New Member with questions

T

TrialByFire01

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#1
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Aug 23, 2023
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#1
Hi All, I just signed up here and not quite sure where to post my question about a Phase Linear MKII repair/verification of a mod I found. I'm rebuilding an PL 400 MKII and I can't remember where I found this mod and need some clarification, all I did was copy past it. If anyone has done this or possibly even wrote the post that this came from. Here is the text in question:

"If you keep the original boards run a 470uf/25 volt audio grade cap for C6. On the foil side of the board run 2 1N4148's back to back across the leads of C6, that will keep the amp from latching up to the positive rail...
The 470uf cap will increase the low frequency response tremendously.."

So i'm not clear as to the terminology used here. Are they referring to C106 (the 120pf cap) on the PL36 board? Also what is meant by "run 2 1N4148's back to back" do they mean Anode to Anode or Cathode to Cathode? Any clarity on this would be greatly appreciated as well as other tried and true mods for reliability. I'm ready to install the outputs but they were expensive and I'd like to do anything I can to stop another backplane failure. I'm sure that I'm probably posting in the wrong place but I think this would happen anyways since I'm not sure where to put this. I tried a search with PL400, C6...etc. but no dice.. Thanks in advance.
 
laatsch55

laatsch55

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#3
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Halfbiass...Electron Herder and Backass Woof
#3
TrialByFire01 said:
Hi All, I just signed up here and not quite sure where to post my question about a Phase Linear MKII repair/verification of a mod I found. I'm rebuilding an PL 400 MKII and I can't remember where I found this mod and need some clarification, all I did was copy past it. If anyone has done this or possibly even wrote the post that this came from. Here is the text in question:

"If you keep the original boards run a 470uf/25 volt audio grade cap for C6. On the foil side of the board run 2 1N4148's back to back across the leads of C6, that will keep the amp from latching up to the positive rail...
The 470uf cap will increase the low frequency response tremendously.."

So i'm not clear as to the terminology used here. Are they referring to C106 (the 120pf cap) on the PL36 board? Also what is meant by "run 2 1N4148's back to back" do they mean Anode to Anode or Cathode to Cathode? Any clarity on this would be greatly appreciated as well as other tried and true mods for reliability. I'm ready to install the outputs but they were expensive and I'd like to do anything I can to stop another backplane failure. I'm sure that I'm probably posting in the wrong place but I think this would happen anyways since I'm not sure where to put this. I tried a search with PL400, C6...etc. but no dice.. Thanks in advance.
Click to expand...

I probably wrote the post you were refering to , doing what White Oak Joe suggested. On the 1N4148's anode to cathode, twist leads together, solder and cut off to 1/4" lenght. Then bend as needed to engage the leads of the cap. On a Ser II, the cap you are looking for is close to the input and 100uf at 16 or 25 volts...
 
Gibsonian

Gibsonian

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#7
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#7
Welcome to the place where the tunes of your dreams can turn into reality........................
 
wattsabundant

wattsabundant

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#10
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Messages
932
Location
Central Ohio
#10
TrialByFire01 said:
Hi All, I just signed up here and not quite sure where to post my question about a Phase Linear MKII repair/verification of a mod I found. I'm rebuilding an PL 400 MKII and I can't remember where I found this mod and need some clarification, all I did was copy past it. If anyone has done this or possibly even wrote the post that this came from. Here is the text in question:

"If you keep the original boards run a 470uf/25 volt audio grade cap for C6. On the foil side of the board run 2 1N4148's back to back across the leads of C6, that will keep the amp from latching up to the positive rail...
The 470uf cap will increase the low frequency response tremendously.."

So i'm not clear as to the terminology used here. Are they referring to C106 (the 120pf cap) on the PL36 board? Also what is meant by "run 2 1N4148's back to back" do they mean Anode to Anode or Cathode to Cathode? Any clarity on this would be greatly appreciated as well as other tried and true mods for reliability. I'm ready to install the outputs but they were expensive and I'd like to do anything I can to stop another backplane failure. I'm sure that I'm probably posting in the wrong place but I think this would happen anyways since I'm not sure where to put this. I tried a search with PL400, C6...etc. but no dice.. Thanks in advance.
Click to expand...
It's C111 on the P/L36. Another term to describe the diodes is reverse parallel.
 
T

TrialByFire01

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#12
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Aug 23, 2023
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#12
laatsch55 said:
I probably wrote the post you were refering to , doing what White Oak Joe suggested. On the 1N4148's anode to cathode, twist leads together, solder and cut off to 1/4" lenght. Then bend as needed to engage the leads of the cap. On a Ser II, the cap you are looking for is close to the input and 100uf at 16 or 25 volts...
Click to expand...
laatsch55 said:
I probably wrote the post you were refering to , doing what White Oak Joe suggested. On the 1N4148's anode to cathode, twist leads together, solder and cut off to 1/4" lenght. Then bend as needed to engage the leads of the cap. On a Ser II, the cap you are looking for is close to the input and 100uf at 16 or 25 volts...
Click to expand...

Thanks laatsch55 and all for the great welcome. Just for clarity you are referring to the C11 in the pic included here with the cathodes directed towards the + side of the cap I would imagine? Can anyone explain how this prevents the + rail from latching up? I'm super confused on this one.
 

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mlucitt

mlucitt

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#15
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Jun 24, 2011
Messages
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Jacksonville, FL
#15
They say a picture is worth a thousand words:
WOA Rev A Control Board.jpg

This is the back of a White Oak Audio (WOA) Rev A Control Board. Later revisions had places for these diodes on the front side of the board.
The diodes shown above are located on C6L and C6R and finally prevented the dreaded "Latch up" for the first time ever. The four diodes alter the charging state of the associated capacitor.
The equivalent Capacitors on the Phase Linear Boards are:
PL400C - No equivalent
PL14A/B - C6L and C6R
PL20/20A/20B - C23L and C23R
PL36 - C111 and C211 (This mod was never duplicated on a PL36 control board). The PL36 control board as used in the Series II amplifiers, is considered by many to be best replaced by a WOA Control Board as soon as possible.
 
WOPL Sniffer

WOPL Sniffer

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#17
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Minnie-Soda
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Screw it
#17
mlucitt said:
They say a picture is worth a thousand words:
View attachment 77153

This is the back of a White Oak Audio (WOA) Rev A Control Board. Later revisions had places for these diodes on the front side of the board.
The diodes shown above are located on C6L and C6R and finally prevented the dreaded "Latch up" for the first time ever. The four diodes alter the charging state of the associated capacitor.
The equivalent Capacitors on the Phase Linear Boards are:
PL400C - No equivalent
PL14A/B - C6L and C6R
PL20/20A/20B - C23L and C23R
PL36 - C111 and C211 (This mod was never duplicated on a PL36 control board). The PL36 control board as used in the Series II amplifiers, is considered by many to be best replaced by a WOA Control Board as soon as possible.
Click to expand...

Thanks god we have advanced as a race and found NEW WOPL STUFF.... Out with the old shit and in with Green paint.
 
KJ4LAA

KJ4LAA

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#18
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Sep 8, 2023
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#18
I'm restoring a PL400 Serial # 7266 with 8 cooling fins on the rear and the driver board is labeled 14B. All the electrolytics will be replaced as my first task. I don't see any burned-up components so far, although I do see there was some work done on this amp in the past. A little solder flick here and there and 2 different transistors. "One of the things doesn't look like the other." I have not powered it up and don't plan to until I have at least it's recapped and then bring it up on a variac. Additionally, I found F2 and F3 fuses missing which might be red flag.

Looking at the transistors on the rear backplane:
- All 4 columns on Row 1 are populated with RCA410 transistors (as expected per the schematic)
- Column 1 Row 3 and Column 2 Row 3 have Toshiba 2SD424 transistors (which should be PL909)
- The rest of the Columns 1,2,3,4 have PL909 as expected.

I'm not sure of the compatibility between the PL909 and the Toshiba 2SD424. Can anybody shed some light on compatibility?
More than likely I will just replace all the PL909's and the 2SD424 with MJS2119G's.
 
gene french

gene french

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#19
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guayabo de bagaces, guanacaste, costa rica....
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music...the healer of souls...
#19
TI7/AA5NX
welcome to the jungle!!!
fuses are sign of shorted outputs...probably...
1. DO NOT continue without dim bulb tester...
easily found with google search...variac limits voltage...dim bulb limits current...use 100 watt incandescent bulb...that will limit to less than 1 amp...and saves components...AND UNDERWEAR...
2. get dc protect board...at wattsabundant.com
...speaker saver...your speakers will thank you...always test with disposables ...
3. pics...laatsch rule #1...no pics...didnt happen..
4. wealth of smarts here...ask...
5. prepare for the addiction...lol
6. may the force be with you...
 
KJ4LAA

KJ4LAA

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#20
Joined
Sep 8, 2023
Messages
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#20
gene french said:
TI7/AA5NX
welcome to the jungle!!!
fuses are sign of shorted outputs...probably...
1. DO NOT continue without dim bulb tester...
easily found with google search...variac limits voltage...dim bulb limits current...use 100 watt incandescent bulb...that will limit to less than 1 amp...and saves components...AND UNDERWEAR...
2. get dc protect board...at wattsabundant.com
...speaker saver...your speakers will thank you...always test with disposables ...
3. pics...laatsch rule #1...no pics...didnt happen..
4. wealth of smarts here...ask...
5. prepare for the addiction...lol
6. may the force be with you...
Click to expand...
Thank you Gene. googling a dim bulb tester now. I guess it's not like rebuilding a Heathkit SB-220. 73, KJ4LAA
 
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