Adcom GFA-5800 wattage question

exojam

I am going to apologize upfront if this is a super simple question, so please bare with me.

What I am looking to do is a bias check/adjustment (in necessary). According to the service manual, below is the first step of the procedure.

"With amplifier connected to 8 ohm resistive load, apply a 1khz sine wave at the input to achieve 83.3 watts at the output."

So my question is, is there a formula for finding out what values I would need to calculate to find the wattage value?

I know the voltage will be between 115-120, but I do not know what my current would be or where I would check for it. I have attached the pdf if anyone is interested and sorry for the crazy question.

Side question, anyone know a decent 8 ohm resistive load that does not break the bank or do a lot of folks here make their own.

Thanks.

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exojam

I found where I would be checking the current at, I would be disconnecting the B+ from the board and putting a meter in between the wire and the board.

Ben Mah

Paid Member
Power = Vsquared/R, therefore V = Square Root (Power x R)

With an 8R load and 83.3W, V = Square Root (83.3W x 8R) = 25.8V

So with an 8R resistive load on the amplifier speaker output, 25.8V across the 8R load will be 83.3W output.

For a reasonably priced resistor load, mount two 4R 100W resistors on a heat sink.

Example of a thick film non-inductive resistor: 100W 4R non-inductive resistor

1 user

Nelson Pass

Paid Member
Nice big 120W resistors, 4, 8 ,16 Ohms at mpja.com

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poseidonsvoice

Paid Member
Another option, but might be expensive for some folks.

Best,
Anand.

1 user

exojam

Ben,

Thank you very much for typing out that very detailed formula for me. I do greatly appreciate it.

Thank you to the other, respondents for the information pertaining to the load device.