Kenny Nelson's WOPL 400 conversion.

[Gepetto]

or a curve tracer if you can lay your hands on one of those.

 

[Gepetto]

Your meter test will not show that up, voltage is too low.

 

[laatsch55]

Second pair of new ones gets me this, at 501 mv input , 47 watts output.

 

[NavLinear]

or a curve tracer if you can lay your hands on one of those.

We used to have a Keithley curve tracer at work - will have to see if we still have it burried away somewhere. I just google'd Keithley and it seems they were bought out by Tektronix.

 

[mlucitt]

This might be the first case of MJ21194 failure, no? Makes you wonder if the MJ21196 would have fared any better. Any thoughts as to the outputs frying in relation to the R2L and R2R getting a little too warm? Possibly, the loose meter screws shorted the -75VDC to the case and the weakest link in that path was the floating ground resistor between chassis ground and PS ground?

Just a thought.

 

[laatsch55]

Why would a quarter watt resistor go before a fuse?? Had to be the short was there at power up and kept the current below 5 amps but enough to fry the resistor??

 

[NavLinear]

I think it means that the weakest link went first in this case. The mains fuse is rated at 5 Amps and the first in the series resistors would go with less than 1 Amp (see Joe's post #149).

 

[laatsch55]

Missed that one, damn....

 

[laatsch55]

What I did not do was test with just the RCA-410's UNDER LOAD. I can find no other source for the anomoly. I'll demount the 4 21194's and check just the drivers next.

 

[laatsch55]

Joe, what would be a good loaded output to test just the drivers. I have gone to 2 watts, just wonder if that's enough....

 

[laatsch55]

When driving the drivers loaded past 2.33 wattts with 128 mv input, bias jumps to 2.564 volts +DC

 

[Gepetto]

I could give you a long procedure Lee but it is probably quicker just to swap out the RCA410s for ones that have not been subjected to any potential abuse.

 

[Gepetto]

Hi Lee
With a load on the output, it is expected that the bias will jump if you are measuring across R38. In the case where only the predrivers are loaded into the amp, the predrivers will attempt to drive the load through the 10 ohm R38 and R39. If you are driving an 8 ohm load, whatever you are outputting into the 8 ohm load is reflected in the 10 ohm in the ratio of 10/8ths or 1.25 times the voltage you are seeing on the 8 ohm resistor. It is normal to see the bias jump in this case since you have lost all the current gain of the ouput mains.

Have you checked R40, 42, 43, 44, 45, 46 and your favorite R41 to see if they are still intact?

 

[laatsch55]

R41 yes, the other emitter resistors , yes. I'll swap em out.

 

[laatsch55]

Also at the nodfe of R18,17 I'm 2-1/2 volts short. Onstead of 15.5 I've got 12.98

 

[laatsch55]

With new 410's I start clipping the top at 3.5 watts. Loaded into 8 ohms. 145MV input.

 

[laatsch55]

One pair of 21194's on and took it to 60 watts, clean and green. Second set, coming up. 8 ohms, 402mv input.

 

[laatsch55]

2nd pair took to 124 watts and the bottom half started breaking up......8 ohms, 844mv input...

 

[laatsch55]

3rd pair took to 34 watts 408mv input, 8 ohms and we got this stuff......

 

[jbeckva]

3rd pair took to 34 watts 408mv input, 8 ohms and we got this stuff......

And theeen??? (suspense is killing me)