[AMPS] SB1000 parasite question for Tom and Rich+

Tom Rauch W8JI@contesting.com
Thu, 3 Aug 2000 22:12:00 -0400

> Rich it seems to me that one way to reduce vhf gain would be not to use
> tubes ( very expensive ones) that have max. ratings to 500 mhz  on
> frequencies of 30 mhz or below. if it will amplify at 200 mhz it should
> also oscillate.....yes??   HANK

Hi Hank, 

How do all those big fancy amplifiers with lighthouse tubes or big 
tubes in cavities with extreme Q's not oscillate?

Actually that is exactly backwards. The most stable HF amplifiers 
use tubes that are good well up into VHF or UHF.

The LEAST stable amplifiers use tubes that marginally work at 30 
MHz, like 811A's or 572B's.

It's always been that way and will always be that way.

It isn't difficult at all to check an amp for stability, almost anyone 
can do it.

The real reason this nichrome thing has gone on so long is 
because people want a single simple answer to any problem they 
might have. It makes anyone an instant expert, and they don't have 
to understand a thing about tubes, oscillators, switches, radios, 
relays or anything else.

All they have to do is click their heels together and say...."there's 
no problem but parasitics...there's no problem but parasitics..."

Before you know it, your an expert on the sole cause of any failure 
or abnormal operation....and you know the sole cure....a sprinkle of 
something that doesn't hardly change the VHF Q.


73, Tom W8JI

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