Phase Linear 4000 Restoration

[BlueCrab]

I recently purchased this actual PL 4000 and am trying to restore it. The unit has a PL30 in place of the PL03 Tone Amp board and no Decoder board PL06 as shown in the photo, the white wires running from the PL30 to the socket of the PL06. Does anyone have information on this modification?

This seems to be the identical unit that nadude98 posted in the media section.

 

[Lazarus Short]

Nice, clean innards, so you don't have a lot of clean-up to do.

 

[BlueCrab]

Indeed. Fairly clean both in and out. Cleaner than a bunch of old radios I've restored from the 30's, 40's, and 50's. I've stripped it down completely - removing all panels - both front and back - for a through cleaning anyways. Front and back look great.

Looks like this modification bypasses the Peak Unlimiter and Decoder (since it's removed) and the audio goes straight to the Logic board. I'd like to restore it to original configuration but don't have what I assume is the original Tone Amplifier nor the Decoder.

 

[WOPL Sniffer]

The Joystick version? I fought with those connectors on the cards/mother board too many times. Bad design. I don't believe I've seen the Mod you are talking about. Where did you read about it?

 

[WOPL Sniffer]

that is the one NAdude98 had posted, did you try contacting him?

 

[BlueCrab]

Yes, yes, and no. It is the joystick version and it is the one NAdude98 posted, but I haven't tried contacting him. This is not a modification I've seen anywhere and I'm sure the purpose was to bypass the Peak Unlimiter and Decoder thereby reducing signal path and reducing noise and distortion. And increasing reliability a bit. I'll try reaching out to NAdude98.

 

[WOPL Sniffer]

maybe he can give you a little info on the unit like, if it worked or there were other issues with it. I have seen some crazy crazy mods that don't work. You didn't say if it works..... or not

 

[BlueCrab]

Yes, it does work - or at least I can pass a signal through it, both channels. Volume, tone controls, balance and the like all function. It does seem to have a low end roll off. I tested it with my signal generator and scope - a square wave looked reasonable to 10kHz. I'll get more serious in testing after I clean it up, replace a bunch of caps, and figure out what's going on with this unusual mod.

 

[WOPL Sniffer]

after going through the "Issues not considered failures" in the Fast Field Service Manual, (https://www.hifiengine.com/manual_library/phase-linear/4000.shtml ), are you sure you want to restore one? They have a lot of quirks and were considered not very reliable. They called them "Nuisance Complaints" that was a whole page not counting the 4 or 5 pages of real problems.

 

[BlueCrab]

Ha ha. Absolutely! I have tons of experience and have tackled more complicated and difficult equipment. Plus I'm retired, so time is not an issue and I have the test equipment - I like projects like this. I get enjoyment bringing equipment like this back to life. The challenge is half the fun. But thanks for the warning - this is not for everyone.

 

[laatsch55]

Keep us appraised of your progress. If you need boards let me know. I have 3 of those things laying around here somewhere...

 

[WOPL Sniffer]

I am just saying, they were not that good of a pre....

 

[BlueCrab]

Photo attached is the current progress...

laatsch55: Thanks for your offer. I do believe I'll be after the Tone Amplifier board at least. If you could let me know if you have one I'm willing to purchase it.

 

[marcok]

It should be the third version : ambience function instead SQ decoder .
Check the front panel ! Furthermore the front board is soldered to the mother board .

Ciao
Marco

 

[Steve K]

Here are a couple of pics of one that I bought new in the seventies.

 

[BlueCrab]

This solves my mystery! And is the perfect answer. Yes, the front panel has an Ambience switch and the front panel is soldered to the main board. Thanks for the pics, Steve K. Appreciate the help. Now I'll be looking for the schematic of that PL30 board, not that it is essential for going forward, but I'd like to have a complete set of documentation.

 

[WOPL Sniffer]

I looked and I couldn't find anything on the PL30 board. But the again, I didn't see ANY documentation on the newest mods. the book still shows the motherboard before they actually soldered it in.

 

[Steve K]

Maybe Mark is still around!

 

[Steve K]

Should have been a pic with that post!

 

[marcok]

In the Steve' s version in Phase Linear they changed the Rca connectors ; original ones are the real plague of PL4000.
Replace them soon ! There's no documentatation of Ambience circuit , but I presume that the circuit is
very similar to PL 2000 preamp .
I restored one PL 1000 and two PL 4000 s equipped with SQ logic decoder , that is able to perform ambience function ,too
Check all caps : they must be 50V. There are some boards with 35V .

Ciao
Marco
Ps: see also my posts about PL 4000 restoration .