Also check out this page for more info on your amp:
http://www.metaxas.com/pages/products/solitairex.html
This passage seems possibly relevant:
3. OUTPUT TRANSISTOR BIASING: The SOLITAIRE has 4 pairs of output transistors and when 'biasing' the amplifier it is wise to check the biasing of ALL the output transistors to ensure that one or more of the devices are not conducting more current than the others. This is especially important when replacing a power transistor. Also check the different biasing currents between the NPN and PNP devices. If there is a large discrepancy, replace the 'driver transistor' (also mounted to the heat sink).
http://www.metaxas.com/pages/products/solitairex.html
This passage seems possibly relevant:
3. OUTPUT TRANSISTOR BIASING: The SOLITAIRE has 4 pairs of output transistors and when 'biasing' the amplifier it is wise to check the biasing of ALL the output transistors to ensure that one or more of the devices are not conducting more current than the others. This is especially important when replacing a power transistor. Also check the different biasing currents between the NPN and PNP devices. If there is a large discrepancy, replace the 'driver transistor' (also mounted to the heat sink).