Comments for page: Eico Cortina 3070

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Posted by Max H February 25, 2012 - 08:06 pm
Hi Steve -I sent you an email. Let me know if it didn't go through.

Posted by Steve L. February 24, 2012 - 02:33 pm
Hi Max, Yes, the good ol' 667 should do the job. I used to use that transistor test function before I bought the Peak unit. Will be interested to see the pix. I hope that you will post a link. BTW, my email address is on the About page. May I have yours?

Posted by Max H February 24, 2012 - 12:53 pm
An engineer from Jensen did an interesting article about the Sweet Sixteen concept, in Audio magazine a year or two after the original PE article, complete with a lot of measurements. It can't really be fixed by eq, it has awful comb filtering, a large midrange peak, very little low bass, and basically measures like a loud table radio. The frequency response errors could be corrected using DSP or eq, but it would probably just end up killing the efficiency of the system, and over powering the little drivers below their resonant frequency.

So you are right, it's more about a project than about creating a hi-fi speaker system. I also think it might sound good with music which was mixed to sound good on cheap table radios and phonos, since it basically will have the same frequency response. (i.e. early rock music)

I was trying tro figure out how I will measure the beta of the driver transistors to match them, until it struck me - my EICO 667 tube tester also tests transistors, and will directly measure Beta. Using an EICO to fix the EICO is cool. Of course I will follow your advice and use higher current for the output transistors.

This weekend I'll put some high resolution photos of my units on a photo hosting website. I was comparing the multiplex board from memory, so I am not surprised I was a little bit off. It's very smilar though. There are some small differences between my 3070 and yours, for example the woodgrain cover on mine has a lip folded on the back side, which makes it look a bit less flimsy from behind.

Posted by Steve L. February 24, 2012 - 08:32 am
Max, A little postscript: Close comparison of the 3566 multiplex board with the one pictured on the 3200 catalog page shows that they aren't actually identical (though similar). The 3200 version appears somewhat smaller and the arrangement is a bit different.

Posted by Steve L. February 24, 2012 - 08:15 am
Hi Max, I remember the Sweet-16 article from when I was a kid. Of course, the harsh reality was that putting together 16 poor speakers did not make a good speaker. There is also the issue of the directionality of a large area radiator. But please don't let that heartless logic intrude on your project dream! Hey, we never said that our hobby made any practical sense! Maybe you could make a silk purse out of that sow's ear, like I did with a few tweaks on the Cortina. EQ anyone? (Bose did it.)

The Eico 3566 on eBay is fascinating. Interesting observations about the OEM speculation. I will have to re-write that paragraph . Strange how they mixed cord wood style component wiring with PCBs. The power amp is clearly an earlier design, as it uses driver transformers. Doesn't appear to have a PCB. I would be tempted to go for it, except for various factors (price, condition, etc.)

Posted by Max H February 23, 2012 - 04:03 pm
The Lil Tiger is a neat project. I miss the hobbiest magazines, I wasn't around for its heyday, but was a subscriber to Popular Electronics for the last ten years of its existance. I had a similar experience with the JLH 10 Watt class "A" amplifier I built (speaking about paying for electric heat!). It's amazing how quickly one little slip can destroy every transistor in a DC coupled amplifier. Good thing 2N3055s are so cheap!

One PE project I intend to build in the somewhat near future is the January 1961 "sweet sixteen", more out of curiosity than anything else. Just need to find a source for the 16 speakers. Who knows, maybe it will be matched with the Cortina.

There is an EICO 3566 receiver on eBay right now. The internal photo shows that the RF, IF, and multiplex boards are identical to those used in my Cortina 3200 tuner. So the 3566 must be an Eico product, rather than OEM. The power transformer also looks very similar to out Cortina amplifiers, but the power section is completely different.


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