Or should that be Odyssey?
You might be thinking that since this was the "Original Problem" that brought it here I would have tackled it first, and I did do some troubleshooting very early on this assembly.
BUT....(always one of those...) when I noticed the underrated capacitors, the extra parts on this board, the out-of-date "Service" Manual that doesn't match the "As Built" configuration, and the tuning mechanism that fell apart in my hand, et al, I knew I needed to address those issues before I continued on.
So I took care of all the other issues this receiver had before going into the Power Amp.
After carefully bringing it up on my "Variac" while monitoring the current (YAY! NO smoke!), I started checking the voltages on all the transistors. ALL of them were way off, indicating some other issues on the board. A search on the AudioKarma forum showed that this is commonly caused by some of the diodes used to bias the transistors were failing. Sure enough, two of the six diodes used were shorted, and both of the 12V Zener Diodes had failed; One shorted, and the other not regulating at 12 Volts. Unfortunately this took out a couple of small signal transistors on the board, so I have to make another trip down Substitution Lane to find some suitable, currently made transistors.
So the work continues, one step at a time......
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I worked on a Fisher 500 once. Transistor stereo designed by tube theorists. What a nightmare. Everything was direct coupled. No isolation caps, and the whole channel was pnp/npn complementary pairs. The first stage popped and POOF, EVERYTHING went.
ReplyDeleteWhat year was that one made in? This one dates to the late 70's-early 80's. Mr. Fisher sold the company to Emerson Electric, who sold it to Sanyo a few years later, so this one is a "Sanyo/Fisher". It's an obvious victim of aggressive cost cutting, from component choice to construction. Workmanship is OK, except for the repairs done by others.
DeleteMust have been late 60's. It was the first generation solid state. Replaced the 400 before it which was mostly vacuum tube. With no audio you could feel heat coming off the finals heat sink.
DeleteSome of the early solid-state stuff wasn't designed very well.
DeleteI enjoy reading about the restoration of old gear.
ReplyDeleteI built a homebrew audio power amp out of discrete parts in push/pull configuration which worked well at the time. I think I had an old Radio Shack tuner/preamp that I used. Those were the good old days.
6L6's? They can sound great with a good output transformer. The Hallicrafters SX-42 I had used a pair, and sounded gorgeous, once I recapped it. I haven't had much tube gear other than my own go through here. I fixed a Fender Twin Reverb for a guy, and a Marantz FM tuner, but that's about it. None of the Hams I've met here have known of anybody who works on, or uses, tube Ham gear. Boat Anchors just don't seem to be popular here.
DeleteIt has become an odyssey...
ReplyDeleteJust so the Sirens don't lure me onto the rocks!
Delete