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Discussion Starter · #1 ·
Hi all,

I wonder why the GP-5000 is so dim although it is a 9" PJ.

I remember that it is very similar to the 7" GP-3000 and that one has the same lumens rating.

Could it be that the HV supply and other electronics are just the same as in the GP-3000 and so the average beam current and brightness also seems the same?

Wouldn't that mean that the 5000s tubes live much longer as the same beam current fires a much bigger area?

Best Regards

Roland
 

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Discussion Starter · #2 ·
*bump*

No idea???

Roland
 

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Yes, I've found that 9" tubes do last quite a bit longer than the 10K hours that the typical 7 or 8" set is rated for.

As for the lack of brightness of the 5000, I guess it was just the technology at the time.


Not that that really makes sense, since the same vintage BArcos were 1200 lumens, but at a cost of the Sony tubes shorting out all the time.


Curt
 

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Discussion Starter · #5 ·
For my understanding brightness of a PJ depends on the efficiency of the phosphor and the beam current.

The beam current is limited by

1. The cathode emission

2. The HV voltage (limits peak lumens)

3. The ammount of current the HV supply can put out (limits ANSI lumens)

4. The G2-Vltage

5. The G1-Voltage versus the kathode


I am just wondering if a GP-5000 can be boosted in lumens.

If it is the cathode emission one could increase the heating voltage.

G2 can be changed

G1 may also be driven higher

Onnly if it was HV voltage or current it may be more difficult...

Roland
 

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The heater voltage and HV isn't really an issue. It's the cathode drive that's underdriven on these tubes compared to other ones. As for cranking up the cathode voltage, I don't know if the grid could survive very long - maybe, maybe not.
 

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Discussion Starter · #7 ·
Cathode drive?

With HV and heater left away there is only cathode-G1 which is controlled by the contrast setting and cathode-G2 which is controlled by the screen- or G2-pots.

Do you mean that the amplifier on the neckboard is too weak?

Roland
 

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Weak might be a bit extreme - I'd prefer to say deliberately driven to a "conservative" level.... ;)
 

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Discussion Starter · #9 ·
So if one would turn up the brightness and contrast of the PJ and the gain and bias of the tubes then the limitinf factor would be clipping of the amp on the neck board?

Why not increase its supply voltage or mod it in another way?
 

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That would be a real hot-rod job, and could fail in multiple ways. The tube face-heating would not be a problem, with those incredibly huge glycol reservoirs.
 
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