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Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Ash Small wrote ...
Proud Mary wrote ...
Those LOPTs were designed to operate with external doublers/triplers.
Thanks, that's what I thought. Any idea what the purpose of the HV capacitor is in the second photo in the OP?
I'm pretty certain that this is yer actual boost capacitor which charges up and raises the cathode voltage of the booster diode. This means that the anode voltage has to rise to a higher value for conduction to start. This ensures that the booster diode does not conduct until the start of active scan time, so there is little damping during the fly back period.
During this valve/semiconductor hybrid period of the 1970s, the doublers and triplers were solid state, while the booster diode was still a thermionic device, such as PY80 or PY83.
Registered Member #977
Joined: Thu Aug 30 2007, 06:57PM
Location: England
Posts: 74
Ash Small wrote ...
Do you mean the one in the middle, HDF? Where you can clearly see the HV capacitor, or are you saying the bottom one also has a capacitor and is rectified?
The bottom one, the bobbin on the left leg with all the pins coming out of it is a high voltage capacitor. Twirlywhirly555 described it as a winding with foil and plastic, they are the capacitor's plates and dielectrics.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Thanks, PM.
I found this quote: "The damper diode recovers the energy stored in the horizontal deflection coils during flyback. This boosts the supply voltage to the output stage, hence it is also called the booster diode." here:
Presumably, in order to operate the flyback as an AC flyback I need to remove the capacitor, otherwise it is likely to cause all sorts of problems with resonance, etc?
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Ash Small wrote ...
Presumably, in order to operate the flyback as an AC flyback I need to remove the capacitor, otherwise it is likely to cause all sorts of problems with resonance, etc?
Ditch the capacitor, and remove the primary bobbin with its different windings, as these are unlikely to be useful for anything other than TV service.
It is quite possible that some of the pins on the secondaries are N/C not connected, and may have been intended to provide mechanical stability (soldered to something rigid) and/or to act as tag strips for mounting components.
Once having clipped the secondaries free of all encumbrances, you should measure the ohmic resistance between whatever pins you have and eachother, and also between these and the EHT output socket, and then try to draw a diagram that makes sense out of your readings.
I expect you will find the secondaries have three terminals i.e. EHT+, focus, and the cold end, EHT-, but don't be surprised if you find something a bit more complex than this. We can sort it out.
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
Depending upon the era, flybacks were designed to provide EHT at frequencies which were harmonics of the scan frequency.
In the 70's segmented windings were used in which the leakage inductances were tuned by the distributed capacity up to the 9th harmonic. (146 kHz for the NTSC system
This produced marvelous AM radio disturbance.
The efficiency, in general, over the decades followed the deflection angle of the CRT. The first sets had very long tubes, and often there was a extension cup on the back where the connection end was located.
You can sniff out M.Buechel IEEE VOL.BTR16, No 1, P23 1970.
One never knows when long dead TV technology will be of use.
I remember distinctly having to explain how the damper recovered energy in the shops practical part of the examination for a TV technician license.
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LOPT/Flyback questions.
