> 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 escribi?:
>>
>> 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
>>
>> _______________________________________________
>> Amps mailing list
>> Amps@contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>_______________________________________________
>Amps mailing list
>Amps@contesting.com
>http://lists.contesting.com/mailman/listinfo/amps
>
- R. L. Measures, a.k.a. Rich..., 805.386.3734, AG6K,
www.vcnet.com/measures.
end
|