Hi all,
I am trying to modify the attached circuit to use two parallel section of a 6922 tube for the gain stage instead of the 6GK5 while keeping the second 6GK5 cathode follower. In a previous version of this mod I had the two parallel section of the 6922 followed by a mosfet buffer and all worked fine.
The heaters are 12.6 DC regulated DC heaters with the tube connected in parallel. The original circuit had the two heaters for the 6gk5 on each channels connected in series. With the first tube a 6922 I can no longer do this as the 6922 and 6gk5 heater have different impedances and thus the voltage on each heater will not be the same. I modified the heater supply to feed two 6922 in series and the two 6gk5 heaters in series. both of these are connected in parallel to the 12.6v regulated supply. In doing so I am getting a high buzz on the output of the preamp. Music is playing and it looks like the voltages measure OK but the buzzing is very high. Any idea what's going on?
Thanks,
Ron
I am trying to modify the attached circuit to use two parallel section of a 6922 tube for the gain stage instead of the 6GK5 while keeping the second 6GK5 cathode follower. In a previous version of this mod I had the two parallel section of the 6922 followed by a mosfet buffer and all worked fine.
The heaters are 12.6 DC regulated DC heaters with the tube connected in parallel. The original circuit had the two heaters for the 6gk5 on each channels connected in series. With the first tube a 6922 I can no longer do this as the 6922 and 6gk5 heater have different impedances and thus the voltage on each heater will not be the same. I modified the heater supply to feed two 6922 in series and the two 6gk5 heaters in series. both of these are connected in parallel to the 12.6v regulated supply. In doing so I am getting a high buzz on the output of the preamp. Music is playing and it looks like the voltages measure OK but the buzzing is very high. Any idea what's going on?
Thanks,
Ron
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It's
a conrad johnson Pr14 and yes, the heaters to have a ground reference. See attached schematic
Disconnect the filament connections and turn it on with the battery. See if this. buzz ..can be removed?
where ground ? filimant not conect to ground . The circuit inside the blue circle is for hum reject not for buzz.
The lifted filament power supply is +40v and +52v between the fillament terminals. If I connect it to ground, will I not short the B+ power supply to ground? How do I ground this?
It cannot be grounded ,,, the manufacturer used a Ham rejection circuit. And grounding it contradicts its function. Remove this circuit and ground it with a 68 ohm resistor. please Test it nothing happens to the power supply.
The lower power supply is isolated from the upper one. There is no danger unless there is something we don't see in the schematic.
Hum and buzz is caused by leakage current between the heater and cathode,
Never leave a heater circuit floating; must have a DC reference. Grounding one side is simple and often sufficient. use 100 ohm .
Never leave a heater circuit floating; must have a DC reference. Grounding one side is simple and often sufficient. use 100 ohm .