| 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 |
| 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. |
| Posted by Steve L. | February 23, 2012 - 01:48 pm |
| Hi Max, Bear in mind that when you replace the drivers, their betas should be matched. Well, the paralleling story is understandable enough. While the typically low feedback in tube amps lets you get away with it, I'm kind of uncomfortable with it there, too. Anyway, nothing to be embarrassed about. All part of the learning process. I had a trying experience with an amp, when I was in high school, too. I was building a SWTPC amp kit called the L'il Tiger, for a friend. It had a circuit somewhat like the one in the 3070. http://www.swtpc.com/mholley/PopularElectronics/Dec1967/PE_Dec1967.htm Due to various problems, we had gone through two sets of output transistors. Finally, we got it all working, and turned it off. I had the cover and a screwdriver in my hand and was about to put it on, when the screwdriver slipped out of my hand and fell into the amp. I thought I saw a little spark, from the charge left in the power supply cap. Breathlessly tried the amp again--sure enough it was dead! A defeat snatched from the jaws of victory! To this day, I'm very nervous, holding anything metal above a solid state power amp! :) |
| Posted by Max H | February 23, 2012 - 12:52 pm |
| I plan to replace all electrolytics in both tuner and amp. Like you I'll get a full set of transistors for both channels, just to be on the safe side. It's a shame the little ones on the driver board will no longer say RCA on them, but at least it should be functional! To be honest, the reason the amp has sat so long, is I am a bit embarassed by how it got damaged in the first place. When I was still in high school, I was frequency sweep testing a speaker, and decided that more power was needed. Why not put my recently re-capped EICO in mono, and parallel the speaker outputs? It worked very briefly, then fuses blew, and goodbye EICO. I knew enough about electronics even then to know it was a bad idea, but I thought hey, you can parallel a Dynaco ST-70, this thing should be able to handle it too! I realized there was some risk involved, but assumed that worst case I'd blow the fuses. New fuses did nothing, and now the voltage measurements were all off. At the time I was more interested in tube amplifiers, so the EICO was put into storage. The tuner stayed part of my system for years after, but eventually it stopped working properly, and was replaced by a Pioneer. I'll worry about the tuner once the amplifier is working. I have experienced what you are talking about with small electolytic coupling capacitors. The worst device I have ever worked on for this problem, is a Phase Linear 4000 preamplifier. It must have 100 1uF capacitors in it, and nearly all of them on the verge of failure. I replaced them one at a time, and gave up on it for the time being. Some day it will be a rebuild project too, but for now I am appreciating the more minimalist EICO. |
| 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. |