Description

Two pairs of matched On Semi / Fairchild KSC1845, for input section of Adcom GFA-535, GFA-545, GFA-555, and many other amplifiers. Matching is performed at 1mA collector current. Includes copper foil tape and heat-shrink tube for thermal bonding.

Contact me if you need transistors matched for a different collector current, for a different amplifier. Labor charges apply for special matches. In my experience, transistors matched at 1ma will also match well at higher currents.

Thermally bonding the input transistors:

The transistors should be thermally bonded, so their Vbe and Hfe will track with heat.

Wrap the copper foil tape around the pair of transistors. Be careful the foil doesn’t touch any leads.

Some transistors pairs have their faces front-to-front and others are front-to-back. Observe the component outlines on the board.

No thermal paste! It’s not needed, and might eventually seep oil onto the board, which attracts dust. The copper foil does a great job keeping the transistors tracking thermally.

Install the transistors and heat-shrink around them.

Snip the tops of the heat-shrink.

This is the jig I use to find the matching pairs of transistors. Read all about it here on this thread at DIYaudio.com.

I match the devices to within 1% on the jig, with the fan keeping their temperatures even, and then confirm that result with the transistors thermally bonded in still air. Assuming the rest of the amplifier is running well, with the inputs shorted, you should see less than 20mV on the outputs of a GFA-5×5 MKI, and less than 5mV on a MKII. (MKII has a DC servo, so the DC offset you see at the output is not an indicator of good matching.)