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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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17th Jun 2018, 7:57 am | #41 |
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Re: Cathode follower anode resistor.
" ....to people whose maths is only at MBA level " my playschool level maths makes reading analysis of circuits using lots of formulae hard and I have no idea how to use a spreadsheet, but will try to follow along.
Regarding cathode followers, in amplifiers they are often used to drive difficult loads that can have a capacitive or inductive element like OP valve grids and reverb tanks, hence my original question. I've had no trouble so far though when using cathode followers. A.
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17th Jun 2018, 8:49 am | #42 |
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Re: Cathode follower anode resistor.
Sorry, Andy, you missed the joke. G-J got it, though. It's a background thing
It was a swipe at managers who can't understand what you are doing, but add up all the costs and want everything justifying. It's very difficult to justify something to someone with no background and no interest in what it does. David
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17th Jun 2018, 9:13 am | #43 |
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Re: Cathode follower anode resistor.
MBA = Master of Business Administration.
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17th Jun 2018, 10:18 am | #44 | |
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Re: Cathode follower anode resistor.
Quote:
Yes looking at those diagrams that kalee20 has drawn is completely within my comfort zone in terms of understanding what he is trying to say. |
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17th Jun 2018, 12:53 pm | #45 |
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Re: Cathode follower anode resistor.
Note that the circuit might not be as simplistic as a simple R and small C in the emitter. Doing my best Tom Jones impersonation "It's not unusual" for the small capacitance at the source/emitter of a transistor to look like a short circuit up at UHF. This might be due to a resonance with some wire or the equivalent.
When this happens the circuit can still oscillate up at UHF but the feedback path will be quite different. With a shorted source pin (at UHF) the Colpitts equivalent circuit we have been considering up till now ceases to function because the capacitive tap is now grounded and the feedback path is killed. When this happens, it's the drain to gate capacitance that can become the bad guy that forms the critical feedback path. This alternative oscillator feedback is actually easier to model and understand. Of course, it will get very muddy if you end up halfway between the two cases. The feedback path becomes very difficult to visualise and it's best to try and model it on a simulator. The circuit below looks very similar but because the source is shorted to ground at UHF the internal feedback path is quite different. Fortunately, adding a series 100R resistor in the drain kills this mode as well.
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17th Jun 2018, 12:56 pm | #46 | |
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Re: Cathode follower anode resistor.
Quote:
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17th Jun 2018, 1:25 pm | #47 |
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Re: Cathode follower anode resistor.
Barton L McJunkin
David
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18th Jun 2018, 11:24 am | #48 | |
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Re: Cathode follower anode resistor.
Quote:
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29th Nov 2021, 9:57 pm | #49 |
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Re: Cathode follower anode resistor.
re-opened. Someone would like to introduce himself, so I won't spoil his surprise.
David
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30th Nov 2021, 7:28 am | #50 |
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Re: Cathode follower anode resistor.
Not Lord Lucan?
Andy.
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