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



Forgot to mention, if the tube to be balanced is in the middle of a series string, the string must continue.  

I last used this method on the HFO of a National  NC-101X.  Before the change, hum modulation was terrible on 20m and above. 

Paul, W9AC

Sent from my iPhone5

On Dec 9, 2012, at 6:00 PM, Paul Christensen <w9ac@xxxxxxxx> wrote:

> 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!
> _______________________________________________
> SHARE THE FUN: JOIN THE COLLINS COLLECTORS ASSOCIATION TODAY !
> http://www.collinsradio.org/?page_id=37
> 
> NETS: Tues & Thur: 3.805 MHz-2000 Central + Fri: 3.895 MHz-2000 Pacific
>  SUNDAYS: 14.263 MHz-2000 UTC  +  AM Net: 29.050 MHz-1200 Central
>  1st Wednesday AM Net 3.880 MHz-2000 local (ET, CT, MT, PT)
> 
> The Collins Reflector reserves the right to refuse access to anyone.
> 
> LIST HELP?  ADMIN EMAIL:  collins-owner@xxxxxxxxxxxxx
> This ONLY goes to the list admins and does not post to the group!




This archive was generated by a fusion of Pipermail (Mailman edition) and MHonArc.