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Phase Linear 400 II resto/mod.

Artie

Artie

Super Member
I'm trying to get my PL 400 II game plan together, and have a question. I'm going to go with White Oak Audio boards, but I'm not sure I want to go the extra expense of the backplane boards. I know the TO-3 sockets are problematic, but is this because they're cheap/poor quality to begin with? Would modern gold-plated sockets resolve the main problem with them?

And, I'm assuming I can still go full-comp even if not using the backplane boards?

Thanks;
Artie
 
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You should also post on Pheonix Audio Community Forums. The White Oak founder contributes regularly as do others with extensive, and I mean really extensive, experience with those modifications.
 
I recently aquired a PL-700. Can't help with your question, I've spent hours reading... and am still not clear on some details.

I can handle simple stuff but this appears to be... either a sale or going full WO. I already have nice amps, so not sure which way I'll go. WO is tempting because I already have a C-1 that I did the Bill-D mod on and it's nice.
 
62vauxhall said:
You should also post on Pheonix Audio Community Forums.
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I registered there, but never got a confirmation email. I just tried to sign on, and it worked. Apparently, I never needed one.

Dingman said:
I recently aquired a PL-700. Can't help with your question, I've spent hours reading... and am still not clear on some details.
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I've heard nothing but rave reviews about the sound, and reliability, of this amp after the full WO treatment. I'll probably end up going with the full board compliment, but if I could save a couple sheckles, well, that would be good too.

Anyway, I might repost this question over there.
 
Well, I guess you do need the confirmation email. I can log in, and update my profile. But I can't see attachments or post. I PM'ed laatsch55, so hopefully, he can get me squared away.
 
The nice thing about the white oak stuff is that you can do it in steps. I have a PL 400 series I that I did both the backplane and the driver boards. I have also replaced most everything except the chassis and transformer.

I would definitely recommend all the white oak stuff. My amp sounds absolutely amazing and puts out a solid 250 WPC.

It was a lot of work and you need to have good soldering skills. Just take your time and triple check everything.

I would also recommend replacing main caps, bridge rectifier and getting a speaker relay board. Can't remember the person, but someone sells pre-made relay boards that are essentially drop-in.
 
Also, you can technically run the amp full comp without the backboards but that would require extensive re-wiring of the original output transistor circuit. I wouldn't recommend this.

You could also buy the new driver board and wire it for quasi then when you want to make the jump to full comp make the adjustments at that point.
 
Serious question. I have a PL 200. Half the power of the 400. When one makes these "modifications" are the Amps still a Phase Linear???
 
FWIW, the PL400 I'm currently involved in will not have new back panes, just a new board. I did receive from another Phase Linear aficionado nearby me some output transistors "harvested" from other PL amps he's got underway and a set of driver transistors - RCA 66546, same as RCA 410. According to his analyzer, power output now 265 WPC.

The example I have is fairly early and a 4 fin. The 323rd amp made in March, 1973 and came with (very) dark tinted Honeywell meters. So dark you could barely see that the original bulbs were working. Opted for a White Oak LED board and the Bright White LED color option is significantly better.
 
mjstriker5 said:
It was a lot of work and you need to have good soldering skills. Just take your time and triple check everything. I would also recommend replacing main caps, bridge rectifier and getting a speaker relay board.
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Yup. I'm a card-carrying, NASA certified solderer. Tested and retrained annually. (Until I just retired.) So no prob there. :)

mjstriker5 said:
Also, you can technically run the amp full comp without the backboards but that would require extensive re-wiring of the original output transistor circuit. I wouldn't recommend this.
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I really don't mind doing this as the backplane kit is $128, and I assume I need two. I could save over $250 if I do it myself. I have the skill. My only real concern is that I wonder if Joes' backplane kit doesn't also include some mods, that enhance the performance of the amp. If that's the case, it would behoove me to buy the kit. On the other hand, I wish there was a schematic of the backplane board. I still can't post at the Phoenix forum.

I'm still wondering if modern, gold-plated TO-3 sockets help alleviate the PL 400 socket problems. I want to do this project right, but I am on a tight budget.
 
A lot of where the backplane boards help is that they have more copper between the leads. I haven't been into a 400, but I've been into a couple of 700s. If the leads between sockets on the 400 aren't much different than what the 700 uses, its not a terribly fat buss wire. Maybe 16 or 18 awg? I never had any particular issues with the connections, and I'd be slightly leery of new "gold" sockets if they are not known high quality. Maybe bumping the size of that wiring wouldn't be the worst idea though. Seems to me you could get some solid 12 or 14 awg copper wire Home Depot, etc and make yourself new busses.
 
gadget73 said:
Seems to me you could get some solid 12 or 14 awg copper wire Home Depot, etc and make yourself new busses.
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That's exactly what I was thinking. And I would only use good "brand name" USA TO-3 sockets. Like something from Amphenol or similar. (If I go that route.)
 
Cool. I just hear "gold plated" and I think new crappy Chinesium tube sockets.

I recently replaced the filter caps and bridge rectifier on my Pro 700 (basically a black 700 Series II) and it made a big difference. I had previously re-capped and replaced some off value resistors on the stock driver board. The driver board rebuild didn't do much for it, but the filter caps did far more than I ever would have expected. If you haven't yet, make sure the power supply is looked at before you get further along. Even if you do go with the White Oak driver board, it will still benefit from having the power supply in good shape.
 
gadget73 said:
Cool. I just hear "gold plated" and I think new crappy Chinesium tube sockets.
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To be honest, that's exactly what I was contemplating, 'til I saw your comment. Then I decided to back-pedal and pretend I was going hi-fi from the get-go. :D

gadget73 said:
If you haven't yet, make sure the power supply is looked at before you get further along. Even if you do go with the White Oak driver board, it will still benefit from having the power supply in good shape.
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Yup. I'm going to do the full Monty on the power supply. ;)
 
Artie said:
Yup. I'm a card-carrying, NASA certified solderer. Tested and retrained annually. (Until I just retired.) So no prob there. :)

I really don't mind doing this as the backplane kit is $128, and I assume I need two. I could save over $250 if I do it myself. I have the skill. My only real concern is that I wonder if Joes' backplane kit doesn't also include some mods, that enhance the performance of the amp. If that's the case, it would behoove me to buy the kit. On the other hand, I wish there was a schematic of the backplane board. I still can't post at the Phoenix forum.

I'm still wondering if modern, gold-plated TO-3 sockets help alleviate the PL 400 socket problems. I want to do this project right, but I am on a tight budget.
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I am not too sure about the sonic benefits of the backplanes. I agree the boards are way better quality than what is in there now so for longevity sake that would be a plus. As you say you could completely redo the backboard with better quality wire wire, sockets, etc. I think the biggest bang for your buck is redoing the power supply, new driver board, new output transistors and a speaker relay. That right there is going to set you back some change not even including the possible $250.

The biggest hurdle is overcoming the change in wiring to go full comp. I have a PL 700 series one that I am about to do exactly what you are wanting to do. The kicker is that the White Oak backplane kit doesn't physically fit so I am also going to have to re-wire the backboard myself. I lucked out as the PL 700 series II is full comp so I can copy that. Not that difficult, but you have to plan it out.
 
mjstriker5 said:
I am not too sure about the sonic benefits of the backplanes. I agree the boards are way better quality than what is in there now so for longevity sake that would be a plus. As you say you could completely redo the backboard with better quality wire wire, sockets, etc. I think the biggest bang for your buck is redoing the power supply, new driver board, new output transistors and a speaker relay. That right there is going to set you back some change not even including the possible $250.

The biggest hurdle is overcoming the change in wiring to go full comp. I have a PL 700 series one that I am about to do exactly what you are wanting to do. The kicker is that the White Oak backplane kit doesn't physically fit so I am also going to have to re-wire the backboard myself. I lucked out as the PL 700 series II is full comp so I can copy that. Not that difficult, but you have to plan it out.
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Yeah . . . I think this is going to be one of those "measure twice", solder once, type 'o thangs. Good luck on your project.

BTW, the good folks at the Phoenix forum got my issues sorted out. Now I can post, and see attachments. :)
 
The Series II 700 is LED, looks like the eyes of the original Cylon from Battlestar Galactica. Those came out somewhere around 1977 I think. My Pro 700 is from 1982 and uses the same display. Don't rightly know about the 400, or if that ever went LED.

Forgot about the full comp / quasi comp thing on the earlier ones. My friend's 700 Series II that I worked on was quasi-comp, mine is full-comp. I think the White Oak boards assume full comp, so just keep that in mind if you're rebuilding the backplanes with stock-like parts.
 
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