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Lee, You didn't mention which board you were touching so I will assume it is the Rev D board and not Don's DCP. Follow the disassembly procedure in the Phase Linear 400 service manual..... "Remove the (2) hold-down nuts from the Rev D board, flip the circuit board over and gently pull towards...

Lee, Now that you've repaired the amplifier..... Did you ever get a chance to re-test the amplifier at rated output both channels driven 20Hz-20KHz? Ed

When Dean worked on Phase Linear 4000's he would send a set of unpackaging instructions along with the preamp.

I have never been a big fan of mechanical connections. Particularly after my experiences with Molex connectors on Phase Linear 4000 pre-amplifiers. I also have never been a big fan of double-sided through hole plated pc boards. In many cases you have to decide whether to try and save the board...

Marco, Yes there were problems with the rear connectors (RCA jacks) cracking and breaking. The early 4000's that used Molex connectors between the front panel pc board and motherboard had issues. Most of these units did not have the slide out bottom cover like the later units had which also...

Marco, Lots of comments and questions from your (3) posts. It will take a while to reply to them all. I took a look at my (2) 4000 series 1 (Lynnwood Washington) owner's manuals and indeed they incorporated the comments about the "extra long connectors". However, I didn't see anything about...

Joe, Regarding TO-3 style sockets which were used in Phase Linear 400's and 700 series amplifiers: The first generation of sockets Phase Linear had square corners were made by (United International Dynamics Corp) UID Electronics division of AMF (UID part number PTS-10E). UID had a number of...

Lee, As a side note: Larger wattage resistors are less noisy than smaller wattage resistors. Ed

I only took a quick look at the documentation I have for the Rev D before I typed my previous posting. What resistor size is for a quasi-comp and which was used for a fully comp? I thought the 10 ohm was quasi and the 44 was for fully-comp? Where did the 22 ohms come in? So is it that the (2) 44...

Marco, I just acquired an early Edmonds, Washington version of the 4000 owner manual. In it is a single page "Phase Linear 4000 Addendum" I have never seen before which talks about a number of things including the following: I. "PHONO PLUGS: The phono plugs with extra long center connectors...

Lee, With amplifiers that have blown, I have found the "Octopus Tester" (a.k.a. "component tester") to be a handy device to find/locate leaky semiconductors quickly. It is particularly useful when 1 channel is good and the other is bad. Simply going back and forth between channels and looking...

Amar Bose died in 2013

Lee Is this a Rev D board? If so, is R78 a 44.2 ohm 1/4 watt resistor? Ed

Ouch! I wouldn't expect that into 8 ohms both channels driven. I might expect it into a 4 ohm load. Particularly if the Zobel network resistors are to low a wattage. If the amp is a 400 series 1 with 5 amp B+ and B- fuses you might consider going from 5 amps to 8 amps like they did on the 400...

Lee, The frequency response of most Phase Linear amplifiers was rated at 1 watt into 8 ohms (or 2.83V output) +0 / -1dB Ed

I would love to see the numbers at rated output (either 200 or 210 watts per channel) (approx 40 volts output) into 8 ohms both channels driven at the same time from 20Hz to 20KHz. Ed

Marco, I have 4 versions of the owner's manuals. Two from when they were in Edmonds, WA and two from when they were in Lynnwood, Washington. I only have 2 of the 3 service manuals I am aware of. I have the 6/76 and 6/81 versions. I do not have a copy of the "fast field service manual" which...

I've already give away much of what knowledge I have of Phase Linear for free. How many people would really be interested in a book on Phase Linear? I think there would be a larger market at the moment for something else that I have experience with. Ed

Marco, I just went to take a look at the 3000 and 3500 owner's and service manuals: The 3000 series two owner's manual: page 9; "LOUDNESS SWITCH" Push in to activate loudness contour circuitry; used to compensate for apparent low frequency loss at low volume listening levels. page 12...

Marco, I revised my previous post and am elaborating further here...... If my memory (after approx. 20 years) serves me correct, the explanation provided to me by Dean about the units built after S/N 2500 which had a boost at 20KHz of 2 to 4dB (and a increase at 20Hz of 7 to 10dB?) may also...