Hello All,
I have a pair of UTC-A-28 output transformers and would like to make 3-5w amplifier.
I do not care about the limitations of the iron, and I know there are many better design ideas. I would like to make these buggers sing, just for the fun of it.
Two NPN's class A per/ch is what I would like to do, but not sure what transistors to use. I will include A-28 data
I have built the JLH amplifier kit off flea-bay using newer NPN's than 3005's, and it is a fine amplifier.
I haven't designed any SS equipment from scratch before, but have made many tube amplifiers.
Thank you
Mich
I have a pair of UTC-A-28 output transformers and would like to make 3-5w amplifier.
I do not care about the limitations of the iron, and I know there are many better design ideas. I would like to make these buggers sing, just for the fun of it.
Two NPN's class A per/ch is what I would like to do, but not sure what transistors to use. I will include A-28 data
I have built the JLH amplifier kit off flea-bay using newer NPN's than 3005's, and it is a fine amplifier.
I haven't designed any SS equipment from scratch before, but have made many tube amplifiers.
Thank you
Mich
Attachments
These are 1960s transformers. You grab your 1960s G.E. Transistor Manual.
There is a design chart for push-pull (class B... in 1960 you would never work two transistors in A because B is so much less heat). It does not go to 48r 5W but 500r 12V gives 0.5W so 50r with 12V is near 5W.
On another page is a 0.5W amplifier. This is how they ALL were. This is what the transformers were designed for. It calls for 300r 12V to get the 0.5W, indicating that the design chart took NO allowance for losses.
Because your load is 6.25X lower, everything has to be 6X beefier. The interstage transformer (which is hard to design-out if you go close to class B), the driver, and probably an additional stage because the input is already silly-low impedance.
There is a design chart for push-pull (class B... in 1960 you would never work two transistors in A because B is so much less heat). It does not go to 48r 5W but 500r 12V gives 0.5W so 50r with 12V is near 5W.
On another page is a 0.5W amplifier. This is how they ALL were. This is what the transformers were designed for. It calls for 300r 12V to get the 0.5W, indicating that the design chart took NO allowance for losses.
Because your load is 6.25X lower, everything has to be 6X beefier. The interstage transformer (which is hard to design-out if you go close to class B), the driver, and probably an additional stage because the input is already silly-low impedance.
Attachments
Thank You
Many thanks PRR for the guidance with my experiment with this amplifier.
A half watt may be all I really need to drive my speakers 105 dB/m to easy listening levels.
I will give it a go, and post picture as well as a link to the audio after it is tweaked out.
Have a great day,
Mich
Many thanks PRR for the guidance with my experiment with this amplifier.
A half watt may be all I really need to drive my speakers 105 dB/m to easy listening levels.
I will give it a go, and post picture as well as a link to the audio after it is tweaked out.
Have a great day,
Mich
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