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ukcol · 13th Sep 2017, 7:37 pm

As Peter says above, the clue is the AGC line going slightly positive and it could be V3.

Try this:

Wait for the fault to appear and the AGC line to go positive. Tune the set off station so there is little or no signal. The AGC line should stay positive or go even more positive. Gently pull V3 (6AT6) out of its socket and if the ddt valve is responsible the positive voltage will go.

If the positive voltage remains, V1 (6BE6) or V2 (6BJ6) could be responsible.

If the positive voltage doesn't go when you pull V3, switch off and refit V3 in its socket. Turn the set on again and wait for the fault to reappear and repeat the test pulling V2 from its socket. Finally, if necessary, do the same with V1. The positive voltage will go when you pull the faulty valve.

BTW this test is safe for the radio because the valve heaters are parallel fed from a transformer. It is not a good idea to unplug a valve from a powered up set if it uses a series heater chain.

13th Sep 2017, 7:37 pm	#16
ukcol Rest in Peace Join Date: May 2003 Location: Harlaxton, Lincolnshire, UK. Posts: 3,944	Re: Toaster FB10 elusive fault As Peter says above, the clue is the AGC line going slightly positive and it could be V3. Try this: Wait for the fault to appear and the AGC line to go positive. Tune the set off station so there is little or no signal. The AGC line should stay positive or go even more positive. Gently pull V3 (6AT6) out of its socket and if the ddt valve is responsible the positive voltage will go. If the positive voltage remains, V1 (6BE6) or V2 (6BJ6) could be responsible. If the positive voltage doesn't go when you pull V3, switch off and refit V3 in its socket. Turn the set on again and wait for the fault to reappear and repeat the test pulling V2 from its socket. Finally, if necessary, do the same with V1. The positive voltage will go when you pull the faulty valve. BTW this test is safe for the radio because the valve heaters are parallel fed from a transformer. It is not a good idea to unplug a valve from a powered up set if it uses a series heater chain.