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1. [Amps] 8877 input Z (score: 1): Author: "Hardy Landskov" <n7rt@cox.net>; Date: Thu, 27 Mar 2014 07:55:40 -0700; I am looking for the input impedance of an 8877. I found one source and that was K6DC's (SK) article years ago that said it was 54 ohms with no frequency dependency or reactive component. The input C; /archives//html/Amps/2014-03/msg00173.html (6,435 bytes)
2. Re: [Amps] 8877 input Z (score: 1): Author: Bill Turner <dezrat1242@wildblue.net>; Date: Thu, 27 Mar 2014 08:14:01 -0700; ORIGINAL MESSAGE: (may be snipped) On 3/27/2014 7:55 AM, Hardy Landskov wrote: I am looking for the input impedance of an 8877. I found one source and that was K6DC's (SK) article years ago that said; /archives//html/Amps/2014-03/msg00174.html (7,183 bytes)
3. Re: [Amps] 8877 input Z (score: 1): Author: TexasRF@aol.com; Date: Fri, 28 Mar 2014 13:54:41 -0400 (EDT); Hardy, the 54 ohms is a nominal figure that will vary with rf drive level. Certainly close enough for designing input networks. Higher drive levels will result in a lower input impedance; lower drive; /archives//html/Amps/2014-03/msg00177.html (7,697 bytes)
4. Re: [Amps] 8877 input Z (score: 1): Author: Vic Rosenthal K2VCO <k2vco.vic@gmail.com>; Date: Fri, 28 Mar 2014 11:00:57 -0700; You can design the input circuit as a pi-section lowpass filter with a cutoff above the highest band (I used 32 MHz). You can use standard tables for a 50-ohm input/output impedance because 54 ohms i; /archives//html/Amps/2014-03/msg00178.html (8,687 bytes)
5. Re: [Amps] 8877 input Z (score: 1): Author: Larry Benko <xxw0qe@comcast.net>; Date: Fri, 28 Mar 2014 12:48:23 -0600; If the load is 50 ohms (using 50 just for example purposes) in parallel with 42pF a series inductance matches well enough that a given inductance will be good for more than 1 band. However if you add; /archives//html/Amps/2014-03/msg00179.html (9,211 bytes)
6. Re: [Amps] 8877 input Z (score: 1): Author: TexasRF@aol.com; Date: Fri, 28 Mar 2014 15:40:53 -0400 (EDT); Larry, you may be right. But there are no commercial 8877 amplifiers using that scheme and don't recall seeing any published homebrew amps using it either. The 54 ohms and 42 pF are not in a series c; /archives//html/Amps/2014-03/msg00180.html (10,887 bytes)
7. Re: [Amps] 8877 input Z (score: 1): Author: "Carl" <km1h@jeremy.mv.com>; Date: Fri, 28 Mar 2014 15:41:48 -0400; That sounds like you can use an old Drake, Johnson, B&W, etc LPF right at the socket and replace the fixed output cap with a trimmer for a perfect match. Carl KM1H You can design the input circuit as; /archives//html/Amps/2014-03/msg00181.html (9,992 bytes)
8. Re: [Amps] 8877 input Z (score: 1): Author: TexasRF@aol.com; Date: Fri, 28 Mar 2014 16:04:11 -0400 (EDT); Heck you could just use a .57 uH inductance in parallel with a variable C (or switched fixed C) adjusted to resonate on the band in use. About 57pF (less 42pF) at 28MHz up to about 883 pF (less 42pF); /archives//html/Amps/2014-03/msg00182.html (10,839 bytes)
9. [Amps] 8877 input Z (score: 1): Author: "Jim Thomson" <jim.thom@telus.net>; Date: Mon, 31 Mar 2014 02:01:04 -0700; Hardy, the 54 ohms is a nominal figure that will vary with rf drive level. Certainly close enough for designing input networks. Higher drive levels will result in a lower input impedance; lower drive; /archives//html/Amps/2014-03/msg00190.html (8,421 bytes)

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