Radio Serviceman's Exam.

Radio Record, Volume V, Issue 28, 22 January 1932, Page 23

Radio Serviceman's Exam.

A Moder Power Pack

THIS week we deal with the fourth question on thé paper set in the Radio Servicenjan’s Examination: "Sketch the circuit diagram of the niodern powerpack employing full-wave valve rectification."

TTHERE are literally dozens of modern powerpacks, so the candidate has plenty of choice. The circuit of a modern powerpack-a perfectly straightforward one-is reproduced. Note: the following points which we think the question calls for :- 1. Powerpack complete, with filter devices and voltage divider. 2. Filament windings. 3. "B-’ connected to earth. This is in accordance with the regulations. 4. The yalues of the condensers. It is usual in the filter to have the largest

condenser nearest the voltage divider, where it is refétred to as a reseryoir condenser, althongh sometimes it is placed between both chokes. 5. Note the values of the chokes from 20 to 40 henries. oe 6. Individual tappings by-passed to ad; atid 7. No provision in the powerpack for grid bias. This nowadays is provided by resistances in the grid return of the yalves. The method of obtaining it in directly heated valves is shown inthe diagram: .