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RADIO AGE for February, 1927
The Magazine of the Hour
15
Power Six Is Elaboration of the Counterphase Six
Popular Circuit Changed to Include New Heavy Duty Tubes
SO THOROUGHLY has the radio public been sold on the question of power amplification through the use of the 112, 171 and 210 types of power tubes that manufacturers today are all including arrangements for operation of a power tube in the last stage.
Bremer-Tully's popular circuit known as the Counterphase Six (described by Ray G. Piety on page 23 of the May, 1926, issue of Radio Age) has been altered in a few circuit respects and provision made for the use of a UX112 or UX171 in the last stage. (For the UX210 the filament supply would be AC and furnished by a step-down transformer.)
Pictorially and diagrammatically we are showing in this article the "Power Six" which consists of three stages of tuned radio frequency amplification, non-regenerative detector, and two stages of audio amplification.
Filament control is by a master rheostat.
Experimenters will note, on close inspection of the circuit diagram on page 16, one departure from the Counterphase Six in the addition of three 1500 ohm fixed resistances, one placed in each of the three radio frequency grids to allow the sensitivity of the tuning to be maintained at an equal value over the entire broadcast band. Another point of difference is the use of a single unit 500,000 ohm variable resistance instead of the dual type used previously. Antenna coupling has been changed from the tapped coil in the previous design to the inductive form in the present receiver with a switch permitting change from short to long antenna. Jacks have been inserted in the first and second stages of audio to allow the listener to cut the volume at will. Neutralizing condenser design has been changed to a simpler and better
form. Individual radio frequency chokes are placed in each of the three RF plate leads. It is not recommended that this set be shielded since that job alone is an exceedingly tough proposition unless the reader has had considerable experience. In the new coils some of the connections have been made inside the forms whereas in the older type these connections were made by the builder himself. The 1500 ohm fixed grid resistances together with the 500,000 ohm variable resistor in the 90 volt lead of the set serve to maintain the amplification of the receiver practically constant over its range. The variable resistor is simply a volume control. Grid biasing is used on both the radio frequency and audio grids. This sums up the alterations made in the later model, changes being made to bring the set to its highest efficiency.
On page 15 is shown a rear
Rear view of the completed receiver. Either binding
or a plug connection may be used by the constructor