BUSH AND LANE PIANO CO.

MODEL 10

BUSH & LANE PIANO COMPANY

MODEL 10
Voltage and Service Notes

NEUTRALIZING and RESONANCE TESTS

Neutralizing the Bush & Lane Chassis No. 10 De Luxe is an extremely simple and rapid operation. A near-by powerful station may be used for this purpose, but a much more desirable and accurate means is by use of a modulated oscillator, that is, a vacuum tube oscillator generating an audible note. Buzzer modulated, or other types of oscillators, are entirely satisfactory. The circuit of a very simple oscillator is given in Fig. 5, which is of the grid leak and condenser modulated type. It will be apparent, to a person unfamiliar with such apparatus, that is is nothing more than a regenerative detector circuit. For neutralizing purposes the switch across the grid leak and condenser is left open, and no deflection will be had on the 0-2 milliampere DC meter.
Tune receiver to approximately 1200 kilocycles, and the oscillator to the receiver, which should result in a strong audible signal in the speaker. If the receiver was previously oscillating at 1200 kilo cycles, first neutralize at a lower frequency, about 800 or 900 kilocycles, and repeat at 1200 kilocycles.
Replace the third R.F. tube (third from rear) with a " dead " tube, whose filament has been opened by drilling into the tube base near a filament prong and breaking that filament wire. Adjust neutralizer NC3 (third from rear) until a minimum of the oscillator signal is heard. If oscillator signal is weak, move oscillator closer to antenna, or even connect one of the resonance testing clips onto antenna. When minimum point is found, replace the good tube and allow it to heat to normal operating condition.
Next replace the second R.F. tube with the " dead " or neutralizing tube, and adjust NC2 (second neutralizer from rear) for a minimum of signal. Re place good tube, allowing it to heat. Finally, replace the first R.F. tube with the " dead " tube and adjust NC1, (neutralizer nearest rear) for a minimum of signal. Replace good tube and allow to heat to normal operating temperature,
It is advisable to place shield over " dead " tube, each time, while neutralizing.
After neutralizing, the receiver should be stable over the entire frequency range, and if not, the trouble is due to tubes, ungrounded shielding of four

Gang condenser, coil shields, tube shields, or altered wiring under the base.
Accurate resonance tests may be made with an oscillator indicating resonance by the " dip " of a meter in either the plate or the grid circuit of the oscillator tube. The simple oscillator shown in Fig. 5 may be used for this purpose by closing the switch across the grid leak and condenser, shorting them, when a deflection of the 0-2 milliampere meter will be noted, showing the circuit to be oscillating. One wire from the 8 - turn pickup coil is connected directly to the " ground " or chassis. The other wire from this coil terminates at two.00025 Mfd. grid condensers in series which in turn are attached to a clip. These condensers must be as near the clip as possible. A single.0001 Mfd. condenser is sufficient.
Attaching the clip and condensers to the stator of the first condenser (this may be done below the base, at grid terminal of first coil) rotate dial of oscillator tuning condenser until a " dip " or " wiggle " of the milliammeter is found, indicating that the oscillator is in resonance with the circuit under test. Note oscillator dial reading. It should be repeated when moving clip and fixed condengers to each of the other coils, with receiver tuning condenser left in the same position.
A check for resonance with receiver tuning con denser plates nearly full " in " and nearly full " out " is sufficient,
If the oscillator dial is calibrated from 0 to 100, a difference in reading of one degree on the dial is considered fairly good resonance, though limits are held much more closely at the factory. Unless compensated for, while making resonance tests, the oscillator will usually show a variation in detector coil and antenna coil from the second and third coils. This is caused by the antenna coupling and detector coupling systems, and need not be considered alarming.
Service laboratories desiring any further testing information than given in this instruction manual may obtain same by writing the factory testing department.

BUSH & LANE PIANO COMPANY

MODEL 10 Chassis