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1. [Amps] More instability problems (score: 1): Author: N1BUG <paul@n1bug.com>; Date: Fri, 12 Apr 2013 10:02:34 -0400; Recently I asked about an instability problem after my 10 year old HB 4CX1500B amp suddenly started destroying vacuum relays. Thanks for all the advice! I discovered under certain conditions it was g; /archives//html/Amps/2013-04/msg00083.html (8,233 bytes)
2. Re: [Amps] More instability problems (score: 1): Author: "Jim W7RY" <w7ry@centurytel.net>; Date: Fri, 12 Apr 2013 07:28:13 -0700; On the higher bands I am also seeing instability when tuning. While adjusting the tune and/or load caps, I'm seeing sudden jumps in antenna SWR and power output. 73, Paul N1BUG Perhaps you have an an; /archives//html/Amps/2013-04/msg00085.html (7,729 bytes)
3. Re: [Amps] More instability problems (score: 1): Author: N1BUG <paul@n1bug.com>; Date: Fri, 12 Apr 2013 10:49:27 -0400; The problem is occurring with several different antennas. However, there is on thing I have not yet taken apart for inspection: an antenna switch. What makes me think oscillation is: Suppose I have t; /archives//html/Amps/2013-04/msg00086.html (8,032 bytes)
4. Re: [Amps] More instability problems (score: 1): Author: Zev Darack <zevdarack@gmail.com>; Date: Fri, 12 Apr 2013 10:57:42 -0400; That sounds like a bad coax jumper. -- Sent from my mobile device _______________________________________________ Amps mailing list Amps@contesting.com http://lists.contesting.com/mailman/listinfo/am; /archives//html/Amps/2013-04/msg00087.html (9,370 bytes)
5. Re: [Amps] More instability problems (score: 1): Author: N1BUG <paul@n1bug.com>; Date: Fri, 12 Apr 2013 11:02:22 -0400; What makes me think oscillation is: Suppose I have the amp tuned for maximum output at 28 MHz. Indicated antenna SWR is low, output is 1500 watts. Now assume that for the following procedures I maint; /archives//html/Amps/2013-04/msg00088.html (8,975 bytes)
6. Re: [Amps] More instability problems (score: 1): Author: Vic K2VCO <k2vco.vic@gmail.com>; Date: Fri, 12 Apr 2013 08:20:37 -0700; It does sound like a parasitic of some kind. But why suddenly? Another possibility: something in the system is arcing. An arc might have a similar 'jumping' characteristic. What I would do at this po; /archives//html/Amps/2013-04/msg00089.html (9,548 bytes)
7. Re: [Amps] More instability problems (score: 1): Author: "Gary Schafer" <garyschafer@comcast.net>; Date: Fri, 12 Apr 2013 22:32:04 -0400; Check the screen bypass capacitor. Are you driving the grid or the cathode? Is there a tuned input or a passive input? Does the plate current and output jump around with a dummy load connected direct; /archives//html/Amps/2013-04/msg00096.html (10,124 bytes)
8. Re: [Amps] More instability problems (score: 1): Author: N1BUG <paul@n1bug.com>; Date: Tue, 16 Apr 2013 10:43:21 -0400; Once again I would like to thank everyone for your input on my amp woes. There was a massive pile of private responses, which I have not fully worked through in terms of replies. Each and every one i; /archives//html/Amps/2013-04/msg00119.html (9,144 bytes)
9. Re: [Amps] More instability problems (score: 1): Author: Bill Turner <dezrat1242@yahoo.com>; Date: Tue, 16 Apr 2013 08:25:55 -0700; REPLY: One way to add a tuned input is a bit clunky, but works: At the input to the amp you no doubt have an SO-239 coax connector. Just connect a T-fitting there and that will give you a place where; /archives//html/Amps/2013-04/msg00120.html (8,575 bytes)
10. Re: [Amps] More instability problems (score: 1): Author: Vic K2VCO <k2vco.vic@gmail.com>; Date: Tue, 16 Apr 2013 08:47:04 -0700; I remember that it is a 4CX1500 or 4CX1000 but I don't recall the configuration -- was it cathode-driven or grid-driven? You certainly do NOT need a tuned input if it is grid-driven class AB1. The 50; /archives//html/Amps/2013-04/msg00122.html (10,579 bytes)
11. Re: [Amps] More instability problems (score: 1): Author: Eddy Swynar <deswynar@xplornet.ca>; Date: Tue, 16 Apr 2013 12:17:50 -0400; Hi Paul, Make an OUTBOARD tuning arrangement of pi-tank coils--one per band, switch-selectable, mini-box mounted--similar to what was shown years ago in the ARRL book, "HINTS & KINKS". ~73~ de Eddy V; /archives//html/Amps/2013-04/msg00124.html (8,645 bytes)
12. Re: [Amps] More instability problems (score: 1): Author: N1BUG <paul@n1bug.com>; Date: Tue, 16 Apr 2013 12:35:52 -0400; It is a 4CX1500B, cathode driven. Screen: direct to chassis. Grid: RF grounded, 6000 pF (3 x 2000 pF). Bias currently fed through 150 ohm resistor with bypass/feedthrough cap The 50 ohm RF load resis; /archives//html/Amps/2013-04/msg00126.html (10,163 bytes)
13. Re: [Amps] More instability problems (score: 1): Author: "Jim W7RY" <w7ry@centurytel.net>; Date: Tue, 16 Apr 2013 17:40:27 -0700; I have a question... Why are you using a regulator for the relay coils on your RF relays? Are you sure the voltage is holding up on initial keyup? Are the relays chattering? It would be better if you; /archives//html/Amps/2013-04/msg00131.html (11,488 bytes)
14. Re: [Amps] More instability problems (score: 1): Author: N1BUG <paul@n1bug.com>; Date: Tue, 16 Apr 2013 22:13:31 -0400; The regulator supplies power for switching transistors Q1, Q2 and the opto-isolator U2 (which handles bias switching). The relay coils are powered directly from the ~35V supply (before the regulator); /archives//html/Amps/2013-04/msg00134.html (10,128 bytes)
15. Re: [Amps] More instability problems (score: 1): Author: "Jim W7RY" <w7ry@centurytel.net>; Date: Tue, 16 Apr 2013 20:59:35 -0700; I see that now Paul. My mistake. 73 Jim W7RY --Original Message-- From: N1BUG Sent: Tuesday, April 16, 2013 7:13 PM To: Jim W7RY Cc: amps@contesting.com Subject: Re: [Amps] More instability problems; /archives//html/Amps/2013-04/msg00143.html (10,685 bytes)

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