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Title: Parasitics in Some Beam Power Tubes Explained Post by: Tom WA3KLR on June 18, 2010, 03:49:07 PM I just came across this dissertation on the negative resistance in the screen circuit of pentodes. Some of you may find this an interesting article:
http://mysite.verizon.net/dpnewkirk/ej/beam_power_tube_parasitics/ Title: Re: Parasitics in Some Beam Power Tubes Explained Post by: AB2EZ on June 19, 2010, 10:59:27 AM Tom
Thanks! It's interesting to see the mix of engineering theory and practice that folks were stuggling with in the 1930's... and to compare that to the present. Until I read this, yesterday, I didn't know about any of the effects being discussed. Best regards Stu Title: Re: Parasitics in Some Beam Power Tubes Explained Post by: ka3zlr on June 19, 2010, 11:26:20 AM Myself I like Reading what Bill Orr has to say on the subject W6SAI.
73 Title: Re: Parasitics in Some Beam Power Tubes Explained Post by: Tom WA3KLR on June 26, 2010, 09:28:12 AM A bit of ambivalence on the situation didn’t help.
From The Radio Handbook, Twelfth Edition, 1949, Chapter 5 - High Frequency Power Amplifiers, page 103 - 104: “Shielded 807 Amplifier The versatile 807 unquestionably is the transmitting tube most frequently used by amateurs. But it also is a very frequently maligned tube due to its tendency toward spurious signal generation and parasitic oscillation, Nevertheless, the low price and unusual capabilities of the tube overweigh any misgivings about using the tube as a result of its unfortunate tendency toward self-oscillation. It has been more or less established that the 807’s enthusiasm for parasitic oscillation is the result of two factors: (1) the extremely high power gain of the tube, and (2) the sizable screen-lead inductance due to the rather long piece of small wire between the tube socket and the screen element within the electrode structure.” Title: Re: Parasitics in Some Beam Power Tubes Explained Post by: AB2EZ on June 26, 2010, 10:08:24 AM Tom
Yes... It is interesting that there are often (usually?) multiple (candidate) explanations for some sort of undesired or unexpected bahavior. We try one solution ... and it may or may not work. It might work even if the explanation that led us to that solution is wrong. "The difference between theory and practice is larger in practice than it is in theory" Anon Stu Title: Re: Parasitics in Some Beam Power Tubes Explained Post by: KM1H on June 26, 2010, 10:40:52 AM When I first made the transistion from hollow to solid state I thought the days of parasitics and neutralization were over, that was a sad assumption ;D And you didnt even have the benefit of watching a runaway display ::)
Carl Title: Re: Parasitics in Some Beam Power Tubes Explained Post by: w7fox on September 02, 2013, 11:37:52 PM cant get to the article, it is "locked". anyone know how to unlock it? thanks.
Title: Re: Parasitics in Some Beam Power Tubes Explained Post by: Pete, WA2CWA on September 03, 2013, 03:13:17 AM cant get to the article, it is "locked". anyone know how to unlock it? thanks. This might be the same article: http://dpnwritings.nfshost.com/ej/beam_power_tube_parasitics/ Title: Re: Parasitics in Some Beam Power Tubes Explained Post by: w4bfs on September 03, 2013, 04:53:47 AM thanks Pete .... I also was 'locked' .... 73 John
Title: Re: Parasitics in Some Beam Power Tubes Explained Post by: W3RSW on September 03, 2013, 10:01:00 AM Fascinating. Thanks for the link. Read also the Frostburg links, the Wingfoot 6cl6/ 813 stuff and on and on. AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
Also Makes you want to run out and buy a T-60. ;D One of the lab experiments in my 1963 Marietta college electronics course was making up a negative resistance Osc. on purpose with I think a 6au6. I always thought 6146's were squirrelly but that 807's were super stable in comparison. Well. -- Learn something every day. Heck, even my Citation II with KT88's has 100 ohm grid suppressors. Whatever it took to tame the beasts, empirical or otherwise over the years. |