The EICO 150 Solid State Signal Tracer redux, part 3: Replacements.
Wednesday, May 27, 2026 at 05:45:40
The EICO 150 was back on the bench tonight for some transistors. I started by adding a new terminal for Q4’s output, meter tie point, and transformer input.
I replaced Q4 with a NOS NTE152, new grease, and a new mica insulator of the proper size. Yeah, I got some shiners on the wire there, I tried to be careful but even my orange stick went through the insulation. I’ll get some nail polish and touch those later to coat the wire.
The part I used was an EGC152, which is the same thing as an NTE number, as NTE purchased the ECG line from Philips way back when, who in turn had purchased the line from Sylvania.
Q3 also was replaced at this time, with a generic 2N3906.
I did some noise testing to see what was going on now:
Noise levels had calmed down substantially:
There was still too much noise, so I went ahead and replaced the other two transistors.
Noise levels calmed down to what I would consider just background nosie. So are modern transistors that much better, or were these simply dying? Well, I replaced Q4 with a device that’s barely 10 years older than the one in there, so it’s certainly not “modern” - I’d have to guess that the transistors were simply breaking down from years of abuse. The Internet seems to think that these are a “replace with capacitors” item for this unit, so maybe there’s some truth in there.
There’s a little more to do, I want to make some measurements for posterity, and adjust the meter drive a little - you really have to crank the gain to get meter deflection, much like an eye tube unit. I want to dial that back some so a comfortable listening level gives noticeable deflection.
Back to the transistors, here’s what I pulled out of the unit:
Q1:
Q1 was originally an EICO number, but the previous owner replaced it with an SK3124, twice. I assume that’s because they blew it out by connecting input to B+ on a tube device. I used a 2N3391A as it’s replacement.
This part would have been an EICO part as well, but it had a Motorola HEP 726 instead. This is a generic AF transistor, ala 2N3904, etc. I used a 2N3391A as it’s replacement.
Here we have our first EICO part. This is the complement to the output transistor, and as such is PNP. Almost any PNP AF transistor will work, but may have to be selected to reduce or prevent oscillations. I used a 2N3906 which seemed to work well.
Here’s the big boy. It’s some EICO number, un-cross-referenceable. It’s an NPN power transistor, almost anything with a few watts of dissipation and an hFe of 100 or so will work here. I used an NTE/ECG152 on the suggestion of the Internets. It recieved a new mica insulator and new grease as well. The old insulator was just a little round piece of mica and the previous owner delicately balanced it under the transistor.
I’m happy with the noise levels here, all I can really hear now is the hum from the power supply. There’s a few things left to do, I want to measure voltages for posterity, and adjust that meter level some. One more part, and then final thoughts. Stay tuned!
References
Youtube playlist: https://www.youtube. … yAcib71v-995pS_-4jDr
Manual: https://wereboar.com … 0and%20Parts.pdf.zip
Fixing the speaker: https://wereboar.com … -and-final-thoughts/
Next part of this series: https://wereboar.com … ah-that-doesnt-work/
Previous part of this series: https://wereboar.com … rt-two-measurements/
Wrapup and final thoughts: https://wereboar.com … -and-final-thoughts/