Home Mike's Geeky Stuff Amplifiers



The UC6550 is a tube amplifier operating in either triode or ultralinear mode with selectable degrees of feedback. Below is the front and back panels. Each knob and plug will be explained.

amp screen


Emergency Shutoff - This is only to be used in emergencies, such as a tube glowing bright red, or sparks, fire, etc. It only kills power to the tubes. Use the power switch on the Power Supply to kill all power.

Input - Self-explanatory

Feedback - higher feedback decreases distortion and output impedance, both desirable effects, but you will have to turn the volume knob higher if you use higher feedback. Try different settings to see which you prefer. If you use the ultralinear setting (see below), you will definitely need higher feedback.

Volume - manual control. The knob actually turns when the remote control is used.

Arduino Reset - Do not use. This is only used during programming of the Arduino at the factory. :)

Arduino Input - This is only used during programming of the Arduino.

Data Screen

Bias Adjust Knobs - adjust these until the cathode currents on the main screen are close to equal and around 60ma. Adjust slowly, as the cathode currents respond slowly to adjustments. Also, only make adjustments when there is no sound coming from speakers and after at least 10 minutes of warmup.


Topology - IMPORTANT! DO NOT change Topology settings with the power on - arcing could occur across the switch and damage it. Two settings:

Inputs - This corresponds with the switch on the front panel. Note that the top row is RIGHT and the bottom row is LEFT

Speaker Jacks - Be sure that the COM wire corresponds with the COM wire (usually black) on the speaker. The other wire should be plugged into either 4 ohms or 8 ohms, depending on your speakers. Most speakers these days are 8 ohms, unless otherwise indicated on the speaker. Note again that the top row is RIGHT and the bottom row is LEFT. The connections shown below are for 8 ohm speakers.

amp screen

Ground Screw - This is just a ground point for all circuits in the chassis. It serves no purpose and is not dangerous to touch.

Power Cord Input - a little confusing to use, but once you get everything lined up, its not too bad. Gently rotate the power cord until the tab is at the bottom and insert gently into the amp input. Rotate the plastic locking nut to secure it.

amp screen


Just a cheapo remote. Eventually will upgrade to a more substantial one. Self-explanatory.

amp screen