Waveform Interpretation needed.

[mlucitt]

Joe, I never questioned the MJ15024 as a replacement for the RCA410, although I did like the RCA drivers soundwise (if the gain is matched in each channel pair) and I was probably the last adopter of the MJ devices.

Is there a better modern TO-3 substitute for the RCA410 with a closer gain figure? I know we don't need the power dissipation of the MJ15024 in the driver position.

I'll try the bias test for "as-is" amps that come along.

 

[laatsch55]

Still there and still disappears at 620mv., loaded.

 

[laatsch55]

Disappears at a higher KHZ than before at 385 MV. It now disappears at 3KHZ instead of 1KHZ.

 

[Gepetto]

Are the resistors on the backwall originals Lee or have they been replaced by alternate types? D13 still intact and acting like a diode on the PL20 driver board?

 

[laatsch55]

All emitter resistors are original. Have to lift a leg on D13 iirc.

 

[laatsch55]

I have not run a load sharing test on this amp this time, I'm embarrased to say.

 

[Gepetto]

what load are you driving with this Lee? When you see the waveform blivit?

 

[laatsch55]

8 ohm above 3KHZ, at 300mv input equating to 9.6 volts out.

 

[Gepetto]

Have you switched load banks on us Lee? It almost has the look of a load that is highly inductive that you are driving. Any changes there Lee? What does it look like driving a test loudspeaker?

 

[laatsch55]

I'm using that BPI load center Ed sent. I will look at it through a test speaker.

 

[laatsch55]

With the test speaker it occurs further down the waveform. Instead of in the middle about two thirds down.

 

[laatsch55]

Gpoing to bed, had the bacon guys, appreciate all your help.

 

[laatsch55]

With C11 replaced, all 21194's replaced it disappears at 410mv, all frequecies. That's unloaded bias measurement.

 

[Gepetto]

So it has something to do with the Black Gates in that location, it would seem.

 

[Gepetto]

That was my initial suspicion

 

[Gepetto]

Is the Zoebel stock Lee? What you were seeing is a reaction to an inductive load that wasn't being properly damped by the Zoebel

 

[laatsch55]

Yes it is Joe. It's getting swapped out before it goes. It did survive an hour of extremely loud horn pushin when James Burke was here. He dropped off the 400.

 

[Gepetto]

You left James deaf and dazed

 

[laatsch55]

Somewhat, they certainly had their ears ringing.

 

[speakerman1]

So is it fixed? Which BG was bad?

Larry