PL400 glad I found this forum.

Well that pretty much covers Drivers and outputs.
I'll put my 410 s in as my drivers

How can the protection circuit with two transistor 4 or 5 diodes couple caps and resistors give me a fit. So maybe I'm getting feedback from wrong drivers causing my distorted sinewave stating at 8khz?
 
laatsch55 said:
Possible. I'd lift the 33 pf caps off and look again.
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Ok results for hf oscillations w 33s lifted only change I see is sawtooth happens earlier, also no change on right channel hf distortion.

So installed 410s ( seemed good from original) left channel , new 410s right side. Well it didn't go well bias left very low and can't get to 350, 299 max, rchannel adjust 350 easy. Still right channel hf distortion and still sawtooth hf.
Installed xpl909 now it's like staring all over again left channel out , right channel not so good and me ready to throw hole mess in trash can.

I was hoping to just get unit up and running till I can afford White Oak upgrade . I did get a carcass 400 from Eric that is going Wo upgrade all. The 14 board is much nicer than mine and all sockets no abuse at all and intact.

My final dream is Joe's. Cap set clamp type, pl20g1 quasi set up for now cause $. Yep this forum is definitely saving me money.
Praying Gary
 
Are there any ferrite beads on the busbars on the backwall?
 
GaryCooper said:
I don't see any not saying it didn't need after all this was a thanksgiving built unit stacy wired it per sticker on cap might have had turkey on the mind.
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Gary
From what I understand, as you crank the frequency up towards 20KHz, the signal turns into a sawtooth instead of a sine wave. Is that understanding correct? That would say that the sawtooth fundamental frequency is the same as what you are inputting?? The ferrite beads were to suppress multi megahertz oscillations and have no impact on the fundamental audio frequencies.
 
Gepetto said:
Gary
From what I understand, as you crank the frequency up towards 20KHz, the signal turns into a sawtooth instead of a sine wave. Is that understanding correct? That would say that the sawtooth fundamental frequency is the same as what you are inputting?? The ferrite beads were to suppress multi megahertz oscillations and have no impact on the fundamental audio frequencies.
Click to expand...
Well I set my generator to freq then turn up amplitude until clipping , 20,200,2k work fine clips into square wave from sine wave. But at 20k as I approach where it should clip it turns into a sawtooth unless I turn amplitude down .
 
Ok so if im understanding then please correct me what im seeing is not HF ocsillations , I would have thought it would be oscillations riding on the sine wave? It has been many years for me i have forgot most of circuit principles only remimber basics but some will come back but the math that i used to know is long gone unfortunatly thats why I was glad i found this forum for all you smart guys can do the math for me lol.
 
GaryCooper said:
Ok so if im understanding then please correct me what im seeing is not HF ocsillations , I would have thought it would be oscillations riding on the sine wave? It has been many years for me i have forgot most of circuit principles only remimber basics but some will come back but the math that i used to know is long gone unfortunatly thats why I was glad i found this forum for all you smart guys can do the math for me lol.
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Gary, if the amp is oscillating, you will see that show up as a high frequency signal riding on top of the fundamental sine wave that your frequency generator is inputting. Have you moved off of the DBT at the point you are making these measurements? Or still using the DBT?
 
Joe still DBT without load , I should be able to see 20k clip like 2k and below right?
also right channel w D9,D10 inplace causes above 8K to breakdown from sine to distorted waveform and trips watts relay, i have yet to find that problem replaced Q8,9 ,diodes i am stumpt on that problem D9,10 lifted no issues. left channel was fine .
 
GaryCooper said:
Joe still DBT without load , I should be able to see 20k clip like 2k and below right?
also right channel w D9,D10 inplace causes above 8K to breakdown from sine to distorted waveform and trips watts relay, i have yet to find that problem replaced Q8,9 ,diodes i am stumpt on that problem D9,10 lifted no issues. left channel was fine .
Click to expand...
Does the DBT become brighter when you try to clip at 20KHz? Your rails may be sagging which may be affecting the differential pair in the control board front end.
 
Gepetto said:
Does the DBT become brighter when you try to clip at 20KHz? Your rails may be sagging which may be affecting the differential pair in the control board front end.
Click to expand...
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.
 
This set is what was working i got 4 years ago when I bought this unit just in case ha.
The two 14 boards right one mine 14a
The left one says 14a on back however it missing components showing me it's a 14B missing C12,13&r22
Along with updates to
C3=47/100v
C6=100/63v
C15,16=47/40v
 
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.
 
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