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Old 30th March 2005, 01:45 AM   #1
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Default Placement of power amp imput resistor

What is best practice for placement of the input load resistor of a tube power amp? On the jack, or in the circuit closer to the tube grid?
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Old 30th March 2005, 09:17 AM   #2
EC8010 is offline EC8010  United Kingdom
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It doesn't matter much. I would probably put it close to the valve, but Quad put it on the input socket of their Quad II power amplifier.
The loudspeaker: The only commercial Hi-Fi item where a disproportionate part of the budget isn't spent on the box. And the one where it would make a difference...
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Old 30th March 2005, 09:34 AM   #3
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I put mine directly on the input tubes socket.
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Old 30th March 2005, 11:09 PM   #4
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It does not matter from the grounding point of view.

I put it on the input socket to reduce the mess on the tube. Especially if you are using twin triode tubes, there is too many components there already.
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Old 31st March 2005, 12:14 AM   #5
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I recommend placing it on the tube socket if at all possible. This will apply its low pass filtering (allong with the tube's miller capacitance) to remove radio frequencies on the amp input AND picked up anlong the wire to the tube. But it is not very critical, and many amps work just perfectly without this resistor. I sometimes try to have the tube socket physically close to what drives it (either volume pot or input jacks) and then use the input resistor as the connection between them to save wiring.
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Old 31st March 2005, 01:15 AM   #6
anatech is offline anatech  Canada
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I've always seen it on the input jack. Especially on old equipment, and I really respect the older engineers who designed those. The tube sockets are busy enough already.
Guess where I install mine.
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Old 31st March 2005, 02:47 AM   #7
Sherman is offline Sherman  United States
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How about putting the input jack close to the tube (on the opposite side from the heater wires) and soldering it to both?
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