Topic-4: Search and Destroy

I was off on vacation for a week so there’s some catching up to do. For starters, I am going to post some links and, over time, come back and explain in more depth how these links can help you…

OBSOLETE PARTS?
As mentioned, upgrading opamps in the audio path can a bit of a mine field. But not ALL opamps are in the signal path – the side-chain of vintage dbx compressor-limiters, for example, have opamps that do all sorts of fun stuff. So, when an opamp’s functionality is circuit-critical, check the manufacturer’s website first, because sometimes you can get lucky and find a compatible replacement.

As the link shows, the LM308 has been DISCONTINUED, but to the right is a link to the LM308 DATASHEET as well as it’s replacement – in the ALSO RECOMMENDED box – the LM8261. You’ll want to download the datasheet for both parts…
POWER SURPRISE
Power Supplies are often the weak link in many products, not necessarily by circuit design so much as the lack of consideration of how heat shortens life over long periods of time. In general, electronics components should not be so hot as to burn, but ‘too hot to fail’ happens all too often, especially when you consider how often rack gear is mounted with no space in between. Over time, parts just burn themselves out.
RECTIFIERS Convert AC to DC and there are many types, from Half Wave to Full Wave, Single Voltage to Bipolar as well as Voltage Doubler.

Can You NAME THAT RECTIFIER?

Once AC is converted to DC it needs to be regulated – it must tolerate variations at the power outlet – it can’t sag when the Air Conditioner or Heater comes on and must be there if the device being powered demands more juice.
SIMPLE REGULATION
Theses days, pretty much every solution comes as a single Integrated Circuit or IC, with a minimal amount of support parts. But if you work on vintage Gear, you’ll see many Variations on the Regulation Theme.

If you ever wanted to know more about regulated power supplies, National Semiconductor published this useful FUNDAMENTALS pdf.

CAPACITOR CONFUSION
Back in the vacuum tube daze, capacitors were big enough to tell you alot about themselves. Then, large and small value caps relied on color code. Now reading and translating much small conventional (axial or radial) capacitors can be confusing, because limited space forces manufacturers to abbreviate. It’s even crazier with surface mount (SMT) parts. I’ll be posting a chart soon, but in the meantime, here’s a cool link that explains alot about what some of the abbreviations mean. Note that some of these abbreviations might be on the schematic as well.

more to come…

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