130 Ohm 3w ceramic explanation

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JMPGuitars
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Re: 130 Ohm 3w ceramic explanation

Post by JMPGuitars »

5W or 10W doesn't matter.

The only thing that matters is that you bias correctly. You can use this calculator to determine that: https://robrobinette.com/Tube_Bias_Calculator.htm

You want to bias the tubes between 75 to 85%. Assuming a typical transformer, you probably need 180 ohms, but you can measure and determine that later.
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Re: 130 Ohm 3w ceramic explanation

Post by davemojo »

JMPGuitars wrote:
Sat 03/20/21 7:30 am
5W or 10W doesn't matter.

The only thing that matters is that you bias correctly. You can use this calculator to determine that: https://robrobinette.com/Tube_Bias_Calculator.htm

You want to bias the tubes between 75 to 85%. Assuming a typical transformer, you probably need 180 ohms, but you can measure and determine that later.
Thanks Josh, I will check on that too.

So I bet that if the Stewmac build (Let's leave aside if is a crap building option :lol: ) but I would assume that if they made that build with in mind the consideration of correct Bias so it would mean that 130 Ohms 3W suggestion should be the correct Bias based on that build?
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Re: 130 Ohm 3w ceramic explanation

Post by JMPGuitars »

davemojo wrote:
Sat 03/20/21 7:54 am
Thanks Josh, I will check on that too.

So I bet that if the Stewmac build (Let's leave aside if is a crap building option :lol: ) but I would assume that if they made that build with in mind the consideration of correct Bias so it would mean that 130 Ohms 3W suggestion should be the correct Bias based on that build?
Nope. For one thing, most of the kits around are based on dated variables. For example, source AC was lower 40 years ago, but they still just copy the same components and values. Higher source AC = higher voltages in your circuit.

Don't trust the kit, trust the math. Do the math and adjust the kit.
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Re: 130 Ohm 3w ceramic explanation

Post by zaphod_phil »

JMPGuitars wrote:
Sat 03/20/21 8:32 am
For one thing, most of the kits around are based on dated variables. For example, source AC was lower 40 years ago, but they still just copy the same components and values. Higher source AC = higher voltages in your circuit.

Don't trust the kit, trust the math. Do the math and adjust the kit.
Hear, hear!!
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