Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: firemedic on November 16, 2011, 06:13:23 am

Title: filament transformer CT
Post by: firemedic on November 16, 2011, 06:13:23 am

This has probably been covered elsewhere but here goes:
I'll be using an auxiliary 4A 6.3v transformer in addition to my center tapped PT in my new build. The aux tranny is also center tapped. Is it better to use the CT on it, or to do an artificial CT w/ 100 ohm resistors? For that matter, if the heater supply on the PT is center tapped, should I use both CTs, neither, or some variation?

Title: Re: filament transformer CT
Post by: sluckey on November 16, 2011, 08:12:44 am

I always use a CT if it is available rather than build an artificial CT. Others prefer the artificial CT. The CT connection (real or artificial) provides a ground reference for the filaments. This ground reference is responsible for reducing filament hum injected into the tubes.

Any and all PTs that supply filament voltage to tubes in the signal path need a CT ground reference. Sometimes the filament CT will be connected to a positive voltage source. In this case, the ground reference is made through the filter caps or cathode cap if connected to the cathode of a self biased tube.

Title: Re: filament transformer CT
Post by: John on November 16, 2011, 08:42:35 am

Sluckey, why do you prefer the CT over the artificial? Simply easier or another reason? I have one of each type amp, so  I'm just curious as always. :smiley:

Title: Re: filament transformer CT
Post by: sluckey on November 16, 2011, 08:51:50 am

It's easier and less components. Both methods work very well. I haven't done any comparisons or scientific studies on this.
 

Title: Re: filament transformer CT
Post by: John on November 16, 2011, 11:19:05 am

I've guessed right again... that's twice now!  :laugh:


Thanks.