[Amps] SB-220

[Will Matney]

Steve,

That's the way I always looked at it too. But, and here's a big but, I 
read a few webpages that says VHF oscillations are a bunch of bologna. 
These very authors was or still might be high up in the ARRL, I'm not 
sure, and did work for, or still do, the amp manufacturers. They say 
that it's impossible and that it couldn't cause arcing in components. 
Now to me, if the lead(s) length is correct, and the gain high enough, 
the internal capacitance of the tube along with the inductance of the 
lead(s) could make up a VHF oscillator. Another thing is that most tank 
circuits in production amps are hand wired. The lead lengths aren't 
strictly controlled so they cant tell from one to another if they hit 
the sweet spot or not!

It would look to me that over this many years of using parasitic 
suppressors, and having found direct formulas for them from a lot of 
experimentation, anything that says VHF oscillation don't exist would 
have been caught. As far as I know, the ones saying it doesn't happen 
has only been in the past few years. I would think that 60+ years is a 
loooong time to go before catching it? From this, I'd like to hear a 
good discussion and or debate about it.

Best & 73's

Will Matney



Steve Thompson wrote:

>On Wednesday 03 November 2004 18:23, Will Matney wrote:
>  
>
>>To all,
>>
>>A quick question here, and may open up a big can of worms, if there is
>>no such things as parasitics in amplifiers, why do they all come with
>>parasitic suppressors on the anode leads? 
>>    
>>
>There certainly are parasitics (unwanted vhf oscillation) - especially with 
>tubes with long grid leads - but not every amplifier will have the 
>gain/feedback/load to allow oscillation if suppressors aren't fitted.
>
>It's likely that few amplifier builders have the equipment to properly assess 
>whether their amplifier needs a supressor, and/or whether the suppressor they 
>fit actually does the job of reducing the gain by the right amount at the 
>right frequency.
>
>Steve
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