The original G2DAF was a grid driven amp with a swamping resistor to define 50
ohms.
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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