frequency,causing boost voltage to drop a lot but the CRT should still light up.

If the Line Out stage conditions allow extended running, then check the CRT pin voltages. It may be biased off despite the low boost volts.

25th Apr 2011, 8:54 am	#5
AndrewM Pentode Join Date: Apr 2009 Location: Melbourne, Australia Posts: 115	Re: Help with a HMV TV As mentioned above, with a low boost voltage I would be concerned about the Line Output stage operating conditions. Check that the screen, grid and cathode voltages are within spec for the 6CM5 output valve. If they are close to correct then you can safely leave the set running for more in depth troubleshooting on the CRT. It is most important that the 0.14 volts on the cathode not be much above 0.18 or so volts (measured with an analogue multimeter) or the Line Output transformer will be overly stressed. If voltages are near correct, the Horizontal Oscillator may be running off frequency,causing boost voltage to drop a lot but the CRT should still light up. If the Line Out stage conditions allow extended running, then check the CRT pin voltages. It may be biased off despite the low boost volts.