Hello from Tasmania, Australia. I have a problem with my Tektronix 7603 CRO which I hope someone might be able to help me with. I have lost the EHT. A little while back the CRO lost power which turned out to be a faulty bridge CR811 in the power supply. I replaced the bridge and recapped the power supply. I now have all the voltages, as specified in the service manual, except the EHT. The High Voltage Oscillator appears to be functioning correctly because it oscillates at 47v pp, measured at the collectors of both Q1216 and Q1218 at 42kHz, with the x4 multiplier and high voltage diode CR1232 disconnected. The diode tests okay out of circuit on a high voltage supply. The tube was replaced in 1987 and has worked perfectly before the power supply problem. My thoughts are the x4 multiplier is shot but I would be more than happy to hear anyone else’s opinion on this matter.
Hello Eric. I stumbled upon this article from 2010 that may help you (unless of course you by now already have your 7603 working). Here’s the link: https://rfscientific.eu/sites/default/files/articleextra/tektronix_7603_repair.pdf
@peteb2 Many thanks for the article. Unfortunately my 7603 is still not working. All the LV voltages are fine, just the EHT output to the CRT anode that has failed.