AVO VCM Mk IV Question - UK Vintage Radio Repair and Restoration Discussion Forum

Jeffreyabb · 18th Mar 2019, 3:41 pm

Hi I have started rebuilding a AVO MkIV VCM, beginning with the Component Board. The S/N is 1936. My question is about replacing the diodes on the board.
There are 3 sets of 2 diodes in series on the board with 2M2 resistors across each diode, one pair without resistors and a single diode. I am going to replace all diodes with BYW96's. Can I replace the pairs of diodes with 2 BYW96E's with a single one? also if I have to use 2 diodes do I need to replace the 2M2 resistors? There are different circuit diagrams with having different combinations of the above.
Regards
Jeff
G6CQH

Dekatron · 18th Mar 2019, 5:05 pm

You can replace the two diodes in series with one BYW96E and also remove the 2.2Meg resistors - this will make it look and work like the later circuits.

There are a maximum of four (4) sets of two diodes in series with 2.2Meg resistors across each diode in the earliest AVO MkIV VCM, one pair for Anode, Grid and two (2) for the Grid-voltage circuit.

Jeffreyabb · 18th Mar 2019, 9:53 pm

Hi Martin
Thank you for the info. It is what I hoped for.
Regards
Jeff
G6CQH

18th Mar 2019, 3:41 pm	#1
Jeffreyabb Pentode Join Date: Apr 2009 Location: Durham, UK. Posts: 165	AVO VCM Mk IV Question Hi I have started rebuilding a AVO MkIV VCM, beginning with the Component Board. The S/N is 1936. My question is about replacing the diodes on the board. There are 3 sets of 2 diodes in series on the board with 2M2 resistors across each diode, one pair without resistors and a single diode. I am going to replace all diodes with BYW96's. Can I replace the pairs of diodes with 2 BYW96E's with a single one? also if I have to use 2 diodes do I need to replace the 2M2 resistors? There are different circuit diagrams with having different combinations of the above. Regards Jeff G6CQH

18th Mar 2019, 5:05 pm	#2
Dekatron Octode Join Date: May 2009 Location: Linkoping, Sweden Posts: 1,465	Re: AVO VCM Mk IV Question You can replace the two diodes in series with one BYW96E and also remove the 2.2Meg resistors - this will make it look and work like the later circuits. There are a maximum of four (4) sets of two diodes in series with 2.2Meg resistors across each diode in the earliest AVO MkIV VCM, one pair for Anode, Grid and two (2) for the Grid-voltage circuit. __________________ Martin, Sweden

18th Mar 2019, 9:53 pm	#3
Jeffreyabb Pentode Join Date: Apr 2009 Location: Durham, UK. Posts: 165	Re: AVO VCM Mk IV Question Hi Martin Thank you for the info. It is what I hoped for. Regards Jeff G6CQH