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1376 HANDBOOK OF PROJECTION FOR
must carry a fairly heavy current — 60 mils. For proper safety allowance they should be capable of carrying 100 mils at least.
It is quite simple to find a substitute for the 48,000 ohm resistance connected between the input transformer and the negative B, which, by the way, is extremely unlikely to develop trouble. It may be replaced by resistance carrying practically no current, and if no such resistance is at hand, in ninety-nine cases out of every hundred it can be shorted out without any great harm resulting.
Should the bias resistance become open circuited it can be replaced by two 10-watt, 110-volt lamps wired in parallel, though this gives just a trifle too much bias. One 25-watt lamp might be used, but this would not be quite as effective, as the resistance would be about 100 ohms too low, which would cause the plate current to be quite heavy.
Either of the chokes can be cut out, one located next the meter being of least importance. They may be replaced, in emergency, by any choke capable of carrying 60 mils and not having too high a D. C. resistance. Of course, however, if the choke has less inductance than the one it replaces it will not be quite so effective. If it should have too much inductance then the D. C. resistance will also be high, which will reduce the voltage at the plates. This will reduce amplification slightly and may cause the amplifier to overload on loud reproduction.
Any of the condensers may be left out, with the exception of the half mike used across the biasing resistance. There is only a low voltage across this condenser and it will probably never give any trouble. If it should, however, it may be temporarily replaced by another which is at least as large.