phase linear 400

laatsch55 said:
If you are going to keep the 400C and recap it, replace C8 with a 470uf, 25 volt electro cap. That will improve the bass rolloff point. Also read this..
https://forums.phxaudiotape.com/thr...-up-tendency-in-phase-linear-amplifiers.2307/

In your case, C6 that they arer referring to on the Pl14 board is C8 on yours...
Click to expand...
do i need the back to back diodes on the updated c8 on the 400c board as you described in the link...
or is that just for the pl14??
and changing the cap will surfice....
 
Thanks to all of you who covered for me. Been on the road six straight weeks. Finally got home and got caught up a little bit today. It’s not all bad. Got to hang out with Spencer one night while in Houston.
 
laatsch55 said:
Yep...
Click to expand...
a little more info please....
value of the diodes...and where does the second diode connect....you explained the first diode...but, i dont understand where the second one is...
specifics bob, specifics....lol....lets see how many know that movie???
guess i aint ready for the big boy forums just yet...
thanks again...
gene
 
wattsabundant said:
Thanks to all of you who covered for me. Been on the road six straight weeks. Finally got home and got caught up a little bit today. It’s not all bad. Got to hang out with Spencer one night while in Houston.
Click to expand...
thanks for taking care of my order....sincerely appreciate it...
gene
 
gene french said:
a little more info please....
value of the diodes...and where does the second diode connect....you explained the first diode...but, i dont understand where the second one is...
specifics bob, specifics....lol....lets see how many know that movie???
guess i aint ready for the big boy forums just yet...
thanks again...
gene
Click to expand...



1N4148 diodes, set them side by side, polarity reversed to each other, twist the leads together , then solder across the leads of C8 on the on the trace side of the board.
 
good morning,
well, this morning i heard a scratchy sound emitting from the left channel...it did go away...but, i took it off line anyway...i read in places on the internet that this was probably a loose connection of some sort...i could not fuse the speakers as suggested...smallest fuse available in my pueblo is a 5 amp....better safe than sorry....i will check the bias and offset voltages today also, if i can find out how to do that...i am sure it is in the service manual....(it was on the sx1080)....mr don of wattsabundance fame has shipped the protection board, i have a cap kit on the way also along with the recommended c6/c8 capacitor change that was recommended by the gentleman AND scholar (laatsch55)...
mr. joe has received my order for the cap upgrade and he recommendation for the proper light kit for my tinted lenses that another member brought to my attention....
i am truly grateful for all of the advice....looking forward to more advice....still trying hard to get more educated so i can stay in the big boy forums...
take care guys
pura vida
gene french
 
i read the service manual on how to set the offset...after warming up 5 minutes...
my left offset was around 9mv....and easily adjusted to less than 1 mv...
the right offset was 63mv....and easily adjusted to less than 1 mv...
i read somewhere that a high offset will cause scratching in the speakers...
anyway...i made a little progress today!!!!
wattsabundant said:
Scratchy, hissing noises are often times the front end transistors. In this case Q1/2.
Click to expand...
yes....i was warned about those..
supposedly replacements on the way!!!
thanks very much....
 
i dont really know...a fellow member here predicted future problems and sent them....i think it was the offset....it was 63mv after warm up...and i believe it was out of limits...I AM NOT A TECH...just living where techs are non existant...what do you suggest for replacementsbif they prove to need replacing...
i will advise when they arrive in a few weeks!!!
thank you...
 
so far, there has been no more scratching or popping after the bias adjust...it only scratched on first power up and only lasted momentarily....i dont plan on changing anything (except the caps) until a problem develops...or until i know more about these amps...what do you suggest...one member suggested that if at this point i was only planning to recap the 400c board...to keep an eye on q1/2...as they were prone to failure...so, i will add it to my spare parts collection...
so far i have ordered joes power supply cap kit, joes light kit (not yet shipped)...i then ordered dons protection circuit (shipped)...finally a cap kit for the 400c (shipped) i found on ebay...
i also see a semiconductor "repair kit" for my board for 40 bucks...should i stock that???
thanks for your advice...i do appreciate it...i need all the help i can get...wanna earn my place in the big boy world of phase linear!!!
lol
 
gene french said:
so far, there has been no more scratching or popping after the bias adjust...it only scratched on first power up and only lasted momentarily....i dont plan on changing anything (except the caps) until a problem develops...or until i know more about these amps...what do you suggest...one member suggested that if at this point i was only planning to recap the 400c board...to keep an eye on q1/2...as they were prone to failure...so, i will add it to my spare parts collection...
so far i have ordered joes power supply cap kit, joes light kit (not yet shipped)...i then ordered dons protection circuit (shipped)...finally a cap kit for the 400c (shipped) i found on ebay...
i also see a semiconductor "repair kit" for my board for 40 bucks...should i stock that???
thanks for your advice...i do appreciate it...i need all the help i can get...wanna earn my place in the big boy world of phase linear!!!
lol
Click to expand...
Your scratchiness could well be the offset pot you adjusted just being dirty. That happens, especially after 40+ years. Likely one of the reasons that PL eventually got rid of that adjustment, along with cost reduction being a consideration.
 
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