Comments for page: Eico Cortina 3070

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Posted by Max H February 22, 2012 - 04:34 pm
Hi Steve,

Thank you for your response! I never really thought of the Cortina as classic, but you may have changed my mind! I have the matching FM tuner for my Cortina as well, and the pair made a nice compact hi-fi setup. I rescued the pair from my dad's uncle (who bought them new) in the early 1990s, changed all of the large electrolytic capacitors, and used them for a while before the accident. I was actually searching for info on the tuner when I stumbled across your website.

I found that surplus sales of nebraska has the RCA 40312 for a very nice price, provided I can make their minimum order, etc. I was planning to make an order to Mouser for another project anyway, so adding the other components to fix up the EICOs will have a very low incremental cost.

http://www.surplussales.com/semiconductors/Transistors-SCR-3.html

An additional motivaiton for this project is that the recent increases in the cost of electrical energy motivated me to acquire a plug-in watt meter, of the type used to measure power use of appliances. Apparently my all tube hi-fi setup uses almost 450 Watts just to sit idle! At current electricity rates and with how often I use the stereo, that translates into about $6 per month, or $75 per year.

Considering the trouble I've gone to to change all the lights in my house to CFL, and other means to reduce energy consumption, it seems appropriate to revive the EICO for non-critical music listening.

I will add a comment once I've made some progress. Thank you for the excellent website.

Best Regards

Max

Posted by Steve L. February 22, 2012 - 03:40 pm
Hi Max, Yes, good TO-220 replacements would have been SO much easier to find. The issue, of course, is the physical mounting. I guess you could remove the socket, bolt the TO-220 to one of the TO-3 holes and solder wires to the TO-220 leads. Of course, you would need to use a TO-220 insulating kit.

The only engineering downside I see is the fact that the TO-220 would have about half the contact area with the chassis, that the TO-3 does. That could increase the effective thermal resistance. I don't know how significant that would be. In my case, I wanted to restore the unit close to the original for historical/aesthetic reasons.

I imagine that you saw the section "Matching Power Transistors" on page-1. There, I recommended a beta match of 20% or better. In the final results, we found that the channel with the new, higher-beta transistors performed much better than the other one. That indicates that the design is significantly affected by the output transistor (and driver) beta. Hence, a substantial unbalance in beta between the positive and negative driver/power transistors would be expected to increase distortion. Of course, the better the match, the lower the distortion, until other factors limit the result. If the transistors are unmatched, the variation could easily be 50% or more. I hope that you decide to bring the Cortina back to life. If you have any further questions, I will be happy to help.

Thank you for the interesting questions.

Posted by Max February 22, 2012 - 02:45 pm
I've had one of these sitting in a box since the mid 90s, when one of the output transistors shorted due to my carelessness. Very interesting to read your project. Had you considered using TO-220 output transistors as replacements? Also, how critical is matching of output transistors?

Posted by Steve L. October 28, 2011 - 08:39 pm
Thanks Andres. Very kind of you to say that.

Posted by Andres F. October 28, 2011 - 07:29 pm
Good job. Congratulations Steve

Posted by Steve L. October 27, 2011 - 09:36 pm
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