14-10-2017, 10:07 PM
Hi.
Some further progress was made today.
Although the HT feed to the line output stage is stabilised it still wasn't that stable on the EHT side. Yesterday the EHT flashed over a couple of time on low brightness so I thought I should come up with a better solution.
I thought about using a series network of Avalanche diodes, after a rummage through the spares box I found a couple of dozen BYV95C Diodes. These are rated at 600v so I thought I'd put 9 in series and see if it would work. I carefully made up a network and insulated it with a few pieces of heat-shrink tubing and connected it to the CRT final anode after the smoothing circuit and feed resistors. I have to say this was a total success with 5500Kv on the anode irrespective of beam current, i did though up the HT to the line stage from 89v to 101v by adding an extra 10v zener to the shunt stabiliser.
I've now also got the G2 volts correct on the CRT. Focus is really good now.
I still need to do something with the frame circuit but I think the output transformer is the problem.
Pictures..... Test card F= 180 lines
..................Test card C is actually 240 lines
Some further progress was made today.
Although the HT feed to the line output stage is stabilised it still wasn't that stable on the EHT side. Yesterday the EHT flashed over a couple of time on low brightness so I thought I should come up with a better solution.
I thought about using a series network of Avalanche diodes, after a rummage through the spares box I found a couple of dozen BYV95C Diodes. These are rated at 600v so I thought I'd put 9 in series and see if it would work. I carefully made up a network and insulated it with a few pieces of heat-shrink tubing and connected it to the CRT final anode after the smoothing circuit and feed resistors. I have to say this was a total success with 5500Kv on the anode irrespective of beam current, i did though up the HT to the line stage from 89v to 101v by adding an extra 10v zener to the shunt stabiliser.
I've now also got the G2 volts correct on the CRT. Focus is really good now.
I still need to do something with the frame circuit but I think the output transformer is the problem.
Pictures..... Test card F= 180 lines
..................Test card C is actually 240 lines
