Last update: Aug. 9, 2003
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Welcome to Tube Amplifiers
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Japanese version is also available.
Here are my latest products; 171A class A push-pull monaural amplifiers.
The amplifier consists of, left to right on the photo, 280, two 171A, an interstage transformer with Ni core and two 227. All tubes used in this amplifier were produced in 1920's and early 1930's. They still work without any troubles.
227 is a low-mu triode with an indirect heater.
171A is a power triode for the final stage. However, its output is no more than 0.79 watts with single class A operation. It is estimated that the operation of 171A is class A2 due to a driver transformer.
280 is a full-wave rectifier.
The chassis is a very cheap 1mm thick alminium box painted with violet paint. The side panels are also cheap. The chassis costs less than \2,000 including paint spray each!
A close view of final stage tubes and a rectifier.
A left-side channel amplifier. The rectifier 280 is replaced with '80.
This Japanese Mazda '80 was taken from an old radio.
A frequency-response curve of 171PP shows poor low frequency responce which is due to a cheap interstage transformer. However, high frequency response is good. The tone characteristics of this amplifier is probably determined by the Ni-core interstage transformer.
Added on Aug. 9, 2003
The interstage transformer was exchanged with Tamura B-5001 which gave much better frequency response.
6AC5-GT single stereo amplifier
A popular positive-grid triode 6AC5 was used as the final stage. I didn't use 76 as a driver of 6AC5, because the chasis is very small. I used 6EA7 instead. 6EA7 contains 2 unit as same as 76 inside. However, the plate of each unit is connected inside.
The amplifier consists of 12AX7(1/2) - 6EA7(1/2) - 6AC5 per channel. The rectifier is 5Y3GT. So this tiny stereo amplifier contains only 5 tubes. This amplifier is used for LASER Disk player especially for music programs.
E406-N single stereo amplifier
E406-N is a direct-heated output triode made in France. It is not a direct replacement of PX-4 in U.K. but one can replace PX-4 with E406-N. E406-N operates at more high plate voltage with fewer plate current than PX-4 does. This amplifier consists of 6SH7(red metal) - E406-N - GZ37. The rectifier can be 5U4G but I selected GZ37 because the size and shape of GZ37 resembled those of E406-N.
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