|
|
|
|
|
|
|
|
|
|
|
This is a Norton Chimes unit currently under restoration. The machine is composed of a turntable, mixer/preamp/driver, power amplifier, and power supply. The system is mounted in a 6FT BUD rack. This is what a 150-200 watt tube-type audio amplifier looked like in the 1940's.
The turntable visible in the top section is a Garrard RC60. A collector friend has already spoken for it. While it might be amusing to play a side of Frank Zappa's "Freak Out" album or "Switched On Bach" over the air, it's prohibited by law to use an amateur station for that purpose.
The next lower section is the control section. It contains a mixer and a small push-pull 6B4G amplifier of about 10 watts. A switch selects whether the 10 watt amplifier drives the church PA system or drives the large power amplifier for the church bells (Chimes is the industry standard term).
The next section is a 150-200 watt power amplifier using four 845's in push-pull parallel. The chassis contains from right to left, the output transformer (500 ohms), driver transformer, and filament transformer. Each 845 required 10 Volts at 3.25 Amperes for the directly heated cathode (what we called a "filament" in the olden days). The chassis also contains two regulator tubes for the grid bias circuit. The 845 needs 150-200 Volts negative bias and operates class AB1. More detail will be given on this section later.
The lower section is the power supply. The high voltage for the 845 stage is rectified by a pair of 866 mercury vapor rectifiers and the low voltage for the mixer/driver is provided by a 5U4. The circular device next to the 866's is a timer. The mercury rectifier requires a warmup time of 30 seconds minimum in order to vaporize the mercury before high voltage is applied. More detail will be given on this section later.
Its ultimate destination will be as a high fidelity driver for the modulator of the Tucker transmitter. The transmitter does not "require" anywhere near 150-200 watts to drive the grids of the 3-500Z modulators, but the specifications call for 25 watts and it is well known by those competent in the art that a driver for a class B stage should have "several" times the required capacity in order to provide good regulation of the drive voltage under varying load conditions found in a class AB2 or class B amplifier's grid circuit.
