[AMRadio] Smoothing Choke

Larry Taft ltaft at charter.net
Thu May 4 12:40:14 EDT 2006

Typical values for a Gates BC-1G 1 KW broadcast transmitter 2500 VDC 
supply are 5-15 hy at 1 amp swinging choke with 8 uf filter cap.  The 
load is 500 ma continuous for the class C final ( 2 833s in parallel) 
plus another 500 ma variable for the class B modulator ( 2 833s in 
push-pull).   The audio frequency response  is speced at 30 to 12,000 
cycles per second.  The broadcast people used a single supply with the 
final acting as a fixed minimum load to get around the filter resonance 
problem at low frequencies.

Collins also used a cap across a choke for parallel resonance.  For the 
20V3 there is a 10 hy choke with a 0.08 uf cap across it in parallel to 
a second 10 hy choke (no cap) to an 8 uf cap to ground.  Again, the 
final is a fixed load for the single supply.  Tubes are 4-400s. 
Audio speced at 50 to 10,000 cycles per second.

Old technology.  Still good as long as the limits are understood.

Larry  K2LT

Jim candela wrote:
> Rick,
>    I understand your feel for the nostalgia, and passion for pursuing it.
> All of us more or less on this group have some common ground here.

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