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 Part Identification. Correct Me If I'm Wrong......

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ve1arn
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PostSubject: Part Identification. Correct Me If I'm Wrong......   November 25th 2018, 9:42 am

Pulling some parts off some old circuit boards here and have what I am assuming is a glass diode.

Looking at some color code charts, it looks like a 1N14A. However, the 2 brown lines are different shades. Any help and education here would be appreciated.

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Cliff Jones
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PostSubject: Re: Part Identification. Correct Me If I'm Wrong......   November 25th 2018, 2:52 pm

If they are different shades of brown one of them is probably a faded red, or its an in-house color.
Black designates Cathode and is always read left to right. You can also test for voltage drop with a digital meter. .2 to .3Vdc for germanium & .6 to .8Vdc for silicon.
Just use the standard resistor color for reference.

My guess would be 1N142.
Look up the data sheet on line.
I will add more from some of my browsing.

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ve1arn
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PostSubject: Re: Part Identification. Correct Me If I'm Wrong......   November 25th 2018, 3:23 pm

Thanks Cliff.

Here's the link I looked at for the codes. Maybe I should have looked at more than one link. Embarassed

Diode Color Codes

I'll do the voltage tests tomorrow when I am back in my radio room.

Thanks again! Smile
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Cliff Jones
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PostSubject: Re: Part Identification. Correct Me If I'm Wrong......   November 25th 2018, 4:44 pm

I think its all linked to the same graphic.

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ve1arn
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PostSubject: Re: Part Identification. Correct Me If I'm Wrong......   November 28th 2018, 2:13 pm

Hi Cliff, tested all 6 of them that I scrounged from the boards and they are all Germanium.

Into my Germanium storage bin they go.
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Cliff Jones
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PostSubject: Re: Part Identification. Correct Me If I'm Wrong......   November 28th 2018, 5:46 pm

were they all the same color bands?

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ve1arn
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PostSubject: Re: Part Identification. Correct Me If I'm Wrong......   November 28th 2018, 5:50 pm

Yep, all the same color bands with the same 2 shades of brown or red. Me thinks you're right on the diode number too. Smile
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Cliff Jones
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PostSubject: Re: Part Identification. Correct Me If I'm Wrong......   November 28th 2018, 7:27 pm

Great. I have a question. Just in case you do have the book (Sams Photofact Publication).

Title: Practical Transistor servicing (PTC-2) by William Caldwell. Second Edition.

I am kind of stumped at how he gets some math figures that I cannot verify.
I'm sure he was using either a slide rule or by longhand method.
My calculator is close but not that close.
My problem is I may be not looking at all the parameters.
It's very simple transistor Schematic of part of a Radio.
The paragraph is titled Actual Radio Voltages.
on page 106-107 its a diagram Figure 5-15 of a portion of the converter and audio driver.
If you don't have this paperback, that's OK.
It even shows meter probe points and the values diagrammatically

Heres what the book says
Quoting-


Page 106. Actual radio voltages.
In Figure 5 - 15 the 2n252 converter has a 4,700-ohm resistor R 4. In the lead Between the emitter and the 8.3 -Volt “A “line. Collector current flowing through the resistor causes a drop of 1.3 volts across R 4. , leaving 7 volts on the emitter. . If the 2N252 transistor were not conducting, no voltage would be dropped across R 4 and the emitter reading would be considerably higher.
The line. Voltage divider R 2 - R 3. Keeps the base voltage about 2/10 of a Volt less positive then the emitter, as is customary for most PNP circuits. As mentioned previously, however, some PNP converter circuits operate with the bias reversed- that is, the Base may appear to be more positive than the emitter as long as the oscillator is also oscillating. If the schematic calls for a reverse bias between Base and emitter, that is one way to tell if the oscillator is oscillating. The only reason for a bias reversal in this type of circuit is that the oscillator signal is sometimes strong enough to reduce the emitter voltage below normal. If the oscillations are stopped, the bias will return to a normal forward bias.
 
The oscillator tank circuit sends its Signal voltage to the emitter through a 1,000 MicroMicro Farad Capacitor C6 Where the signal is detected by the emitter diode In Figure 5-15., however, the oscillator does not cause a bias reversal.
The Collector circuit contains 2 transformer windings - 1.2-ohm oscillator feedback winding and the 7.5. – ohm I.F. primary.  Neither coil has sufficient resistance to Cause any noticeable voltage drop, so the Collector voltage reads zero period. Figure 5 - 15 also shows the audio driver stage, which employs a 2N403 transistor. The collector has an audio transformer, winding with a DC resistance of 440 ohms. thus, a voltage drop of .4 volts is produced as the collector current passes through that winding. This causes the collector voltage to read .4 Volt positive with respect to ground.
The Emitter of the driver transistor is tied to the. 8.3-volt line.  Through R 14, and 7.5 Volts are measured at the emitter. Base resistors R 12 and R 13 Keep the base slightly negative with respect to the emitter.
Without pictures its hard to see.
The supply is 9 volts through a 220 ohm resistor whence it becomes + 8.3 volts (A Line)
Here’s the first voltage divider
R12 =3300 ohms tied to the A line of + 8.3 volts
R13 =22K ohms to ground on one end and tied to the base of audio driver which shows 7.3 volts and that’s tied to a block diagram of the second I.F.
 
 
6.8 volts shows connected to the base of the convertor 2N252
There is a resistor R 3 of 8200 ohms that taps off of + 8.3 volts and connects to R2 of 39 Kohms (one side to the base of the converter 2N252) and the other end of that resistor ties to ground. Hence 6.8 volts.
That’s part of the circuit I am having calculations that don’t match up

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Rod Clay
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PostSubject: Re: Part Identification. Correct Me If I'm Wrong......   November 29th 2018, 11:10 am

Cliff,
Well, all the voltages as listed look ok to me. There is a .2 volt Base Emitter drop on both the converter and driver stage as you would expect for germanium transistors. The converter is forward biased in the example and does not appear to be operating at reduced or "reverse bias" as the author said could occur with strong oscillations.
73, Rod  WB6FBF
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Cliff Jones
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PostSubject: Re: Part Identification. Correct Me If I'm Wrong......   November 29th 2018, 12:51 pm

Thanks Rod
Last night I stayed up working on the math. The currents had to be found by voltages and resistance calculations.
I started by making a pencil drawing of the circuit. Then I made a list of the applicable resistors and following that from the designations on the schematic. One thing I added was Identifying the voltages by a V1, V2, V3, ect. and listing them with the printed voltage along side.

Then I started to analyze what formulas were needed. That was the difficult part for Me.
I ended up using the 9 volts as a starting path through the resistor (R18, of 220 ohms) in series with the supply voltage.
I used the method of subtracting the supply (9volts) from the "A" line voltage of +8.3 volts.
That answer I found was used as the voltage drop ( 0.7v ) across R18.
then used the E/R = I which was .7 / 220 = .0035a
So that was the maximum allowable current.
then i did the same voltage subtractions with the remaining voltage differences.
This is where I stopped. It was 12:30 in the evening. I was getting tired at that point.
I will get on it later in the afternoon .
So I am just in the training stages of repairing portable radios. I am prepping myself by developing a pattern to use in diagnostic methods. Making schematics, Identifying resistances and parts designations into a list. Same with voltages and currents. Funny thing is I had Solid-state Courses in college back in the 80-90s. Has it been that long? Rolling Eyes I don't remember a cotton picking thing. Embarassed
---------------------
Forging ahead. Have a lot on my plate. Especially on my computer with consolidating Hundreds of PDF files ( 6,590 according to my windows explorer) and almost a Hundred Excel workbooks 96 to be exact, with many duplicate sheets in many workbooks not including Text and word files. Reducing those to a more controlled environment.
Organizing my inventory records for radio components, Test Equipment, Radio related books and Service manuals. One problem is sorting what class of file goes into what folder because of many topics in each book .
Such as it it a fundamental book or is it a formula and calculation folder? Or is it Ham radio related Folder, or theory, or servicing or Troubleshooting and the list goes on.
Then i still have to start sorting all my gear, tools, books, Test equipment and Radios of course.
So I am getting off my recliner, turn off the TV and get busy. bounce

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Rod Clay
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PostSubject: Re: Part Identification. Correct Me If I'm Wrong......   November 29th 2018, 3:56 pm

I thought the writers description of the voltages in the circuit was the key to understanding it and what to look out for in a real radio. 

I also studied solid state electronics back in the 1980s at what was then Memphis State University. We looked at biasing transistors, voltage drops, amplifiers, oscillators, and power amplifiers. These could be of the class A, B, C, and D types for Bipolar junction transistors. In some later classes we did some design work.

Interestingly, bipolar RF power amplifiers of the class C and D types do not need any initial biasing of the base-emitter junction to operate. They get all their drive requirements from the previous stage. So the writers comment about biasing receiver oscillator stages and what you might get in measuring the voltages in a working circuit got me to thinking. 

One thing: I would expect you would need to use a high input impedance probe with a VTVM or FET VM to measure any voltages in the oscillator circuit so you don't upset it. Standard for tube circuits.

The other thing was that it might be possible to design and build a class C solid state oscillator stage without any initial base-emitter bias. Usually such circuits require something to get them going. In tube circuits it is a bit of random noise, the positive feedback mechanism, and the oscillator's biasing network (gridleak resistor/coupling capacitor combination) that ensures the control grid is driven positive for part of the cycle in class C operation.

Well, in one class project, we had to design an AM superheterodyne radio. In particular, we had to determine the power output requirements for the oscillator stage yet we were given no guidance on this. As far as I can remember, I designed the oscillator stage to be able to deliver 50 milliwatts thinking this would be enough injection to the mixer stage. It was just a guess. Good enough since it was accepted by my professor.

For my oscillator circuit, I used conventional biasing as you would in any class A amplifier stage. I used the standard two resistor network as the writer described to set up the base-emitter biasing circuit to establish the emitter current. The collector current will be slightly less than the emitter current being equal to the emitter current minus the base current. As a practical matter, we would assume that Ic was equal to Ie in small signal amplifiers. 

73, Rod  WB6FBF
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Cliff Jones
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PostSubject: Re: Part Identification. Correct Me If I'm Wrong......   November 29th 2018, 9:02 pm

His book starts out on ;
1. understanding the transistor
2  circuit components and their functions
3.  learn to troubleshoot AM transistor radios
4.  learn to troubleshoot AM-FM transistor radios
5.  normal transistor voltages
6. defective voltages and their meanings
7.  testing transistors
8.  troubleshooting AM automobile radios
9.  troubleshooting AM-FM automobile radios
10. case histories of actual troubles.
NOTE: No math that's complicated if any at all.

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