This circuit is based on the classic Mullard amplifier design of the 1950's and holds with our philosophy of keeping things simple and allowing the tubes to work their magic. Even though we use factory matched KT120's, they are still different enough that individual tube bias adjustment is required. To that end, we now use the excellent AB-Q auto bias module. Bias is pre set by us and from then on will never require adjustment again. The Auto Bias module will compensate for aging tubes as well as the slight difference bewteen each KT120 power tube to keep the bias for each tube at the pre set optimum operating level for the best sound and longevity of each KT120 output tube.
Power is supplied by our own power transformer and that is custom built for us by Heyboer Transformers. It is a solid state rectified and choke input power supply followed by a CRC circuit to arrive at the various levels of the high voltage B+ required by Buddy.
A Lundahl LL1638 choke is used to ensure the best possible filtration for the power supply.
To limit inrush current when first powered up, we use an NTC (Negative Temperature Coefficient) thermistor.
Only high quality components are used in the construction of Buddy. All power supply electrolytic capacitors are Nichicon high voltage snap in caps. Film capacitors are WIMA, and coupling capacitors are Russian PIO (Paper In Oil), hand picked and matched by us from our very own collection. Resistors in the signal paths are Vishay CMF and RN low noise military spec film resistors. RCA sockets are gold plated, and speaker posts are Rhodium.
The printed circuit boards are designed in house and manufactured to FR4-TG standards. They are double layer with full ground planes on both sides to ensure complete screening of the circuits.
The power transformer is our own design, custom built for us by Heyboer Transformers. The power supply choke is none other than the superb Lundahl LL1638. The output transformer is the first class Lundahl LL1676.
Power output with 4x Tung Sol KT120 power tubes: 120Watts from 17Hz to 40KHz at less than 1% THD in ultra linear mode.
IMD: < 0.38% (18Khz and 21Khz) at rated power
Frequency response: 10Hz to 35Khz +/- 0.1dB at 120Watts
Power bandwidth: 17Hz to 40Khz +/- 0.3dB at 120Watts
Sensitivity: 1.5 volt in for 120Watts out
Damping Factor: 14
Input impedance: 270,000 ohms
Hum & noise: > 95dB below 120Watts output
Power requirement: 120VAC 60Hz; or it can be wired for 220-240VAC 50Hz;
Weight: 45lb each
Dimensions: 10"W x 17"D x 9"H