Transistor Testing
The Secret to a Reliable Repaired Crown Amplifier
Transistor Testing and Grading
PROBLEM
BJT transistor resistance decreases as they get hotter.
This is a problem when making big amplifiers with BJT transistors. To create higher power amplifiers (greater than 100 watts), these transistors need to be connected in parallel.
When multiple BJT devices are connected in parallel, if one of them has a lower resistance, it will handle the greatest amount of the power.
This causes the transistor to get hotter and its resistance to drop further, which requires it to handle an even larger portion of the amplifier’s total power.
This heating, lowering of resistance, then further heating continues until the device fails.
This is called Thermal Runaway.
CROWN SOLUTION
All linear topology amplifiers made by Crown use bi-polar (BJT) output transistors.
A significant part of the Crown reliability can be attributed to grading and then only using output transistors in grade matching sets, avoiding the fatal Thermal Runaway issue.
For your amplifier to perform like it did when it was new, it is very important to only use graded output transistors to repair your Crown amplifiers.
At AE Techron we conduct multiple tests on each of our BJT power output transistors before they are used in the repair of your linear amplifier. We are the only company in the world able to grade and match parts to original Crown factory standards.
How can we do this?
AE Techron purchased and uses the same custom programed transistor grader Crown used to select and match the output transistors put into your amplifier when it was new.
TRANSISTOR GRADING
What tests does the transistor grader perform?
SOA Test: This test verifies that each device we use meets original Crown Safe Operating Area (SOA) standards. Not all parts do. The rejects are set aside.
On Resistance Test: Transistors are tested and divided up into one of 10 grades based on when they turn on. These are the numbers written in felt tip on each transistor.
When repairing your amplifier, we can match the grade level of the replacement part with the parts already in your amplifier.
Your amplifier uses these output transistors connected in parallel, this test verifies that the new part(s) will share well with the original parts.
SCHEDULE YOUR REPAIR
LOCATION: We are centrally located in Elkhart, IN with next day UPS Ground service to much of the midwest.
COST EFFECTIVE: No surprises! Our bench rates and parts costs are similar to present Crown/JBL service rates.
You can reach our Repair Center by phone or email from 8 AM – 5 PM EST.
Email us at: [email protected]
Or, call us at: +1 574-295-9495
