UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post

Noopy2014 · 22nd Nov 2018, 4:29 pm

Oh, didn´t realize that the brightness controls are at minimum. That´s strange.

The brightness isn´t controled by the CPU, it goes directly to the tube driver amps.
CRT-Settings are the only things that you can´t control over GPIB.

I think you have more than one problem.
Regarding the brightness there could be a problem in the brightness-control-circuit in the CRT-amp. Unfornunately it´s also possible that there is a failure in the power supply which generates the voltage for the voltage control grid. There is a small transistor taking the control voltage from the tube amp and adjusting the control grid voltage around 100V on the Basic high potential (~3kV).
There is also a protection Diode on the tube base board (D1) which in case of failure could lead to a potential on the brigthness-control-grid so that the reading is very bright.

22nd Nov 2018, 4:29 pm	#9
Noopy2014 Tetrode Join Date: May 2014 Location: Eichstätt, Germany Posts: 88	Re: Gould 407x display help Oh, didn´t realize that the brightness controls are at minimum. That´s strange. The brightness isn´t controled by the CPU, it goes directly to the tube driver amps. CRT-Settings are the only things that you can´t control over GPIB. I think you have more than one problem. Regarding the brightness there could be a problem in the brightness-control-circuit in the CRT-amp. Unfornunately it´s also possible that there is a failure in the power supply which generates the voltage for the voltage control grid. There is a small transistor taking the control voltage from the tube amp and adjusting the control grid voltage around 100V on the Basic high potential (~3kV). There is also a protection Diode on the tube base board (D1) which in case of failure could lead to a potential on the brigthness-control-grid so that the reading is very bright.