Re: Significantly drop G2/brightness (4600 raster hack)?

From: Rodger Boots <rlboots_at_cedar-rapids.net>
Date: Mon Dec 23 2002 - 13:29:58 EST

John Robertson wrote:

> Any risk of excess cathode current flow if the grid is shorted to
> ground? I'm thinking that this might stress the picture tube too much.
> BUT I am definitely not a picture tube expert.
>
> John :-#)#

No, cathode current goes down. Basically cathode current = brightness,
so less bright is less current.

As for current in the grid itself, it's not significant.

>
> At 12:38 AM 23/12/2002 -0600, Rodger Boots wrote:
>
>> Gregg Woodcock wrote:
>>
>>> OK, here is a very interesting udpate.
>>> By putting increased resistance, I was able to drop the previously
>>> lowest
>>> (stock/non-modified) G2 of 375V to about 200V with not a bit of
>>> difference
>>> in brightness. Well I figured I'd show the macine who was boss so I
>>> shorted
>>> the G2 pin to ground (0V). I got a picture that was about half as
>>> bright as
>>> it should have been to be perfect. What is up with THAT? I got
>>> roughly the
>>> same brightness with it ungrounded. I am going to use the
>>> rejuvenator to
>>> check for G2 short in the tube but as I recall, I backed this one up to
>>> another machine that was working fine and it proved without a doubt
>>> that the
>>> tube was fine (95% sure about that). I must have some kind of a ground
>>> problem but I just don't see how/where...
>>>
>>
>>
>> If running G2 grounded still gives a fairly bright picture you have
>> either too high high voltage or not enough cathode to grid 1 bias.
>>
>> Since dropping G2 to ground DOES get the brightness low enough you
>> might just add a second resistor from G2 to ground to whatever
>> resistance you already have from G2 to the screen pot so the
>> effective voltage range of the pot is where the CRT needs it. It's
>> not going to hurt anything to run G2 near ground, but make sure the
>> high voltage isn't excessive.
>>
>>
>>
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Received on Mon Dec 23 10:31:22 2002

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