Each PCB holds two cathode-coupled line-stage amplifiers; thus, one board is all that is needed for stereo unbalanced use (or one board for one channel of balanced amplification). The Cathode-Coupled PCB makes building a standard-setting line stage amplifier a breeze. This assembled board with a chassis, volume control, selector switch, power transformer, and a fistful of RCA jacks is all that is needed.
This FR-4 PCB is extra thick, 0.094 inches (inserting and pulling tubes from their sockets won’t bend or break this board), double-sided, with plated-through heavy 2oz copper traces. In addition, the PCB is lovingly and expensively made in the USA. The boards are 5 by 6 inches, with four mounting holes, which helps to prevent excessive PCB bending while inserting and pulling tubes from their sockets.
Redundant Solder Pads This board holds two sets of differently-spaced solder pads for each critical resistor, so that radial and axial resistors can easily be used (radial bulk-foil resistors and axial film resistors, for example). In addition, most capacitor locations find many redundant solder pads, so wildly differing-sized coupling capacitors can be placed neatly on the board, without excessively bending their leads.
Multiple Heater Arrangements The Cathode-Coupled PCB allows either 6.3V or 12.6V heater power supplies to be used; and 6V tubes, such as the 6CG7, can be used with 12V tubes, such as the 12BH7.
Dual Coupling Capacitors The board holds two coupling capacitors, each finding its own 1M resistor to ground. Why? The idea here is that you can select (via a rotary switch) between C1 or C2 or both capacitors in parallel. Why again? One coupling capacitor can be Teflon and the other oil or polypropylene or bee’s wax or wet-slug tantalum…. As they used to sing in a candy bar commercial: “Sometimes you feel like a nut; sometimes you don't.”
Each type of capacitor has its virtues and failings. So use the one that best suits the music; for example, one type of coupling capacitors for old Frank Sinatra recordings and the other for Beethoven string quartets. Or the same flavor capacitor can fill both spots: one lower-valued capacitor would set a low-frequency cutoff of 80Hz for background or late night listening; the other higher-valued capacitor, 5Hz for full range listening. Or if you have found the perfect type of coupling capacitor, the two capacitors could be hardwired together on the PCBs via jumpers J11, one smaller one acting as a bypass capacitor for the lager coupling capacitor. On the other hand, each coupling capacitor can feed its own output, for example, one for low-frequency-limited satellites and one for subwoofers.
Multiple Input and Output Configurations The Cathode-Coupled 9-pin stereo PCB can accept either balanced or unbalanced input signals. With a balanced input signal, the Cathode-Coupled amplifier can be viewed as a balanced-to-unbalanced converter, as its output is unbalanced. With an unbalanced input signal a new option is available: a negative feedback loop that will return a portion of the output signal to the grid of the second triode in the input differential amplifier. This will lower the gain, the distortion, and the output impedance of the Cathode-Coupled line-stage amplifier.
Made in the USA PCB comes with 16-page user guide that holds schematic and design examples.