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221. [Amps] plate voltage meter shunt (score: 1): Author: John Lyles <jtml@losalamos.com>; Date: Sat, 03 Nov 2012 22:31:56 -0600; Both Caddock and EBG offer some very high voltage precision 1 and 0.1% film resistors. Not cheap but when you want performance, they have it. I assume you mean meter multiplier resistors, not meter s; /archives//html/Amps/2012-11/msg00034.html (8,578 bytes)
222. [Amps] Amplifier sale scam (score: 1): Author: "John Lyles" <jtml@losalamos.com>; Date: Fri, 11 Jan 2013 09:40:54 -0700; I did a search on Craigs list (nationwide) about a QRO amplifier, as there seemed to be a deal floating around. It was a QRO HF 2500 going for $1500 or 1600. It turned up in Boston and also in LA, si; /archives//html/Amps/2013-01/msg00069.html (8,431 bytes)
223. [Amps] How to get the blue markings off of aluminum stock (score: 1): Author: "John Lyles" <jtml@losalamos.com>; Date: Tue, 22 Jan 2013 18:36:48 -0700; The manufacturers of commercial equipment will remove it with abrasive action. Usually all sheet metal panels can be orbital sanded lightly to not only remove this but also the various tics and surfa; /archives//html/Amps/2013-01/msg00137.html (8,756 bytes)
224. [Amps] 500 uh plate choke (score: 1): Author: John Lyles <jtml@losalamos.com>; Date: Thu, 24 Jan 2013 05:34:28 -0700; K5UJ posted a really great idea to test an RF Choke for resonances, without needing even a GDO, (although every ham should still have one of these - in addition to an Almost All Digital L/C IIB meter; /archives//html/Amps/2013-01/msg00139.html (7,822 bytes)
225. Re: [Amps] Peter Dahl transformers (score: 1): Author: "John Lyles" <jtml@losalamos.com>; Date: Wed, 13 Feb 2013 10:38:01 -0700; Peter did make some nice transformers. He was not the first to make tape wound steel cores of course. I have them in an ancient Raytheon chassis that ran them at 10 KHz for ultrasonics. Westinghouse; /archives//html/Amps/2013-02/msg00101.html (8,182 bytes)
226. [Amps] reasonable design (score: 1): Author: "John Lyles" <jtml@losalamos.com>; Date: Thu, 21 Feb 2013 14:04:27 -0700; I have followed recent threads that go back and forth about cooling transformers and use of switch mode technology for HV. I have two practical examples that I will share that demonstrate that these; /archives//html/Amps/2013-02/msg00177.html (11,009 bytes)
227. [Amps] Freescale and NXP VHF LDMOS Fets (score: 1): Author: John Lyles <jtml@losalamos.com>; Date: Sat, 23 Feb 2013 09:41:00 -0700; The newest LDMOS high power transistors are being grabbed up by commercial amplifier production, for HDTV (band II VHF and into UHF) and FM broadcast amplifiers and for scientific. I didn't mention m; /archives//html/Amps/2013-02/msg00217.html (9,902 bytes)
228. [Amps] Freescale LDMOS devices (score: 1): Author: "John Lyles" <jtml@losalamos.com>; Date: Thu, 7 Mar 2013 20:19:12 -0700; We've been testing a commercial amplifier using 8 of the 1250 watt CW rated MRFE6VP61K25H parts at 200 MHz, and have a solid 5.5 kW output. Its pulsed at about 10% on time so runs pretty cool to the; /archives//html/Amps/2013-03/msg00092.html (6,722 bytes)
229. Re: [Amps] Freescale LDMOS devices (score: 1): Author: John Lyles <jtml@losalamos.com>; Date: Sun, 10 Mar 2013 15:44:49 -0600; So far they have been operating just over half their rating, for reliability and linearity. We aren't planning to push them to their limits and test as we bought the amplifier, for use in our RF syst; /archives//html/Amps/2013-03/msg00151.html (9,130 bytes)
230. [Amps] Coupling a blower to an air system socket (score: 1): Author: John Lyles <jtml@losalamos.com>; Date: Sat, 16 Mar 2013 16:01:46 -0600; This technique (below) is used in a lot of air cooled cavity amplifiers, esp of the broadcast FM style. The Eimac SK300A socket has too much openness to offer effective isolation between input and ou; /archives//html/Amps/2013-03/msg00225.html (10,764 bytes)
231. [Amps] Coupling a blower to an air system socket (score: 1): Author: John Lyles <jtml@losalamos.com>; Date: Sun, 17 Mar 2013 14:48:02 -0600; Good summary of the actual mechanism of cooling finned anodes in tubes, Ian. I might mention that hams designing with these tubes should always consider the air density where they plan to operate the; /archives//html/Amps/2013-03/msg00238.html (14,543 bytes)
232. [Amps] Coupling a blower to an air system socket (score: 1): Author: John Lyles <jtml@losalamos.com>; Date: Sun, 17 Mar 2013 14:49:54 -0600; I learned this in 1981 when 4CX20,000A/8990 tetrodes in Broadcast Electronics FM30 transmitters would have a darkened center post for filament as the silver tarnished from heat. We applied a thermoco; /archives//html/Amps/2013-03/msg00239.html (13,509 bytes)
233. Re: [Amps] Alpha 87A (score: 1): Author: John Lyles <jtml@losalamos.com>; Date: Sat, 30 Mar 2013 18:23:52 -0600; Running the tubes with only filament on for at least 30 minutes before applying HV is a good practice. Longer is certainly more conservative but more than 24 hours is not needed. After a few hours th; /archives//html/Amps/2013-03/msg00377.html (16,318 bytes)
234. [Amps] HV Resistor Source (score: 1): Author: "John Lyles" <jtml@losalamos.com>; Date: Wed, 17 Apr 2013 14:24:17 -0600; The "industry standard" for such a resistor is a pulse rated R like a Kanthal Globar. The company has changed names a lot recently, so search for them. These are carborundum bulk resistors, non induc; /archives//html/Amps/2013-04/msg00163.html (9,798 bytes)
235. Re: [Amps] HV Resistor Source (score: 1): Author: John Lyles <jtml@losalamos.com>; Date: Wed, 17 Apr 2013 23:10:36 -0600; Carborundum resistors were also common in tube FM broadcast transmitters down to 1 kW level for the same application. Dale or Ohmite (or Ward Leonard!) 25 watt wirewound resistors don't hold off volt; /archives//html/Amps/2013-04/msg00173.html (9,151 bytes)
236. [Amps] Measuring tank coil inductance (score: 1): Author: "John Lyles" <jtml@losalamos.com>; Date: Wed, 24 Apr 2013 18:27:51 -0600; As others have expounded on their preferred ways to do this, I will supplement what was said (no disagreement here) with one more technique that I have used for 20 years, and built some high power RF; /archives//html/Amps/2013-04/msg00204.html (9,353 bytes)
237. [Amps] 4CX5000A in common grid circuit (score: 1): Author: Jtml <jtml@losalamos.com>; Date: Thu, 02 May 2013 16:28:16 -0600; 4CX5000A is in the Collins design in the 1964 Ed of Pappenfus' SSB Principles. It will give you a reference point. If you can find the NAB handbook from the 1986 era, I wrote the section in FM transm; /archives//html/Amps/2013-05/msg00046.html (6,659 bytes)
238. Re: [Amps] FW: 4CX5000A in common grid circuit (score: 1): Author: "John Lyles" <jtml@losalamos.com>; Date: Mon, 6 May 2013 19:00:46 -0600; Hi I am back from the underground. Much of my experience has been at VHF, 100-200 Mhz range. However, same applies for HF, except neutralization and circuits are different. Tetrodes work well in grou; /archives//html/Amps/2013-05/msg00116.html (10,769 bytes)
239. [Amps] Solid state amplifier cooling (score: 1): Author: "John Lyles" <jtml@losalamos.com>; Date: Thu, 6 Jun 2013 19:03:28 -0600; As Jim mentioned, multiphase cooling is the way it is done these days in high power RF tubes. The large Eimac and Thales tubes use it, as do the big MW klystrons for scientific work. We use this tech; /archives//html/Amps/2013-06/msg00139.html (9,255 bytes)
240. [Amps] Monitoring temperature in SS amp (score: 1): Author: "John Lyles" <jtml@losalamos.com>; Date: Wed, 12 Jun 2013 19:18:37 -0600; I agree with Manfred's assessment of temperature sensors around RF amps. The BE FM broadcast transmitters always had an LM35 mounted on a small PCB above the cavity amplifier exhaust RF shielded port; /archives//html/Amps/2013-06/msg00220.html (7,587 bytes)

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