The Analog Bros. Model 42 is a single channel, medium power (approximately 35 Watts), solid state rectified amplifier with a pair of push-pull, fixed bias EL34 tubes configured as triodes. It was conceived as a minimum signal path design with no integrated FX or loops available. |
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The story of the Model 42 picks up where the Model 32 left off. We were looking for a “flat out”, hard rocking amp tone and again searching for minimum component count and low TSR. Playing through our collection of “classic” amps, one thing we found was that we tended not to use the amplifier EQ controls beyond a very small range. One of our favorite amp is a 1950s Fender Champ. It would be difficult to find a simpler, better sounding circuit than this. An on/off switch and a volume control are all that there is, with one 12AX7, one 6V6 and a tube rectified power supply. Though the output power is limited by the single ended 6V6 power stage, the tone is about as pure as can be. Playing this amp through a 4x12" cabinet surprises many of our clients! While the actual volume produced when running a 6 Watt output into a very efficient cabinet with as large a radiating area as four twelve inch speakers is pretty impressive, we wanted to go a bit further and add some impact. We turned to another favorite “large” tube, the EL34. Rather than wire them as pentodes for maximum power, we wired up a push-pull pair as triodes. We found this configuration smoothed down the top end response and still put out sufficient power to meet our design goals. In most cases 50 Watts is the absolute maximum useful power level and in many cases it is still way too much. Triode wiring at the power supply voltage and output transformer ratio we used results in between 30-40 Watts, which we felt was just about right. With the goal of no front panel EQ controls, this both simplified and complicated the design process. The tone was pretty much left intact not having to go through the insertion loss and subsequent recovery amplification of a passive EQ stack, but was still not “right on," having a bit of high frequency rasp. We came up with a fixed feedback network around the first gain stage that in conjunction with some other fine tuning resulted in the tone we were looking for. We could have settled on just the pre-amp volume control and left it at that, but decided to experiment with our frequency compensated beta control in the power amp section. This provided just the right degree of versatility. The Model 42 is extremely interactive with the guitar used. Subtle changes at the guitar in either volume, pick up selection or tone roll off, and the playing dynamics and touch responsiveness, are enhanced and much more apparent than with many other amps where complex circuitry isolates the source and imposes its own overly dominant signature. The Model 42 consists of a two stage, frequency compensated pre-amp feeding a high gain phase splitter. This drives a push-pull pair of triode configured EL34 output tubes. A fairly stiff, well de-coupled solid state rectified power supply maintains constant voltage during high output conditions. Standard Features: Front panel standby/operate switch Output amplifier beta control A variable line level output (1/4" unbalanced) which is useful for slave amping, direct connection to recording or reinforcement consoles, tuner output, etc. Optionally, we offer an additional low-impedance, transformer-coupled balanced output on a 3 pin (Pin 2 Hot) XLR-3-F connector with ground lift switch. The Model 42 head is available in the following configurations:
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