[HAM] DC filtering to the heater filament voltage of the AO28

[Scott Hawthorn]

At 07:10 AM 12/21/2007, David Anderson wrote:

>Hi Kon,
>
>You still want a free lunch.
>
>What I mean by that is what I said earlier about rectification not
>being 100% efficient. You need a certain number of Watts to run the
>tube filaments, and this power comes from the transformer's filament
>winding; it has to come from SOMEWHERE. There is no getting around
>the fact that running the filaments on DC requires a slightly higher
>rated filament supply winding--unless you've found a way to get power
>from thin air....
>
>The simplest solution to this is to get a stand-alone filament
>transformer and build a supply based on it. You could even get a
>little toroid for low EM radiation.
>
>I have noticed that the heater wiring in some AO-28s is neater and
>more carefully done than in others. If you have more hum than you
>want, you might try replacing the heater wiring with more tightly
>twisted pairs and routing them as far as possible from low-level or
>very high impedance signal paths. This can make a difference,
>especially around the 12AX7 with the high impedance line from the
>swell capacitor.
>
>David

I confess to being puzzled by this whole discussion. It's just that I have 
never known hum to be a problem with AO-28 amps, unless the amp is broken. 
Of course it has been famously said that these organs are not HI-FI 
equipment. I guess if somebody wants to phool around with it, then that's a 
fascinating hobby, but really, the bottom line is that it's pointless, IMHO.