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previous: GVB I use a "generic" method of setting... -- 1/26/1998 12:44 PM

Re: Right bias for JCM 800?

1/26/1998 2:13 PM
Doc	Re: Right bias for JCM 800? ".....supposedly done with no load (i.e.,no speaker)" This should be done not using a speaker, yes, but there MUST be a resistive load connected, corresponding to the nominal impedence required by the output winding. (For an 8ohm speaker, use an 8ohm power resistor.) What you are setting is quiescent idling current (zero signal operating point) of the power stage. you need a correct size load connected with resistance but no reactance. That's why the speaker gets disconnected, but it gets temporarily replaced with a resistive load. You can possibly fry an output transformer primary under certain conditions with an open secondary. Don't take the chance. Doc

1/26/1998 2:13 PM

Doc

Re: Right bias for JCM 800?

".....supposedly done with no load (i.e.,no speaker)"

This should be done not using a speaker, yes, but there MUST be a resistive load connected, corresponding to the nominal impedence required by the output winding. (For an 8ohm speaker, use an 8ohm power resistor.)

What you are setting is quiescent idling current (zero signal operating point) of the power stage. you need a correct size load connected with resistance but no reactance. That's why the speaker gets disconnected, but it gets temporarily replaced with a resistive load. You can possibly fry an output transformer primary under certain conditions with an open secondary. Don't take the chance.

Doc

Replies:

GVB Exactly, this is what I was taught,... -- 1/26/1998 3:02 PM