"Stealth AX"

12AX7 Pre with 6BQ5/6GK6 Output Tube Amplifier


This is the assembled Stealth AX PCB. After doing the design, layout, routing and artwork here the raw PCBs were ordered from an overseas board house, then assembled back here with parts from Mouser. Notice the extra size 2.4mm thickness to prevent flex during tube insertion. It's built like a tank.


Stealth AX is a modernized update to the power section of Harmon Kardon's A224 "The Trio."

A cathode current mirror under the power tubes insures such exact DC balance through the OPT that even ungapped line transformers can be used.

To maximize gain and minimize distortion V2A's plate load is directly bootstrapped by the cathode connection to V2B and positive feedback, further increasing gain, is obtained by feeding R12 into R6.


The original Stealth AX fitted with SPECO T-7010 line transformers


Stealth AX refitted with NOS Harman Kardon OPTs

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