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21. Re: [Amps] grounding grids (score: 1): Author: TexasRF@aol.com; Date: Wed, 29 Jul 2009 22:15:20 EDT; You are right Joe. It was the SB200 that used the cutoff bias through the antenna relay scheme. 73, Gerald K5GW In a message dated 7/29/2009 8:46:28 P.M. Central Daylight Time, lists@subich.com write; /archives//html/Amps/2009-07/msg00379.html (20,174 bytes)
22. Re: [Amps] grounding grids (score: 1): Author: "k7fm" <k7fm@teleport.com>; Date: Wed, 29 Jul 2009 19:24:14 -0700; The Heath SB-220 used an rf choke to ground the grid, bypassed by 3 x 200 pf capacitors. Interestingly, the Drake L4 amplifier used an rf choke to ground the grid, bypassed by 3 x 200 pf capacitors.; /archives//html/Amps/2009-07/msg00381.html (9,093 bytes)
23. Re: [Amps] grounding grids (score: 1): Author: "Bill W5WVO" <w5wvo@cybermesa.net>; Date: Wed, 29 Jul 2009 20:26:35 -0600; _______________________________________________ Amps mailing list Amps@contesting.com http://lists.contesting.com/mailman/listinfo/amps; /archives//html/Amps/2009-07/msg00382.html (20,524 bytes)
24. Re: [Amps] grounding grids (score: 1): Author: "Bill W5WVO" <w5wvo@cybermesa.net>; Date: Wed, 29 Jul 2009 20:27:17 -0600; In the SB-220, cutoff bias (during "receive" periods) of +130V is applied to the cathodes of the 3-500Zs via the center-tap of the filament transformer, thus placing the potential of the grounded con; /archives//html/Amps/2009-07/msg00383.html (20,667 bytes)
25. Re: [Amps] grounding grids (score: 1): Author: "Bill, W6WRT" <dezrat1242@yahoo.com>; Date: Wed, 29 Jul 2009 20:29:07 -0700; ORIGINAL MESSAGE: REPLY: Also, that isn't true negative feedback anyway. It is just gain reduction. True negative feedback means taking a sample of the output, inverting the phase (if needed), and fe; /archives//html/Amps/2009-07/msg00384.html (9,641 bytes)
26. Re: [Amps] grounding grids (score: 1): Author: "Gary Schafer" <garyschafer@comcast.net>; Date: Wed, 29 Jul 2009 22:51:58 -0500; How much does it vary from band to band? The idea is the higher in frequency you go the lower the impedance is due to the capacitor. At lower frequencies the capacitor has higher impedance but the im; /archives//html/Amps/2009-07/msg00385.html (21,090 bytes)
27. Re: [Amps] grounding grids (score: 1): Author: "Gary Schafer" <garyschafer@comcast.net>; Date: Wed, 29 Jul 2009 22:55:37 -0500; The main problem with the 572B is the long internal grid leads of the tube. 73 Gary K4FMX The SB-200 is even _______________________________________________ Amps mailing list Amps@contesting.com http; /archives//html/Amps/2009-07/msg00386.html (7,959 bytes)
28. Re: [Amps] grounding grids (score: 1): Author: "Gary Schafer" <garyschafer@comcast.net>; Date: Wed, 29 Jul 2009 23:03:51 -0500; Rich Measures claims that the grid bypass capacitors used in the SB 220 are series resonant at or near the parasitic frequency of the tubes and actually provide a lower impedance to ground than a pie; /archives//html/Amps/2009-07/msg00387.html (14,856 bytes)
29. Re: [Amps] grounding grids (score: 1): Author: "Gary Schafer" <garyschafer@comcast.net>; Date: Wed, 29 Jul 2009 23:09:16 -0500; How then would you account for the reduced IM products of a tube operated in GG verses the same tube operated in a standard grid driven configuration? 73 Gary K4FMX _________________________________; /archives//html/Amps/2009-07/msg00388.html (10,296 bytes)
30. Re: [Amps] grounding grids (score: 1): Author: "Fuqua, Bill L" <wlfuqu00@uky.edu>; Date: Thu, 30 Jul 2009 00:28:36 -0400; Let see. RF plate voltage is proportional to RF plate current,,,,RF cathode current is proportional to plate current....RF voltage across the cathode drive impedance is proportional to RF cathode cur; /archives//html/Amps/2009-07/msg00390.html (11,753 bytes)
31. Re: [Amps] grounding grids (score: 1): Author: Roger <sub1@rogerhalstead.com>; Date: Thu, 30 Jul 2009 00:48:54 -0400; and should reduce the need for carefully balancing the tubes. 73 Roger (K8RI) _______________________________________________ Amps mailing list Amps@contesting.com http://lists.contesting.com/mailman; /archives//html/Amps/2009-07/msg00393.html (12,184 bytes)
32. Re: [Amps] grounding grids (score: 1): Author: Ian White GM3SEK <gm3sek@ifwtech.co.uk>; Date: Thu, 30 Jul 2009 08:15:14 +0100; It was claimed (here on AMPS a few years ago, if I recall correctly) that Heath came under heavy pressure from Eimac to use that capacitor-RFC circuit. Personally I agree with Joe that all the claime; /archives//html/Amps/2009-07/msg00397.html (10,669 bytes)
33. Re: [Amps] grounding grids (score: 1): Author: "Bill, W6WRT" <dezrat1242@yahoo.com>; Date: Thu, 30 Jul 2009 04:38:21 -0700; ORIGINAL MESSAGE: REPLY: I can't say. I am not an expert on IMD, but I stand by my previous statement - simply adding a resistor (or network) in the grid circuit is not negative feedback, it's just g; /archives//html/Amps/2009-07/msg00398.html (9,527 bytes)
34. Re: [Amps] grounding grids (score: 1): Author: Ron Youvan <ka4inm@tampabay.rr.com>; Date: Thu, 30 Jul 2009 10:31:13 -0400; One factor with GG is most of the drive is added to the power from the amplifier and is perhaps like adding some pure signal to the mixture of signal and distortion from the amplifier. -- Ron KA4INM; /archives//html/Amps/2009-07/msg00399.html (9,240 bytes)
35. Re: [Amps] grounding grids (score: 1): Author: Bill Fuqua <wlfuqu00@uky.edu>; Date: Thu, 30 Jul 2009 11:28:38 -0400; My previous message applied to the negative feedback in a grounded grid amplifier due to the cathode and drive impedances.Similar to the negative feedback due to an un-bypassed emitter resistor in a; /archives//html/Amps/2009-07/msg00404.html (9,363 bytes)
36. Re: [Amps] grounding grids (score: 1): Author: "Bill, W6WRT" <dezrat1242@yahoo.com>; Date: Thu, 30 Jul 2009 08:30:57 -0700; ORIGINAL MESSAGE: REPLY: Another possible reason for reduced IMD is the added grid resistor smoothes out the load over the RF driving cycle, in the sense of a "swamping" resistor, although in series; /archives//html/Amps/2009-07/msg00405.html (9,350 bytes)
37. Re: [Amps] grounding grids (score: 1): Author: "Bill, W6WRT" <dezrat1242@yahoo.com>; Date: Thu, 30 Jul 2009 09:09:36 -0700; ORIGINAL MESSAGE: REPLY: An un-bypassed emitter resistor is not negative feedback, it is just gain reduction. For true NFB you have to take a sample of the output and feed it back to the input, out o; /archives//html/Amps/2009-07/msg00407.html (10,505 bytes)
38. Re: [Amps] grounding grids (score: 1): Author: "Bill W5WVO" <w5wvo@cybermesa.net>; Date: Thu, 30 Jul 2009 11:53:02 -0600; So there seems to be some difference of opinion as to whether the Heath SB-220 grid-grounding implementation actually suipplies negative feedback or not, actually reduces IMD components in the output; /archives//html/Amps/2009-07/msg00409.html (11,425 bytes)
39. Re: [Amps] grounding grids (score: 1): Author: "Steve" <groups.steve@earthlink.net>; Date: Thu, 30 Jul 2009 15:19:21 -0400; A resistor in series with the emitter of a BJT causes negative 'current' feedback as opposed to negative voltage feedback. In either case, the gain of the overall circuit is reduced and the IMD perfo; /archives//html/Amps/2009-07/msg00410.html (11,578 bytes)
40. Re: [Amps] grounding grids (score: 1): Author: "DF3KV" <df3kv@t-online.de>; Date: Thu, 30 Jul 2009 21:48:43 +0200; The un-bypassed emitter or cathode resistor is still causing NFB, the voltage developed across the resistor is out of phase with the input signal and in phase with the output voltage. That kind of NF; /archives//html/Amps/2009-07/msg00411.html (10,978 bytes)

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