[Photo] accurate bile duct matching method

April 22, 2020

Regardless of the configuration of the final stage of the amplifier, the power amplifier tubes must be strictly matched (that is, the single-tube single-ended class A machine, the parameters of the two-channel bile duct should also be as consistent as possible). This paper introduces a dual-tube same-screen same-grid test method, with simple circuit and high accuracy.
The principle is as shown in the figure below, using the bridge balance principle, without the need for output transformers and inverter circuits, the specific requirements are: 1. The difference between the resistance of two 500Ω resistors should be ≤0.1Ω (military wire wound resistors can be used); 2. The filament voltage must be the rated voltage of the tube under test; 3. The screen voltage should be the same as the screen voltage of the production circuit. The grid voltage is continuously adjustable from -100 to 0V without the need for voltage regulation. The working principle is: the difference between the screen flow of the two tubes ΔIP is proportional to the reading of the voltmeter V1, that is, ΔIP = V1 / 500. V2 is used to measure screen current (tube consumption), and V3 is used to measure grid voltage (both can be measured with table V1). Examples of static and dynamic pairing: 1. Insert the tube and preheat for two minutes, add the screen pressure, and observe the reading of V1. If V1 ≤ 1V, then ΔIP ≤ 2mA, it can be considered as a paired tube. If V1 ≤ 50mV, the two tubes measured at this time are already the best pair of tubes. The screen flow can be selected at several points (continuous adjustment of grid voltage) within the allowable tube consumption to further match the test; 2. Adjust the grid voltage, input the audio signal at the IN terminal (the audio signal generator can be produced in accordance with the "Electronic News" 1997 edition of the "Speaker Parameter Amateur Test"), observe the V1 reading, and also use a double-track oscilloscope to hang on the anode Observe the waveform (this can find the best AC working point of the bile duct), and the dynamic matching is good, which is helpful to reduce the fundamental wave and nonlinear distortion. The reading of V1 below 200Hz should be ≤1V, 200 ～ 500Hz should be ≤500mV, and 500Hz ~ 5kHz should be ≤250mV. If it is a four-pole or five-pole tube, the curtain grid pressure should be added for testing; if it is a direct heating tube, the voltmeter V1 should preferably use a pointer meter.




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[Photo] The manufacture of bile duct integrated power amplifier

This article introduces a "

Posted at 2006-04-15 13:05 • 766 views
[Photo] The manufacture of bile duct integrated power amplifier
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