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gjaky
Joined: 05 Jun 2010
Posts: 2802
Location: Budapest, Hungary
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| Posted: Thu Feb 18, 2016 11:14 am Post subject: |
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| redfox001 wrote: | | gjaky wrote: |
I just got an idea for the 909. the method used in the PG xtra could be used there too. With not tying the hybrids emitter peaking network to ground instead to a high freq PNP transistor etc. and after buffering connect it to G1.
This of course would increase the actual gain of the amplifier, therefore you could lower contrast, getting to a better bandwidth.
For starting there is a -40V line in the PS unit, that is an opportunity to save almost 40V on the cathode drive voltage... |
Barclay once said after trying lug tubes on marquee that possible with lug you need to drive cathode only. Because there is an extra grid somewhere on lug? He said lug bloomed very early with g1 and cathode drive. |
G90 also have LUG tubes with push-pull drive, and there is no know focus problem with them, neither with contrast.
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projectors in the past : NEC 6-9PG xtra, Electrohome Marquee 6-7500, NEC XG 1351 LC ( with super modified Electrohome VNB neckboard !!!)
current: VDC Marquee 9500LC
The MOD: VNB-DB, VIM-DB
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redfox001
Joined: 16 Mar 2009
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Location: The Netherlands
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| Posted: Thu Feb 18, 2016 12:52 pm Post subject: |
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Ok it is just those thomson yokes on the marquee. Barco never had problems with early blooming anyway.
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redfox001
Joined: 16 Mar 2009
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Location: The Netherlands
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| Posted: Thu Feb 18, 2016 6:09 pm Post subject: |
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| the dude wrote: | | Im meant the emitter peaking network on the neckboard. But this is some kind of magic... |
Looked up something on emitter peaking is it not simple trying other cap vallues? Could this peaking filter be moddelled in spice using a simple transistor emitter folower?
 image by Radio Head, on Flickr
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Last edited by redfox001 on Thu Feb 18, 2016 6:15 pm; edited 1 time in total
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gjaky
Joined: 05 Jun 2010
Posts: 2802
Location: Budapest, Hungary
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| Posted: Thu Feb 18, 2016 6:14 pm Post subject: |
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| redfox001 wrote: | | the dude wrote: | | Im meant the emitter peaking network on the neckboard. But this is some kind of magic... |
Looked up something on emitter peaking is it not simple trying other cap vallues? Could this filter be moddelled in spice using a simple transistor?
image by Radio Head, on Flickr |
In theory yes, and in fact in the XG it was used this way. On my actual XG this caused the color bleeding effect, the transistors had some leakage... So in the end I removed all of them, and indeed you really don't need nowadays switchable peaking network, you just have to figure out what suits best, and leave at that
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projectors in the past : NEC 6-9PG xtra, Electrohome Marquee 6-7500, NEC XG 1351 LC ( with super modified Electrohome VNB neckboard !!!)
current: VDC Marquee 9500LC
The MOD: VNB-DB, VIM-DB
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redfox001
Joined: 16 Mar 2009
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Location: The Netherlands
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| Posted: Thu Feb 18, 2016 7:04 pm Post subject: |
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Another option would be to lower the gain on the output amp and replace the ad835 with a better multiplier and set some higher gain there?
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redfox001
Joined: 16 Mar 2009
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Location: The Netherlands
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| Posted: Fri Feb 19, 2016 2:10 pm Post subject: |
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You guys all have these?
It shows something on the internal of the hybrids. I think the vpa18 is the one used? It says 180MHz.
External peaking on two places.
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gjaky
Joined: 05 Jun 2010
Posts: 2802
Location: Budapest, Hungary
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| Posted: Fri Feb 19, 2016 8:47 pm Post subject: |
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This is more interesting 
I really tried but I think it is impossible to look inside the shielding box of the hybrid without damaging it...
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projectors in the past : NEC 6-9PG xtra, Electrohome Marquee 6-7500, NEC XG 1351 LC ( with super modified Electrohome VNB neckboard !!!)
current: VDC Marquee 9500LC
The MOD: VNB-DB, VIM-DB
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redfox001
Joined: 16 Mar 2009
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Location: The Netherlands
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| Posted: Fri Feb 19, 2016 8:54 pm Post subject: |
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He that bfq166 is only 1 GHz! Replace it 
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gjaky
Joined: 05 Jun 2010
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Location: Budapest, Hungary
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| Posted: Fri Feb 19, 2016 8:56 pm Post subject: |
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| redfox001 wrote: | | He that bfq166 is only 1 GHz! Replace it |
First I though this too, but if you scroll further in the datasheet it becomes apparent that it is a 2,5GHz transistor, 1GHz is the absolute minimum which is guaranteed at 300mA. the peak current in the videopack is about 100mA, since the output voltage is 100V and the load resistor is 1k ohm, at 100mA it has more than 2,5GHz ft.
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projectors in the past : NEC 6-9PG xtra, Electrohome Marquee 6-7500, NEC XG 1351 LC ( with super modified Electrohome VNB neckboard !!!)
current: VDC Marquee 9500LC
The MOD: VNB-DB, VIM-DB
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the dude
Joined: 11 Sep 2013
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gjaky
Joined: 05 Jun 2010
Posts: 2802
Location: Budapest, Hungary
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| Posted: Sat Feb 20, 2016 11:12 am Post subject: |
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 Yesterday I was about to post the same IC, but I've changed my mind
To me the barco hybrid looks like made by Philips.
BTW you will hardly find any better video transistor other than what was used in the Marquee: MRF548/549 (MRF544/545). Philips also had one simlar transistor pair though: BFQ232/252 but I hardly think these were used in the Barco hybrid as they are only 100V transistors.
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projectors in the past : NEC 6-9PG xtra, Electrohome Marquee 6-7500, NEC XG 1351 LC ( with super modified Electrohome VNB neckboard !!!)
current: VDC Marquee 9500LC
The MOD: VNB-DB, VIM-DB
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redfox001
Joined: 16 Mar 2009
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| Posted: Sat Feb 20, 2016 11:20 am Post subject: |
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The videopack dock also speaks from hybrid chips with fbet/lsbt chips. What does that mean fbet/lsbt
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gjaky
Joined: 05 Jun 2010
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| Posted: Sat Feb 20, 2016 11:25 am Post subject: |
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They were technology names that was invented/used by Sanyo. Obviously other manufacturers had similar technology steps, but were less marketed by the name...
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projectors in the past : NEC 6-9PG xtra, Electrohome Marquee 6-7500, NEC XG 1351 LC ( with super modified Electrohome VNB neckboard !!!)
current: VDC Marquee 9500LC
The MOD: VNB-DB, VIM-DB
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redfox001
Joined: 16 Mar 2009
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Location: The Netherlands
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| Posted: Sat Feb 20, 2016 11:33 am Post subject: |
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Ok so they reduced paracitic capacitance.
I was playing with the peaking on the driver and in the end put it all back because I could not improve upon it. The strange thing is that the low frequency peaking now works less while I changed nothing there. Anyway I do not thing the peaking on the rtb driver is a way to go. By the way I cleaned with alcohol I am starting to think I do not understand what is going on there.
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the dude
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redfox001
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| Posted: Sat Feb 20, 2016 12:02 pm Post subject: |
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If you want the motorola better buy some marquee neckboards at 25 euro.
About the peaking on the driver I calculated. It seems emitter peaking.
The lowest peaking has C=12p L=3u3 that give resonant fres=25.3 MHz
The middle has C=8p2 L=1u5 that gives fres=45.4 MHz
The high has C=2p2 L=0u47 that gives fres=157 MHz
In the owners manual they say.
The following frequency areas are available:
Low Frequency Peaking 15-45 Hz
Mid Frequency Peaking 45-85 Hz
High Frequency Peaking 85-110 Hz
Assumimg they mean MHz.
Emitter peaking with lc should give a bumb I guess because a cap gives a slope.
Perhaps there is an error in the schematics and that they use other vallues on the boards. I check that.
I used http://www.daycounter.com/Calculators/LC-Resonance-Calculator.phtml to calculate.
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redfox001
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| Posted: Sat Feb 20, 2016 12:17 pm Post subject: |
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Ah I get it. In the calculation I have to model the complete emiter peaking network and there is a common cap too. I guess the owners manual is accurate and nothing to improve there.
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gjaky
Joined: 05 Jun 2010
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| Posted: Sat Feb 20, 2016 12:39 pm Post subject: |
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One thing has to kept in mind always, these projectors were multi thousand dollar items, designed by experienced and well paid engineers. So what are in those circuits are not because they did not know what they do. I'm sure Barco engineers also spent a lot of time with optimizing the signal path already, but there has to be make sacrifices always, and there are goals.
The signal path of the latest CRT projectors all built on earlier designs, which are originated from '92-'95. The signal bandwidth of the CRT projectors were sufficient enough for their time, when these projectors were coming out there were barely any signal source that could fully take advantage even of a 100MHz analog bandwidth path.
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projectors in the past : NEC 6-9PG xtra, Electrohome Marquee 6-7500, NEC XG 1351 LC ( with super modified Electrohome VNB neckboard !!!)
current: VDC Marquee 9500LC
The MOD: VNB-DB, VIM-DB
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redfox001
Joined: 16 Mar 2009
Posts: 2257
Location: The Netherlands
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| Posted: Sat Feb 20, 2016 1:30 pm Post subject: |
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Ok I got the best results setting 3.2pF on the high frequency peaking cap. Officialy there is a 2.2pF but I measured those to be 3.2 also on one driver and my peakatlas cap meter allways was pretty accurate with caps. But making the cap bigger makes it worse peaking the mid frequencies. Making it smaller makes it worse too using 1080p@60.
Measured on m204 neckboard with groundwire direct on tip.
high freq peaking on
 Untitled by Radio Head, on Flickr
peaking off
 Untitled by Radio Head, on Flickr
Hmmm a little bit
 Untitled by Radio Head, on Flickr
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Last edited by redfox001 on Sat Feb 20, 2016 1:46 pm; edited 2 times in total
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redfox001
Joined: 16 Mar 2009
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| Posted: Sat Feb 20, 2016 1:37 pm Post subject: |
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| gjaky wrote: | One thing has to kept in mind always, these projectors were multi thousand dollar items, designed by experienced and well paid engineers. So what are in those circuits are not because they did not know what they do. I'm sure Barco engineers also spent a lot of time with optimizing the signal path already, but there has to be make sacrifices always, and there are goals.
The signal path of the latest CRT projectors all built on earlier designs, which are originated from '92-'95. The signal bandwidth of the CRT projectors were sufficient enough for their time, when these projectors were coming out there were barely any signal source that could fully take advantage even of a 100MHz analog bandwidth path. |
Yes you are right. Not much we can improve on the work of the Barco engineers. It takes some redesign I am afraid. Peaking on the emitter of the hybrid will probable not give much but I am trying to model it in spice anyway just to be sure
In fact they use the bfq166 with emitter peaking to compensate.
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