My Knight KG-686 signal generator is missing one transistor (never installed), and John Kusching (thanks) helped me yesterday determine that another one is bad. The bad one is marked 131, then below that, the Motorola symbol and 744. Reading the assembly manual, it seems that both should be the same part number.

The NTE book lists the 131 as a NTE108 which is an RF amp. The 744 crosses to an NTE128 which is an audio driver. I don't think these crosses are valid for your application.

The assembly manual shows a part number of 660-131 for both transistors. That comes up as NTE123AP, a NPN audio amplifer, or switch. One of them, TR-6 on the schematic, serves in the 100kHz oscillator (internal crystal calibration section), and the other TR-2 on the schematic, serves as a E. F. (whatever that is).

In this case, "744" is most likely a date/lot code from 1974.

Rich

I'd think E.F. is simply an emitter follower.

Keeping NPN for NPN etc, have you tried subing whatever you have on hand?

Unless you are working with VHF/UHF, low noise, or power amplifier devices, there are usually a lardge number of devices that will work well. Often those substitution types are a GROSS approximation of what the original device was, and most any device will work well enough.

I don't have any transistors, so have nothing to substitute. I could take one from a pocket radio, but it works, so I'll order some from Mouser and see what happens.

When you consider that a few hundred substitution part numbers manage to subsitute for thousands of different parts, there HAS to be a lot of compromise in many cases.

FStephenMasek .-
Just today piked one KG-686 for rebuild.
Please can you suply a manual´s copy ?

correo@candiles.org

Thanks