First PL-400 Restoration

[dtafil]

Hey guys...

Thanks for the warm welcome last week... I also learned a lot about hair conditioner, lol.

In any event, wrapping up a Sansui restoration, but need to wait for a few parts. Moving into my first PL-400 restoration as I've got a 700b waiting patiently in line for the full WOPL build; figured I'd cut my teeth on this one first.

Pictures attached. Prior owner indicated it blew a fuse every time he brought it up (and not sure who owned it prior). It's a really clean amp, looks to be untouched other than an interesting set of fuses. The one that's blown is the 1 1/4" AGC8, 32V fuse (I'm thinking that's supposed to be 8A, but probably a minimum of 125V (I'm ordering AGC-8, 250V). The other 2 AGX (1") fuses are not blown, but one is an AGX-30(!) 32V, the other an AGX-8, 32V. I'm ordering a bunch of AGX-5 and AGX-8's... I want the 8A's to test after restoring to check what max output before clipping looks like. Any suggestions on fuses most welcome if I'm missing something. They're all coming from Digikey.

The plan, after a dim-bulb test with the correct fuses (I have a Variac as well) would be a recap of the main board, a replacement of the main filter caps, and addressing any other needed areas. Not sure of any known-trouble spots in these (pointers welcome), and happy to document as I go for others to follow. Definitely want to add the Watts Abundant board, probably have questions about the Zobel networks I'm seeing, as I probably want to keep just the one in the amp vs the new board. Also, any bridge rectifier replacement best practices, etc. Same thing on upgrading the main board transistors where needed, and probably the trimmer as well.

As always, thanks for any tips/suggestions! Here's the pics as she sits right now. I'll pull the transistor covers next time to see what's under there.

 

[laatsch55]

Damn clean.....

AGX 5 amp for the rails and AGX 10 amp for the mains...

How about a pic of the burnt fuse, that can tell a lot..

 

[dtafil]

Sure thing, thanks. Tried my best to focus on it... it's definely a 1 1/4" fuse in there now. Fails a diode test on my MM. Are you also thinking scrap the 8A's AGX fueses for the supply fuses, just run 5 AGX?

 

[laatsch55]

WEas that the mains fuse??

 

[laatsch55]

Nope, the heatsink is correct.

 

[dtafil]

That one came out of the 8 AGC line fuse holder.

 

[silver_face]

Is definitely clean,

will make a fine WOPL 400., you got a copper bus bar between the 2 bulk capacitors, mine had a large gauge wire that I had to make a copper
bus bar......

 

[laatsch55]

That was a soft blow on that fuse. I'd replace it and bring it up on a dim bulb and variac and see what happens..

 

[oldphaser]

Is definitely clean,

will make a fine WOPL 400., you got a copper bus bar between the 2 bulk capacitors, mine had a large gauge wire that I had to make a copper
bus bar......

If my memory serves me correct the caps you had in the photo were made by Temple(?)
If so, I hope you replaced them. They had a very high failure rate.

 

[marcok]

Some questions ( better curiosities ) :
-My father's PL 400 has the fuse holder for 1" and not for 1 - 1/4 " .
-If my memory serves me caps are 6800 uF
-Power transistors are Motorola and not Delco
I had understood that Motorola came with series II
This unit was sold new by my hifi Guru approx . 40 years ago .
S/N is 14xxx. Thereafter it's located in my father's living room .
Only two issues : bulbs and I had to spray paint the alu frames of VUs .

My father's Pl 700B has fuse holder for 1"-1/4"

Ciao
Marco
PS : reading some Pioneer service manuals for Canada only
higher fast blow fuses for mains are required .
I did not know thare are different safety rules between Canada and USA .

 

[Northwinds]

Nice looking 400, I had a few that looked like that. I think the PL400 is the best looking Phase Linear amp of all time, even over the 700B

 

[mlucitt]

In the process of adding the DC Protect board, you can search for and locate, a good article here on this forum about an improved grounding method for this amplifier. Re-routing a few wires and creating a STAR ground, can improve reliability and reduce 60 Hz hum and potential RF noise.
Additionally, I would invest in a new White Oak Control Board, there are also now several good-used Revision B to Revision E Control Boards on this forum, and that alone will improve reliability and performance better than any other mod you can do to your PL400. Better that throwing parts at the original one-sided control board, as I did initially.

 

[wattsabundant]

If you install the DCP relay board the zobel network is on the board. This is because the relay board mounts to the binding post to avoid drilling the chassis. You could install the original zobel on the Phoenix connectors if you really wanted to. It should not be installed on the binding posts as the zobel would be disconnected during power up. When the White Oak back planes are used the zobel is on the back planes so the zobel gets removed from the relay board.

 

[WOPL Sniffer]

Some questions ( better curiosities ) :
-My father's PL 400 has the fuse holder for 1" and not for 1 - 1/4 " .
-If my memory serves me caps are 6800 uF
-Power transistors are Motorola and not Delco
I had understood that Motorola came with series II
This unit was sold new by my hifi Guru approx . 40 years ago .
S/N is 14xxx. Thereafter it's located in my father's living room .
Only two issues : bulbs and I had to spray paint the alu frames of VUs .

My father's Pl 700B has fuse holder for 1"-1/4"

Ciao
Marco
PS : reading some Pioneer service manuals for Canada only
higher fast blow fuses for mains are required .
I did not know thare are different safety rules between Canada and USA .

I thought the Line fuses were AGC's (1.25") and the rails were AGX, unless they all get changed out to AGC fuse holders like all my amps.

 

[WOPL Sniffer]

I hope you opt for NEW outputs not somebody's old Outputs..... they are an accident waiting to happen... tick tick tick tick tick tick

 

[marcok]

I thought the Line fuses were AGC's (1.25") and the rails were AGX, unless they all get changed out to AGC fuse holders like all my amps.

AGC 4A and AGX 5A
The problem is that is "difficult " to find 1 " fuses .
Standard sizes now are 6 x 30 mm ( 1 X 1,25 ") and 5x 20 mm.
Ciao
Marco

 

[mlucitt]

I hope you opt for NEW outputs not somebody's old Outputs..... they are an accident waiting to happen... tick tick tick tick tick tick


View attachment 39540

But the current sharing test is so much more fun with the original outputs in place. With the new ON Semiconductor outputs, the test is boring.

 

[WOPL Sniffer]

indeed

 

[WOPL Sniffer]

AGC 4A and AGX 5A
The problem is that is "difficult " to find 1 " fuses .
Standard sizes now are 6 x 30 mm ( 1 X 1,25 ") and 5x 20 mm.
Ciao
Marco

HUH??? Standard sizes where YOU are from....... We still get AGC's Those scrawny ass fuses are bullshit.

The picture at the top of this page shows 5A AGX for rails, and 8A AGC for the main, a 700B/Series II is 5 amp AGX for the rails and 10 AMP AGC for mains... I shit can all that for ALL AGC's... No short ass midget dick fuses for me bro......

 

[WOPL Sniffer]

Oh, your GURU might have changed your stuff (to scrawny sizes)