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61. [AMPS] AL1500 (score: 1): Author: paulc@mediaone.net (Paul Christensen); Date: Thu, 6 Dec 2001 08:22:35 -0500; That is correct Ian. Right again. In essence, Q2 "samples" the emitter current on the darlington pair. Yes. I failed to mention that the R20 sample point also routes over to the multi-meter circuit; /archives//html/Amps/2001-12/msg00143.html (10,193 bytes)
62. [AMPS] AL1500 (score: 1): Author: paulc@mediaone.net (Paul Christensen); Date: Thu, 6 Dec 2001 09:02:18 -0500; By comparison, my PA70-V uses the same darlington EBS circuit to the cathode, but Q2 does not exist as this was a feature "enhancement" in the PA-77 which later replaced the PA70 series. Instead, a 1; /archives//html/Amps/2001-12/msg00144.html (11,871 bytes)
63. [AMPS] AL1500 (score: 1): Author: 2@vc.net (2); Date: Thu, 6 Dec 2001 06:38:19 -0800; \\ However, when the cathode electrons strike the floating grid it acquires a negative charge, which should reduce anode current. With the grid floating, there should be no grid current. - R. L. Mea; /archives//html/Amps/2001-12/msg00146.html (11,799 bytes)
64. [AMPS] AL1500 (score: 1): Author: 2@vc.net (2); Date: Thu, 6 Dec 2001 06:55:19 -0800; A conventional relay adds c. 15mS delay. My assumption - based on 8877 autopsies - is that this delay may be problematic because gold-sputtering occasionally happens. In my experience, fast fuses se; /archives//html/Amps/2001-12/msg00147.html (8,890 bytes)
65. [AMPS] AL1500 (score: 1): Author: W8JI@contesting.com (Tom Rauch); Date: Thu, 6 Dec 2001 19:07:20 -0500; Now, to Rich's point (I believe)...the fuse may in fact blow faster in Fuses are notoriously unreliable, if you doubt that test some...or look at references. Unreliability is the whole problem with f; /archives//html/Amps/2001-12/msg00151.html (10,587 bytes)
66. [AMPS] AL1500 (score: 1): Author: 2@vc.net (2); Date: Thu, 6 Dec 2001 20:31:48 -0800; // Any port in a storm. In the Alpha 70-V, a fast fuse successfully protected the grid. In my Fluke DMM, a fast acting fuse protects the instrument. // Surely, if it is a slow-blow fuse. Fast acting; /archives//html/Amps/2001-12/msg00154.html (11,349 bytes)
67. [AMPS] AL1500 (score: 1): Author: Peter.Chadwick@zarlink.com (Peter Chadwick); Date: Fri, 7 Dec 2001 07:58:05 -0000; If you use a resistor as a fuse, how do you guarantee the fusing characteristics (except for fusible resistors)? Even fusible resistors have enormous tolerances on them, while similar resistors from; /archives//html/Amps/2001-12/msg00156.html (8,047 bytes)
68. [AMPS] AL1500 (score: 1): Author: 2@vc.net (2); Date: Fri, 7 Dec 2001 07:57:57 -0800; // The original L-4B, SB-220, and TL-922 circuits used approx. 1mH, 1A rated chokes in the grid to gnd DC returns. Such chokes act as fuses somewhat above 10A since the current envolved occasionally; /archives//html/Amps/2001-12/msg00161.html (8,671 bytes)
69. [AMPS] AL1500 (score: 1): Author: Ian White, G3SEK" <g3sek@ifwtech.com (Ian White, G3SEK); Date: Fri, 7 Dec 2001 11:06:06 +0000; Paul Christensen wrote (regarding the Alpha PA-77): After downloading the PA-77 manual and schematic (from the excellent "Boat Anchor Manuals" site, http://bama.sbc.edu) it seems that the circuit is; /archives//html/Amps/2001-12/msg00166.html (11,068 bytes)
70. [AMPS] AL1500 (score: 1): Author: Ian White, G3SEK" <g3sek@ifwtech.com (Ian White, G3SEK); Date: Fri, 7 Dec 2001 12:03:28 +0000; The break time of a fuse depends crucially on the size of the overload. Remember that a fuse operates in a very simple way, by heating up a piece of very thin wire until it melts. For the fastest bre; /archives//html/Amps/2001-12/msg00167.html (11,678 bytes)
71. [AMPS] AL1500 (score: 1): Author: 2@vc.net (2); Date: Fri, 7 Dec 2001 10:55:02 -0800; // Autopsies inddicate that some electronic trip circuits are not be able to prevent gold-sputtering in an 8874, 3cx800A7 or 8877. Circumstantial evidence is that a 0.25A fast fuse makes an 8877 har; /archives//html/Amps/2001-12/msg00169.html (10,983 bytes)
72. [AMPS] AL1500 (score: 1): Author: W8JI@contesting.com (Tom Rauch); Date: Sun, 9 Dec 2001 22:00:32 -0500; Rich Measures suggests (or has suggested) using resistors to replace electronic systems, rather than using fuses. Fuses are bad enough. I can't imagine anyone depending on a conventional resistor to; /archives//html/Amps/2001-12/msg00179.html (8,882 bytes)
73. [AMPS] AL1500 (score: 1): Author: 2@vc.net (2); Date: Sun, 9 Dec 2001 07:51:57 -0800; // Close. I suggest replacing grid protect circuits - which have a track record of failure - with a fast-acting fuse or a carbon-film resistor. // The AL-1500 seems to occasionally gold-sputter the; /archives//html/Amps/2001-12/msg00180.html (8,303 bytes)
74. [AMPS] AL1500 (score: 1): Author: clive@gm3poi.prestel.co.uk (c penna); Date: Thu, 4 Nov 1999 21:21:50 -0000; Hi , I have a problem with an AL1500 which came on suddenly. The grid current indicated is now showing about three times what it used to. The meter even indicates 10ma on cw standby ie no drive. My O; /archives//html/Amps/1999-11/msg00155.html (7,179 bytes)
75. [AMPS] AL1500 (score: 1): Author: measures@vcnet.com (measures); Date: Thu, 4 Nov 1999 13:58:37 -0700; I would check the valve for gold sputtering, Clive. To do this you need a high-pot. tester. The grid is common. The anode is hot. Apply pos. 8kV. If the leakage is above 10mA you may have a problem.; /archives//html/Amps/1999-11/msg00156.html (7,748 bytes)
76. [AMPS] AL1500 (score: 1): Author: mike@g0mjw.freeserve.co.uk (G0MJW); Date: Fri, 5 Nov 1999 08:30:03 -0000; used Rich is probably correct about it being a problem in the valve (tube). However, do check there is nothing wrong in the metering and PSU circuitry. I think a leaky cathode bypass cap might produ; /archives//html/Amps/1999-11/msg00168.html (7,519 bytes)
77. SV: [AMPS] AL1500 (score: 1): Author: sm5ki@algonet.se (Hans Goldschmidt); Date: Fri, 05 Nov 1999 10:41:17 +0100; Hej! I do not have the schematic on this amplifier but maybe it uses a similar circuitry as the SB220? I repaired one years ago that draw a lot of grid current even without without drive and if I rem; /archives//html/Amps/1999-11/msg00169.html (8,780 bytes)
78. [Amps] AL1500 (score: 1): Author: n4xp@juno.com; Date: Sun, 3 Apr 2005 19:29:15 -0400; Would those with or having had an AL1500 please provide me insight as to its abilities. Also pros and cons would be appreciated. 73 Tom N4XP _______________________________________________ Amps maili; /archives//html/Amps/2005-04/msg00069.html (6,029 bytes)
79. Re: [Amps] AL1500 (score: 1): Author: R.Measures <r@somis.org>; Date: Mon, 4 Apr 2005 03:23:35 -0700; Tom -- It has the ability to occasionally oscillate at VHF -- because it is the only HF 8877 amplifier on this planet that uses no VHF suppressor whatsoever. http://www.somis.org/8877-gs2.JPEG Richar; /archives//html/Amps/2005-04/msg00071.html (7,130 bytes)
80. Re: [Amps] AL1500 (score: 1): Author: R.Measures <r@somis.org>; Date: Mon, 4 Apr 2005 09:07:06 -0700; Tom -- MFJ did that because the "expert" who designed it does not believe that an 8877 can oscillate in amplifier service. This expert also does not believe that a SB-220/221 can occasionally oscilla; /archives//html/Amps/2005-04/msg00076.html (8,756 bytes)

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