PL400 glad I found this forum.

[Gepetto]

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.

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.

 

[WOPL Sniffer]

I think the only consistent thing on these amps was the use of non polarized AC plugs, only because they were not yet available in the 70’s.

No, the terrible workmanship was consistent.

 

[GaryCooper]

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.

Upon replacing 909s found 2 open BE, 2 shorted BE . The 410s good as are the mj15024g.
Installing now.

 

[GaryCooper]

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.

 

[GaryCooper]

18khz
Line 128vac at bridge
B+84.7
B-85.0
Offset .003 both
Bias L.359 R.350

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.

Problem was it was a 4 speed and i broke ring and pinion.

 

[GaryCooper]

So I 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.

 

[laatsch55]

At what output and input?

 

[GaryCooper]

I kn

At what output and input?

I knew someone was going to ask what input about 2v pp

 

[GaryCooper]

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.

 

[GaryCooper]

At what output and input?

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 .

 

[laatsch55]

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]

Offset on both .003

 

[GaryCooper]

Offset on both .003

Yes I matched Q1,2,3,4.

 

[gene french]

how does it sound when you play music???

 

[Gepetto]

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 .

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.

 

[GaryCooper]

how does it sound when you play music???

Left good
Right squeals then trips watts relay also right will not operate with a load with or without D9,10 lifted.

 

[GaryCooper]

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.

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.

 

[GaryCooper]

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.

 

[GaryCooper]

how does it sound when you play music???

Gene it plays music good listening for 30 min it will be fine.

 

[gene french]

i am so happy for you!!!
congratulations..