Bugera 1960 Infinium Schematic -

Here’s a technical write-up for the Bugera 1960 Infinium Schematic , aimed at amp techs, DIY builders, and advanced guitarists.

Bugera 1960 Infinium Schematic – Technical Write-Up 1. Overview The Bugera 1960 Infinium is a high-gain, 120-watt all-tube guitar amplifier head inspired by the classic “hot-rodded” British valve amp topology (e.g., Marshall JCM800 2203, but with an extra gain stage and modern features). Its standout feature is the Infinium Tube Life Multiplier system, which actively monitors and biases the power tubes individually. A schematic for this amp is essential for troubleshooting the Infinium auto-bias system, the high-voltage supply, and the multi-stage preamp. 2. Preamp Section (Schematic Highlights) The preamp is a four-stage cascaded 12AX7 design :

V1A (Input Stage): Standard common-cathode gain stage with a 2.2kΩ cathode resistor (bypassed with a 0.68µF cap for treble boost). Input grid stopper: 68kΩ. V1B (Gain Stage): Direct-coupled or cap-coupled (depending on channel switching). Cold-clipper stage often follows with 10kΩ cathode resistor for asymmetrical clipping. V2A/B (Gain & Cathode Follower): Additional gain stage followed by a cathode follower to drive the tone stack – classic FMV (Fender–Marshall–Vox) tone network: Bass, Middle, Treble. V3 (Phase Inverter): Long-tailed pair (LTP) with 47kΩ plate resistors, 470Ω shared cathode tail resistor (unbypassed), and a Presence control connected to the NFB loop.

Switching: The 1960 uses relay-based channel switching (Clean/Crunch/Lead) controlled by optocouplers or small signal diodes, all referenced to the schematic’s logic section. 3. Power Amp & Infinium System The output section uses four matched power tubes (6L6GC or EL34, switchable via a bias voltage adjust). Conventional section: Bugera 1960 Infinium Schematic

Ultra-linear or pentode output transformer (approx. 1.7kΩ primary impedance). Screen grid resistors (470Ω–1kΩ) on each tube. Negative feedback taken from 8Ω tap to LTP tail.

Infinium circuit (key for reading the schematic):

Each tube’s cathode connects to a 0.1Ω sense resistor to ground. A small microcontroller (or discrete op-amp comparators) reads voltage drop across each sense resistor → calculates plate current. Individual bias voltage is sent to each control grid via a digitally controlled analog trimmer or PWM-controlled FET. LED indicators on the front panel are driven by the same IC. Here’s a technical write-up for the Bugera 1960

Without the schematic, you cannot properly troubleshoot a failed Infinium system – for example, one tube constantly redplating despite “good” bias readings may indicate a failed sense resistor or dead IC channel.

4. Power Supply (As Shown on Schematic)

Mains: 120V/230V primary with center-tapped high-voltage secondary (approx. 450–480VAC). Rectification: Solid-state bridge (fast/soft recovery diodes) into a pi filter (two 100µF/500V caps with a 5W choke). Low voltage: Heater supply (6.3VAC center-tapped) and a separate 12V or 5V regulated supply for the Infinium logic and relays. Bias supply: Negative voltage rail (-55V to -35V) derived from a separate winding, filtered, then distributed to the Infinium control circuits. Its standout feature is the Infinium Tube Life

5. Common Failure Points (Schematic-Based) | Area | Typical Fault | Schematic Clue | |------|---------------|----------------| | Infinium PCB | One tube reads 0mA | Open 0.1Ω cathode sense resistor | | Bias supply | All tubes redplate | No negative bias voltage at IC input | | Preamp | No sound on one channel | Faulty relay or JFET switching transistor | | Heaters | Hum, no power | Broken solder joint on 6.3V center tap | | Phase inverter | Distortion at low volume | Leaky coupling cap (0.022µF) from V3 plate | 6. Accessing the Schematic Official Bugera schematics are not publicly hosted on their site, but they are available through:

Authorized Music Tribe service centers. Independent amp repair forums (e.g., The Gear Page , EL34World ) – often as PDF scans. Direct request from Bugera support for service technicians (provide serial number).