[Amps] 813 No parasitics

[rlm]

>	Ok, you asked Skip; but let me suggest or better saying, ask, could be
>the 30 MHz highest frequency for full ratings?, or maybe at lower
>ratings you could have parasitics also?.

A grid-driven 813 has 0.2pF of (output-input) feedback-C, and even less 
feedback-C in G-G configuration with both grids grounded..  This is 
similar to the feedback-C of modern tubes which have 4 to 12 times the 
max frequency rating of the 813's rating of 30MHz.  Thus, at frequencies 
that are high enough for the XC of the 813's feedback-C to be low enough 
to support regeneration, the 813 does not have enough gain to support 
oscillation.  At 27 - 29MHz, the gain of an 813 is falling like a rock.  
813s are unsurprisingly not popular with CBers.  
>
>Best regards
>Guillermo - LU8EYW.
>
>Rick Cole VK3YM escribió:
>> 
>> Skip wrote
>> >I've not had a case of parasitic problems in grid
>> >driven 813 amplifiers, but I've had my share of
>> >oscillation problems. So few people are building
>> >new 813 projects that most threads quickly wind
>> >down to a dull roar.
>> 
>> Skip.. I am very interested in your remark about the 813 tube...Can you 
>enlighten me...very briefly..as to the reason for lack of parasitics..what 
>makes the 813 so stable as compared to other/similar tubes...
>>            Rick   VK3YM
>> 
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-  R. L. Measures, a.k.a. Rich..., 805.386.3734, AG6K, 
www.vcnet.com/measures.  
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