Screen to current ratio

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Riffmonster
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Screen to current ratio

Post by Riffmonster »

Hey,

I am currently trying to figure out if an PT that I have left over is fitting a PP 6v6 amp. I am having trouble understanding how much current the amp will draw. With a plate voltage of about 400 V, I figured out that the 6v6 will consume about 60mA. I will throw in probably two 12ax7, that makes up 4mA, so in total 64mA. Concerning the valve wizard I still need to calculate the screen current, which I can calculate from the screen to anode current ratio. Where in the tube data sheet can I see that ratio? Here it just says: "the data sheet suggests a screen to anode ratio"... : http://www.valvewizard.co.uk/smoothing.html

Thanks!
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JMPGuitars
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Re: Screen to current ratio

Post by JMPGuitars »

You also need to consider the heater current for every tube. Do you know the brand/model of the PT?
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Riffmonster
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Re: Screen to current ratio

Post by Riffmonster »

Hey,
Yeah I forgot to mention I already checked the heater current. I have 4,5 A available on the PT which is more than enough!
For the HT it’s 150 mA, which is probably more than enough too but I want to understand the process.
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colossal
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Re: Screen to current ratio

Post by colossal »

Riffmonster wrote:
Thu 07/04/19 2:09 pm
Hey,

I am currently trying to figure out if an PT that I have left over is fitting a PP 6v6 amp. I am having trouble understanding how much current the amp will draw. With a plate voltage of about 400 V, I figured out that the 6v6 will consume about 60mA. I will throw in probably two 12ax7, that makes up 4mA, so in total 64mA. Concerning the valve wizard I still need to calculate the screen current, which I can calculate from the screen to anode current ratio. Where in the tube data sheet can I see that ratio? Here it just says: "the data sheet suggests a screen to anode ratio"... : http://www.valvewizard.co.uk/smoothing.html

Thanks!
Your "application" of course is not listed on the typical datasheet. But if look at example applications for a pair of 6V6GTs in Class AB1 push pull (315V plate, 285V screen is closest), you take the max signal current for plate and divide by max signal current for screen, you'll see that ratio is about 6.8:1 plate-to-screen current. EL84s are about 8.8:1, by comparison.
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Riffmonster
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Re: Screen to current ratio

Post by Riffmonster »

Thanks man, that helped a lot!
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