>
>The original G2DAF was a grid driven amp with a swamping resistor to
>define 50 ohms.
>
? In Class AB1, surely. However, with the grid drawing current, the
grid swamping resistor defines nothing.
- later, John ZS5JF
>
>----------
>> From: Tom Rauch <w8ji@contesting.com>
>> To: amps@contesting.com
>> Subject: Re: [AMPS] The DAF Amp
To: <amps@contesting.com>
>> Date: 13 July 1999 07:06
>>
>>
>> > ? In the DAF circuit, it seems to me that there is no RF neg. feedback.
>> > Am I missing something, Tom?
>>
>> Yes, or maybe I am.
>>
>> The G2DAF circuits I've seen might have been modifications of the
>> original design, but they were all cathode driven with screen voltage
>> robbed off the exciter power.
>>
>> All cathode driven amplifiers have negative feedback, because the
>> input is in series with the output. The same current flows through
>> both.
>>
>> The feedback is set by the ratio of anode load impedance to
>> cathode driving impedance. The smaller the impedance ratios, the
>> more the negative feedback.
>>
>> Of course none of that applies to a grid driven PA, unless you add
>> an RF friendly cathode resistance to induce the same type
>> feedback.
>>
>> > >I've seen that in measurements here. However,
>> > >the same tube has ALWAYS been cleaner with the DAF circuit
>> > >disconnected in tests I've made.
>> > >
>> > >I should also point out I can get good IMD performance at one drive level
>> > >with a class C power amp, if I carefully tune it.
>> >
>> > ? However, there are infinite drive levels with voice modulation.
>>
>> That's one reason why a fixed level two tone test is a poor indicator
>> of voice performance in an amplifier, especially one with imperfect
>> power supplies and biasing.
>>
>>
>> 73, Tom W8JI
>> w8ji@contesting.com
>>
>> --
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>
>--
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>
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
--
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