6/30/2023 0 Comments 6sn7 cathode followerI dropped 4 E元4s into the sockets and collected the data in the right hand column. As you look over the table below you probably should mentally multiply the distortion figures for the Edcor transformer by 2.Īlso, I cannot account for the ups and downs in the distortion using the Edcor transformer as opposed to the monotonic decrease observed with the Hammond. I am using the same transformer, the same tubes, the same inverter/driver circuit, and the same DC bias voltages and currents. I really can't account for the difference in any other way. Is this enough to introduce a significant amount of negative feedback? This looks like another side bar investigation. This amounts to a voltage drop of 1.2 volts across a 100 ohm resistor. From this and with the help of a program I wrote I calculate a peak current of 12 mA per tube. At 50 watts the DC (average) current rises to 27.5 mA. The no-signal screen current is measured as 5 mA for all four tubes. The increase in plate current won't be as large as it would have been if the screen voltage had not changed. When the control grid is positive going, the plate and screen current both increase and the screen grid voltage will decrease slightly. Can 100 ohm resistors in series with each screen grid really cut the distortion in half? It is negative feedback. I left them in when going back to the conventional pentode connection. When I tested the ultra linear configuration I had to connect 100 ohm resistors in series with each screen grid to suppress oscillation. I had gotten 2% before but it isn't exactly the same circuit. This time I got 1% at 50 watts and 1000 cycles. In order to check for repeatability I fired up the same amplifier with the Hammond transformer and measured its distortion again. This transformer also has a primary impedance of 3400 ohms. You can't order from their web site but they do have a toll-free order number. Three months after testing the amplifier with the Hammond output transformer I tried it with the product of a new player on the tube transformer stage, Edcor. The 6L6s were connected in a conventional pentode configuration. I used the 6SN7 cathode follower to drive the grids of the 6L6s and the phase inverter/driver to drive the 6SN7. This transformer has a primary impedance of 3400 ohms when the secondary is wired for 8 ohms and terminated in 8 ohms. I set up the tubes with a Hammond 1650K Output transformer. I have this nice amplifier test bed so let's use it to see how 4 6L6s will behave. One for the power supply and the other for the amplifier. I settled on using two 13-1/2 by 5 by 2 for each amplifier. Building two independent amplifiers on the same chassis wasn't possible given the sizes of those available. The reason is that Hammond doesn't make anything big enough to power two 50 watt channels. The design of a two channel amplifier required separate power transformers for each channel. 50 Watt Monoblock Amplifier.Ī quartet of 6L6s seems to be a good choice for a 50 watt (per channel) amplifier.
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