PL 400 Question?

nadude98

nadude98

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Hello there, I hope everyone had a great Christmas! My question is about whatever it is that is mounted above the fuses on the inside that serves as an insulator. Mine is destroyed and I was wondering if anyone has a suggestion as to what I can use to replace it. I'm not sure what to look for. It looks like coated cardboard of some kind. I appreciate your help!

Cheers,
Jim
 
Gepetto

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nadude98 said:
Hello there, I hope everyone had a great Christmas! My question is about whatever it is that is mounted above the fuses on the inside that serves as an insulator. Mine is destroyed and I was wondering if anyone has a suggestion as to what I can use to replace it. I'm not sure what to look for. It looks like coated cardboard of some kind. I appreciate your help!

Cheers,
Jim
Click to expand...
It is just cardboard...
 
Gepetto

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oldphaser said:
If my memory serves me correct.....

Dean indicated that it was there to prevent arcing with the top cover and chassis.
It may have also been a code requirement.

They also used "fishpaper" on some amplifiers.
"Fishpaper" is the name for the electrical grade of vulcanized rubber.

Ed
Click to expand...
Not likely Ed, the spacing to the closest AC point, the fuse tip, is over 10mm to the top cover. EN60950 only calls for 6mm through air for 250VAC safety spacing and this in the unvented side of the cover. The only additional thing I can think of is preventative for untrained techs that may have put the top cover on backwards since it is not keyed in any way. The cover slots would be right over the fuse tip in that case.
 
nadude98

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Another question... I just want to double check and make sure I am reading things right. The bias transistors are 2N3403's, I picked up some on mouser, they have the heat sink on them. I read the pin out from the flat side facing me, is that correct.
 
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nadude98 said:
Another question... I just want to double check and make sure I am reading things right. The bias transistors are 2N3403's, I picked up some on mouser, they have the heat sink on them. I read the pin out from the flat side facing me, is that correct.
Click to expand...
With the flat facing you and leads pointed down, the pinout is E-C-B from left to right.
 
nadude98

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Installed my new bias transistors and now I am feeling a tad silly... I was trying to check the bias according to the service manual but I am not getting a reading on the DMM. I connect the leads in parallel with R38 correct? Also R38 and R39 are the two resistors wired in parallel and in series with a cap at the outputs if I'm not mistaken. Not sure what I am doing wrong..... oh boy!
 
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E-C, C-B, E-B. You check transistors in isolation, not behind other components IIRC

Do you have your meter set in the proper range? Crank it down.
 
Last edited:
laatsch55

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You need to clip your leads to either side of the 10 ohm resistor on the back wall stuffed under the emitter resistors. About 2/3rd the way up. Be sure to let the caps bleed off before venturing in there with the leads...
 
oldphaser

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The original carbon composition 10 ohm resistors are typically measuring out-of-tolerance these days.
I would suggest measuring the resistance of each 10 ohm resistor (with the amp turned off of course and the power supply discharged).
If the value of the (2) 10 ohm resistors in each channel is not closely matched (i.e. .1 ohm) you will also get different bias readings between the (2) resistors.
Although the Phase Linear 400 series 1 service manual allows for a difference in bias reading of 20% (between the (2) 10 ohm resistors in each channel) you should be able to do much better than that.


Ed
 
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nadude98

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laatsch55 said:
You need to clip your leads to either side of the 10 ohm resistor on the back wall stuffed under the emitter resistors. About 2/3rd the way up. Be sure to let the caps bleed off before venturing in there with the leads...
Click to expand...
Thanks, I got it done and set the bias to .35vdc, now I just am waiting to get my 4 caps in tomorrow for the bridge rectifier and then I'll hook it up...! In about a month I'll be WO'ing it! :happy2:
 
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