phase linear 400

I happened to be visiting a friend at the hospital when one of those "pickers" shows was on the TV (sorry I am not familiar with those shows as I rarely watch TV) - they were admiring an 8-fin 400 and reminiscing about Phase Linear's history of building killer amps. The bargaining went back and forth, but the amp looked to be in very good shape - $275 took it.
 
gene french said:
joe,
why should i upgrade to your chassis....what do you have that stock chassis dont have??
when my stuff all gets here...i think i will desire another chassis....
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Multiple reasons Gene but primary reasons are that PL should have done all these things in the first place...peruse the attached.
 

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then there was none.....mornin joe....
Gepetto said:
Multiple reasons Gene but primary reasons are that PL should have done all these things in the first place...peruse the attached.
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i have a box of nut plates and tinnemans left over from the airplane days....but, you have addressed that....
it is a shame that these were left off...but, then they could not have sold them for 1 dollar per watt....
double edged sword....
but, thank goodness you have these to offer....and you have done your homework....
thanks for the explaination joe...
you dont advertise your chassis much....glad i have the opportunity to understand....
 
I have one of Joe's replacement chassis for a 700, but I'm not sure which one I'm going to use it on. One of them had a torn ear from rack mounting... That one either has a new chassis or an ebay posting in its future.

What is the general consensus - for my first 700b build, is it easier to use the existing chassis or the WO new and improved chassis? Wondering if it's better to start with a blank canvas or a dirty one with outlines. Ultimately I'm going to do both, but just wondering which one should go first.
 
ABebar said:
I have one of Joe's replacement chassis for a 700, but I'm not sure which one I'm going to use it on. One of them had a torn ear from rack mounting... That one either has a new chassis or an ebay posting in its future.

What is the general consensus - for my first 700b build, is it easier to use the existing chassis or the WO new and improved chassis? Wondering if it's better to start with a blank canvas or a dirty one with outlines. Ultimately I'm going to do both, but just wondering which one should go first.
Click to expand...
i have the same situation....i new wopl....an 8 fin and two 4 fins....
one of the 4 fins is missing parts...but i have collected parts and maybe i can get lucky with them all...
considering one of joes....
 
ok....got the extra parts in today from george, the solder and the liquid flux....without incident....lol
george of the jungle....thank you very much....pulled out the two 2n1304....one tested strangely....not open or shorted...but different values on the forward bias...both sides....
the other tested equal to the existing right channel....so that is the one i used i cleaned up the board as best as i can....it wasnt as nasty as the 200...but not far off....it looks a lot better....i can still clean a little...but it is 95% clean....or more...lol
the board you sent, george, is the 14b....the quality of that board is way ahead of the 400c...the older board looks crude to the newer one...
i am beginning to understand where joe is coming from....about leaving a lot to be desired....of course this is 50 year old stuff...and the 4 fins were almost prototypes....so to speak....i will learn more after the 8 fin gets here....
after checking the bias transistors, i powered up....with dbt....light bright and then dim....with the dcprotect out of circuit...but, i did hear the relay click on and off as it should....
no more dc on the left channel output...
both channels are about 50mv....hooray!!!!
i have not set offset yet...as i was afraid it would blow up again...but, i already know it is not out of specs...
i think i set the bias last time...but i definitely will check it again before i hook it to the speakers...
soon as i quit shaking....lol
stressful for me!!!!
let the wife reclaim her dining room table....and moved my work project into one of the spare rooms....she was tickled about that....
at last some progress !!!!!
thanks for hanging with me....
 

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No idea about the bias on the original board Gene, but your new work space looks very nice. I would suggest adding a side table to sit your hand tools and parts on. I use a Goodwill sourced old timey end table beside my half sheet of plywood.
I do have a thought about the bias. Perhaps that old trimpot is questionable and perhaps there's a suitable sub on that other old board?
 
thank your mr. george....
well ,,,. i was watching all of the voltages...etc....letting the machine run without inputs/outputs....
ran 30 to 45 minutes....then i noticed the dcp relay cut out....took dcp out of circuit again....
i disconnected and waited for the caps to discharge...maybe 5 or 10 minutes....put the dvm on left output (now disconnected from the dcp) and chassis gnd....
i repowered ....dbt acted normal...bright then dim....and for about 30 seconds all was fine....8 or 9 mv....as i am watching the meter....then the dc voltage start climbing on that left channel again....kinda goes up in stages....was the negative voltage rail again....
if you let the caps discharge....the cycle repeats....
q8 and q5 were both changed....q8 was in a repair kit i bought when i got the cap kit for the 400....
q5 i took off of your board....
in circuit...they both check the same as the other channel....i am definitely missing something....
 
gene french said:
thank your mr. george....
well ,,,. i was watching all of the voltages...etc....letting the machine run without inputs/outputs....
ran 30 to 45 minutes....then i noticed the dcp relay cut out....took dcp out of circuit again....
i disconnected and waited for the caps to discharge...maybe 5 or 10 minutes....put the dvm on left output (now disconnected from the dcp) and chassis gnd....
i repowered ....dbt acted normal...bright then dim....and for about 30 seconds all was fine....8 or 9 mv....as i am watching the meter....then the dc voltage start climbing on that left channel again....kinda goes up in stages....was the negative voltage rail again....
if you let the caps discharge....the cycle repeats....
q8 and q5 were both changed....q8 was in a repair kit i bought when i got the cap kit for the 400....
q5 i took off of your board....
in circuit...they both check the same as the other channel....i am definitely missing something....
Click to expand...
I don't know. Perhaps a output transistor is wounded and cross conducting. You did build it back up row by row and checked bias stability with each row? If not, then that's what I would do.
 
George S. said:
I don't know. Perhaps a output transistor is wounded and cross conducting. You did build it back up row by row and checked bias stability with each row? If not, then that's what I would do.
Click to expand...
what is the minimum i can power on with....just the bottom two rows on left side???
 
George S. said:
I don't know. Perhaps a output transistor is wounded and cross conducting. You did build it back up row by row and checked bias stability with each row? If not, then that's what I would do.
Click to expand...
something is breaking down....takes about 30 seconds for the dc to show up.....i am not convinced the q5 on that used board is not the culprit....
one of them did not test normal....
was not shorted...nor open....
but in forward position....values were off from the other side...
the second one tested normal....and i used that one...
oh well....
 
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