Strange as it may seem, viewers have asked for additional info on output transformers. Here we cover how to fool output tubes into seeing a different load, and why you'd want to.
Howdy. No intention to be a wise guy. Increasing the tube impedance with a series resistor with the loudspeaker will shift the low end roll-off upwards. The iron will saturate at a higher frequency. Might be good to have in mind. Regards.
Your comment is appreciated - you're only being a 'wise guy' in the most positive sense. Your observations are correct, although those effects will be relatively minor in a guitar amplifier when just tweaking the secondary load to observe the overall effects (output power, distortion characteristics).
@@auburnamplifiers1786 Howdy again. Thank You very much. I observe Hammond guitar output trafos roll off at about 70 - 80 Hz on spec power. So Yes. Minor effect. Regards again.
Is there any way you would make a video on different parameters of output transformer let's say for 100W plexi and tell how all of the parameters affect the tone
On the project I am building the original OT had 8 and 15 Ohm taps on the Sec side. The cab that came with the amp originally had 2 x 8 Ohm speakers wired in series, so I assume the 8 Ohm tap from the OT was not utilised. However all three wires, Common, 8 & 15 ohm went from the OT to a three pin Switchcraft male jack. A cable with switchcraft female three pin XLR plus jacks on each end connected the head to the cab. If the OT sec winding had a 15 Ohm impedance but a 16 Ohm speaker load is connected, does this increase or decrease the effective load on the plates. The schematic states an 8000 Ohm anode to anode impedance for the EL84's.
Sorry for the late replay, Allan. A 16 ohm speaker load on a 15 ohm secondary tap decreases that plate-to-plate load to about 8.5k (higher impedance = DEcreased load). In practical terms this will have very little impact on the power delivered to the load. There may be slightly more third order distortion. As an experiment, try the 8 ohm tap into a single speaker and see if you can detect a difference in the distortion character. Given the nonlinear nature of speaker impedance, the difference will be very subtle. Have fun!
