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101. Re: [Amps] Amps Digest, Vol 43, Issue 70 (score: 1): Author: "Tom W8JI" <w8ji@w8ji.com>; Date: Tue, 18 Jul 2006 10:10:39 -0400; That "trash" starts at anything over zero watts Ed, and it can get better and worse as power is increased. Transistors of course limit with a much more defined change in transfer characteristics tha; /archives//html/Amps/2006-07/msg00570.html (11,183 bytes)
102. Re: [Amps] Life and gain of 3-500Z (score: 1): Author: "Tom W8JI" <w8ji@w8ji.com>; Date: Tue, 18 Jul 2006 12:28:32 -0400; The trend is generally this: Higher quiescent current for fixed bias and HV generally indicates lower mu, not higher. It takes more negative bias to reduce anode current as mu is increased. Lower mu; /archives//html/Amps/2006-07/msg00581.html (9,710 bytes)
103. Re: [Amps] Life and gain of 3-500Z (score: 1): Author: "Tom W8JI" <w8ji@w8ji.com>; Date: Tue, 18 Jul 2006 12:29:58 -0400; What is the fusing current rating of the resistor? Why would you fuse a grid? 73 Tom _______________________________________________ Amps mailing list Amps@contesting.com http://lists.contesting.com; /archives//html/Amps/2006-07/msg00582.html (9,033 bytes)
104. Re: [Amps] RF Chokes (score: 1): Author: "Tom W8JI" <w8ji@w8ji.com>; Date: Tue, 18 Jul 2006 15:28:07 -0400; The actual specs for that choke place the "freespace" series resonances at 11.8 and 16.8 MHz. With a wall 1 inch away the series resonances move to 10.8 and 15.4 MHz. It is 275uH minimum on 1.8 MHz,; /archives//html/Amps/2006-07/msg00586.html (9,338 bytes)
105. Re: [Amps] RF Chokes (score: 1): Author: "Tom W8JI" <w8ji@w8ji.com>; Date: Tue, 18 Jul 2006 16:14:04 -0400; Let's look at that factually for an AL12 series amplifier: The choke reactance is 3120 ohms. The load impedance is 2500 ohms at 1.75kW The RMS voltage is 2100V The RMS choke current is .673 amperes; /archives//html/Amps/2006-07/msg00589.html (9,723 bytes)
106. Re: [Amps] Life and gain of 3-500Z (score: 1): Author: "Tom W8JI" <w8ji@w8ji.com>; Date: Tue, 18 Jul 2006 19:07:27 -0400; Hi Jim, Yes. For a clearer example, look at tubes with very similar internal geometry and ratings but different mu. Try the 3CX3000A1 and 3CX3000A7 You will see the higher the mu, the less grid bias; /archives//html/Amps/2006-07/msg00603.html (11,902 bytes)
107. Re: [Amps] RF Chokes (score: 1): Author: "Tom W8JI" <w8ji@w8ji.com>; Date: Tue, 18 Jul 2006 19:09:14 -0400; The gaps are indeed the key. For the reason I have described many times in the past. 73 Tom _______________________________________________ Amps mailing list Amps@contesting.com http://lists.contest; /archives//html/Amps/2006-07/msg00605.html (8,895 bytes)
108. [Amps] Hi Mu correction (score: 1): Author: "Tom W8JI" <w8ji@w8ji.com>; Date: Tue, 18 Jul 2006 22:55:55 -0400; I do think I made an error in the post about mu, but I deleted my post. Higher mu in a given tube means less bias is needed to maintain the same plate current. Lower mu means more bias is needed to c; /archives//html/Amps/2006-07/msg00612.html (6,296 bytes)
109. Re: [Amps] Hi Mu correction (score: 1): Author: "Tom W8JI" <w8ji@w8ji.com>; Date: Wed, 19 Jul 2006 05:56:23 -0400; It's just the opposite Tony. Lower mu tubes need more bias to maintain a certain plate current, all other things equal.This means lower mu tubes of a given type have more idle current at a certain b; /archives//html/Amps/2006-07/msg00614.html (7,907 bytes)
110. Re: [Amps] 6m AMP Santa Monica (score: 1): Author: "Tom W8JI" <w8ji@w8ji.com>; Date: Wed, 19 Jul 2006 10:43:57 -0400; Stay away from it. It is a CB amplifier and the tubes are obsolete anyway. _______________________________________________ Amps mailing list Amps@contesting.com http://lists.contesting.com/mailman/l; /archives//html/Amps/2006-07/msg00633.html (7,155 bytes)
111. Re: [Amps] Grid fuses (was: Life and gain of 3-500Z) (score: 1): Author: "Tom W8JI" <w8ji@w8ji.com>; Date: Wed, 19 Jul 2006 13:53:35 -0400; Why would a person put a fuse between a control grid and ground? First, if we want to protect for grid current from drive power it should be an electronic protection. Any fuse is well-known to be to; /archives//html/Amps/2006-07/msg00641.html (11,285 bytes)
112. Re: [Amps] Hi Mu, Low Mu (score: 1): Author: "Tom W8JI" <w8ji@w8ji.com>; Date: Thu, 20 Jul 2006 05:53:28 -0400; There are a number of reasons for having the choice available Barry. In an RF amplifier with widely varying load resistance, or with class C operation, the designer generally want lower mu. The reas; /archives//html/Amps/2006-07/msg00658.html (7,584 bytes)
113. Re: [Amps] Grid fuses (was: Life and gain of 3-500Z) (score: 1): Author: "Tom W8JI" <w8ji@w8ji.com>; Date: Thu, 20 Jul 2006 06:08:44 -0400; Bill, What is the typical reliable opening current and opening TIME of a fuse compared to the safe holding current? Have you ever looked at it? What is the reliable opening point (where it goes near; /archives//html/Amps/2006-07/msg00659.html (8,737 bytes)
114. Re: [Amps] Grid fuses (was: Life and gain of 3-500Z) (score: 1): Author: "Tom W8JI" <w8ji@w8ji.com>; Date: Thu, 20 Jul 2006 06:27:42 -0400; It depends on the tube Paul. It's actually accumulated damage over time in gold plated grids. Any period of excessive grid current will cause some gold migration since the kinetic energy of the elec; /archives//html/Amps/2006-07/msg00660.html (11,793 bytes)
115. Re: [Amps] grid fuses (score: 1): Author: "Tom W8JI" <w8ji@w8ji.com>; Date: Thu, 20 Jul 2006 06:38:02 -0400; That's my point exactly Joe. A fuse in the grid is exactly the opposite of what common sense and technically solid logic would dictate in any design. Worse yet, one person advocates removing reliabl; /archives//html/Amps/2006-07/msg00661.html (7,908 bytes)
116. Re: [Amps] grid fuses (score: 1): Author: "Tom W8JI" <w8ji@w8ji.com>; Date: Thu, 20 Jul 2006 11:46:52 -0400; <But for an amateur transmitter, you can replace a resistor (yes, a little <more work involved) and get on the air again. If the fault is severe, both <systems will keep you busy until the problem is; /archives//html/Amps/2006-07/msg00676.html (10,147 bytes)
117. Re: [Amps] Grid fuses (was: Life and gain of 3-500Z) (score: 1): Author: "Tom W8JI" <w8ji@w8ji.com>; Date: Thu, 20 Jul 2006 12:00:06 -0400; No wonder the resistors opened. At 100mA grid current there are already 0,27W heating them up. Most resistors are rated with their wattage at a 25°C environment.>> Actually resistors and fuses bo; /archives//html/Amps/2006-07/msg00678.html (10,895 bytes)
118. Re: [Amps] Grid fuses (was: Life and gain of 3-500Z) (score: 1): Author: "Tom W8JI" <w8ji@w8ji.com>; Date: Thu, 20 Jul 2006 13:13:23 -0400; Not quite Bill. The very reason a tube flashes over in the first place is the anode has a conductive path to the closest element inside the tube, the grid. If we allow the grid to rise by virtue of; /archives//html/Amps/2006-07/msg00681.html (10,705 bytes)
119. Re: [Amps] Grid fuses (was: Life and gain of 3-500Z) (score: 1): Author: "Tom W8JI" <w8ji@w8ji.com>; Date: Thu, 20 Jul 2006 13:37:57 -0400; I suppose it depends on the definition of a few seconds. Littlefuse says the opening time of a low current 3AB fast acting fuse fuse is 15 seconds maximum at 200% overload, and it will eventually fa; /archives//html/Amps/2006-07/msg00683.html (8,712 bytes)
120. Re: [Amps] Grid fuses (was: Life and gain of 3-500Z) (score: 1): Author: "Tom W8JI" <w8ji@w8ji.com>; Date: Thu, 20 Jul 2006 18:42:42 -0400; I calculated that force long ago based on the saturated emission limits of the 3-500Z. The force was in the order of several grams. Normal operating forces caused by AC in the filament were higher.; /archives//html/Amps/2006-07/msg00698.html (10,864 bytes)

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