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Does the PL400 Capacitor Upgrade Kit work in all Phase Linear 400 Amplifiers?
It works in all but the earliest PL400s.  The earliest PL400s produced had the power supply capacitors mounted directly to the left side of the amplifier chassis using 2 round capacitor brackets.  The rectifier bridge was also mounted to the chassis side in this amplifier vintage.  The White Oak Audio Capacitor upgrade WILL NOT install in amps of this vintage.  The kit WILL install in any PL400 that has the transformer mounted with the aluminum die cast bracket that incorporates both the capacitor cradle and bridge rectifier mounting.  This includes the Phase Linear 400 Series II although due care must be taken in the series II amplifiers because the front panel LED logic boards in this series of amplifiers leaves very little room.
Does White Oak Audio have a Capacitor Upgrade Kit that works in Phase Linear 700B Amplifiers?
Not at this time.  The Phase Linear 400 series of amps used a very obscure 1.75" diameter capacitor which are no longer in volume production making reliable, high quality replacements very hard to find, especially at a reasonable price.  This void in market availability is what drove White Oak Audio Design to develop its popular replacement kit based on readily available 35 and 40mm diameter snap in capacitors.  The Phase Linear 700B uses a much more standard capacitor size which allows users to find quality, high reliability replacements with comparable ease in the market in the original computer grade format.  If market conditions change, White Oak Audio Design will respond by introducing a kit to satisfy this application.
Does the PL400 LED Light Board work in all Phase Linear 400 Amplifiers?
It works in all but the earliest PL400s (but is not applicable for the PL400 Series II).  The earliest PL400s produced used 2 fuse type incandescent bulbs above the upper edge of each of the VU meters instead of the 4 grain of wheat style incandescents that installed into holes in the lower edge of the later Dixson or the less common Honeywell VU meters. Generally speaking, if your amp has a Phase Linear PL18 light board in it, the White Oak Kit will work in your amp. The White Oak Audio PL400 LED Light Board Upgrade Kit WILL NOT install in amps using the fuse style lamps above the meters.  The kit WILL install in any PL400 that has the PL18 PC board.  The PL400 LED Light Board Upgrade kit is NOT APPLICABLE for the PL400 Series II.
How do I test my VU meters to know that they are working properly?
It is easy to test your VU meters.  Using a 1.5V AA cell battery and a 3.9K ohm resistor, attach the negative side of the battery to the minus terminal of the meter.  Attach the positive side of the 1.5V battery to one side of the 3.9K ohm resistor.  Attach the other side of the 3.9K ohm resistor to the plus terminal of the meter.  If the meter is good, the needle should move to approximately the -4 dB meter position on the meter scale.
Can I send my amp to White Oak Audio Design to have it upgraded if I cannot perform the upgrade myself?
Generally speaking, White Oak Audio Design is NOT in the business of installing upgrades in Phase Linear amplifiers. White Oak Audio Design's business is designing and marketing high quality upgrade products for installation by DIYers or by a qualified service professional.
We do work with and rely on qualified upgrade and repair professionals to install our upgrade products. These professionals are well versed in White Oak Audio products and are master upgrade technicians that perform quality repairs and restorations.
  • Western US Region: Lee Laatsch of Laatsch Production Services in Gillette WY (contact us if interested in getting in touch with Lee Laatsch).
  • Eastern US Region: Mark Lucitt is a former Navy electronics technician located in Northern Virginia (contact us if interested in getting in touch with Mark Lucitt).
  • France and surrounding European Region: Atlantic Audio Vintage (contact Alain Limas at Atlantic Audio Vintage)

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