WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
Building, troubleshooting and testing of these amplifiers should only be
performed by someone who is thoroughly familiar with
the safety precautions around high voltages.
Hi everyone, I have built a rogers cadet 3 power amp, I have used replacement opt transformers that only have 4 + 8 ohm speaker connections, is there anybody who can help regarding the feedback connection to 8 ohms as it comes from a 15 ohm terminal. Many thanks, Paul
The key fact to getting the requisite value adjustment is that the impedance ratio is the square of the turns ratio. Remember, the signal at an 8 Ω tap has been stepped down further than the signal at a 15 Ω tap. Therefore, the % of the O/P voltage fed back has to be reduced.
We should mention too, that if you get oscillation with the feedback connected (anything from a loud squeal right down to a low rumble) then reverse the 2 primary anode connections. So do not use your best speakers for initial testing.