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Old 11th February 2014, 10:21 PM   #51
rleejr is offline rleejr  United States
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Originally Posted by SY View Post
If they're direct coupled, it's important. If they're AC coupled, it isn't.

Does this mean that if I have a LTP with 43K plate loads and a CCS in the tail, and the first grid is AC coupled via a 0.22u cap followed by a 1 Meg resistor to ground, while the second grid is only AC coupled via a 0.22u cap to ground, that there will only be balanced currents through the loads during signal (program) conditions? At idle with no signal applied, only the first triode will conduct due to the cathode bias via the 1 Meg resistor? Is this correct? When I built my amp, I measured a voltage drop on one triode load but no drop on the second.

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Old 11th February 2014, 11:28 PM   #52
SY is offline SY  United States
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What's the DC reference of the grid that's cap coupled to ground?

If the input half of the diff amp is DC ground referenced, take the second section grid straight to ground. At AC, your balance will then be as perfect as the matching of the plate resistors. At DC, the plate voltages will vary unless the sections are perfectly matched or you put some sort of adjustment in the cathodes.
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