Free Services  

  • MONITOR KEYWORDS
  • Enter keywords & we'll notify you when a new patent matches your request (weekly update).

  • ORGANIZER
  • Save & organize patents so you can view them later.

  • ARCHIVE
  • View the last few months of your Keyword emails.

  • COMPANY DIRECTORY
  • Patents sorted by company.

Follow us on Twitter
twitter icon@FreshPatents

Browse patents:
Next
Prev

Output circuit of vacuum-tube amplifier




Title: Output circuit of vacuum-tube amplifier.
Abstract: An output circuit of a vacuum-tube amplifier is disclosed. An output circuit of a conventional vacuum-tube amplifier has shortcomings that a front end amplification unit uses a coupling condenser or a transformer to output an AC signal to an output node, a bias voltage of a cathode of a vacuum tube is varied in response to an input signal in an output buffer and, when the bias voltage is higher than a voltage set by a bias resistor, signal attenuation by the difference between the bias voltage and the set voltage is generated. To solve these shortcomings, the output circuit of the vacuum-tube amplifier includes a front end amplification unit for amplifying an input signal using a vacuum tube and an output amplification unit for power-amplifying the output signal of the front end amplification unit using a vacuum tube. The output circuit of the vacuum-tube amplifier further includes a zero voltage-maintaining circuit for detecting a voltage of a cathode of the vacuum tube of the front end amplification unit and controlling a voltage applied to a plate of the vacuum tube to maintain the DC voltage of the cathode as 0V, and a variable self-bias circuit for maintaining a bias voltage of a cathode of the vacuum tube of the output amplification unit uniform irrespective of a variation in the input signal. ...


USPTO Applicaton #: #20090224825
Inventors: Soung Whan Chung


The Patent Description & Claims data below is from USPTO Patent Application 20090224825, Output circuit of vacuum-tube amplifier.

BACKGROUND

- Top of Page


OF THE INVENTION

1. Field of the Invention

The present invention relates to an output circuit of a vacuum-tube amplifier, and more particularly, to an output circuit of a vacuum-tube amplifier, which maintains a voltage between a ground terminal and an output terminal of the vacuum-tube amplifier as 0V to output an amplified signal without using a coupling condenser or a transformer and maintains a voltage of a cathode of a vacuum tube of an output stage uniform by a variable self-bias circuit to obtain linearity of output power in proportion to an increase in an input signal without being affected by the cathode when the input signal is increased, increase the output power and improve distortion.

2. Background of the Related Art

In spite of advantages of a semiconductor device, lovers of music still prefer an audio amplifier using a vacuum tube because the audio amplifier using a vacuum tube has sound quality higher than that of a semiconductor amplifier.

FIG. 1 is a circuit diagram of an output circuit of a conventional vacuum-tube amplifier. Referring to FIG. 1, the output circuit of the vacuum-tube amplifier includes an amplification unit and an output buffer unit. The amplification unit receives an input signal through a grid G of a vacuum tube 1, receives a voltage V1 through a plate P of the vacuum tube 1, amplifies the input signal, and outputs the amplified signal through a cathode K of the vacuum tube 1. A coupling condenser C1 and a bias resistor R1 are connected to the cathode K of the vacuum tube 1 such that the amplified signal is output to an output node N1 through the coupling condenser C1.

In case of a multi-stage amplifier, multiple vacuum tubes having the same configuration as the vacuum tube 1 are connected in parallel, a bias resistor and a coupling condenser are connected to the cathode of each of the multiple vacuum tubes, and output nodes are commonly connected in parallel. FIG. 1 illustrates only one vacuum tube.

The output buffer unit receives the signal of the output node N1 of the amplification unit through a grid G1 of a vacuum tube 2 and outputs the amplified signal to a speaker 4 through a plate P1 of the vacuum tube 2. A resistor R2 and an AC bypass condenser C2 are connected in parallel with a cathode K1 of the vacuum tube 2 to construct a self-bias circuit 5.

To output a signal amplified by the vacuum tube 1 in the amplification unit, the coupling condenser C1 or a transformer for cutting off a DC voltage must be used at the cathode K of the vacuum tube 1. A general method sets the resistance of the resistor R1 such that a voltage, obtained by halving the plate voltage V1 of the vacuum tube 1, is set to the cathode K of the vacuum tube 1. That is, when the amplification unit is directly connected to a following amplifier, the coupling condenser C1 or a transformer must be used in order to cut off a DC signal and pass only an AC signal because there is a DC components in a signal transmitted to the following amplifier.

The output buffer unit connects the resistor R2 of hundreds to thousands ohm to the cathode K1 of the vacuum tube 2. A bias voltage is applied to the vacuum tube 2 using a voltage drop according to the resistance R2. That is, a self-bias method is used in the output buffer unit.

FIG. 2 illustrates cathode and output power characteristics with respect to an input signal of a self-bias amplification circuit. In the self-bias circuit as illustrated in FIG. 1, when the voltage applied to the grid G1 is increased, current of the cathode K1 is increased in proportion to the increase in the voltage applied to the grid G1. Here, the voltage is increased in proportion to the current by resistance set to the cathode K1. A voltage according to a basic current value of the cathode K1 and the input signal of the grid G1 are increased in proportion to the input signal voltage in a satisfactory manner in response to the amplification factor of the vacuum tube 2. When an input signal having a voltage exceeding the voltage according to the basic current value of the cathode K1 and the input signal voltage of the grid G1 is applied, however, an increase in the voltage of the cathode K1 attenuates the input voltage of the grid G1 by the increase in the voltage of the cathode K1. Accordingly, the input signal and output power do not achieve satisfactory linearity, as illustrated in FIG. 2.

SUMMARY

- Top of Page


OF THE INVENTION

Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and it is an object of the present invention to provide an output circuit of a vacuum-tube amplifier, which employs a zero voltage-maintaining circuit that maintains an output terminal of a front end amplifier as 0V to transmit a signal without using a coupling condenser or a transformer for cutting off a DC voltage at an output node of the front end amplifier.

Another object of the present invention is to provide a variable self-bias circuit of a vacuum-tube amplifier, which prevents a voltage set to a cathode of a vacuum tube from being varied irrespective of the power level of an input signal applied to a grid in an output amplification stage of the vacuum-tube amplifier.

To accomplish the above objects, according to the present invention, there is provided an output circuit of a vacuum-tube amplifier including: a front end amplification unit for amplifying an input signal using a first vacuum tube; an output amplification unit for power-amplifying the output signal of the front end amplification unit using a second vacuum tube and outputting the amplified signal to the outside; a zero voltage-maintaining circuit for controlling a voltage applied to a plate of the first vacuum tube in response to the voltage of a cathode of the first vacuum tube to maintain the DC voltage of the cathode of the first vacuum tube as 0V; and a variable self-bias circuit for maintaining a bias voltage of a cathode of the second vacuum tube uniform irrespective of a variation in the input signal.

The front end amplification unit includes: the first vacuum tube having a grid connected to a signal input port and a cathode connected to an output node; a resistor R11 for applying a negative voltage V3 to the cathode of the first vacuum tube; a resistor R12 for applying a positive voltage V1 to the plate of the first vacuum tube; the zero voltage-maintaining circuit continuously controlling connection/short-circuiting of a resistor R17 for dividing the positive voltage V1 with the resistor R12 in response to a predetermined time constant based on the voltage of the cathode of the first vacuum tube and maintaining the DC voltage of the cathode of the first vacuum tube as 0V according to the control of the positive voltage V1; and a first smoothing condenser connected between the plate of the first vacuum tube and a ground terminal and a second smoothing condenser connected between the ground terminal and the terminal of the negative voltage V3.

The zero voltage-maintaining circuit includes: the voltage-dividing resistor R17 connected to the plate of the first vacuum tube; a power amplifier connected to the output terminal (−) of the voltage-dividing resistor R17; and a differential amplifier having a non-inverted input terminal (+) receiving the voltage of the cathode of the first vacuum tube through voltage-dividing resistors R13 and R17 and a time constant condenser C13 and an inverted input terminal receiving the voltage of an output terminal of the differential amplifier through voltage-dividing resistors R14 and R15 and a time constant condenser C14, the output terminal of the differential amplifier being connected to an output terminal (+) of the power amplifier.

The variable self-bias circuit of the output amplification unit includes: a differential amplifier having a non-inverted input terminal (+) receiving the output voltage of the cathode of the second vacuum tube, which is divided by two resistors, and an inverted input terminal (−) receiving a reference voltage set by a zener diode; a power amplifier having an input terminal (+) connected to the an output terminal of the differential amplifier and an output terminal (−) connected to the cathode of the second vacuum tube through a resistor R23; and a smoothing condenser connected between the cathode of the second vacuum tube and the ground terminal to smooth a peak value.

While the zero voltage-maintaining circuit is used in a circuit in which the front end amplification unit and the output amplification unit are connected in the present invention, the zero voltage-maintaining circuit can be used in any amplifier circuit using a vacuum tube, which requires an AC coupling condenser or a transformer at an output stage, to output an AC signal without using the coupling condenser or the transformer.

The variable self-bias circuit is applied to the output circuit of any power amplifier circuit using a vacuum tube to maintain the bias voltage of an output stage uniform, obtaining stable output power characteristic.

BRIEF DESCRIPTION OF THE DRAWINGS

- Top of Page


The above and other objects, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments of the invention in conjunction with the accompanying drawings, in which:

FIG. 1 is a circuit diagram of an output circuit of a conventional vacuum-tube amplifier;

FIG. 2 illustrates the relationship between an input signal and an output power of a conventional vacuum-tube amplifier;

FIG. 3 is a circuit diagram of an output circuit of a vacuum-tube amplifier according to the present invention;

FIG. 4 is a circuit diagram of a zero voltage-maintaining circuit of the vacuum-tube amplifier according to the present invention; and

FIG. 5 illustrates the relationship between an input signal and an output power of a variable self-bias circuit of the vacuum-tube amplifier according to the present invention.

DETAILED DESCRIPTION

- Top of Page


OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

FIG. 3 is a circuit diagram of an output circuit of a vacuum-tube amplifier according to the present invention. Referring to FIG. 3, the output circuit of the vacuum-tube amplifier according to the present invention includes a front end amplification unit 10 for amplifying an input signal using a vacuum tube 11 and an output amplification unit 20 for power-amplifying the output signal of the front end amplification unit 10 using a vacuum tube 21 and outputting the amplified signal.

The output circuit of the vacuum-tube amplifier further includes a zero voltage-maintaining circuit 12 for controlling a voltage applied to a plate P11 of the vacuum tube 11 based on the voltage of a cathode K11 of the vacuum tube 11 of the front end amplification unit 10 to maintain the DC voltage of the cathode K11 as 0V, and a variable self-bias circuit 22 for maintaining a bias voltage of a cathode K21 of the vacuum tube 21 of the output amplification unit 20 uniform using a self maintaining circuit irrespective of a variation in the input signal.

The front end amplification unit 10 receives the input signal through a grid G11 of the vacuum tube 11 and applies a voltage V1(+) to the plate P11 of the vacuum tube 11 through a resistor R12. A voltage V3(−) is applied to the cathode K11 of the vacuum tube 11 through a resistor R11. The zero voltage-maintaining circuit 12 is connected between the cathode K11 and the plate P11 of the vacuum tube 11.




← Previous       Next → Advertise on FreshPatents.com - Rates & Info


You can also Monitor Keywords and Search for tracking patents relating to this Output circuit of vacuum-tube amplifier patent application.
###
monitor keywords

Keyword Monitor How KEYWORD MONITOR works... a FREE service from FreshPatents
1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored.
3. Each week you receive an email with patent applications related to your keywords.  
Start now! - Receive info on patent apps like Output circuit of vacuum-tube amplifier or other areas of interest.
###


Previous Patent Application:
Optimized uplink efficiencies for transmission of satellite data
Next Patent Application:
Output circuit of vacuum-tube amplifier
Industry Class:
Amplifiers
Thank you for viewing the Output circuit of vacuum-tube amplifier patent info.
- - -

Results in 0.04316 seconds


Other interesting Freshpatents.com categories:
QUALCOMM , Apple ,

###

Data source: patent applications published in the public domain by the United States Patent and Trademark Office (USPTO). Information published here is for research/educational purposes only. FreshPatents is not affiliated with the USPTO, assignee companies, inventors, law firms or other assignees. Patent applications, documents and images may contain trademarks of the respective companies/authors. FreshPatents is not responsible for the accuracy, validity or otherwise contents of these public document patent application filings. When possible a complete PDF is provided, however, in some cases the presented document/images is an abstract or sampling of the full patent application for display purposes. FreshPatents.com Terms/Support
-g2-0.2067

66.232.115.224
Browse patents:
Next
Prev

stats Patent Info
Application #
US 20090224825 A1
Publish Date
09/10/2009
Document #
File Date
12/31/1969
USPTO Class
Other USPTO Classes
International Class
/
Drawings
0


Vacuum Tube

Follow us on Twitter
twitter icon@FreshPatents





Browse patents:
Next →
← Previous
20090910|20090224825|output circuit of vacuum-tube amplifier|An output circuit of a vacuum-tube amplifier is disclosed. An output circuit of a conventional vacuum-tube amplifier has shortcomings that a front end amplification unit uses a coupling condenser or a transformer to output an AC signal to an output node, a bias voltage of a cathode of a vacuum |