JLH1969 Class A amplifier build

[manir]

It is not "Compulsory" though best results (lowest distortion) are obtained with Output Transistors of approximately equal current gain (hfe).

If the gains of the output transistor are unequal, the Output Transistor with the higher current Gain should be used as TR-1.

Do note that no catastrophic failure4 will result even if you use Output Transistors with significantly different Hfe.... Only distortion will be slightly higher.

There is a Good Site devoted to this amplifier & circuit, including the original article (attached) in the April 1969 issue of Wireless World.

The original article also discusses in detail, the use & effects of un-matched output transistors.

I have used 2N3055 devices as the output transistors, without any matching, and the results were sonically very good to my ears

Thanks Guru

 

[manir]

More pictures.

Bro... any link for purchase Armstrong or Other Power Transistor Fitting kit ? Thanks

 

[manir]

Slowly gathering Knowledge and spares my JLH1969...with all your help...

 

[Kannan_madhu]

made some pcb for jlh some time back but dint get time to build it

 

[manir]

Today received Heatsink for my JLH project,(500mm)
Thanks for the FMs for guiding to Perfect Metals, Bangaluru
Very slow in progress.

 

[manir]

Today received Heatsink for my JLH project,(500mm)
Thanks for the FMs for guiding to Perfect Metals, Bangaluru
Very slow in progress.

what is the optimum spacing between 2N3055 placed horizontally in Heatsink , such in JLH

 

[Kannan_madhu]

what is the optimum spacing between 2N3055 placed horizontally in Heatsink , such in JLH

While proper biasing at 1.2A for 8 ohm speakers is important for good performance, it can also lead to heat generation in JLH amplifiers, especially if using horizontal heat sinks. This might cause some to run a cooler amplifier by under-biasing it, but that can negatively impact sound quality and stability.

Horizontal heat sinks: These can be less effective at dissipating heat compared to vertical heat sinks due to reduced airflow.
Proper bias current: 1.2A for 8 ohm speakers is a recommended bias current for JLH amplifiers for optimal performance.
Heat generation: JLH amplifiers can get hot, especially with horizontal heat sinks and proper bias current.
Under-biasing: Running a JLH amplifier with lower than recommended bias current may lead to cooler operation but can also cause distortion and instability.

 

[Kannan_madhu]