Single-ended triode Amplifiers using zero-bias transmitting tubes
Michimori Hirokuni

This is my first time to set up a homepage;
My main reason is to introduce myself to you before the ETF2008 which I hope to join. I hope this homepage will give us a chance to contact other participants before the events. I look forward to receiving your e-mail.

I have been working on homemade audio Amplifiers for nearly 20 years. It is my pleasure to design and construct good quality tube Amplifiers to the point of my satisfaction and enjoy hands-on assembly which has been lost in the field of Ham radio.
It has been 50 years since I got the license for amateur radio station JA2AEY.
At first, I made all the equipment by myself. Soon the times have changed to the SSB age and I also challenged to buildSSB generators and various Linear Amps which used color-TV sweep tubes and transmitting tubes such as 811A, 813 and 4-1000A.
It is a wonder that tubes of the old days have revived nowadays in the audio scene, in spite of the semiconductor age.
I am still active on the Ham radio but ironically all of my equipment is made by manufactures, including linear amplifiers, which are all made of semiconductors. It is impossible to build quality HAM equipment better than manufactures both technically and financially. Last remaining field for homemade equipments was the high power linear Amps.
My last constructed linear amp, Eimac 8877 (3CX-1500A7) was replaced with JRC FET linear amplifier long time ago.

Under the above circumstances, naturally I was interested in the late Mr.Sisido's "Roll over inter-stage transformer Amps " using transmitting tubes designed for B & C class operation.
The reasons for choosing the zero-bias tubes, Mr. Sisido mentioned, is that nowadays it is nearly impossible to get a good quality conventional high power triode tubes such as 211, 845, DA60, DA100 and RS237 etc.
On the contrary, zero-bias transmitting tubes have less demand so that we can still get good quality tubes with reasonable prices.

The theory of Mr. Sisido's roll over inter-stage transformer Amp is:
It is rational drive circuit for B and C class transmitting tubes using Inter-stage transformer so that,
1)the setting grid bias of power tube is free, and
2) it cancels DC magnetization by flows primary plate current for drive tube and secondary grid current for output tube in the opposite direction.
3) Consequently to get a good frequency response and efficiency of drive even with small size of Inter-stage transformer. 
 This inter-stage transformer is a Key component and should have optimum matching conditions between drive tube and power tube otherwise lowered output power. We have to provide special ordered Inter-stage transformers individually for different drive tubes and power tubes. 

As an alternative to the costly Inter-stage transformers, I designed new drive circuit , using 5998A twin triode regulator tube, connected to 811A grid directly by cathode follower circuit and another unit of 5998A is used as series constant current source load with minus power supply.
New drive circuit fulfilled following conditions;
1) applies stable plus Grid bias for 811A (dc+18.5V),
2) supply grid current of peaking 18mA ,and
3) applies maximum drive signals for 811A without clipping (47Vrms) to get 22W of output power.
This regurator tube dorive 811A Amp was inserted in MJ (Japanese Audio magazine ) published  April on 2003.
Using same drive method, I constructed 100TH and 838 single-ended Amplifiers afterward which will publish on this home page in due order.

New 4P1L-811A Amp 2013

Renewed 801A PSE Amp 2011

Renewed 100TH SE Amp 2010


Renewed 811A SE Amp 2009

8025A stereo Amp 2008

801A PSE Amp 2007



838 SE Amp 2006

100TH SE Amp 2003

811A SE Amp 2000

ETF 2008 Presentation

Wrap up of my amplifier

Attended in ETF2008

Attended in ETF2008

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