UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Marconi Valve Voltmeter TF1041C

Cathode Ray · 4th Feb 2019, 10:38 pm

Ok so I have arrived at a possible PSU problem.

The HT+ line is stated as +230v in the manual, but the regulator can only muster +220v despite having +276v on its anode.
Likewise the HT- is stated as -120, but it's only producing -112V

Adjusting the slider RV12 from 16v to 3v has virtually no effect on the HT voltage, whereas the manual says this should be set to produce +230v HT+.

The voltage between R59 and C7 is also 220v (anode of V6b)

See diagram below.
The resistors are within tolerance and C7 was replaced.

Does this look like a soft 12BH7 valve to you guys?

I'm not sure of this is causing the dc offset problem, but it's a all I have at the moment.

Thanks

4th Feb 2019, 10:38 pm	#17
Cathode Ray Pentode Join Date: Dec 2018 Location: County Meath, Ireland Posts: 242	Re: Marconi Valve Voltmeter TF1041C - repair thread Ok so I have arrived at a possible PSU problem. The HT+ line is stated as +230v in the manual, but the regulator can only muster +220v despite having +276v on its anode. Likewise the HT- is stated as -120, but it's only producing -112V Adjusting the slider RV12 from 16v to 3v has virtually no effect on the HT voltage, whereas the manual says this should be set to produce +230v HT+. The voltage between R59 and C7 is also 220v (anode of V6b) See diagram below. The resistors are within tolerance and C7 was replaced. Does this look like a soft 12BH7 valve to you guys? I'm not sure of this is causing the dc offset problem, but it's a all I have at the moment. Thanks Attached Thumbnails __________________ Regards Ray Last edited by Cathode Ray; 4th Feb 2019 at 10:50 pm.