murphyv310 wrote:Hi Harry.
Many thanks for your nice words.
No problems as Steve mentioned its a great display thanks for posting here or i would of missed it ,i am a member of the forum you posted to but i forgot about it i mainly hang around here
it has spurred me on to do some more last night and today.
Thats good keep on going its a beautiful display ,i hope mine can get to that stage ,i am using an old magnetic small CRT have no information to so all trial and error ,i will b e right if i can get the horizontal sweep a touch better .
Most of the parts for all the modifications have come from the "junk box" but there were a few things I needed that I don't have.
That's even better using junked parts spare parts handy to fix it ,don't really have tv's that size laying around that i have even see here our displays started large from the start so ,if you collect tv's here you better have room their all around the same size big !
One of the things I have been short of was a suitable capacitor for EHT smoothing.
This was a problem i thought i had when making the SSTV i wasn't saw till testing but the little HV module from china worked fine see construction diary it sure saved room as well using that .
viewforum.php?f=19I did fit a 0.1uF rated at 6Kv, the value was OTT and 6Kv didn't really have enough headroom so I have ordered some 1nF at 10kV from RS.
Yes HV caps are hard to find only ones i have are from scrapping tv's never good to use a low lower voltage one they all die quick .
These will be ideal. The other thing that the modification needs is some form of line stage regulation. Adjusting the line frequency between standards and setting brightness and contrast changes width and EHT voltage, the reason for this is the use of a large value resistor to get the timebase running at a low voltage. The line scan transformer is intended for a 19 or 23 inch CRT with 110 degree deflection with 16 to 18Kv. I only need 6-7Kv and a scan deflection of 57 degrees.
Thats the problem using the line frequency to get the EHT i never do this i just make its own circuit to make the EHT if you noticed my Youtube video no change to raster size 32 to 1000 lines apart from lines matching up closer as they should ...if you don't mind changing the circuit and just make an oscillator and used a valve as you are now to drive the eht transformer it would fix you problem out right .
You could have more than 2 standards as i do .
I have found between 95 to 100 volts, the timebase runs beautifully. So today I added a very basic shunt regulator using a BU2508 line output transistor as a regulator, a zener diode and one additional resistor. The feed to the line output stage is now a solid 98 volts irrespective of brightness or line frequency. The transistor is bolted to the chassis and is running cold.
I still need to sort out a little amount of striations on the left hand of the picture and frame linearity, once the new caps arrive I'll work on the EHT side.
It sounds like you don't mind changing the circuits to make them work ,these things are all trial and error again on the EHT side just make is own circuit so its not effected but frequency change so EHT voltage change ...any case you must be close picture looks great .