PL 400 Rebuild

laatsch55 said:
Mike, it sounds like that is as good as its gonna get without replacing the big caps.
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Got new bulk caps in today! Well, caps all tucked in so ran her up and... no change!


I'm still at 73vdc with turn on pops very much alive. Turn on pops maybe a bit more airy with a wider soundstage;)


Well, I now suspect it's anything but the caps so asking if I should back track and measure X-former voltage? Check DC at no load or mark, pull and test outputs?


I do plan to replace driver board but very curious why my DC rails are low.


Thanks for your time.


Mike
 
Yep,unhook the caps and check. Remember, Bob's brother wound a lot of the transformers at Phase , and if was after 10 am.......well.....I have one with 108 on the rails......
 
Unhook the unfused from the caps too. Your looking to measure an UNLOADED bridge rectifier....
 
laatsch55 said:
Unhook the unfused from the caps too. Your looking to measure an UNLOADED bridge rectifier....
Click to expand...

Are you asking me to measure the DC across bulk caps with both left and right channels power feed wires disconnected? I would remove both the two red wires on lug and two left channel black wires on lug. This will lock out drivers and control board power?
 
Measure the DC plus and DC minus on the bridge rectifier...without anything hooked to it through the caps connection...
 
Magic Smoke said:
Got new bulk caps in today! Well, caps all tucked in so ran her up and... no change!


I'm still at 73vdc with turn on pops very much alive. Turn on pops maybe a bit more airy with a wider soundstage;)


Well, I now suspect it's anything but the caps so asking if I should back track and measure X-former voltage? Check DC at no load or mark, pull and test outputs?


I do plan to replace driver board but very curious why my DC rails are low.


Thanks for your time.


Mike
Click to expand...

Are you at 120VAC input and can you trust your meter? If something was dragging down your rectified bulk voltage, you would know it because of a lot of heat being generated somewhere in the amp.
 
Gepetto said:
Are you at 120VAC input and can you trust your meter? If something was dragging down your rectified bulk voltage, you would know it because of a lot of heat being generated somewhere in the amp.
Click to expand...

Love the caps, make for smaller neater supply. The DBT flashes bright with initial inrush.

With the two red wires on right and two black wire on left removed, only green from bridge and all ground wires attached to each respective cap.

Variac set at 117, 79 vdc across each cap. My wall voltage is running 122 so direct to wall I get 82 vdc across each bulk cap. The light x-former tap reads 5 vac. As in past post, nothing but control board caps just slightly warm to touch with power fins slightly warm after 30 minutes or so. Bias was also posted. My old 179 is smack on DC but compares close to kill a watt on AC line so should be OK?

What you guys think?

Mike
 
I just got home from the bar, so bear with me, 79 volts UNLOADED, 73 volts idling with caps and board and back wall online??
 
Magic Smoke said:
Love the caps, make for smaller neater supply. The DBT flashes bright with initial inrush.

With the two red wires on right and two black wire on left removed, only green from bridge and all ground wires attached to each respective cap.

Variac set at 117, 79 vdc across each cap. My wall voltage is running 122 so direct to wall I get 82 vdc across each bulk cap. The light x-former tap reads 5 vac. As in past post, nothing but control board caps just slightly warm to touch with power fins slightly warm after 30 minutes or so. Bias was also posted. My old 179 is smack on DC but compares close to kill a watt on AC line so should be OK?

What you guys think?

Mike
Click to expand...
all quite normal Mike
 
Gepetto said:
all quite normal Mike
Click to expand...

OK, i'll put control board and drivers back to rails, thanks.

I guess I'm back to square one. I'm betting my "start-up pop" problems are somewhere on the 40 year old control board at this point.

Till funds allow, would pulling and checking outputs be something to do? Somewhere in the past someone has installed mica insulators, were not the rubber ones not standard? Is there a good procedure for testing with meter posted? All I can think of is comparing junctions with meter?

Thanks again for help,

Mike
 
Magic Smoke said:
OK, i'll put control board and drivers back to rails, thanks.

I guess I'm back to square one. I'm betting my "start-up pop" problems are somewhere on the 40 year old control board at this point.

Till funds allow, would pulling and checking outputs be something to do? Somewhere in the past someone has installed mica insulators, were not the rubber ones not standard? Is there a good procedure for testing with meter posted? All I can think of is comparing junctions with meter?

Thanks again for help,

Mike
Click to expand...

Hi Mike
Start up problems will be on the control board but they are exacerbated by worn out bulk caps. You have that out of the way so you are down to the control board. Mica insulators were standard issue at the time of manufacture. The silicone/fiberglas ones did not come along until much later on.

Yes you can check your outputs using the diode scale on your 179. Check for diode drops on the forward junctions and opens in the reverse polarity direction as well as open on the C-E junction in both polarity directions.

When you get to it, you should consider modern output transistors to replace the originals.
 
Gepetto said:
Hi Mike
Start up problems will be on the control board but they are exacerbated by worn out bulk caps. You have that out of the way so you are down to the control board. Mica insulators were standard issue at the time of manufacture. The silicone/fiberglas ones did not come along until much later on.

Yes you can check your outputs using the diode scale on your 179. Check for diode drops on the forward junctions and opens in the reverse polarity direction as well as open on the C-E junction in both polarity directions.

When you get to it, you should consider modern output transistors to replace the originals.
Click to expand...

Thanks Joe

modern output transistors? Are you talking about moving from quasi to full complimentary? I plan to stay quasi but read or mis read posts about the "old ignition" transistors and other posts say Bob got this right.

Lol, do I sound confused?

I think I'm asking questions asked a thousand times but the modern transistors will let you stay in original quasi format? If so, is there an upgrade kit or procedure to help keep me from destroying defenseless transistors?

Mike
 
Magic Smoke said:
Thanks Joe

modern output transistors? Are you talking about moving from quasi to full complimentary? I plan to stay quasi but read or mis read posts about the "old ignition" transistors and other posts say Bob got this right.

Lol, do I sound confused?

I think I'm asking questions asked a thousand times but the modern transistors will let you stay in original quasi format? If so, is there an upgrade kit or procedure to help keep me from destroying defenseless transistors?

Mike
Click to expand...

Hi Mike
Phase Linear used what they had at the time that were capable of doing the job. That was the Delco transistor private labeled as a PL909 for PL. Today the ON Semi MJ21196 NPN transistors that are far superior to the old PL909 transistors in every regard, SOA, power handling, distortion, gain uniformity, etc.

If you are staying quasi comp it is important to keep the RCA410 devices in the lower row. MJ21196 devices can be populated in upper 3 rows.
 
Gepetto said:
Hi Mike
Phase Linear used what they had at the time that were capable of doing the job. That was the Delco transistor private labeled as a PL909 for PL. Today the ON Semi MJ21196 NPN transistors that are far superior to the old PL909 transistors in every regard, SOA, power handling, distortion, gain uniformity, etc.

If you are staying quasi comp it is important to keep the RCA410 devices in the lower row. MJ21196 devices can be populated in upper 3 rows.
Click to expand...

OK, thanks for that. I found those on the WO site so will include next order if wife does not have me killed.

BTW, I replaced only B+ fuse and brought up. DC was 78 VDC with DBT voltage drop. Kill A watt read 14 watts. Removing and replacing only B- fuse loaded supply to 75 volts and drew 19 watts. I think this put Q5 in protection as it was running very warm.

Anyway thanks again.

Mike
 
Magic Smoke said:
OK, thanks for that. I found those on the WO site so will include next order if wife does not have me killed.

BTW, I replaced only B+ fuse and brought up. DC was 78 VDC with DBT voltage drop. Kill A watt read 14 watts. Removing and replacing only B- fuse loaded supply to 75 volts and drew 19 watts. I think this put Q5 in protection as it was running very warm.

Anyway thanks again.

Mike
Click to expand...

Are your bulk readings with the DBT in or not in?
 
Gepetto said:
Are your bulk readings with the DBT in or not in?
Click to expand...

The DBT in so lower readings. With both fuses back in I cranked the variac up, still on DBT. I now set for 120 VAC on bridge but bulk caps loaded so i get the old 77 VAC. Kill a watt shows 33 watts at idle but DBT in line.

After 10 minutes I noticed left channel peg meter for split second. I placed clips across 10 ohm resistor and still 390 ma, as when first checked last week. I decided to set both channels to 350ma. I found the left pot had no effect but possibly peg meter at a 1 minute rate where bias dropped out during each period. Q8 and Q9 under R20 were running very warm. I think I just found my first problem on this board? I put it up for tonight but will check pot and anything else you might add.

thx, Mike
 
To check bulk voltages the DBT has to be outta circuit...
 
laatsch55 said:
To check bulk voltages the DBT has to be outta circuit...
Click to expand...

Correct, I'm just being chicken. And re-checking my old notes, I apologize, the new caps did raise my B+ 5 volts! I see 82 VDC with wall @120vac. I must have bumped the dial when taking first after cap readings. Lots going on here with sick black lab taking my time...

Mike
 
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