>Rich Measures wrote:
>>
>>This circuit is not found in *Care and Feeding of Power Grid Tubes*.
>
>So?
>
>If it isn't in "C&F" or some other 30-year-old publication, does that
>mean that it can't exist or can't be correct? A few new things have
>happened since then.
IMO, the laws of physics do not change substantively. For example, 'Cold
Fusion' doesn't.
>
>> I liked Ian White's comment that, due to phase shift, every
>>negative-feedback [neutralization] circuit (at the fundamental frequency)
>>becomes a positive-feedback [regeneration] circuit at some higher
>>frequency.
>
>No, not "some higher frequency": I said "some DIFFERENT frequency".
>My own main concern is with VHF/UHF amps that need to be stabilized on
>LOWER frequencies. It just shows that you have to consider each case
>very carefully on its own merits.
As long as capacitive reactance decreases with frequency and capacitive
susceptance increases with frequency, the chance of parasitic
oscillations on lower frequencies seems a bit unlikely to me. How many
amplifiers do we see with VLF suppressors?
>I still have to smile about the alleged damage caused by VHF
>oscillations to tubes such as the 3CX800 and 8877, which will happily
>pump out 1kW or more in amplifiers for 50, 144, 220 and even 432MHz.
In a VHF amplifier, there is one resonant circuit connected to the
anode--i.e., the VHF tank itself. However, in an HF amplifier, two
resonant circuits are connected to the anode. One circuit is
HF-resonant. The other circuit is VHF-resonant. This can be checked out
yourself with a dipmeter, Ian. If you find that I am in error, please
publish your findings here. Too bad you don't live a bit closer. I
have a decapitated 8877 on the shelf that--when viewed under a
microscope--provides a pretty good example of early-stage gold
sputtering. There are five areas of gold pooling and a number of gold
blisters on the grid that have burst their tops and strewn gold
melt-balls about the cathode--as Eimacs' Mr. Foote described.
And.........if you get smiled-out on that one, I have another gold
sputtered 8877 in the garage that WE can decapitate and examine for
another round of laughs.
Rich---
R. L. Measures, 805-386-3734, AG6K
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
|