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previous: Derrick Can anyone shed some light on ... -- 5/4/1998 10:31 AM

Re: Not your typical bias problem!

5/4/1998 2:49 PM
Doc	Re: Not your typical bias problem! First of all, can you describe how you are measuring the current flow? Is the bias voltage stable? At the operating voltages you've stated, that idling current is not excessive, unless the tubes are already bad. The screen grid should never become incandescent. If it does, the wires will sag and dimensionally distort, usually causing permanent tube damage. The grid alignment & spacing will become screwed up, and you wiill get completely changed tube characteristics and possible short circuiting. Arcing is a tell-tale sign. In a class AB circuit such as that marshall, the plates should not glow red.

5/4/1998 2:49 PM

Doc

Re: Not your typical bias problem!

First of all, can you describe how you are measuring the current flow? Is the bias voltage stable?

At the operating voltages you've stated, that idling current is not excessive, unless the tubes are already bad.

The screen grid should never become incandescent. If it does, the wires will sag and dimensionally distort, usually causing permanent tube damage. The grid alignment & spacing will become screwed up, and you wiill get completely changed tube characteristics and possible short circuiting. Arcing is a tell-tale sign.

In a class AB circuit such as that marshall, the plates should not glow red.

Replies:

Derrick Yes, Doc. The bias voltage is stab... -- 5/4/1998 3:13 PM