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Article #15435Re: Query - How valves and transistors work
From: John Woodgate
Date: Tue, 05 Jan 1999 00:00
Date: Tue, 05 Jan 1999 00:00
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<36918728.5ED6F1BF@ieee.org>, Roy McCammon <rbmccammon@ieee.org> wrote: > >Again speculating from very little info, >I again wonder if the lowish ra in a triode wasn't >because of capacitive feedback. No, the ra is low even at d.c. Upping the plate voltage pulls more electrons through the grid from the space-charge. In a pentode, the electric field from the plate stops at the (grounded) suppressor, so the space charge never 'sees' any change in plate voltage. One thing about tubes is that it's easy to see how they work. > Were these things >charcterized by a gain-bandwidth product >like compensated op-amps whereby the gain >went down as 1/f ? If you mean 'Was a GB product quoted in data sheets'?, the answer is no, at least in general. I don't know about UHF triodes like 955, EC53 and EC91. If we take the 12AT7/ECC81, its ra is 10 k. I don't know what Cag is, but if it's 1 pF, and Ra is also 10 k, the grounded-cathode gain is 3 dB down at 32 MHz due to Cag. One would only use a triode normally as an oscillator at such a frequency (until UHF, when the grounded-grid configuration is useful). -- Regards, John Woodgate, Phone +44 (0)1268 747839 Fax +44 (0)1268 777124. OOO - Own Opinions Only. You can fool all of the people some of the time, but you can't please some of the people any of the time.
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X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: 107d45,6f59d673fceaf3aa X-Google-Attributes: gid107d45,public X-Google-Thread: 114713,6f59d673fceaf3aa X-Google-Attributes: gid114713,public X-Google-Thread: 112d1e,6f59d673fceaf3aa X-Google-Attributes: gid112d1e,public X-Google-Thread: 1110fe,6f59d673fceaf3aa X-Google-Attributes: gid1110fe,public X-Google-Thread: 10b271,6f59d673fceaf3aa X-Google-Attributes: gid10b271,public X-Google-Thread: 111d0a,6f59d673fceaf3aa X-Google-Attributes: gid111d0a,public X-Google-Thread: 1118be,6f59d673fceaf3aa X-Google-Attributes: gid1118be,public X-Google-Thread: fcc1a,6f59d673fceaf3aa X-Google-Attributes: gidfcc1a,public From: John Woodgate <jmw@jmwa.demon.co.uk> Subject: Re: Query - How valves and transistors work Date: 1999/01/05 Message-ID: <zNH$ufAcIdk2EwWE@jmwa.demon.co.uk> X-Deja-AN: 429145648 X-NNTP-Posting-Host: jmwa.demon.co.uk:158.152.135.100 References: <368691bc.0@stargazer.actinet.net> <76b08g$jo4$1@news-1.news.gte.net> <76b8i0$rqm$1@computer.my.domain> <fuNEGVAumei2EwR5@jmwa.demon.co.uk> <76dss3$fhq$1@computer.my.domain> <d1dLzCAjKri2EwAr@jmwa.demon.co.uk> <76ibj9$rhc$1@computer.my.domain> <76ja03$gud$1@news-2.news.gte.net> <36902872.9500D4B6@ieee.org> <FGjCsOAN6Gk2EwhO@jmwa.demon.co.uk> <36918728.5ED6F1BF@ieee.org> X-Complaints-To: abuse@demon.net X-Trace: news.demon.co.uk 915569771 nnrp-05:23272 NO-IDENT jmwa.demon.co.uk:158.152.135.100 Organization: JMWA Electronics Consultancy MIME-Version: 1.0 Newsgroups: sci.physics,fj.sci.physics,sci.physics.electromag,tnn.physics,news.electronics.basics,sci.electronics.basics,sci.electronics.components,sci.electronics.design,sci.electronics.misc