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Question about 118b
#10

There is a specific reason for use of the bleeder resistor in the 118. This radio uses a class AB triode output stage, and as such the plate current drawn from the power supply varies greatly with audio output level. Because the field coil of the electrodynamic speaker requires a fairly constant minimum level of current to maintain the magnetic field, the bleeder resistor was added to supply this minimum current through the field coil under all volume level conditions.

All the Philco radios using the triode connected 42 "Super class A" output stage also use this bleeder, 16B, 650 etc. As mentioned previously, there is no simple way to modify the circuit to eliminate the resistor unless you replace the field coil speaker with a PM type.


Messages In This Thread
Question about 118b - by fields 100 - 09-09-2014, 04:14 PM
RE: Question about 118b - by Steve Chambers - 09-09-2014, 06:39 PM
RE: Question about 118b - by SteveJB - 09-09-2014, 07:51 PM
RE: Question about 118b - by Arran - 09-09-2014, 09:25 PM
RE: Question about 118b - by morzh - 09-10-2014, 08:04 AM
RE: Question about 118b - by Ron Ramirez - 09-10-2014, 08:35 AM
RE: Question about 118b - by morzh - 09-10-2014, 02:04 PM
RE: Question about 118b - by fields 100 - 09-10-2014, 02:12 PM
RE: Question about 118b - by morzh - 09-10-2014, 02:21 PM
RE: Question about 118b - by Mondial - 09-10-2014, 07:12 PM
RE: Question about 118b - by Arran - 09-11-2014, 02:54 AM
RE: Question about 118b - by Ron Ramirez - 09-11-2014, 07:08 AM
RE: Question about 118b - by Mondial - 09-11-2014, 08:37 AM



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