>
>Tom Rauch wrote:
>>> > One factor that apparently
>>> >increased the Warrior's VHF instability was so-called
>>> >"neutralization".
>>>
>>> "So-called" is correct. According to the schematics, it consisted of a
>>> feedback capacitor from the output end of the pi-tank, back to the
>>> cathode. This will produce feedback of variable amplitude and phase,
>>> depending on the settings of the bandswitch and the tuning and loading
>>> controls. It's hardly surprising that the amp was more liable to
>>> oscillate at some frequency.
>>
>>That is NOT correct Ian. Bad enough that Rich says things without
>>being fully aware what is going on!
>>
>>The feedback in the Warrior is from the anode, through a capacitor,
>>through a phase inverting transformer, to the filaments.
>>
// Rich is fully aware that the 811's filament is the "cathode" (Ian).
>>The tuning of the tank has a very minimal effect on phase shift.
>>This is a simple modified bridge system.
>>
>>I think you are wrongly confusing it with the system in a Yaesu
>>572B amplifier where feedback is taken AFTER the output tank,
>>which of course WOULD shift phase with tank tuning and
>>destabilize the amplifier at HF with some tank settings.
>>
>Sorry, it appears I was confusing the Warrior with another amp... maybe
>the Yaesu, though I don't recall ever seen that schematic.
>
// The Warrior and the Gonset 4, 811A amplifier used the same
neutralization scheem.
>I agree that a phase inverting transformer, coupled as you describe,
>produces a bridge neutralizing arrangement which is pretty much as
>broadband as the transformer itself.
>
// However, there must be a frequency-dependent phase shift somewhere
since such is known to regenerate above HF.
>>> >Gonset also used neutralization in their 4, 811 amplifier.
>>>
>>> I'm not familiar with that schematic: would that be real
>>> neutralization, or more of the bogus kind?
>>
>>Before you say "bogus", you should look at the system. It works
>>very well in Heath's amp and other amps. It has nothing to do with
>>VHF oscilations, it is to stabilize the amp at upper HF.
>>
>I applied the term "bogus" to the system I described, not the one that
>is actually in the Heath Warrior.
>
// blowin' smoke
>>Let's not feed people trying to learn misinformation Ian!
>>
>Sorry, I was misinformed myself!
>
// perhaps not.
cheers, Ian
- R. L. Measures, 805.386.3734,AG6K, www.vcnet.com/measures.
end
--
FAQ on WWW: http://www.contesting.com/FAQ/amps
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
|