|
Some Application Examples:
CIRCUIT DESCRIPTION
The heart of the Amplifier is a single ECL82 tube. Enclosed in it's
envelope is a triode alongside a penthode, the latter making up the
output stage of this single-ended circuit. Input level control
potentiometer at the input is optional and can be replaced with a 1
Meg Ohm fixed resistor to ground. The final stage utilizes the penthode driving the output
transformer. The ECL82 is operated purely in cathode bias mode. There is a Negative Feedback signal taken from the secondary transformer wiring. Feedback is taken to the cathode of the triode.
Power Supply requirements are 250-280 VDC/45mA and 6.3V/800mA AC or
DC filament voltage.
Fig.1 Tiny Amp Schematic
Fig.1
Specifications:
Frequency Response: 50Hz - 20kHz (-3dB)
Input sensitivity: 0.3 V
Input Impedance: 250k
Supply Voltage: 250 - 280 VDC/35-45mA
Power Output:3 Watt Max.
Tube: ECL82/6BM8
| MAIN PARTS | ||||
|---|---|---|---|---|
| REF. # | DESCRIPTION | QUANTITY | PART No: | SUPPLIER |
| NA | Hammond Chassis 13.5" x 5" x 2" | 1 | P-H1441-18BK3 | www.tubesandmore.com |
| P1 | Potentiometer 250K audio w. switch | 1 | R-V250K-N2 | www.tubesandmore.com |
| NA | 9 pin tube socket, chassis mnt. | 1 | P-ST9-511 | www.tubesandmore.com |
| NA | 1/4" input jack | 1 | W-SC11 | www.tubesandmore.com |
| NA | terminal strip, 5 position | 4 | P-0501H | www.tubesandmore.com |
| NA | binding post | 2 | S-H266B | www.tubesandmore.com |
| V1 | 6BM8/ECL82 vacuum tube | 1 | T-6BM8 | www.tubesandmore.com |
| TR2 | Output Transformer SE | 1 | P-T31 | www.tubesandmore.com |
| C6 | capacitor 4.7uF/350V | 1 | C-ET4D7-350 | www.tubesandmore.com |
OTHER PARTS: Resistors (0.25W 5% unless noted otherwise): R1 = 2.2K R2 = 220K R3 = 820K R4 = 560R/1W R5 = 33K R6 = 33K/0.5W R7 = 1K Rs = series resistor 470 Ohms 2 Watts (see note* below) Capacitors: C1 = 0.22uF/100-250V film cap C2 = 0.033uF/400V film cap C3 = 100pF/100-1000V film or ceramic C4 = 220uF/25-50V electrolytic C5 = 0.01uF/400-630V film C6 = 4.7uF/350-450V electrolytic Semiconductors: BR1 = rectifier bridge 400V/1A (Fig.3) D1, D2 = 1N4007 (Fig.4) Misc.: fuse holder, Fu1 0.2A MDL, Fu2 0.1A AGC, rubber feet.
 |
WARNING! Potentially lethal voltages can be present. Do not touch any part of the device with bare hands while under power. After disconnecting power, wait until filter capacitors are discharged. Measure voltage with voltmeter to be sure. If you do not know how to handle high voltage circuits, do not build this device. Get help from a qualified technician. |
If measurements turn out O.K, let the amp warm up for 10-15 minutes. Watch the tube for any signs of overheating. Only the filament and the cathode (center part of the tube) should glow orange. Any other part of the tube should remain dark.
Fig.2 Wiring example
Power supply shown in Fig.3
A center tap transformer is used in the power supply shown in Fig.4
The power transformer TR1 must provide at least 60mA continuous plate current and 800mA filament current. Cathode and screen resistors of the output tube are calculated for 270 Volts plate voltage. If your power supply has different plate voltage, the resistors should be re-calculated accordingly. Alternatively the series resistor should be increased or decreased in order to adjust the voltage to the correct value.
Fig.3 This type of configuration works with a transformer without center tap. R20 is the bleeding resistor.
*NOTE: the series resistor [Rs] determines the B+ output voltage and should be sized accordingly.
Fig.4
| POWER SUPPLY PARTS | ||||
|---|---|---|---|---|
| REF. # | DESCRIPTION | QUANTITY | PART No: | SUPPLIER |
| TR1 | Power Transformer, Fig.4 | 1 | P-T269EX | www.tubesandmore.com |
| TR1 | Power Transformer, Fig.3 | 1 | P-T261G6 | www.tubesandmore.com |
| C20, 21 | capacitor 47uF/350V axial | 2 | C-ET47-350 | www.tubesandmore.com |
| R20 | bleeding resistor 150k 1W | 1 | R-E150K | www.tubesandmore.com |
MAXIMUM TUBE RATINGS:
penthode plate current: 40mA
penthode plate voltage: 300 VDC
penthode screen current: 8mA.
Exceeding these ratings will damage or shorten the life of the tube.
TROUBLESHOOTING
Condition: upon power-up a loud high pitch noise or motoring sound comes out of the speaker.
Solution: Negative Feedback is at wrong phase. Reverse the output (speaker) wires on the transformer.
Condition: sound is distorted.
Solution: check all tube voltages, compare to values indicated above. Adjust your input voltage if its to high. Replace the tube if unsure of its condition.
Condition: tube outside (anode) glows dark red.
Solution: BIAS voltage to low. Increase cathode resistor R4.
Condition: tube outside (anode) glows dark red. BIAS is O.K.
Solution: output transformer plate winding resistance too low or shorted. Replace transformer.
Condition: amp is dead, no sound. Voltages checkout O.K.
Solution: wiring error, no input signal or input shorted. Bad output transformer or speaker.
DISCLAIMER OF LIABILITY:
THESE PROJECTS ARE PROVIDED 'AS-IS', WITH NO WARRANTY OF
ANY KIND.
USE OF THESE CIRCUITS SHALL BE ENTIRELY AT THE USER'S OWN
RISK.
The publisher of this web site does NOT assume any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights.