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 Transistor circuits

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Cliff Jones
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Join date : 2010-11-22

PostSubject: Transistor circuits   April 21st 2012, 1:33 am

Here two books in PDF covering a total of 200 transistor cicuits

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FrankB
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PostSubject: Transistor radios xistor & cap probs.   August 5th 2013, 11:40 pm

Here are a couple of tips on the xistor radios:
No audio or weak audio- check for bad elect. coupling cap to volume control. -In view of the age of many of the radios, replacing all the electro caps is not a bad idea. most will check out bad with ESR.

No audio- Also check that dandy little earphone jack for corroded or tarnished contacts. Another common problem. This holds true for home stereos too.

Germanium xistors are starting to fail with great regularity. I fixed one car radio that had 3 Shocked  bad. Seems to be a contamination or internal breakdown problem causing leakage.

On subbing xistors: I have thousands of salvaged xistors. Trying to organize them by number has been a nightmare- not to mention taking up mass space in drawers.
The easy solution is to get an ECG/TCG/NTE cross ref. book or download the program from NTE.
look up the cross for the xistor you have and put under their cross ref. number.
Then when you need a specific type, it will be in that drawer.

Take careful note though- the cross ref is a generality and the ratings may be different than what you need. Look up the original specs for that part you need. The cross ref is only to aid in sorting and storage. The NTE parts often have higher ratings than the part they replace. Suspect 
Use your common sense and verify ratings or you can let the factory smoke out of the parts.

Now there is a program I found someplace on the 'net that shows what the ECG/TCG/NTE parts "real world" part number is. You can buy the real world part for a fraction of the NTE parts price! Often several dollars savings on just one part.

Remember: Universal replacement semi's" are not always "universal".

On any Sony product, especially TV sets use OEM SONY parts ONLY. They designed the circuits to work with a SPECIFIC set of values; ie: gain, leakage, etc.
Failure to do this can result in more substantial damage in the set.
(I knew a TV tech and his partner that had a shop and put in $175.00 wholesale cost worth of "universal " parts into a Sony TV. It would not work with them. This was in 1970's money- which is like $500.00 now or more.
Replacing the parts with the originals FROM SONY would have solved the problem quickly.)

The following is MY own opinion borne out after many years of service headaches.
Many of the suppliers offer "original" part numbers under the SK brand name. Run away from those.
Every one I ever used failed either immediately or within a day or two. They seem to be substandard/ out of spec/ counterfit parts.

There are many sites on the 'net that do sell counterfit/ re-branded/ out of spec parts too. Remember that price is not everything. Having to go back and repair a failed part costs ytou time, money and fustration.

There are a couple of reliable suppliers out there for OEM quality semis. B&D Enterprises is one (they stock excellent grade caps for TV sets and SMPS applications too; and have some very reasonably priced cap kits). The other is Electronica. Both totally backed what they have sold to me. Any problems were solved immediately. Neither company has "sales drones" their people know what they are talking about, and what they are selling specifically for your application.

Lastly, a GOOD ESR meter is your best friend for finding bad electrolytic caps on xistor radios and TV sets. I have tried many, and prefer the Capacitor Wizard. Also be sure to buy the over voltage protection kit for it.
My Capacitor Wizard came with a COMPLETE schematic and troubleshooting guide, unlike many of the competitors models. It also uses an analog meter, which I have found is easier to use than the LED readout ones. Its also great for measuring low ohmage resistors and coils. The meter makes it quite easy to find intermittent connections also.
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