El34/6L6GC/KT88/KT120/KT150 Push-Pull (Class -AB) Stereo Power

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El34/6L6GC/KT88/KT120/KT150 Push-Pull (Class -AB) Stereo Power

KT150 Push-Pull (Class -AB) Stereo Power Amplifier will be available soon.
You can view this wonderful design by Mr. Y Fujita in T.H.E. Show Newport June 3 – June 5 2016

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With optional KT150 output tube and Lundahl OPT.


This model of ELEKIT amplifier includes an Innovative “Semi-automatic” bias adjustment system for the tube output stage.
- Commonly, there are two methods of biasing a vacuum tube amp. “Self-bias” (automatic) and “Fixed bias”. For a Push-Pull amplifier- the “Fixed bias method” is more effective and advantageous since each power tube can be adjusted for bias. The drawback with the “Fixed bias” method is each tube needs to be checked and adjusted for bias manually one by one.

-The ELEKIT “Semi-automatic” bias adjustment system incorporates “Fixed bias method”- but with no manual steps other than a simple push of the “Auto Adjust” button. The tube bias settings are managed by a microcontroller that adjusts the tube bias in less than a minute- a very unique and innovative system that EK JAPAN is introducing into the tube audio market.

Using the “Auto Adjust” Semi-Automatic Bias Feature
When the “Auto Adjust” button is pressed, the microcontroller executes the following steps automatically.
NOTE: Please make sure before using the Auto Adjust bias feature that the power tubes are fully warmed up (at least 2-3 minutes of being powered on) and the volume on the amplifier is set to the lowest level. Incorrect bias settings and/or an error condition will occur if tubes are not warmed up and if the volume is not set to the lowest level. During the tube biasing process the LED near the output tubes (orange LED in the prototype) will flash rapidly while the bias is being set.

1. In the first step the microcontroller drops bias voltage to a very low level called the “safety zone” to reduce the output tube current. This takes place slowly as to not induce pops or noises to the output to speakers. If the bias current is already detected to be in the “safety zone” it will immediately shift to the next step.
2. The bias voltage is then slowly and automatically adjusted so the cathode current of each output tube is set. NOTE: At this step if “Not Adjustable” is detected (no output tube installed, bad tube, etc.) the microcontroller automatically will return to the “safety zone” and will display an error (flashing LED).
3. When the bias adjustment is finished and stable- the bias value is stored into the flash memory in the microprocessor. If there is an error state- the bias value detected during the “safety zone” (and the error data) will be stored.
4. The amplifier “reads” the stored bias data (and error data if applicable) and outputs it as a fixed bias. Adjustments are finished.
5. If the Auto Adjust biasing finishes successfully- the LEDs will turn OFF. If there is an error- the LED closest to the problematic output tube will flash every 2 seconds. If the output tube does not reach the rated value- the LED flashes once. If the value is more than the rated value (even if in the safety zone) the LED will flash twice. (For safety- it is recommended to turn OFF the power to the amp if the LED is flashing twice). The LED will flash next to the problematic output tube to indicate it is in the safety zone.

You can always have the bias in the safety zone by pressing the “SAFETY RESET” button while the power is ON- even when the output tubes are not warmed up or while the music is being played. When you exchange output tubes, it is safe to press this RESET button and have the bias in the safety zone before turning off the power (or right after turning on the power after tube exchange). When the bias enters the safety zone, the LED stays ON. (It flashes when there is an error.)

We confirmed that our prototype model can automatically adjust the bias of EL34, 6L6GC, KT88, and KT150 tubes.

(Prototype - ALL specifications are subject to change)
EL34/KT120/KT150 Push-Pull (Class -AB) Stereo Power Amplifier
Price :TBA Made in Japan
Designer : Mr. Y. Fujita
SPECIFICATIONS (Pre-production)
VACUUM TUBE - Stock tube set: 4 X EL34(6Ca7), 4 X 5965A (or 12AT7)
You can also use :6L6GC, KT120 or KT150

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