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101. [Amps] Alpha PA-70V (score: 1): Author: "Jim Garland" <4cx250b@miamioh.edu>; Date: Sat, 17 May 2014 16:13:51 -0600; Anybody got one of the old Alpha vapor-cooled amps still running? A friend just acquired one, but it has some problems (a transformer, if I remember right)? If the tube is still good (he doesn't have; /archives//html/Amps/2014-05/msg00103.html (7,351 bytes)
102. Re: [Amps] LK-500 ZB problem (score: 1): Author: MU 4CX250B <4cx250b@miamioh.edu>; Date: Thu, 29 May 2014 00:33:25 -0400; Vic is correct that most vacuum relay problems result from hot switching. You can often repair vacuum relays whose contacts have been welded shut by holding a magnet against the body of the relay. Su; /archives//html/Amps/2014-05/msg00138.html (9,277 bytes)
103. Re: [Amps] 2 Section Tune Cap Wanted (score: 1): Author: "Jim Garland" <4cx250b@miamioh.edu>; Date: Sat, 21 Jun 2014 13:23:29 -0600; Hi Jim, Here's info on an OEP dual section capacitor that is fairly close to your requirements: p/n 73-2-75-56BE, 2-sections, 17-65 pF and 25-318 pF, with .075" spacing, nominal rating of 2500V. This; /archives//html/Amps/2014-06/msg00067.html (9,300 bytes)
104. Re: [Amps] 2 Section Tune Cap Wanted (score: 1): Author: MU 4CX250B <4cx250b@miamioh.edu>; Date: Tue, 24 Jun 2014 06:50:20 -0600; I agree, Carl, those values don't sound quite right. They were marked in pencil on the back of the cap, but I don't know how they got there. I'll do an accurate measurement today and update the value; /archives//html/Amps/2014-06/msg00073.html (12,782 bytes)
105. Re: [Amps] Buck-Boost Transformer Selection (score: 1): Author: "Jim Garland" <4cx250b@miamioh.edu>; Date: Wed, 25 Jun 2014 11:17:56 -0600; Hi Dick, You don't need a 1.5KV rating. Let's say you want to drop the line voltage by 12V and suppose the maximum current drawn from the AC line by the amplifier is 15 Amps. You'd thus need only a 1; /archives//html/Amps/2014-06/msg00077.html (8,929 bytes)
106. Re: [Amps] dual section cap (score: 1): Author: "Jim Garland" <4cx250b@miamioh.edu>; Date: Wed, 25 Jun 2014 17:07:37 -0600; Carl, I remeasured the cap, and the two sections are 17-63pF and 24-316 pF, pretty much what I had measured before N years ago. A single section cap on the same frame would be 379 pF, or maybe a smid; /archives//html/Amps/2014-06/msg00091.html (9,522 bytes)
107. Re: [Amps] dual section cap (score: 1): Author: MU 4CX250B <4cx250b@miamioh.edu>; Date: Wed, 25 Jun 2014 19:32:03 -0600; Interesting, Carl. I don't understand why the minimum capacitance on the small section is so high. I suppose I could remove a plate nearest the frame of the capacitor, but I wouldn't think that would; /archives//html/Amps/2014-06/msg00096.html (11,426 bytes)
108. Re: [Amps] Buck-Boost Transformer Selection (score: 1): Author: "Jim Garland" <4cx250b@miamioh.edu>; Date: Wed, 25 Jun 2014 22:42:10 -0600; Hi Dick, I believe you are misinterpreting the KVA rating in the table. The KVA refers to the power dissipated in the load (i.e., your amplfier) and not the KVA rating of the buck-boost transformer.; /archives//html/Amps/2014-06/msg00098.html (14,285 bytes)
109. Re: [Amps] Buck-Boost Transformer Selection (score: 1): Author: MU 4CX250B <4cx250b@miamioh.edu>; Date: Thu, 26 Jun 2014 11:06:42 -0600; I agree with Manfred's comments exactly. When I referred to "peak power" in my example, what I actually meant was the RMS power drawn by the Quadra from the AC line when it is driven to its maximum o; /archives//html/Amps/2014-06/msg00105.html (11,969 bytes)
110. Re: [Amps] Circuit Board Question (score: 1): Author: "Jim Garland" <4cx250b@miamioh.edu>; Date: Fri, 1 Aug 2014 08:26:30 -0600; I use 0.25 inch trace widths on 1 oz copper (tinned w/solder mask) on a .063" PCB. Lenghs are under 1.5 inch, with PCB-mount power relays doing the switching. Tested extensively at 2.5 KW from 1.8-30; /archives//html/Amps/2014-08/msg00002.html (9,807 bytes)
111. Re: [Amps] Drake L7 issue (score: 1): Author: MU 4CX250B <4cx250b@miamioh.edu>; Date: Thu, 25 Sep 2014 14:17:59 -0600; Joe, measure the 220 VAC and make sure that's what you really have. Next, check the the jumper wiring in the L7 to make sure it's configured properly for your current line voltage. You can measure HV; /archives//html/Amps/2014-09/msg00025.html (8,019 bytes)
112. Re: [Amps] Solid State Amps (score: 1): Author: "Jim Garland" <4cx250b@miamioh.edu>; Date: Fri, 17 Oct 2014 14:22:43 -0600; A fascinating writeup, Manfred. Thanks! Wonder if you could elaborate or provide a referene on "... we need to place our RF power transistors in half bridge or full bridge configurations, with effect; /archives//html/Amps/2014-10/msg00132.html (16,876 bytes)
113. [Amps] Reducing heat in tetrode amps with EBS (score: 1): Author: "Jim Garland" <4cx250b@miamioh.edu>; Date: Thu, 30 Oct 2014 11:51:04 -0600; Some people don't like tri-state EBS to cut down on heat in tetrode amps, but I found it works very well in my homebrew 3-tube GU74B amplfier and is easy to implement. The three bias levels are -120V; /archives//html/Amps/2014-10/msg00258.html (11,091 bytes)
114. Re: [Amps] Reducing heat in tetrode amps with EBS (score: 1): Author: "Jim Garland" <4cx250b@miamioh.edu>; Date: Fri, 31 Oct 2014 05:53:04 -0600; Hi Gary, I agree completely with your numbers. It's not hard to make the input switch at a lower RF level, but I didn't do that because it would have complicated the RF sensing circuit (which now is; /archives//html/Amps/2014-10/msg00271.html (15,547 bytes)
115. Re: [Amps] L4B biasing (score: 1): Author: MU 4CX250B <4cx250b@miamioh.edu>; Date: Wed, 24 Dec 2014 14:30:58 -0700; Mike, it's hard to answer your question without knowing a few more details. Do you operate much CW, or mostly SSB? Also, have you thought about modifying the RF deck to use electronic T/R switching,; /archives//html/Amps/2014-12/msg00098.html (7,999 bytes)
116. Re: [Amps] Power from Pair of Eimac 4 x 150 a / 7034? (score: 1): Author: MU 4CX250B <4cx250b@miamioh.edu>; Date: Sun, 28 Dec 2014 20:31:42 -0700; I'm a bit worried about the reliability of the Chinese 8877s. One in my Alpha 9500 started arcing internally after about 100 hours of service. Alpha replaced it under warranty, and now the replacemen; /archives//html/Amps/2014-12/msg00134.html (14,433 bytes)
117. Re: [Amps] The genius of ham radio (score: 1): Author: "Jim Garland" <4cx250b@miamioh.edu>; Date: Mon, 12 Jan 2015 09:11:14 -0700; This is a recurring debate, a bit off topic, but probably worth rehashing from time to time. The science underlying our hobby is literally undeniable. Further, there is a century of engineering histo; /archives//html/Amps/2015-01/msg00040.html (10,999 bytes)
118. Re: [Amps] The genius of ham radio (score: 1): Author: "Jim Garland" <4cx250b@miamioh.edu>; Date: Mon, 12 Jan 2015 23:07:33 -0700; Hi Guys, This discussion has veered into the interesting area of scientific theories, laws, facts, truths, pseudoscience, etc., and how one can tell which is which. A couple of years ago I gave a spe; /archives//html/Amps/2015-01/msg00070.html (9,971 bytes)
119. Re: [Amps] High Voltage Wire (score: 1): Author: "Jim Garland" <4cx250b@miamioh.edu>; Date: Mon, 19 Jan 2015 15:18:38 -0700; I've lately been using high temperature stranded red test lead wire, 10KV rated, silicone insulation. It's sold by MCM Electronics, part number 201-125, $25.95 for a 50 ft coil and is made by Pomona; /archives//html/Amps/2015-01/msg00158.html (10,820 bytes)
120. Re: [Amps] Topband: Elimination of Treadmill RFI on 160 meters (score: 1): Author: "Jim Garland" <4cx250b@miamioh.edu>; Date: Sat, 31 Jan 2015 07:58:39 -0700; I'm not disagreeing with anything you said, Jim, and I don't believe Tom is either. We're just making the point that a common mode choke's effectiveness in blocking common mode currents depends on th; /archives//html/Amps/2015-01/msg00382.html (12,698 bytes)

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