UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - HP 175A Oscilloscope

Radio Wrangler · 11th Jun 2018, 5:18 am

HV probe definitely!

The 2.5kv range on the AVO takes too much current and loads down scope HT circuitry.

There are some very high impedances in the CRT bias networks. All the 175s had been replaced by 180s before my time at HP, but if they follow the usual practice, there may be dual2.7kv supplies, one for grid one for cathode so that a lower voltage amplifier can blank the trace when the timebase is not triggered.

David

11th Jun 2018, 5:18 am	#4
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,902	Re: HP 175A Oscilloscope - Vanishing Trace HV probe definitely! The 2.5kv range on the AVO takes too much current and loads down scope HT circuitry. There are some very high impedances in the CRT bias networks. All the 175s had been replaced by 180s before my time at HP, but if they follow the usual practice, there may be dual2.7kv supplies, one for grid one for cathode so that a lower voltage amplifier can blank the trace when the timebase is not triggered. David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done