School me on the PL Pro 700

gadget73 · Aug 29, 2014

Good evening gents. I made my way over here after a few posts on AK said this was the place to be for Phase Linear info. I was able to get my friend's PL700-II up and going with assistance from Laatsch55 and others. Thanks again for that. He's as happy as a pig in whatever makes pigs happy.

So what brings me here? Well, tomorrow I'm picking up a Phase Linear Pro 700, the black face model. It looks a lot like the PL700-II, but the output stage is not the same. It surely looks for all the world like PNP/NPN pairs on the back. This one is sporting NEC 2SB600 and 2SD555 outputs. Am I wrong in believing this is fully complimentary vs the quasi-comp that the 700-II ran? What other differences do I need to be aware of with this guy? I'm not having any luck finding a service manual, so I'm hoping one of you guys has some experience with this rare animal.

Short term plan is probably some new beer can caps and likely a refresh of the original driver board with some new caps and any necessary resistor or other component replacements. After that, I'd like to add the output DC protection board if that is possible. From there, who knows. Suggestions? Any common upgrades that definitely do not work with this model?

Talk slow if you don't mind. I'm a tube guy at heart. This whole solid state thing befuddles me a bit.

also, if anyone has leads on a nice faceplate for one, keep me in mind. This one has some battle scars. Will post pics tomorrow when its in my grubby little mitts.

laatsch55 · Aug 29, 2014

WELCOME GADGET!!

Yep , full complementary output. Same outputs the Spec 2(among many others of that era) use. Getting a little long in the tooth. the MJ21195, 96 pairs would do well there.

Ed can help with the schematics, heck I might even have some if I dig deep enough. We you get it pull the covers and take some nudies and we'll see what else you might need . Saw that amp on e-bay 2 weeks ago, got an itchy trigger finger, but I had no business getting it....bought wwhat...21 700's awhile ago...

gadget73 · Aug 29, 2014

laatsch55 said:

Not sure this one was on Ebay. I think i got it before it went there. This one is coming from an AK member thats about 45 minutes from me. I don't need it, but after fooling with my friend's 700-II, I got the bug for some more power. The price was right on this one, and it didn't require trying to ship anything without being destroyed. I figure if I decide I just don't like it, I can always sell it and get my money back out of it.

I wasn't really planning to swap the outputs unless it becomes necessary. Its running as-is, but I will check it out to make sure that its doing what it ought to do. Speaking of that, whats the check-out process on this one? I know the 700-II had a whole chunk of service manual devoted to testing to make sure the amp was running like it should, but I don't know how well that applies to the Pro model.

Skynyrd77 · Aug 29, 2014

gadget73 said:

Not sure this one was on Ebay. I think i got it before it went there. This one is coming from an AK member thats about 45 minutes from me. I don't need it, but after fooling with my friend's 700-II, I got the bug for some more power. The price was right on this one, and it didn't require trying to ship anything without being destroyed. I figure if I decide I just don't like it, I can always sell it and get my money back out of it.

I wasn't really planning to swap the outputs unless it becomes necessary. Its running as-is, but I will check it out to make sure that its doing what it ought to do. Speaking of that, whats the check-out process on this one? I know the 700-II had a whole chunk of service manual devoted to testing to make sure the amp was running like it should, but I don't know how well that applies to the Pro model.

i made him a offer but he didnt like it lol.. glad you got it and made your way here :thumbleft:

laatsch55 · Aug 30, 2014

http://www.ebay.com/itm/27157960737...l2649&ssPageName=STRK:MEBIDX:IT#ht_839wt_1220

laatsch55 · Aug 30, 2014

gadget73 said:

Not sure this one was on Ebay. I think i got it before it went there. This one is coming from an AK member thats about 45 minutes from me. I don't need it, but after fooling with my friend's 700-II, I got the bug for some more power. The price was right on this one, and it didn't require trying to ship anything without being destroyed. I figure if I decide I just don't like it, I can always sell it and get my money back out of it.

I wasn't really planning to swap the outputs unless it becomes necessary. Its running as-is, but I will check it out to make sure that its doing what it ought to do. Speaking of that, whats the check-out process on this one? I know the 700-II had a whole chunk of service manual devoted to testing to make sure the amp was running like it should, but I don't know how well that applies to the Pro model.

99 % of it does, jump in there!!

gadget73 · Aug 30, 2014

so basically grab my copy of the 700-II manual and use that for the checkout? What about bias settings and current sharing tests? I'm guessing its a little different with the different output stage, but i'm really kind of shooting in the dark here. This one is at least a little more standard of an output stage.

and yeah that sure is the same one on ebay. Cash questions aside, he needed a certain amount for it, and it was an amount I was willing to part with. I guess thats what you can consider a fair deal.

8991XJ · Aug 30, 2014

Welcome gadget. Get that amp up and running right and drag it by for a listen at the regular get togethers. I've now got double DQ-10s to use a bit of that power.

gadget73 · Aug 31, 2014

well, its home. I'm being too lazy to go get batteries for the camera, so here are the pics from the ad.

A couple observations about this vs the 700-II I did. The Pro has stepped volume pots vs the smooth turn the other one had. I like this. They aren't real stepped attentuators, but at least you can easily set them to the same place. The faceplate also has markings at each click to match the levels.

The driver board isn't marked as to what it is. It says "400/700 Amp BD. 145-0084-0 02012" I think its a PL-36, or it sure looks like the PL-36. It also has "Sample" hand written on it in marker. Not sure if that means this one is some early production unit or what. I can't find a serial number, but the beer cans are week 19, 1982.

laatsch55 · Aug 31, 2014

Yep, PL 36 board...

gadget73 · Aug 31, 2014

filter caps

Whats the usual replacement for the big filter caps in these? Stock value? something larger ?

Thinking of putting a parts order together to re-cap the PL36 board, replace the 2 7.5k resistors that are way off, and maybe if I'm feeling ambitious I'll swap out the ceramic caps for film. I figure making sure the stock bits are in working shape is a reasonable place to start. I may do the WO boards later, but I want to give this thing an honest shot in stock form first. It definitely does not sound as good as the 700-II I rebuilt for my friend, and that was quasi-comp.

also it seems like I need to do something about these JBL speakers. One of them is sounding f'd up.

**edit** ok, seems one of the woofers on my L-40's is off center a bit. That one has always sounded slightly off, but I guess warming it up a bit earlier made it more off. Running the AR-14 set off my workshop surround sound rig now.

NavLinear · Aug 31, 2014

gadget73 said:

We did a group purchase for the big ass caps as there was a required minimum of 20 with a 10 week lead time. We'll be doing another soon.

United Chemi-Con U36D series
15,000 uF 160V
E36D161HPN153MDA5M
2.500" X 4.125"

gadget73 · Aug 31, 2014

OK, I guess I'll keep an ear out for that. In the meantime I'll do a quick and dirty leakage test and power supply ripple test and see if they are OK enough for the moment. Glad I trashpicked that 160 vdc power supply from work's trash pile. 5 minutes to make a metal bracket to hold the meter in place and we're golden.

The "growl" was the speaker rubbing. Glad I don't have to start poking around on that board with the scope. I've been down that road before. This one is all in spec, except for those stupid carbon comp resistors. The last one had lots of bad resistors on it. Maybe its just because this guy has fans that keep it cool.

P.L.F. · Sep 1, 2014

Hi Gadget, and if you have time, here is some more read:

- Ed's comment on fully comp output topology: see post #199:
http://www.audiokarma.org/forums/showthread.php?t=293316&page=14
- specific thread on PL700II recapping:
http://www.audiokarma.org/forums/showthread.php?t=484891
- kind of guidelines on PL700II restoration, if you'd not go for WOPL at this moment (WOPL is probably the most reasonable ultimate choice...):
https://dl.dropboxusercontent.com/u/59369897/PLF_Audio_hobby/PL700II restoration advice.pdf

Looking at your pics I see your gear is probably of early edition - Zobel network is based on sand resistors. Later PRO models were having non-inductive wirewounds fixed directly to the chassis for cooling purposes (see the photo attached).

laatsch55 · Sep 1, 2014

The 20 watt Dales were a Claire Bros specified mod ....I don't know if PL then incorporated that into the Pro line or not, but originally it was a Claire Bros spec,,,

gadget73 · Sep 1, 2014

P.L.F. said:

Thanks for the links. Would you happen to know which cap location he's talking about in the first link? I don't have the Pro schematic, so I have no idea if its already there, or if its something to add. I certainly have no issues moving a part if it produces some measurable improvement.

Any thoughts on ditching the ceramic caps for a film cap of some sort? I usually remove ceramics from the signal path in tube amps because they sound horrible. This has a bit of that shrillness that I usually associate with ceramic coupling caps.

At some point it may end up WOPL, but I'd like to give it a listen for a while in properly running stock trim. Think of it like trying a tuneup on a "new" car before going straight to rebuilding the motor. This one is basically healthy. My friend's was probably actually a better candidate. His board had problems, but I fixed it due to budget constraints. This one is mine, so laziness will be the constraint

P.L.F. · Sep 1, 2014

You'd need to ask Ed for PRO related details... Not sure the PL36 PRO scheme was ever published...

Some comments to your points:
- the caps location / upgrade mentioned by Ed => see post #210 of http://www.audiokarma.org/forums/showthread.php?t=293316&page=14 by Don Imlay.
- see pictures of 700 PRO, which I have, for comparisons on caps (for pre-driver caps, ceramic or silver mica types were factory recommended with at least a 100-volt rating).

Attached please find the PL36 comp. version factory scheme and 4 new schematics - separately: left/right/driverPCB/output - of PL700 II in fully complementary topology, redrawn by Nick Soudas (THD+N).

Good luck!

gadget73 · Sep 1, 2014

Thanks for the schematics, this helps a lot. Now I actually have a reference for what is in my amplifier. I'm slowly building a folder with schematics and service bulletins and such.

What exactly am I looking at in the board shots? Looks like the transistors were replaced with a different type? I'm just curious what the reason is for that.

Also it looks like the ceramics were swapped out for mylar caps. Would you by chance have a parts list for that handy? I can brew one up myself if you don't have one already.

Honestly, one thing I find so confusing about all this is that the information is spread out all over the place. Has anyone ever put together all of these various links and pieces of information into one big thread for reference purposes ?

laatsch55 · Sep 1, 2014

No, we havent..

P.L.F. · Sep 2, 2014

gadget73 said:

Ad.1 That was to share specific marking of PL-36 PRO fully complementary output compliant driver board... Replacents were due to some transistors that became obsolete. That particular sub was part of LDX Technology upgrade pack (ebay available).

Ad.2 You should have the parts' list in PL700II user/service manuals. The comp. related differencies should be read directly from schemes I sent you.

School me on the PL Pro 700

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