The EICO 150 Solid State Signal Tracer redux, Wrapup and final thoughts. : comments

The EICO 150 Solid State Signal Tracer redux, Wrapup and final thoughts.

Monday, June 1, 2026 at 09:44:23

Working with this unit has been interesting, especially with the original problem of being a shorted speaker. But, for now at least, the unit is operational but still has some issues to solve later on.

What’s going on?

After the speaker replacement, there was simply a lot of noise. half a volt of noise, to be exact. This was unacceptable, and there were two potential causes - the transistors, which most say to replace with the capacitors, or the carbon composite resistors.

The transistors helped considerably, but only Q3 and Q4 - this reduced the noise levels to about 1/4 of the original, as received value. That’s pretty good, Q4 was noisy and replacing it with a (not really much newer) transistor cleaned that up. The rest, unfortunately, it probably coming from resistors and I’ve read posts indicating that metal film resistors here help considerably. That will be another project later in the year.

Beyond that, I changed the meter drive level. The meter on the front is simply a mechanical version of an eye tube. That is, it’s not calibrated in any way, it’s just deflection. You really had to drive the thing hard to make it move, and I wanted that to happen at a lower input. Paralleling a resistor with the input resistor has allowed that to happen, and it’s placed as such it’s going to be easy to remove should I or a future owner want to bring it back to spec.