OTL = Output Trasformer Less Tube Amplifiers

My consideration on problems of each design

Ciclotron balanced design problems (type 1):
   1] More high output resistence
   2] the duplication of the power supply (2 for each channel)
   3] impossible to use with earphone (because no ground on outputterminal)
   4] you can destroy the loadspeakers if you don't put a protection from DC
   (a simple variation of the bias of one output tube will give high DC on output)

Technics design problems (type 2)
1] Changing the load the first feedback cannot to compensate asimmetry of the output stage.
(In real case the loudspeakers is not a constant impedence)

SRPP (type3)
   1] Very high Output resistence
   2] Work only in Class A so very short life for tubes
   3] Many power lost in cathode resistence
   4] Very low efficiency
   5] High distortion
   6] You need 4 or 6 output tubes for channel

Futerman design (type 4)
At this time I don't have found problems.

Circuits gallery

New design circuits

OTL by A. Ciuffoli

OTL ideas by Takuji Yamamoto (japan)

OTL by Morikawa Chuyu from MJ 1993/4

OTL by unknow Japan company

Yozo Matsuoka - from MJ 01/97

OTL by Yozo Matsuoka from MJ 1995/11

OTL by ? from MJ 1997/7

The COVI Mark II 100 W OTL Amplifier

mirror on my web lee.html

Kaneda ibrid OTL - 40W 1% thd 18db nfb

Kaneda ibrid OTL - power supply

New Kaneda ibrid OTL

ibrid 6C33C OTL by Shinichi Kamijo

EL509 OTL by Shinichi Kamijo

SRPP 20 watt Class A OTL by Fabio Camorani from Sound Practices (I have complete artile)

SRPP 20 watt Class A OTL by Fabio Camorani from Costruire Hi-Fi (I have complete artile)

Transcendent Sound, Inc. complete patent with circuit (I have all pages)

Graaf 20 schema and photo

Old design circuits

Futterman OTL

original Futterman H1 OTL

Technics 20A - 1965 - 75watt on 16 ohm

Schematic by P. Dickie Jr & A. Macovski (June 1954)

6336A PP (Taki OTL) reg.

6AS7 OTL

OTL by ? from Japan

Old OTL design by ? 25W 0.4% thd with 40db of nfb

A design note: I would say that the power supply solution chosen to drive the output tubes in the "OTL by unknow Japanese company" and in the "OTL by Yozo Matsuoka from MJ 1995/11" looks a bit strange to me, because it is designed around is a voltage duplicator where there is a secondary with half voltage and 2 diodes. After a spice 3f4 simulation I have got "terrible" results. The bridge solution is better ! (nevertheless the output current problem ...)