This is weird. The voltage and current through the tubes is about what I was expecting. With a 1.2 volt input each tube has a about .87 volts output. At the input I have two out of phase sine waves. The same on the output but they are a bit fuzzy on the scope. Am I right in assuming there is something going on inside the tube?
The way you have it wired now, the 6L6 grids are connected to ground through the two 270k resistors. Since you also have a -17V bias supply connected to each 6L6 grid, those two -17V supplies are also grounded (connected to 0 volts). Since your 6L6 cathodes are connected to ground through 10 ohm resistors, the 6L6 cathodes are also (effectively) connected to ground.
That means that you're running your 6L6 tubes with zero bias. I'm surprised they aren't red-plating and burning up.
What is the voltage you measure at the cathodes of the 6L6's (pin 8 on each 6L6)? I'll bet it's something like 1.2V (or higher), which would mean 120mA (or higher) through each 6L6.
The correct way to connect the -17V bias supplies to each 6L6 is to connect each 270k grid leak resistor so that one end is connecting to the 6L6 grid and the other end is connecting to -17V. Only the cathodes of the 6L6's should be connected to ground.
--
That means that you're running your 6L6 tubes with zero bias. I'm surprised they aren't red-plating and burning up.
What is the voltage you measure at the cathodes of the 6L6's (pin 8 on each 6L6)? I'll bet it's something like 1.2V (or higher), which would mean 120mA (or higher) through each 6L6.
The correct way to connect the -17V bias supplies to each 6L6 is to connect each 270k grid leak resistor so that one end is connecting to the 6L6 grid and the other end is connecting to -17V. Only the cathodes of the 6L6's should be connected to ground.
--
Thanks rongon. You were partially right. It didn't make much difference as far as current was concerned. The outputs went from 50ma to 44ma approximately. But the real problem is I left a dirent route to ground for the signal. I knew this once but I seem to forget things too often. It now amplifies but I got a buzz as well so I have to sort that. I think its coming from the bias supply.
Hey Everybody! Last week Tube Depot had a sale on all JJ tubes. So I bought a quad of 7591s and a pair of 12DW7's. I also bought the necessary parts to build a copy of the HK500 power amp section. So I have a conservative backup. I've updated the output section to fit 7591.
I'm going to listen to it with the differential 5751 front end a little later. Depending on that test I may stay with it. Mostly because I prefer the sound of the 5751 to the 12AX7. I'll be back later.
I'm going to listen to it with the differential 5751 front end a little later. Depending on that test I may stay with it. Mostly because I prefer the sound of the 5751 to the 12AX7. I'll be back later.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.