Vidor CN417 - UK Vintage Radio Repair and Restoration Discussion Forum

steve.seven · 28th Sep 2020, 6:33 pm

While carrying out a visual check on this newly acquired CN417 I noticed an additional 225 Ohm 5 watt wire wound resistor connected between the secondary H.T. winding C.T. and ground.

The circuit diagram from the RTS servicing books does not show it being fitted and no mention is made of any modifications.

Rectifier Anode to Anode D.C. resistance is 430 Ohms, each half winding to C.T. read 223 & 208 respectively.

Thoughts at this stage are that some models were fitted with a different make of mains transformer and that the resistor was needed to give the correct H.T. voltage, any comments/ suggestions very welcome, radio has not been powered up so far.

Thank You.
Steve.

Silicon · 28th Sep 2020, 9:02 pm

Resistors wired to the centre tap were often used to create a negative bias for AGC and output valve grid bias in some radios.

steve.seven · 29th Sep 2020, 8:47 am

Quote:

Originally Posted by Silicon

Resistors wired to the centre tap were often used to create a negative bias for AGC and output valve grid bias in some radios.

It's a later build radio dating from 1952-53 and using an EBC41 for AGC & EL41 with a cathode biasing resistor. I have seen system you mention but they tend to be used in earlier mainly pre war radios, but thanks for reply.

28th Sep 2020, 6:33 pm	#1
steve.seven Pentode Join Date: May 2006 Location: Stroud, Gloucestershire, UK. Posts: 211	Vidor CN417 While carrying out a visual check on this newly acquired CN417 I noticed an additional 225 Ohm 5 watt wire wound resistor connected between the secondary H.T. winding C.T. and ground. The circuit diagram from the RTS servicing books does not show it being fitted and no mention is made of any modifications. Rectifier Anode to Anode D.C. resistance is 430 Ohms, each half winding to C.T. read 223 & 208 respectively. Thoughts at this stage are that some models were fitted with a different make of mains transformer and that the resistor was needed to give the correct H.T. voltage, any comments/ suggestions very welcome, radio has not been powered up so far. Thank You. Steve. Attached Thumbnails

28th Sep 2020, 9:02 pm	#2
Silicon Nonode Join Date: Jun 2007 Location: Coulsdon, London, UK. Posts: 2,167	Re: Vidor CN417 Resistors wired to the centre tap were often used to create a negative bias for AGC and output valve grid bias in some radios.