PL400 glad I found this forum.

GaryCooper said:
Joe with the mj21196 drivers and mj15024 outputs the bulb did not get bright.
After all talk from post I decided to change drivers to 410s results were the same so I changed outputs back to xpl909s which set me back to the beginning with a new set of problems.
No shorts Dbt dim but does grow brighter as unit is tested im exhausted.
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Hi Gary
If the problems follow the PL909s, it is just one more good reason to move away from them. They were marginal transistors for this application in the 70s and they remain so today.
 
Wow took the governor off and I'm ready for step
V-4
Wish me luck. Feel like I'm going drag racing in my old 55 Chevy back in the day my first car even had mag wheels hehe.
 
IMG_20230524_001708554.jpg
18khz
Line 128vac at bridge
B+84.7
B-85.0
Offset .003 both
Bias L.359 R.350
GaryCooper said:
Wow took the governor off and I'm ready for step
V-4
Wish me luck. Feel like I'm going drag racing in my old 55 Chevy back in the day my first car even had mag wheels hehe.
Click to expand...
Problem was it was a 4 speed and i broke ring and pinion.
 
So IMG_20230523_234121689.jpgI assume I need to lift right channel D9,10 and try again to see if it will behave as left channel.
This picture is 2k at start of clipping with all circuits in.
 
This is 18khz I didn't even get input up to clipping left channel when tight does that also tried 2khz into speaker loaded it started to whistle then distorted.
Gonna lift D9,10 then test post results.IMG_20230524_001708554.jpg
 
laatsch55 said:
At what output and input?
Click to expand...
I tested left channel with load the highest output was at 200 hz just before clipping .905vac In 32.54vac output shy of the 40v per test spec.
Those other test no load.
The right channel input was .340vac to flip sine wave to sawtooth. Something not right with 14a board right channel suggestions welcome .
 
Max output on a 400 is obtained with an input of1-1/2 to 1-3/4 volts.
What's your offset on the bad channel? Have you swapped q1,q2 out yet?
 
GaryCooper said:
I tested left channel with load the highest output was at 200 hz just before clipping .905vac In 32.54vac output shy of the 40v per test spec.
Those other test no load.
The right channel input was .340vac to flip sine wave to sawtooth. Something not right with 14a board right channel suggestions welcome .
Click to expand...
Before it flips to what you are calling sawtooth waveform (post# 129 above) does the signal follow the fundamental? The sawtooth on the right channel in your post# 129 is definitely not following the fundamental input from your signal generator but it is synchronous with it.
 
Gepetto said:
Before it flips to what you are calling sawtooth waveform (post# 129 above) does the signal follow the fundamental? The sawtooth on the right channel in your post# 129 is definitely not following the fundamental input from your signal generator but it is synchronous with it.
Click to expand...
Yes it does up until it distorts
Upper channel is left channel my video is to large to post dont know any other way to post it.
 
Tracing down voltages it lead me down to the frickin wires I redid left side repaired couple on right thinking I'll redo right side before I close it up later Not! Repaired right side wires and BAM listen to the sound of music loaded and tested right channel all good no more distortion.
I can say I did learn a lot about this early model four fin 14a 400 watch out for those buss wires . Also consult new friends on how to do things thanks everyone for your contribution to teaching me how "not to believe everything you read on Internet " haha
Have a safe Holiday.
 
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