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Phase Linear 400 and 700B

laatsch55 said:
OUTSTANDING Fred!!! You still aren't done. I would be awfully curious as to which one is the active squelcher and swap that socket. At least you can get it tested.
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If the old transistors had gobs of grease on the them then there's the possibility of a bad B/E connection. When I see that i pull the heat sink and clean it and the socket. I may be the minority, but I only use silpads. Silpads = no grease.
 
Don, I spend an inordinate amount of time taking the outputs off and cleaning the grease out of the sockets and heat sinks. Mainly due to the fact the last 3 or 4 folks didn't.
 
Is there any truth to the Rumour that a P/L 700 output was equivalent to 1 HP ? That was the rumour back in the 70s to the rabid stereo geeks at the McCallie School in Chattanooga...Of which I was one...(grin)
 
There definitely was a lot of grease in some of the sockets. Looked like white mud with a hole where the output lead went into the socket. Did my best to get rid of the crud.
Will do the heat test and see how she goes.
 
Based on Don's advice
I also wave a hair dryer over the heatsinks from about 12 inches while looking at the bias. The bias should drop with a little heat and then return to normal when the hair dryer is removed. I learned this the hard wway when a 700B didn't thermal track and wiped out all the outputs in one channel.
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The bias is set to about 350mv. When I apply the heat the bias rises slightly about 8-10mv then settles down after removing the heat source.
Don, you suggest it should drop slightly?
 
Sandy G said:
Is there any truth to the Rumour that a P/L 700 output was equivalent to 1 HP ? That was the rumour back in the 70s to the rabid stereo geeks at the McCallie School in Chattanooga...Of which I was one...(grin)
Click to expand...

By definition, 1 horsepower = 746 watts. Actually 745.6999
 
Fhamre said:
Based on Don's advice

The bias is set to about 350mv. When I apply the heat the bias rises slightly about 8-10mv then settles down after removing the heat source.
Don, you suggest it should drop slightly?
Click to expand...

Lee's right. I direct the heat towards the bias transistor. Note the hair dryer should be on low heat and stay away from the board. You can accomplish the same thing by operating the amp into a load resistor until the heatsinks warm slightly. Then remove the signal and immediately check the bias. It should return to the original set point in a minute or two.
 
Ok. Directing the dryer at the bias transistor got the bias to drop just as you said it should. Tested both and they reacted the same.
I needed a little clarity as I was directing the blower to the outputs on the backside.
Thank you gentleman for your great advice. Much appreciated.:banana:
 
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