July 24, 2012 - 11:14 am|
|I built an EICO 3070 back when I was 13 or 14. I sold it years later. I have no idea if its still in use by anyone, and if my young attempts at soldering skills held up.|
As a stroll down memory lane, I purchased a 3070W. I assume that the "W" suffix means it was a factory assembled unit (correct?). BTW, I am in need of a replacement knob, if anyone has one lying around.
BTW, isn't the pic you have of the rear, showing the case on backward? Should not the end with the bent-edge go toward the rear, filling in most of that open gap?
Much thanks for a great article.
March 26, 2012 - 07:55 am|
|Hi Max, Congratulations on restoring the 3200, along with your 3070! Sounds like you have done a thorough job. On the loudness control, you could simply remove C1 and C2, to eliminate the HF boost. Though the Fletcher-Munson curves have been revised somewhat in modern times, the HF boost at low levels has remained more-or-less similar. Perhaps you mean simply that loudness switches have come to be just a bass-boost option in modern usage. In any case, I guess it is a matter of personal preference. http://en.wikipedia.org/wiki/Robinson%E2%80%93Dadson_curves |
March 26, 2012 - 01:16 am|
|Tuner now perfect. After some use, AFC was in and out - traced to a cold solder. Thank goodness too, really didn't want to have to open RF stage.|
Found a box of #49 lamps. Stereo indicator works properly now. Took apart tuning meter and glued scale back in place with contact cement. It was loose and causing needle to bind.
Very happy with the 3200 and 3700. Next time I order from Mouser will get some low noise transistors for line stage of 3700 as per your mod, it would be nice to kill the hiss completely.
Another useful mod, would be to make the loudness control boost treble less, it appears to follow an outdated curve which has excessive treble boost compared to modern loudness controls, and it limits its usefulness.
March 18, 2012 - 06:34 pm|
|I hope the 2N2219A holds up too. I will eventually do some more modifications to the amplifier, but for now am just happy to have it working again. This little amp really packs a punch - with my Realistic Mach One speakers, it has more than enough power. I've noticed it gets fairly warm after it's been operating for a while. |
I replaced all of the many electrolytic capacitors in the 3200 tuner today. With a pair of rabbit ears it's picking up all the local stations with great fidelity. AFC works too. The "stereo" indicator light was burned out, and I replaced it with the wrong bulb, so it's too dim now. Also, the tuning meter doesn't work, so I'm not done yet.
Thanks for taking the time to put all this info online, it motivated me to refurbish my old tuner and amp, with excellent results.
March 18, 2012 - 12:56 pm|
|Hi Max, Congratulations on restoring your Cortina! It's great that you were able to find suitable replacements for the drivers nearby. There is a lot to be said for using something that's handy. In a cursory glance, those seem like good choices. |
The only thing I might carp about would be the 40V max rating of the 2N2219A. I have measured the power supply as high as 45V. When the output swings low, the NPN driver can see almost the full supply voltage. However, I would expect production transistors to exceed their specs, so it should work fine in practice.
Please keep us posted on the Cortina tuner progress. Good work!
March 18, 2012 - 03:30 am|
|Cortina is back in service, after many years. I ended up using 2N2905A and 2N2219A matched as drivers on one side, because they were what I could find locally. TO-66 outputs from Surplus Sales date code 1980. Other side all transistors original. Replaced all electrolytic capacitors. New thermal grease, cleaned controls, etc. |
Amplifier sounds good. Going to take better care of it this time, tuner is next.