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Old April 16th, 2010, 04:37 PM   #1 (permalink)
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Need help with input/grid resistor wiring

I have a VHT Special 6 with the typical high/low input wiring-1meg resistor and pair of 68ks feeding pin 2 of the 12AX7 via shielded wire. I was getting a lot of rf interference so I added a 68k resistor right at the tube socket and that killed it. Should I replace the pair of 68ks on the input jacks with straight wire to prevent the inputs from being loaded down too much?

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Old April 16th, 2010, 06:12 PM   #2 (permalink)
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If you ever want to use the two inputs together, you will need those 68K's, they are not grid stoppers, but mixing resistors.

If the amp has not become too dark for you, then no need to worry about the extra resistor. The series resistance in conjunction with the miller capacitance of the tube form a low pass filter. If its corner frequency is still to high to bother you, but low enough to kill the RF, then you are good go go.
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Old April 16th, 2010, 11:49 PM   #3 (permalink)
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Thanks for the response.
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Old April 18th, 2010, 09:07 AM   #4 (permalink)
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If you should encounter the same problem again solder a 220 picofarad from the grid to the grund.The next step if the interference doesnīt stop is a ferrite bead on the wire to the grid.For now it ainīt broke,so donīt fix it.
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