[Amps] Parasitics

[GGLL]

rlm escribió:

>  
>
>>There's a header that should wake people up!
>>
>>In the latest QST, the article  on maintenance of linears suggests that
>>poor neutralization can lead to parasitics. Not something I've come across
>>before, although obviously, it can depend on exactly what you mean by
>>parasitics - personally, I tend to think of 'parasitics' being 'VHF
>>parasitics' but of course, that's not necessarily the case, although
>>arguably the most common.
>>    
>>
>
>***   I agree, Peter.  Oscillation at the operating frequency is the 
>result of a grid-driven amplifier being out of neutralization.  This is 
>clearly not a parasitic because a parasite is defined as regeneration 
>beyond the operating frequency range. 
>  
>
    I'm chasing a low (400..500 KHz) parasitic oscillation in the output 
brick of a Yaesu FT 747 HF tcvr (1.8 MHz lowest band of transmission).
The output pair starts oscillation at that frequency range at certain 
SWR level, all tcvr taking 10 A from power supply, either SSB or CW. But 
not always and seems not to be related with temperature. It seems to be 
related also with bias regulator transistor. Still chasing the culprit.

Best regards
Guillermo - LU8EYW.