The ultimate dual 500 "rising from the ashes" build

[Gepetto]

My thinking is Shorting C and E. Should create an equal output from both pre drivers and show none or very little Bias voltage

shorting C to E should result in zero bias and it turns the amp into a class B amplifier.

 

[grapplesaw]

Here is the circuit for full comp

 

[grapplesaw]

shorting C to E should result in zero bias and it turns the amp into a class B amplifier.

Right
the problem at the moment is the high base voltage equal to the positive rail

 

[Gepetto]

Right
the problem at the moment is the high base voltage equal to the positive rail

That is a symptom, not the cause. You need to find the cause. What is the op amp doing? Is its output sitting at the +15 extreme? Is the class A NPN transistor any good or is it roached?

 

[grapplesaw]

That is a symptom, not the cause. You need to find the cause. What is the op amp doing? Is its output sitting at the +15 extreme? Is the class A NPN transistor any good or is it roached?

Thanks Joe

you are correct as usual - it is a symptom.

So I thought about it over last night and unconnected the two fly back diodes on the backplane. No change. I bypassed the E and C on the bias transistor and disconnected the B wire. Bias now ok.
Jumped the fly back diodes back to the circuit , all ok. Reconnected the black B wire on the bias transistor, all ok. Removed the bypass jumper on the C and E bias transistor, all ok.

Go figure!!! Did nothing and works, what gremlin remains , we will see

powerd to 240 volts across the two rails

.5 mv offset both channels
.10 mv bias offset both channel, no change when adjusting 1k resistor. No drivers installed.
30.25 volt regulated steady.

Stable for 30 minutes.

Time to reinstall the right protection and recheck. Then resold we fly back diodes.

If all good I will install drivers.

 

[laatsch55]

Did it latch up Maybe?? With new caps sometimes the 14 board would do that.....

 

[grapplesaw]

Did it latch up Maybe?? With new caps sometimes the 14 board would do that.....

Please explain what this latch up is

 

[grapplesaw]

The only cap I did not replace while trouble shooting was the 47uf 100 volt which is part of that bias circuit

 

[laatsch55]

Here ya go Glen, Joe explains it very well....

http://forums.phxaudiotape.com/show...-latch-up-tendency-in-Phase-Linear-Amplifiers

 

[Gepetto]

The only cap I did not replace while trouble shooting was the 47uf 100 volt which is part of that bias circuit

That cap is not part of the bias circuit Glen. It is a bootstrap boost for the upper half of the amp circuit to ensure it is not starved for base drive current on the upper half cycle.

 

[laatsch55]

Whatcha got for a Zoebel network??

 

[Gepetto]

Here is the circuit for full comp

Hi Glen
The resolution on your markup photos is pretty low. Any way you can put up one that can be read when you zoom in?

It looks like you added miller caps to the 2N5416 and 2N3439. Not sure where that came from? What value did you put there? I also see a note about jumpering the 22 ohm resistor in the collector leg of each of those as well. Is the a reason why?

 

[grapplesaw]

Whatcha got for a Zoebel network??

It is the original Zoebel network. Two 10 ohm carbon resistors and a .1 cap 500 volt Sprague. Both checked out ok so reused them.

 

[grapplesaw]

Hi Glen
The resolution on your markup photos is pretty low. Any way you can put up one that can be read when you zoom in?

Will do

 

[Gepetto]

Will do

It looks like you added miller caps to the 2N5416 and 2N3439. Not sure where that came from? What value did you put there? I also see a note about jumpering the 22 ohm resistor in the collector leg of each of those as well. Is the a reason why?

 

[grapplesaw]

Hi Glen
The resolution on your markup photos is pretty low. Any way you can put up one that can be read when you zoom in?

It looks like you added miller caps to the 2N5416 and 2N3439. Not sure where that came from? What value did you put there? I also see a note about jumpering the 22 ohm resistor in the collector leg of each of those as well. Is the a reason why?

Joe the Miller caps are not present as of now. I plan on using 47pf silver mica caps. This was added per the service bulletin pictured.


The resistor is removed and jumper added. This is in the path shown in the full comp segmatic pictured. The other components are also removed as crossed out in my segmatic not on the phase linear segmatic attached. I have a photo of full comp board attached and I do not see this resistor.

You will note the correction in the reversing the E and C on the 2n5416 on my segmatic. This is incorrect on the phase linear comp one. This is also shown in the 2nd attached service bulletin.

 

[grapplesaw]

More photo's

 

[Gepetto]

Joe the Miller caps are not present as of now. I plan on using 47pf silver mica caps. This was added per the service bulletin pictured.


The resistor is removed and jumper added. This is in the path shown in the full comp segmatic pictured. The other components are also removed as crossed out in my segmatic not on the phase linear segmatic attached. I have a photo of full comp board attached and I do not see this resistor.

You will note the correction in the reversing the E and C on the 2n5416 on my segmatic. This is incorrect on the phase linear comp one. This is also shown in the 2nd attached service bulletin.

The Phase Linear Comp schematic looks correct to me Glen with respect to the emitter-collector orientations.

 

[Gepetto]

More photo's

I have all those Glen, I was looking for a high res photo of the schematic you marked up in the earlier post #182

 

[grapplesaw]

I have all those Glen, I was looking for a high res photo of the schematic you marked up in the earlier post #182

Hi had problem getting high res photo loaded
please look again at original post

the phase linear comp drawing I believe is incorrect as per the service bulletin the Violet wire moves from collector to Emiter. I hope this is correct or I have to change back

the back plane also does not show the new B- fused supply to the 2n5416