12-02-2020, 01:04 PM
I've lashed in the darlington voltage dropper for the line output stage. I fitted the TIP121 darlington to the back panel as far as possible from the main regulator transistor to give it the best possible heatsink. Collector to main 27V HT, emitter to LOP HT, base to 470R pot with 330R to 27V and 1K8 to 0V. Gives a sensible range of adjustment.
The back panel now gets quite hot but probably no hotter than it did in the original 625 version.
The lashup could be replaced with a bit of verobaord but it's unlikely to happen on this monitor. Next one perhaps.
The red wire going past in the foreground is part of the temporary CRT heater supply. Next job is to get that back to internal power. I'll float the monitor with an isolating transformer and measure the RMS heater voltage with my Rigol scope. C15 is AOT to give correct voltage.
After that it's time to put the lid on and give it a good long soak test.
The back panel now gets quite hot but probably no hotter than it did in the original 625 version.
The lashup could be replaced with a bit of verobaord but it's unlikely to happen on this monitor. Next one perhaps.
The red wire going past in the foreground is part of the temporary CRT heater supply. Next job is to get that back to internal power. I'll float the monitor with an isolating transformer and measure the RMS heater voltage with my Rigol scope. C15 is AOT to give correct voltage.
After that it's time to put the lid on and give it a good long soak test.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
