Dynaco / Dyna-Kit PAS 3X Tube Preamplifier

18 Feb

 Dynaco / Dyna-Kit PAS 3X Tube Preamplifier

Designed by Ed Laurent and introduced by Dynaco in 1966, the PAS series of stereo amplifiers are renowned by audio enthusiasts the world over.

As with many Dyanco products, the preamplifier was sold under the Dyna-Kit name for $69.95 as a build it yourself kit.  There was also an option to buy it fully assembled for $89.95.

Check the back panel of your PAS preamplifier - if the speaker binding posts and RCA jacks are attached with screws, then it was originally built as a kit.  If there are rivets, you have a factory wired unit.

During the PAS production years, Dynaco sold over 100,000 PAS-2, PAS-3 and PAS-3X preamplifiers.

The difference between the PAS-2 and PAS-3 preamplifier is the PAS-2 has a flat brass faceplate with plastic knobs, and the PAS-3 has a silver anodized faceplate with metal knobs, otherwise both preamps are the same.

The PAS-3X preamp has a revised tone control circuit which takes the tone controls out of circuit when set to the flat position.

More specs and pictures after the break.


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Tubes:

4 12AX7 (ECC-83);

1 12X4;

1 selenium stack.

The PAS preamplifier from Dyanco is made up of 5 essential parts. 1.) A power supply is one part and is common to both channels. This power supply contains a full-wave rectifier and a power transformer. A separate rectifying system is used to provide direct current to heat the filaments of the tubes. This is one of the reasons why there is practically no hum in the Dynakit.

The remaining four sections have several functions. There are equalizer-amplifier stages: high-gain circuits designed to bring up the level of such devices as magnetic phonograph cartridges and at the same time to impose the proper playback characteristic on the frequency response. There is one of these stages for left and another for the right stereophonic channels. The remaining two sections consist of the two amplifying-tone control stages, one for left and one for right channel. High level signals such as those from a radio tuner are fed through these stages, and the functions of volume control, tone control, and similar control functions are accomplished at these points in the circuit.

Differences between Pas-2 / Pas-3 and the 'X" versions:

There are two main circuit differences between the earlier PAS-2 and PAS-3 units.
1.)  The "X" version had tone control potentiometers that were constructed to be electrically removed from the circuit when set to their flat position.

2) A 1uF electrolytic capacitor was placed in each channel’s tone control circuit to block the DC from reaching the audio output.

Dynaco Pas-3X Preamplifier

 

Dynaco Pas-3X Preamplifier

 

Dynaco Pas-3X Preamplifier

 

Dynaco Pas-3X Preamplifier

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