UNIT-III TUNED AMPLIFIERS:

:Coil losses — Unloaded and Loaded Q of Tank circuits — Analysis of Single tuned amplifiers,

double tuned amplifiers, Stagger tuned amplifiers — Instability of tuned amplifiers — Stabilization

techniques — narrow band neutralization using coil — Broad banding using Hazeltine

neutralization — Class C tuned amplifiers and their applications — Efficiency of Class C tuned

amplifier.

3.1 COIL LOSSES:

At high frequencies careful consideration must be paid to the design and construction of the

oscillator.

Factors which are not serious at lower frequencies rapidly become important as the frequency is

increased.

Not all tubes are satisfactory as crystal oscillators at frequency greater than 18MHz. With some

tubes, especially the pentode types, the crystal may be effectively shorted out by the high input

capacity.

Others, having a low feedback capacity and a large electrode spacing, do not operate efficiently.

High frequency triode tubes, such as the 955, 6J5G, HY615, 6E6 and RK34, are the best for all-

around performance.

Pentodes, in general, are not to be recommended although some types can be employed in the

Tri-tet or a modified Pierce circuit with fairly good results.

Parallel feed of the oscillator is seldom successful due to the difficulty of obtaining really good

r.f. chokes.

This means that the tuning condenser will be at a high potential and must be insulated from

ground.

The somewhat common arrangement of inserting a mica condenser in the tank circuit to block

the d.c. voltage so that the tuning condenser can be grounded is not particularly satisfactory;

Mica condensers have appreciable losses at very high frequencies and, if w carry circulating

tank current, there may be a serious drop in power output.

All r.f. leads must, obviously, be short and direct.

By-pass and tank condensers should be of the best quality.

To minimize tank circuit losses, the coils should be self-supporting and wound with heavy

copper wire or tubing.

The low plate impedance of the recommended triode tubes necessitates the use of a high-C tank

for maximum power output.

Along with the increased output, the high-C greatly improves the circuit stability; in fact,

pentode stability is approached when the proper tank values are chosen.

The cathode tank of the Tri-tet must also have a relatively high C, inasmuch as the oscillating

portion is a triode.

LOSSES IN FETS:

With the improvement in high power MOSFET‘s of late — lower gate charge,low loss gate

structures, and much improved frequency capability — it has become more possible to

employ these ―switch mode‖ devices in rf generators at medium hf.

The objective is to improve the ‗power density‘ (W/m3) and efficiency of the equipment.

The most common problem associated with this application is getting the matching right.

For the gate drive side it is matter of obtaining an efficient and repeatable match to a very

small impedance.

On the drain side it is a matter of choosing a proper operating class and power goal for the

device and then designing a network to provide repeatable and cost effective realization.

The discussion below outlines the procedure for both The Input The gate of &power

MOSFET can be modeled as a series RLC circuit

The C is the specified Ciss from the data sheet at the desired operating supply voltage.

The R is the effective series resistance, ESR, of Ciss and includes dielectric losses, gate

metallization (or poly silicon conductor), and bond wire conduction losses.

L is essentially bond wire inductance, generally package specific.

The resonant frequency of this RLC for large switch mode devices is usually in rniddle hf

range, 1.0-30 MHz, and the Q fairly high.

Effective gate C in an amplifier is increased through the action of the capacitance.

Generally the 50 or 25 volt value is a good place to start.

The gate ESR is seldom specified on the data sheet.

Measuring this on a bridge 5V of static bias with the drain-source shorted will yield a

reasonable value.

This value is highly dependent on the die geometry and fabrication process and varies

widely between manufacturers of otherwise similarly specified parts.

The higher this resistance is the lower the frequency limit for efficient , and the more power

will be dissipated in the gate structure.

The gate parasitic inductance is generally between 5 and 15 nH depending on manufacturer,

package and die size.

The circuit topology chosen for the drive is a ferrite loaded transformer with single turn

secondary.

Adjustment of the resonant frequency is one using a series capacitor if the frequency is too

low — it usually is if the device is large.

The gate referenced to ground or bias is supplied through a resistor shunting gate to source.

The procedure for designing the input circuit is fairly straight forward.

The circuit is constructed using calculated and published values.

Using an match indicator connected to the drive input connector, the circuit is energized

with normal drain voltage, and the circuit is adjusted for best match at the operating

frequency.

The match indicator can be anything from a network analyzer to a noise bridge.

The requirements tare that it not inject enough signal to turn on the device and it must be

sensitive enough to indicate a match to the driving impedance.

The number of primary turns is adjusted to bring the input impedance real part close to 50Ω

and then resonate the resulting total inductance by adjusting a series capacitor.

In cases where a smaller device is used and the input capacitance is insufficient to resonate

at the operating frequency, it may be necessary to add a small inductance.

Any loss in the capacitor is drive lost and heating and resulting drift.

However, if the capacitor is large enough the loss may be acceptable, or even desired if the

gain of the amplifier is already too high.

Further, lossy capacitors reduce the Q of the in and thus increase the bandwidth and lower

the tuning sensitivity.

The circulating current is high. Several capacitors in parallel will provide adequate power

dissipation if high D caps are used and will offer a simple means of adjusting the value.

3.2 QUALITY FACTOR:

3.2.1 Unloaded tank circuit:

When the frequency is varied in either direction of resonance the impedance diminishes rapidly.

The impedance peak is less pronounced when the resistance in parallel resonant circuit is large

than when small.

This is due to the fact that a large resistance consumes a considerable amount of power and

draws a relatively large line current

In general it is desirable to have a resonant curve as sharp as possible, in order to provide

necessary selectivity to discriminate between different frequencies

The sharpness of the resonance curve is determined by the quality factor called the Q factor.

The Q factor is defined as the ratio of the reactance of either the coil or the capacitance at the

resonant frequency to the total resistance of the circuit.

Mathematically,

since XL = Xc at resonance, both the expressions result in the same value.

Q is a measure of the ratio of reactive power in the tank circuit to the actual power dissipated in

the stored resistance.

The higher the Q the greater the energy stored in the circuit compared with energy lost in the

resistance during each cycle.

Consequently higher the Q higher is the efficiency.

The quantitative performance of the parallel resonant circuit is easily evaluated by means of the

Q factor.

The higher the Q of the parallel resonant circuit, greater is its resonance impedance and

circulating current(12) and the smaller is the line current.

3.2.2 Loaded tank circuit:

A tank circuit may be used for coupling radio frequency amplifier to a resistive load.

This circuit is shown in the figure. Here the radio frequency energy from the tank circuit (in a

transmitter) is coupled to the load by means of an air core transformer, consisting of coils

L1and L2.

By changing the mutual inductance between the coils, the impedance of the tank circuit can be

matched to the load resistance.

The impedances must be made comparable in value to obtain the greatest possible energy

transferred from the tank circuit to the load .

The easiest way to change the mutual and thus, obtain the required impedance match is to vary

the coupling between the coils by changing the distance between them.

When coil L2 is c to L1 a portion of the load resistance into the primary (tank)circuit and

affects the primary circuit in exactly the, same manner as though resistance had been added in

series with the coil.

This is shown by a dotted line in the plot.

The closer the coupling between the 2 coils the greater is the amount of series resistance

coupled into the tank as being reflected from the load (secondary) circuit to the tank (primary)

circuit.

Increasing the coupling by bringing the coils closer together increases the reflected series

resistance in the tank circuit and, hence, lowers the Q.

The effect of various degrees of coupling on the shape of the impedance curve is seen from the

figure.

When the coils are loosely coupled the reflected resistance small and hence the Q is high and

the resonance curve is sharp.

When the coupling is increased to a intermediate value, the coupled in resistance is large, Q is

1ow and the resonance curve is broader.

Finally when the co between the coils is very tight the reflected re large, Q is low and the

resonance curve is very broad as shown by the bottom curve.

TUNED AMPLIFIERS:

NEED FOR TUNED AMPLIFIERS:

The audio frequency amplifiers used in many applications suffer from two major drawbacks:

They become less efficient at radio frequencies

The gain is independent of signal frequency over a large bandwidth.

Thus the amplifier does not permit the selection of a particular frequency while rejecting all

other frequencies.

Sometimes, we require the selection of a desired frequency or a narrow band of frequencies for

amplification. This is achieved in radio receivers with the help of tuned amplifiers.

Thus the tuned amplifier‘s function is to select the desired rf signal of a particular broadcasting

station and rejecting all other signals.

Amplification of the selected rf signals.

Hence, the tuned amplifiers serve the following two purposes.

Selection of the desired rf signal of a particular broadcasting station and rejecting all other

signals.

The tuned circuit consists of an inductance in parallel with a variable capacitor. The selection of

a particular frequency is based on the phenomenon of resonance.

Tuned amplifiers may be classified into two categories:

Small signal tuned amplifiers

Large signal tuned amplifiers

Small signal tuned amplifiers amplify small signals at radio frequency.

As power involved is small, these amplifiers are operated under class A operation. Hence, the

distortion is negligibly small.

Large signal tuned amplifiers amplify large signals at radio power involved is large, these

amplifiers are operated under B or under C operation. Hence, distortion is large.

But the tuned circuit itself eliminates most of the harmonic distortion.

Here we shall consider only small signal tuned amplifiers.

Small signal tuned amplifier maybe single tuned amplifier or a double tuned amplifier.

In single tuned amplifier, one parallel tuned circuit is used as load impedance.

In double tuned amplifier, two inductively coupled tuned circuits are used per stage and both

the tuned circuits being tuned to the same frequency.

PARALLEL TUNED CIRCUIT:

A parallel tuned circuit is shown below:

It consists of an inductor and a capacitor connected in parallel with each other with respect to

supply source.

In practice; some resistance R is always present with the inductor.

The value of R is negligible small as compared to Other

Further I = IL +IC We know that the current in inductor lags Vs by 90

0 while the current in

capacitor leads Vs by 900.

Thus the two currents are out of phase with each other.

When alternating voltage is applied across the parallel circuit, the frequency of oscillations will

be the same as that of applied voltage.

However, at a particular frequency of applied voltage, the inductive reactance XL equals the

capacitive reactance Xc.

Now the circuit behaves as purely resistive circuit. The phenomenon is called as resonance.

Thus a circuit is said to be resonant when the frequency of applied voltage is equal to the

natural frequency of the circuit.

The resonant frequency is given by,

So under resonance condition:

(3) As IL and IC are in opposite to phase they cancel each and the line current is zero.

(4) The impedance Zr of the circuit is maximum.

The variation of impedance with frequency is shown above. It is clear from figure that

impedance is maximum at resonant frequency fr.

However, the impedance decreases rapidly on both sides of the resonant frequency.

This characteristic of the parallel tuned circuit provides its selective properties.

In this way a parallel resonant circuit selects the resonant frequency and rejects all other

frequencies.

QUALITY FACTOR:

To provide better selectivity, the frequency should be a sharp resonance curve.

This sharp resonance curve means that impedance should fall very rapidly as the frequency is

varied from resonant frequency.

The below figure shows the impedance frequency curves of a parallel tuned circuit for different

values of R.

It is observed that smaller is the resistance of the coil, the sharper is the resonance curve.

The reason is that a small resistance consumes less power and draws a relatively small line

current.

The ratio of inductive reactance of the coil at resonance to its resistance is ,z as quality factor.

This is expressed by Q and is given by,

The below figure shows the variation of parallel circuits impedance as a function frequency for

different Q values.

BANDWIDTH:

The range of frequencies at which the impedance of tuned amplifier falls to 70.7% of the

maximum impedance is called the bandwidth.

Bandwidth = f2-f1=fr/Q.

The difference f1 – f2 is also called as pass band of the circuit.

The frequencies below f1 and above f2 will not pass.

So the band width gives the discriminating property of the resonant circuit .

So higher is the Q value, smaller is the bandwidth.

ADVANTAGES OF TUNED AMPLIFIER:

High selectivity

Smaller collector supply voltage

Small power gain.

SINGLE TUNED AMPLIFIER:

Circuit arrangements:

The below figure shows the circuit diagram of a single tuned amplifier in which the output is

taken with the help of capacitive coupling and the next figure represents the circuit in which

inductive coupling is used.

The signal to be amplified is applied between base and emitter.

R1, R2 and Re fix up and stabilize the operating point.

Ce-is the bypass capacitor

A tuned circuit consisting of inductance L and capacitor C acts as collector load.

C is generally variable so that the resonant frequency of the circuit may be adjusted.

We can also use a variable inductor.

Thus the values of capacitance and inductance of the tuned circuit are adjusted in such a way

that its resonant frequency is equal to the frequency of the applied signal to be amplified.

CIRCUIT OPERATION:

The high frequency signal to be amplified is applied between base and collector.

The value of C of tuned circuit is changed such that the resonant frequency becomes equal to

the frequency of the signal.

At resonance frequency, the tuned circuit offers very high impedance the signal frequency and

thus large output appears across it.

If the signal is complex, then the frequency corresponding to resonant frequency will be

amplified.

Other frequencies will be rejected by the tuned circuit, so, the tuned amplifier selects and

amplifies the desired frequency.

FREQUENCY RESPONSE CURVE:

The voltage gain is given by,

Av=βL/CR rin

Where, rin is the input impedance.

As (L/CR) is very high, and hence voltage gain is very high.

On both sides of resonant frequency, the impedance of tuned circuit decreases.

Hence the voltage gain on either side of resonant frequency decreases.

The frequency response curve is similar to impedance frequency curve.

The range of frequencies at .which the voltage gain of the tuned amplifier falls to 70. 7% of the

maximum gain is called as its bandwidth .

The bandwidth of the tuned amplifier is given by,

BW=f2-f1.

The amplifier will amplify any frequency well within this frequency range.

3.3.2 DOUBLE TUNED AMPLIFIERS:

The circuit shows a double tuned amplifier.

There are two tuned circuits: One (L1 ,C1,) in the collector circuit and the other (L2, C2 in the

output circuit.

The voltage developed across the tuned circuit in the collector circuit is inductively coupled to

the output tuned circuit.

The two circuits are tuned to the same frequency i.e, the frequency of the signal.

By changing the value of C1 the resonant frequency of the tuned circuit is adjusted equal to the

frequency of signal.

Now the tuned circuit offers very high impedance to the signal frequency.

Hence large output appears across the tuned circuit L1 C1.

The output of this tuned circuit is transferred to the second tuned circuit L2C2 through mutual

induction.

FREQUENCY RESPONSE:

The frequency response curve of double tuned amplifier for differ coefficient of coupling is shown

below:

3.3.3’ STAGGER TUNED AMPLIFIER:

In order to increase bandwidth, double tuned amplifiers are preferred but alignment of double

tuned amplifier is difficult.

In stagger tuned circuit, two single tuned cascade amplifiers having a certain bandwidth are

taken.

The resonant frequencies of the two tuned circuit are so adjusted that they are separated by an

amount equal to the bandwidth of each stage.

Since the resonant frequencies are displaced or staggered, they are known as stagger tuned

circuits.

A cascade of stagger-tuned circuits maybe employed to provide a wide pass band response

along with a reduction of skirt response, a give a closer approach to the ideal response

rectangle.

With the several resonant circuits isolated by the amplifiers, the adjustment is simple, and the

method maybe extended to three or four stages, to provide a wide response band.

The flatness of the top of the response, as well as the magnitude of any response ripple, is

dependent on the spacing and sharpness of the separate resonances, or the placement of the

mathematical poles in a pole-zero analysis.

The resultant staggered pair will have a bandwidth i.e times that of each of the individual single

tuned circuits.

The overall s function will be identical form with that of a single stage double tuned system.

3.4 INSTABILITY OF TUNED AMPLIFIERS:

Tuned amplifiers are required to produce an output which does not differ from input in a

significant way .

In actual practice it is impossible to construct an ideal amplifier whose output is an exact

duplication or replica of the input.

The output is always found to differ from the input either in its waveform or frequency content.

This difference between the output and the input of the amplifier is called distortion and leads

to instability.

The distortion may be divided into 2 broad categories:

a. Non linear distortion.

b . Linear distortion.

NON LINEAR DISTORTION:

This occurs when the transistor operates in the non linear region of its transfer characteristics.

When the signal is visualized in the time domain it is called amplitude distortion, in frequency

domain it is called harmonic distortion.

When the input signal has more than one frequency it is called inter modulation distortion.

Non linear distortion occurs in case of large signal inputs when the active device is driven into

the non linear region of its characteristics.

LINEAR DISTORTION:

This occurs when the active is device is working on linear part of its characteristics with small

signal inputs.

It is primarily due to frequency dependent reactances associated with the circuit or active device

itself and occurs when the input signal is composite, i.e. has signals of different frequencies.

However output contains no frequencies other than those at the input It may be further

subdivided into:

i. Frequency distortion: Due to unequal amplification of different frequencies present

in the input signal.

ii. Phase or delay distortion: Due to unequal phase shift of various signal

components.

HIGH FREQUENCY EFFECTS:

The problem with the designing of effective amplifiers , of course, was the grid to plate

capacitance which was 8 pico farads for a typical triode like the type 01- A.

While this type of capacitance was negligible at audio frequencies, it created a real problem in

designing stable RF amplifiers for the 200 to 600 meter wavelengths.

Figure below shows a typical triode RF stage with the grid to plate capacitance, Cgp

emphasized externally with dotted lines.

Because both the grid and plate circuits are tuned or else coupled to tuned circuits, the circuit

contains the necessary elements for oscillation with Cgp providing the feedback path from grid

to plate.

This circuit will always oscillate if enough energy can be fed back from the plate to the grid in

the correct phase to overcome circuit losses.

Unfortunately, the conditions for best gain and selectivity are also those which promote

oscillation.

In order to prevent oscillation in RF amplifiers it was necessary to reduce the stage gain to a

level that insured circuit stability.

This could be accomplished in several ways such as lowering the Q of tune circuits; stagger

tuning, reducing filament voltage on the amplifier tube, loose coupling between stages or

inserting a ―losser‖ element into the circuit.

While all these methods reduced gain, detuning and Q reduction detrimental effects on

selectivity.

Variation of filament voltage was, of course, a universally used method for gain control in the

battery sets of the 1920‘s.

3.4.1 STABILIZATION TECHNIQUES:

Probably the most common technique use to inhibit feedback was the ―losser resistance R,

shown in Figure 2.

This circuit was widely used and is typified in the Atwater Kent receivers of the 1920‘s.

Since R appears in series with the grid to plate capacitance of the tube, it interrupts the

feedback path.

If made sufficiently large R

will prevent oscillation. T

Typical values of R range from 50 to several hundred ohms or more depending on the other

circuit parameters .

With good design, a stage gain of 5 could be obtained on the 200 to 600 meter broadcast wave-

lengths using the gain limiting techniques.

Useful amplification at short wavelengths (below 200 meters) was considered impractical or

impossible by most radio engineers at that time.

NARROW BAND NEUTRALIZATION USING COIL:

Figures below show two other neutralizing circuits employed in receivers of the 1920‘s.

The first one is the RFL (Radio Frequency Laboratory) circuit used.

In Figure below, L is part of the tuned circuit at the next stage grid but is oriented for minimum

coupling to the other windings.

L is wound on a separate form and is mounted at right angles to the coupled windings.

If the windings are properly polarized, the voltage across L due to the circulating current in the

grid circuit will have the proper phase to cancel the signal coupled through the grid to plate

capacitance.

Again, balance is achieved by adjustment of Cn.

The Rice circuit of Figure uses a center tapped coil in the grid circuit.

With this arrangement the voltages at the ends of the tuned grid coil are equal and out of phase

Cn is then adjusted to equal the grid to plate c of the tube to effect neutralization.

Figure is the type of circuitt used in the Radiola 60 and 62 IF stages.

The principle disadvantage of the circuit is that the tuning capacitor is not and makes the circuit

difficult to employ in gang tuned RF stages.

The circuits shown in Figure all fall into a general class of neutralization circuits known as

bridge circuits.

That is, the circuit is electrically equivalent to a balanced electrical bridge network where Cn is

adjusted to achieve a balance.

When Cn is properly adjusted, circuit gain is due to amplifying properties of the tube alone as

the feedback path through the grid to plate capacitance is balanced out to speak.

Many variations of bridge neutralizing circuits exists and find a today, especially in RF power

amplifiers for transmitting equipment.

BRODBAND NEUTRALIZATION USING HAZELTINE METHOD:

Professor L. A. Hazieton introduced the famed neutrodyne circuit in which the troublesome

effect of the grid to plate capacitance of the tube was neutralized by introducing into the

grid circuit a signal which canceled the signal coupled through the grid to plate capacitance.

Figure shows one variation of the Hazeltine circuit.

In this circuit the primary winding of the RF transformer is tapped.

With this arrangement the primary coil end opposite the plate has a voltage out of phase

with

the RF voltage at the plate.

The neutralizing capacitor; Cn, is adjusted to couple the proper amount of out of phase voltage

into the grid to nullify the signal fed through the grid to plate capacitance.

By neutralizing the effect of grid to plate capacitance, higher stage gains without oscillation

were possible.

Because of difficulties in maintaining neutralization over a wide tuning range, stage gains were

limited to not more than 10 with good stability.

Doubling the stage gain did mean that a three stage amplifier could achieve a stable gain of as

much as 1,000 compared to 125 for a similar amplifier without neutralization.

The typical neutrodyne circuit is shown in figure below.

This is an improved version of Hazeltine neutralization.

The neutralization capacitor is conceited to a tap near the ground of the next stage grid coil.

In principle, the circuit functions in the same manner as the circuit of Hazeltine with the

advantage that the neutralizing capacitor does not have the B voltage across it.

The primary and secondary windings of the RF transformer must be properly polarized to allow

neutralization to take place.

Additionally, the primary was frequently inter wound with the ground end portion of the

secondary coil to obtain tight coupling.

TUNED CLASS C AMPLIFIER:

So far we have considered tuned amplifiers operating in class A Operation.

Such amplifiers are used where RF signal has low power level e.g.in radio receivers, small

signal applications in transmitter.

However, owing to low efficiency class A operation, these amplifiers are not employed where

large RF power is involved.

In such situations, tuned class C power amplifiers are used.

Since, class C amplifier has a very high efficiency, it can deliver rnore load power than a class

A amplifier.

Class C operation means that collector current flows, for less than 1800.

In a practica1 tuned class C amplifier, the collector current flows for much less than 180°.

When narrow current pulses like these drive a high Q resonant circuit, the voltage across circuit,

is almost a perfect sine wave.

One very importantt advantage of class C operation is its high efficiency.

The circuit action is as under:

When no a c input signal is applied, no collector current flows because the emitter diode (base-

emitter) is unbiased.

When an a.c. signal is-applied, clamping action takes p1ace .

Then voltage across the emitter diode varies between +0.7V(during positive peaks of input

signal) to about -2Vm (during negative peaks of input signal).

This means that conduction of the transistor occurs only for a short period during positive peaks

of the signal.

This results in the pulsed output i.e. collector current waveform is a train of narrow pulses.

When this pulse output is fed- to the LC circuit, sine wave output obtained.

Since the pulse is narrow, inductor looks like high impedance and the capacitor like low

impedance.

Consequently, most of the current changes the capacitor.

When the capacitor is fully charged, it will discharge through the coil and the load resistor,

setting up oscillations just as an oscillatory circuit does.

Consequently, sine-wave output is obtained.

If only a single current pulse drives the LC circuit, we will get damped sine- wave output.

However, if a train of narrow pulse, drives the LC circuit, we shall get un-damped sine-wave.

EFFICIENCY:

The D.C. input power (Pdc) from the supply is:

Pdc = Po(max) + PD

Where,

PD = power dissipation of the transistor

Maximum collector efficiency :

APPLICATION:

Class C tuned amplifiers are suitable only for RF applications because power losses are very

small (less than 1%) in high Q resonant circuits.

The Class C amplifier is restricted to the radio frequency range since it suffers from very high

distortion.

Therefore resonant circuits should be used as filters in the output :waveform.

An extremely narrow pulse will compensate the losses.

Class C amplifiers are extensively used in amplitude modulated transmitters an receivers.

In transmitter blocks Class C amplifier may be used to amplify the signal after modulation and

then transmitted.

At the receiver the received signal is amplified by this high power amplifier before

demodulating .

Due to very high efficiency the Class C amplifiers are used in television transmitters and

receiver circuits.

These are used as high power amplifiers at the intermediate frequency range to amplify the

composite video signal after modulation.

At the television receiver before the video and the voice signals are separated ,it is amplified.

PART A

1 .What is Quality factor?

2.What is the quality factor for an unloaded circuit?

3 .What are the drawbacks of audio frequency oscillators?

4. How does a tuned amplifier function?

5. How are tuned amplifiers Classified?

6. What are small signal tuned amplifiers?

7. What are large signal tuned amplifiers?

8. What are double tuned amplifiers?

9. Draw a parallel tuned circuit.

10. What are the advantages of tuned amplifiers?

1l.What is a stagger tuned circuit?

12. What are the two types of distortions that lead to instability of tuned amplifier

13. What are the 2 types of linear distortion?

L4.What are the 2 types of narrow band neutralization?

15. What is the principle of Hazeltine neutralization?

I 6.Where is Class C amplifier used?

17. What is the nature of current waveform in Class C tuned amplifier?

I 8.What are the applications of Class C tuned amplifiers?

19. What is a neutrodyne?

20. What are the high frequency effects in tuned amplifiers?