Many hours of testing in class A single ended amps and demanding push - pull circuits; such as the AC30, show it to be the way to go if your amp likes to eat tubes. ... With EL84 's, the Fender Pro Jr. was loud and punchy. Switch to the EL844's and cool stuff starts to happen. At the same settings the distortion was now very nice. Mullard 3-3 is a quite popular 3W electron tube amplifier introduced by Mullard Ltd in 1955. A schematic and the design details of this amplifier are available in the book “Circuits for Audio Amplifiers” by Mullard Limited 1959 and in the book “Hi-Fi Amplifier Circuits” by E. Rodenhuis 1960 Philips Technical Library, and also in the National Valve Museum website article. These pair of Groove Tube EL84 tubes provide clear and harmonic tones that any tube amp connoisseur would enjoy. Groove Tubes GT-EL84-S Duet. $44.95. FREE Ground Shipping. Groove Tubes GTECC83S Select Preamp Tube. These pass every Groove Tubes premium certification for microphonics, hum, physical characteristics and function. Quite simply the. Notes: The above examples of possible combinations are to help you narrow down the choices of transformers for your favorite tube types. How you operate the tubes (push-pull, push-pull parallel, ultra-linear, class, B+, bias, operating points, etc.) will change optimum plate to plate load impedance. Power Tubes. Power tubes, or output tubes, continue to amplify the signal sent from the preamp section so they can drive the speakers. Each set of power tubes will draw a different current (measured in milliamps), affecting how fast the signal gets passed through your amp. The speed of this current will have a big impact of the tone of your.