2 wrote:
>>Feedback C is significant, but is only one of the factors that determine
>>VHF stability. The factor that is usually more important is the length
>>and inductance from grid to ground.
>>
>>When there are no other feedback paths except through the tube, and the
>>grid ring is grounded directly to the chassis by a finger-stock, an 8877
>>amp can be unconditionally stable at all VHF frequencies - that means
>>stable with any input or output loads (or none) in any combination.
>
>** I have autopsied 6 gold-sputtered 8877s from HF amplifiers that
>used the Eimac 135305 grid-grounding collet. [ref Figure 24 on my Web
>site] The inductance of an 8877 grid + base flange appears to be c.
>15nH. The collet appears to have c. 7nH.
How do you arrive at those inductance figures? What do believe they
show, and why?
>>
>>Thousands of 8877 VHF amps out there can testify to that.
>
>** I know of no case of VHF/UHF gold-sputtering in other than HF
>amp;ifiers
How many 887s from VHF amps have you looked at? Again, what do you
believe that shows, and why?
If an 8877 can be made unconditionally stable in a VHF amp, with input
and output deliberately tuned to the same frequency, and then you move
it into an HF amp (keeping the same VHF-style grid grounding
arrangement), then why shouldn't it still be stable at VHF?
--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek
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