Phase Linear 4000 Autocorrelation Preamplifier, Phase Linear 400 Amplifier and two OEM wood cabinets. We prefer to sell as a set, and would require a premium to sell by the piece.  Both the 4000 and the 400 are in working order, with some minimal signs of use due to age. One cabinet is better than the other, please see photos.  DALAUDIO has serviced these units several times over the last few years (see below). We recently took these in on trade as we know quite a bit about them. Our customer was downsizing and purchased a restored vintage receiver. Please see all photos.  
 
Cash Sale No Holds Call or Text for Pick-Up – No Shipping.
 
The 4000 was a collaboration designed by Bob Carver and Bill Skinner designed to expand or decompress the sonics of recorded material, to create more dynamic headroom. The 4000 had the capability of controlling up to six components: a tuner, two tape decks, two turntables and an auxiliary input. The 4000 was manufactured from 1973 to 1977. This unit, a later serial number as shown in photos, was made in 1976 and signed internally after testing. The unit list price was $600, later models, like this unit, sold for about $675.
 
The Phase Linear 400 amplifier was also designed by Bob Carver. At  200 watts per channel and a price tag around $500 it was quite popular. The 400 was introduced in 1972,  and it appears this one was built around the same time as the 4000 in 1976. The 400 featured twin output meters. It has six output transistors per channel, plus two drivers per channel, right below the output transistors. The heatsinks have a large surface area. 
 
How DALAUDIO serviced these units:
- Changed foam on the chassis cover that holds the PC boards , the foam is holding up well.
- All internal PCB boards have been recently removed and inspected. The Molex connectors cleaned (both male and female to the main board). These Molex connectors between the daughter board and motherboards are a well-known source of trouble, as well as solder joints on.
- Capacitors and other components: Some caps that were problematic have been changed. It has not been “re-capped” – as the customer only wanted those that were an issue replaced. We are happy to do it, but it’s very expensive ($200 parts/$400 labor). Capacitors are checked with an in-circuit testing device (Huntron Curve Tracer) and then ESR Meter (BK- 879-B) for telltale signatures of failure. These devices help us test caps, diodes, transistors, resistors, and more in -circuit without having to remove them first.  
- We checked both power supplies, a common source of failure for preamps and amps.
- All switches, selectors, and potentiometers are cleaned with CAIG in a multi-step process. quality contact cleaner, and then re-test all functions for any signs of noise or scratching. Bulbs are replaced with stock type units.
- Testing: We power up the units, run a series of precision sine waves through all inputs, monitoring output levels on our oscilloscope for distortion on both the high and low signal levels. We connect the amplifiers outputs to “dummy loads”, so as to not affect speakers until we verify them.
- Obviously, we then listen to the units after this step and describe what we hear, as best we can. All functions, inputs and selectors were double checked.
 
Note: With all the above actions risks can be somewhat minimized. Please keep in mind, these units have not been completely restored. The prospective buyer must understand that there is still a significant risk that the units may develop issues in the future. Even the most complete recap kits we have seen only address 20% of the total components in these units!  
 
Specs from The Manual and Literature:  
Phase Linear 4000
Frequency response: 20Hz to 20kHz
Total harmonic distortion: 0.25%
Gain: 65dB (MM), 15dB (line)
Signal to noise ratio: 72dB (MM), 83dB (line)
Semiconductors: 45 x transistors, 9 x IC, 57 x diodes, 2 x zener regulators, 2 x LED
Dimensions: 19 x 7 x 10 inches
Weight: 18lbs
 
Phase Linear Model 400 amplifier:
Power output: 210 watts per channel into 8Ω (stereo)
Frequency response: 20Hz to 20kHz
Total harmonic distortion: 0.25%
Damping factor: 1000
Input sensitivity: 1.7V
Signal to noise ratio: 100dB
Output transistors: 12 silicon power transistors, each rated at 150 watts
Cooling: Large heat sink structure