How to test a Bi-Directional Triode Thyristor

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Discussion Overview

The discussion centers on testing a Bi-Directional Triode Thyristor (commonly referred to as a Triac) used in a Carver model M-1.0t stereo amplifier. Participants explore the functionality of the Triac in relation to the amplifier's AC input control and power regulation, as well as methods for testing the device both in and out of circuit.

Discussion Character

  • Technical explanation
  • Experimental/applied
  • Debate/contested

Main Points Raised

  • Some participants suggest that the Triac serves as a safety feature or power control mechanism before the transformer in the amplifier.
  • Others propose that the Triac regulates the power supply and that forcing it on could lead to damage due to potential faults downstream.
  • One participant mentions the importance of measuring the gate voltage across R409 to determine if the Triac is conducting, noting that a typical gate voltage can range from about one to four volts.
  • Several methods for testing the Triac are discussed, including using a light bulb in series and measuring voltage across the device in both circuit and out of circuit configurations.
  • Concerns are raised about the possibility of the Triac failing due to asymmetric firing, which could lead to overheating of inductive loads.
  • Participants express uncertainty regarding the normal operating conditions of the Triac and the implications of its failure on the overall functionality of the amplifier.

Areas of Agreement / Disagreement

Participants have not reached a consensus on the best approach to test the Triac or the implications of its failure. Multiple competing views on its function and testing methods remain present throughout the discussion.

Contextual Notes

There are limitations regarding the understanding of the normal gate voltage for the Triac and the specific role it plays in the amplifier's operation. Some participants express uncertainty about the schematic and the implications of various testing methods.

Who May Find This Useful

This discussion may be useful for individuals interested in electronics repair, specifically those working with audio amplifiers and power control devices like Triacs.

  • #151
Referring to posts #146 (by Jim) & #147 (by Tom) above, the speaker current feedback seems to be explained here:

Particularly in the graphs at the bottom of post #5.
Small Amp Project (Tube/power stage info needed)
 
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  • #152
Good eye Tom !

I hadn't caught that in the Carver,
i only assumed they used current just to invoke a power limit.

But it's right there on the block diagrams , page 8 of service manual.
And specification page says
Damping Factor Greater than 9 - Tube Characteristics

Thanks !