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Welcome to the Tube IMP website.
This site is dedicated to tube testing, and the promotion of a small tester designed and built in the UK for testing double triodes, the Tube IMP mini TT.This instrument is not only useful for conventional emissions and transconductance tests, but is also helpful during the design and tweaking of amplifiers, to locate optimum operating conditions in the circuit.
The tester has fully adjustable HT and grid voltages which makes it easy to calculate self bias resistors for example, plug in a representive tube, dial up the required HT voltage, monitor the cathode current, and adjust the grid voltage. The resistor can then be calculated.
The mini TT can also test gain.
Why test the gain?
The gain of tubes used in amplifying stages will produce different effects according to the type of circuit they are being used in. In open loop circuits, the gain only affects the channel balance. If the tube is used within a feedback loop however, particularly within an equalisation stage, like a phono preamp, the gain of the tube can have a dramatic effect on the overall sound of the circuit. A low gain tube could sound slow and wooly with an indistinct bass and muffled highs, where as a high gain tube which allows the feedback filtering to perform as intended, would sound brighter and crisper with tighter bass and clearer highs.Transconductance measurements
Transconductance is mainly used as a measure of how good the tubes emissions life is. Measured values can be compared to manufacturers data sheets values to find out how much life a tube has left.šIt is also useful for indicating the performance from Cathode follower output tubes, the higher the better.Home
picture of prototype