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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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30th Jan 2014, 7:03 pm | #1 |
Retired Dormant Member
Join Date: Aug 2013
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 330
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"That Cap"
Hi all, I am right in thinking that "That Cap" applies only to valve amp players and not transistor players or am I incorrect in that assumption.
Kevin |
30th Jan 2014, 7:22 pm | #2 |
Rest in Peace
Join Date: Sep 2008
Location: Solihull, West Midlands, UK.
Posts: 4,872
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Re: "That Cap"
Only valves. To be more precise: only situations where a coupling cap comes from a high DC voltage and feeds a high DC resistance. This is unlikely to be found in a transistor amp, but I suppose an analogous situation could occur if an electrolytic went leaky - then the voltages and impedances are all much smaller but could perhaps be in the same ratios as for valves.
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30th Jan 2014, 9:06 pm | #3 |
Dekatron
Join Date: May 2008
Location: Derby, UK.
Posts: 7,735
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Re: "That Cap"
It mostly applies only to valve equipment. Leaky capacitors will upset the biasing in transistor circuits, but this is rarely fatal. Remember valves are voltage-operated, depletion-mode devices, which means they default to full conduction with no bias; and also there is more than enough HT voltage, and the circuit impedances are high enough, for even a slight leak to cause problems.
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If I have seen further than others, it is because I was standing on a pile of failed experiments. |
31st Jan 2014, 3:18 pm | #4 |
Dekatron
Join Date: Feb 2007
Location: Lynton, N. Devon, UK.
Posts: 7,088
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Re: "That Cap"
In fact, leakage in "that cap" will put a positive voltage on the grid, relative to chassis - so it doesn't matter if the valve is an enhancement-mode or depletion-mode device. Either way, there's trouble.
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