CurtPalme.com Home Theater Forum

[tse]

The Marquee uses a resonant configuration in the output amplifier to lower the power dissipation. There is actually a patent dealing with this. The resonant circuit reduces the voltage needed by the amplifier, when compared to a linear amplifier, for a given amount of output. The amplifier switches capacitors in or out depending on the frequency which means one cap value is used for a range of frequencies. Certainly one specific frequency would have an optimum value of cap. If that value were known it might allow an increase in output current without increasing the power supply voltages used by the output amplifier.

Attached is a schematic showing the difference in output voltage needed by a linear amp compared to the resonant circuit amp. Both output currents are the same.

Scott

[tse]

A range of output voltages with caps from 85 to 100nF with horizontal sweep frequency of 68kHz. The minimum peak voltage looks like 95nF (red trace) is lowest. This would allow a little more gain in the amplifier before clipping happens. Spice is cool. Of course the actual world will be a little different.

Scott

[Nashou66]

I love when you do these little "lessons" as it might relate to conversations in other threads :frankenyoke thread

I forgot if lowering the resistance of the dynamic coil was a benefit or if it was the for the Static coil? I deleted that PM. But IIRC it was for the linear amp section for the static.

From what you told me in helping me figure out my old focus board problem and what the manual says is ,caps are switched in to lower power requirements(voltage) for different frequencies, but current stays the same correct? So by finding the best capacitor where all frequencies benefit for the last one in the marquee would be a good idea or if you knew what frequency you were mostly going to use.

Am i close teacher?

Athanasios

[Nashou66]

One more thing Scott, but when you change the cap for the dynamic wont there be some change to the dynamic and vice a versa? I now there is a compensation component that goes to the static from the dynamic, would this change the static to any degree?

And what if you set the sweep frequency to 72Hz? id like to try that cap value, i think it would still be Cx19 that be changed correct?

Athanasios

[tse]

[tse]

[Nashou66]

Yes I meant the Comp Circuit. So I might actually give this a try with a few different values at Cx19 locations since you said in real world test things do change... Do they make a variable Film cap in that range to find the exact value ? It kinda be like what you did with peaking circuit on the Vim.

PS: I still need to find out why those caps are not switching in on my faulty FCM, The signal to the drivers are fine, but there is where it gets screwy, Would a bad Zener diode near the actual switched in AMp cause a wrong reading also near the driver mosfet for the main mosfet?

Athanasios

[1031]

Scott, thanks for the info.

[mp20748]

I spent some time looking at this last night on the scope(s). So now I'm thinking I'll work at putting a set of Barco 909 focus coils in my Marquee.

And if I'm able to get the 909 coils to work, maybe that would also solve getting the other Barco coils to work on Marquees.

[Nashou66]

Mike are do the 909 coils have the same inductance or close to that of the marquee? if not they will need to be rewound. the 1208/808 coils i have here are not even close, but rewinding them to the same inductance as the marquees allows them to work pretty good if not better than the 1292 coils. The astig windings for all coils are all within close proximity.

Athanasios

[mp20748]

[Nashou66]

Inductance is actually more important, for the static a lower resistance will give you more range, but the inductance is what creates the magnetic field to either add or take away from the physical magnet structure. So if the dead( not connected) magnet of the 909 does not focus the grid well you need a lower resistance wind than a stock marquee but still have the same or close inductance. I have rewound the 1208 coils successfully using 34 gauge wire but I think i can get better results using 30 gauge . this will give less resistance and the same inductance and still have enough room on the bobbin to get the correct wind turns for the needed inductance.

use this excellent wind calculator, you need to put in the bobbin measurements and then the inductance you want.
it will then tell you how many winds you'll need with a given wire size. Very cool program.

http://www.pronine.ca/multind.htm

Athanasios

[mp20748]