Re: {Collins} 75A-4 Issues - Hum V13 DC filament



I unground the filament connection of the tube in question, then run twisted pair from the transformer secondary to the sockets. This creates a balanced feed between the transformer and one filament.  A hum pot can then be used if  the transformer has a tapped secondary.  If not, a virtual tap can be created with resistors.  

On doing the above, sometimes there's a big improvement and other times there's little change. For the little effort involved, its worth a shot. 

Paul, W9AC


Sent from my iPhone5

On Dec 9, 2012, at 5:39 PM, Roy Morgan <k1lky@xxxxxxxxxxxxx> wrote:

> 
> On Dec 9, 2012, at 12:03 PM, Paul Christensen wrote:
> 
>> ... As an alternative to DC on V13's filaments, a dedicated twisted pair from the transformer can be run tightly against the chassis just to V13, then use a hum balance pot.
> 
> Paul,
> 
> My 75A-4 manual shows most/all filament returns grounded, presumably at the tube socket.  How do you arrange a hum balance pot for just one of the many tubes?
> 
> Roy
> 
> Roy Morgan
> k1lky@xxxxxxxxxxxxx
> K1LKY Since 1958 - Keep 'em Glowing!
> 
> 
> 




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