>>>? Adjusting C-tune makes little difference in the anode resonance since
>>>C-tune is effectively in series with C-anode, which is much smaller.
>>
>>Not necessarily, Rich. In many, many tubes .......
>>
>? What is the anode-resonance when your amplifier is tuned to 10m? .
>. to 80m?
>thanks.
>
The "typical" anode resonance of a 4-1000A is around 80 MHz. However, with my
current design that uses NO suppressor resistors in the anode, I cannot find a
resonant dip on my GDO in that region or anywhere near it. I've covered this.
What does your question have to do with the validity of the "load pull" test?
>>Additionally, I've always thought that Canode was the capacitance from the
>>anode to ground. Ctune is also connected to ground. So I fail to see how
>>Canode and Ctune are in series.
>>
>? one end of C-anode connects to C-tune through chassis gnd. When
>viewed from the ungrounded ends, these two caps are in series and they
>are in parallel with the interconnecting lead inductance.
>
Let's see. I have a cap to ground an inductor and a cap to ground. Kind of
the same type of circuit as I pi-filter network. It looks like a tank
circuit. But I didn't think you could really consider two elements connected
to ground in a circuit like that to really be in series. Are you saying then
that if Ctune and Canode are each 15pf, then the total capacitance is 7.5 pF?
Still it makes no difference because C-anode is NOT much smaller than C-tune
which was your original point. The capacitance values are each on the same
order of magnitude which means that the values ARE important.
>>And when Ctune is rotated through its value we aren't trying to change the
>>resonant frequency of the anode.
>
>? In practice the resonant frequency typically exhibits little change as
>C-tune is adjusted.
>
Uh...isn't that what I said? I said we AREN'T trying to change the frequency.
Please stop talking in circles. What I did say is we are looking for a
reactive load that will make the gain and phase margins of the amp such that
the amp will oscillate. It will oscillate at that anode resonant frequency.
>>What we are doing is rotating a reactive
>>load around the Smith chart.
>
>? In cases where a C-tune internal resonance happens to be near the
>anode-resonance (AL-80, SB-1000) the test may produce an oscillation.
My C-tune isn't resonant near 80 MHz.
.
> A better test is to provide a continuous string of anode current pulses
>that are passing through the anode-resonant circuit and creating a string
>of damped-waves.
Rich, go back and read my post to the guy who questioned how he could test the
stability of his amp. Point 2 suggests keying the amp at high speeds. Is the
load pull test the ONLY test? Heck no. It is A test and an important one at
that. I guess you know better than most of the rest of the industry.
>>
>>How can you prove to me that a test is useless that so many others
>>including myself have used to find out wether the amp oscillates?
>
>? In my opinion, the test is not a fool-proof way of starting an
>oscillation.
Of course not. But it is a way. It is a test. And it can work.
>>
>>If the value of Ctune makes no difference
>
>? Did I say this?
Uh, yes. I quote from you:
? Adjusting C-tune makes little difference in the anode resonance since C-tune
is effectively in series with C-anode, which is much smaller.
OK, OK I was incorrect. You didn't say "no" difference. You said "little"
difference.
73,
Jon
KE9NA
--------------------------------------------------------------------------
Jon Ogden
jono@enteract.com
www.qsl.net/ke9na
"A life lived in fear is a life half lived."
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