Re: Type CA module in a 545


Morris Odell
 

You should check the voltage divider from pin 15 of the plugin connector. That pin needs to sink 150 mA at 75 volts in all plugins. The 75 volts is derived from the +100 in the mainframe dropped through a couple of 12.6 volt tube heaters. In many plugins including the CA it is connected to a combination of tube heaters and divider resistors with taps to provide bias for various parts of the circuit. In the CA there are also interconnection networks with the +100 and +225 pins. One of those voltages from the divider network is +37.5 that supplies the suppressors of the output amplifier tubes. If that voltage is not right it could affect the gain of those stages. There are also +69 and +12.5 volt taps that are used for DC balance adjustment and to set operating conditions for other parts of the circuit.

Let us know what you find.

Cheers,

Morris

Join TekScopes@groups.io to automatically receive all group messages.