| Posted by Steve L. | February 23, 2012 - 08:20 am |
| Hi Max, Yeah, what would we do without the Net? Ironic that the pinnacle of modern technology is such a boon to supporting vintage audio. On the channel with the good output transistors, one would suspect the drivers, of course. In the tuner, the German sourcing is reminiscent of the vacuum tube HFT9X series, in which the RF tuner was a cast-aluminum module, made in Germany. The one time I ventured inside, I found an amazing a 3D sculpture of components. I tip-toed back the way I came... :) I have found that the larger Eico electrolytic caps are pretty reliable, though filter caps might need to be reformed. Sadly, those little 2uF caps (and similar) are a different story. Those are among the few components that I replace en masse. Ceramics should be fine. |
| Posted by Max H | February 23, 2012 - 01:56 am |
| Dug out the EICO. On one channel, both output transistors are shorted. Other side blows the fuse, but the output transistors test okay. Going to order parts before I continue to troubleshoot, but thankfully the design is simple enough there's only so many things which could be wrong. Took the cover off the tuner. Electrolytic filter caps have a date code of 1967. Tuner is interesting - the RF and IF sections are made in Germany, and with only the multiplex board and power supply made by EICO. Tons of capacitors to replace, mostly axial 2uF electrolytics on the multiplex board. Glad you got the transistors from Surplus Sales - isn't the internet great? |
| Posted by Steve L. | February 22, 2012 - 07:26 pm |
| Hi Max, That is a great find! Thank you so much for posting about Surplus Sales of Nebraska. I just ordered ten units for myself. Have dealt with them in the past but didn't look there searching for the transistors. Google didn't find them at the time, either. It's neat that your great-uncle bought your amp and tuner new. Glad that you're going to save it. By the way, there is a Summary of Modifications on page-2, in case you didn't see it and want to make sure you have all the parts (for the things you choose to do). And yeah, those vacuum tube amps don't get any awards for efficiency. But at least in the winter, when the heat is on, you can be consoled by the fact that 100% of the energy goes into heating the house. One might carp that electric heat is more expensive than fuel-based heat but at least the energy doesn't go to waste. (Of course, summer is a different story!) |
| Posted by Max H | February 22, 2012 - 04:50 pm |
| Just ordered 10 units of real RCA 40312 from surplus sales for $1.50 each, plus shipping... their min. order is now $10. I should be able to get a pair out of ten units, hopefully same date code. |
| 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. |