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  1. walid1

    Audioguru FM Tx

    In fig3 seems to be that figure u use to determine hfe vs the operating IC. Figure 4 is to determine hie. tell me how exactly u use them, and if VCE or frequency is defferent from specified in the curve, how can I use them. thanx.
  2. walid1

    Audioguru FM Tx

    Hi audioguru because I have 4 figures, I'll make this question into two. From What you said:"You should never assume Vbe in a transistor circuit that has a low emitter voltage. It is typically 0.62V on my datasheet." I can understand: 1) Are u tell me to go to datasheets only when determining...
  3. walid1

    BJT biasing formulas

    I understand from your reply that mine is true.
  4. walid1

    BJT biasing formulas

    It is ok, when we come to design such amp, and when choosing Av we must take other things into account at the same moment, that things are the IC value and the VBE value. example: u want Av=10, then u have many values of (RC/RE) which = 10, like 10K/1K, 4.7K/470, 1k/100 .. etc The difference in...
  5. walid1

    Audioguru FM Tx

    I want now to analyze the 1st stage of this Tx according to the discussion in autir's BJT biasing formulas: VCC=5V, RC=10K, RE=470, RB1=160K, RB2=30k The voltage gain Av=RC/(re+RE), but since RE bypassed ==> Av=RC/re, where re = 25m/IC. VB=5*RB2/(RB1+RB2) ==> VB=0.79v assume VBE=0.65V...
  6. walid1

    BJT biasing formulas

    Hi audioguru, What did you mean by the following: 1) Odd resistor values 2) Select the RC and RE resistors first AND why u audioguru tend to make VE very small like 2mA*100ohm=0.2V. I see many circuits in that the VE is greater than 1 volt. WHEN IC is big (10mA), we use a transformer power...
  7. walid1

    BJT biasing formulas

    Hi lets do it again, I'll design a new one close to autir's: Decisions: Vcc=9v, 2N3904 transistor of hfe=230 typically and VBE=0.65v Av=20, VCE=4.5V, IC=10mA Calculations: IB=10m/230=43.5uA, Idiv=10*IB=0.435mA Rc=20RE, VCC-VCE=IC*(RC+RE) ====> RC=428.6ohm and RE=21.5ohm VB=VBE+IC*RE  = ...
  8. walid1

    BJT biasing formulas

    yes autir, Arab food has these "side-effects" but appear after 40 years, so be aware to not have any dog in your house. I hope u enjoy with arab food and thank u for these feelings. I'm from Gaza-Palestine 
  9. walid1

    BJT biasing formulas

    I read carefully autir's design and audioguru's reply and my comment is: If I disregard the low values of R3&R4 for a moment I can say that autir do a good job in organizing this subject and make it more direct. I'll continued autir's design after these lines in the .pdf file (age 2): By...
  10. walid1

    BJT biasing formulas

    IF i have a class a amp with o/p z = RC = 2K ohm and there is a second stage connected to it what the best Zin value of this second stage to not loaded the 1st one is it true Zin2 >= Zo1
  11. walid1

    BJT biasing formulas

    You don't answer this question that i asked before; The voltage gain of this amp = RC/RE, where Re not bypassed. What would this gain be if RE bypassed? thanks. Staigen gains 289 posts by sending 289 Hehe....hoho haha hehe isn't funny!
  12. walid1

    BJT biasing formulas

    Hi guys I learned English through reading Electronic books and articles, so I can talk in this subject. I other sides of English language I'm very weak and depend totally on my dectionary. I want to tell Audioguru something about his new PC like WAW but the language limit my feeling. I want to...
  13. walid1

    Audioguru FM Tx

    So if I want to build this Tx using a mic from a radio/cassitte, then i must put R1 = 4.7K and not 10K, or what would you say?
  14. walid1

    BJT biasing formulas

    Hi Alun I miss u .... I this have petium 1 133MHz PC since march 1997, it is 1300$ that days, today it is less than 100$. I can't buy new one pentium 4, not only for money but because this PC satisfies all my requirements with less problems. Audioguru, have 486 PC So i agree with u that AUTIR...
  15. walid1

    Audioguru FM Tx

    hi all Audioguru: "Half the supply voltage across the mic determines the resistor's value." Walid: lets calculate it:         R1 = 0.5VCC/0.5mA = 2.5V/0.5mA = 5K, not 10k why?
  16. walid1

    BJT biasing formulas

    Hi Autir I downloded this ZIP file and when opening it in WORD97, the document looks like this: EMBED Equation.3  14,28 Ohm. R3=20 EMBED Equation.3  EMBED Equation.3  EMBED Equation.3  285 Ohm. By Kirchoff's second law, the voltage drop across R2 will be VBB=VBE+IC EMBED Equation.3 ...
  17. walid1

    BJT biasing formulas

    The voltage gain of this amp = RC/RE, where Re not bypassed. What would this gain be if RE bypassed? thanks.
  18. walid1

    BJT biasing formulas

    Dear Audioguru, This may be the last question to complete this circle of questions, but i expect u also want to finish this. you said this statement: "A 10:1 ratio in a voltage divider doesn't allow the divided voltage to change much when a low gain transistor causes a 5:1 ratio or a high gain...
  19. walid1

    BJT biasing formulas

    Hi If Zin=R1//R2//(hfe*(re+R4)), where re=25mV/IE, then re = 25/0.55=45.45 Zin = 330k//47k//(230*(45.45+1000) Zin = 330k//47k//240.45k = 35.13K as audioguru said 34.9K Augioguru, why u think this slight difference. I tryed all combinations of 26 instead of 25 and 0.45mA instead of 0.55mA and...
  20. walid1

    BJT biasing formulas

    Hi audioguru u told me before that IE= 0.55mA was wrong and IE actually = 0.45mA please, make another figure like the first one marked "s transistor.png " with the wright numbers. thank you.
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