15 December 2013

4S Universal Preamplifier for 12A_7 Tubes

The 4S Universal preamp is a Super Simple Single Stage (4S) line stage preamp that works well with the entire range of 12A_7 tubes - 12AU7, 12AV7, 12AY7, 12AT7, 12AZ7, and 12AX7. You can change the tube type to vary the gain of the preamplifier by quite a large margin. 

4S Universal Preamp for 12A_7 Tubes
4S Universal Preamp for 12A_7 Tubes
The preamp uses a 6CA4 tube rectified power supply which is very quiet. The preamplifier is built using point-to-point construction techniques and into a die cast aluminum enclosure from Pomona.  The attenuation control is on the output of the preamp.

4S Universal Preamp with 6V6 Lacewood Amp
4S Universal Preamp with 6V6 Lacewood Amp
The 4S Universal is a preamp that can be adapted to the task at hand simply by swapping tubes. It also allows some tube rolling to compare various tubes in your stash. The 4S Universal preamp is a great little unit to really bring out the most in your power amps.  For full details see the 4S Universal Preamplifier Project pageComments and questions about this project are welcome in the 4S Universal Tube Preamp Project (12A*7) thread.

Super Simple Single Stage (4S) preamp with Genalex Gold Lion 12AU7
Super Simple Single Stage (4S) preamp with Genalex Gold Lion 12AU7
The photo above is one of Mark's Super Simple Single Stage (4S) preamplifier builds.  For more information see Mark's 4S Universal Preamplifier for 12A?7 Valves.

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