08-10-2021, 06:22 AM
Although the details are more complex, the LOPT is there to match the output of the valve to the scan coils. Just like any transformer (where the core is not saturated) its own inductance is of relatively minor importance.
This sort of line output stage will only work over a fairly narrow range of frequencies. If designed for 405 or 625 it will not work at all at slow scan frequencies.
I have attached a good article on line timebases that use energy recovery. This is relevant to fast scan TV but barely at all to slow scan.
To give some idea of why energy recovery is essential for fast scan TV, on each stroke a certain amount of energy is stored in the scan coils. If this is not recovered the line timebase for a wide angle CRT would consume many 100s of watts which would have to be disspated somewhere in the set. I once calculated that a first generation colour TV has over 2kW of power circulating in the line timebase. But energy is recovered so efficiently that the line timebase consumes only 10s of watts from the mains.
For slow scan, there are far fewer strokes per second so much less power is needed. For a fairly narrow angle CRT like the 5FP7 the scan power is fairly low anyway. So the timebases are best treated more like audio amplifiers.
This sort of line output stage will only work over a fairly narrow range of frequencies. If designed for 405 or 625 it will not work at all at slow scan frequencies.
I have attached a good article on line timebases that use energy recovery. This is relevant to fast scan TV but barely at all to slow scan.
To give some idea of why energy recovery is essential for fast scan TV, on each stroke a certain amount of energy is stored in the scan coils. If this is not recovered the line timebase for a wide angle CRT would consume many 100s of watts which would have to be disspated somewhere in the set. I once calculated that a first generation colour TV has over 2kW of power circulating in the line timebase. But energy is recovered so efficiently that the line timebase consumes only 10s of watts from the mains.
For slow scan, there are far fewer strokes per second so much less power is needed. For a fairly narrow angle CRT like the 5FP7 the scan power is fairly low anyway. So the timebases are best treated more like audio amplifiers.
www.borinsky.co.uk Jeffrey Borinsky www.becg.tv
