09-11-2015, 11:20 AM
Don't know how I failed to spot this thread but many years ago, about 12 probably, I restored a Mk1 and a Mk2 and wrote how to fix them articles. A web search on AVO Valve Testers should have found me as they went literally all over the world. Maybe some help in understanding and other faults. If you want the articles I can e-mail them to you. Others in Radio Bygones, years later did restorations and drew a more complete circuit diagram if you can get hold of it.
Set Zero pot
"This pot is tricky because of the two controls in tandem. I plotted the characteristics and the front voltage setting control is linear whereas the rear has the characteristic logarithmic long tail. It is this long tail that gives the fine control to easily set zero. I looked at two ways of replacing this."
I wrote up two ideas about getting around this pot being faulty and tried the second one which worked fine but is a little difficult to implement (the first didn't need trying as it was the 10 turn pot idea).
Gary
Set Zero pot
"This pot is tricky because of the two controls in tandem. I plotted the characteristics and the front voltage setting control is linear whereas the rear has the characteristic logarithmic long tail. It is this long tail that gives the fine control to easily set zero. I looked at two ways of replacing this."
I wrote up two ideas about getting around this pot being faulty and tried the second one which worked fine but is a little difficult to implement (the first didn't need trying as it was the 10 turn pot idea).
Gary
