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21. Re: [Amps] Advice (score: 1): Author: Ron Youvan <ka4inm@tampabay.rr.com>; Date: Fri, 04 Dec 2009 03:08:16 +0000; If operated in push pull (double ended) the second harmonic (and other even) is canceled and if pushed into distortion it can mean more power before distorting out of specs. -- Ron KA4INM - The only; /archives//html/Amps/2009-12/msg00102.html (8,875 bytes)
22. Re: [Amps] Advice (score: 1): Author: Roger <sub1@rogerhalstead.com>; Date: Fri, 04 Dec 2009 04:42:14 -0500; And they are relatively cheap and available. I saw a bunch of them for $25 each last week. Remember the "sweep tube" amps of the 70's? AKA the GLA1000 and a bunch of others. Thats when tubes were rea; /archives//html/Amps/2009-12/msg00105.html (10,484 bytes)
23. Re: [Amps] Advice (score: 1): Author: "Carl" <km1h@jeremy.mv.com>; Date: Fri, 4 Dec 2009 09:00:20 -0500; The 813 remains as the best bargain on the market with maybe the 803 or 814/VT-154 in 2nd place. Powers range from modest to legal limit when run in 4 paks.. The 813 (as well as the others) is seriou; /archives//html/Amps/2009-12/msg00107.html (11,426 bytes)
24. Re: [Amps] Advice (score: 1): Author: Paul Decker <kg7hf@comcast.net>; Date: Fri, 4 Dec 2009 17:07:47 +0000 (UTC); One possible advantage of two tubes over a single tube is the blower and airflow. Sometimes using two smaller tubes will require less airflow and have less backpressure than a single tube. Paul Dec; /archives//html/Amps/2009-12/msg00113.html (8,695 bytes)
25. Re: [Amps] Advice (score: 1): Author: "Bill, W6WRT" <dezrat1242@yahoo.com>; Date: Fri, 04 Dec 2009 22:58:30 -0800; ORIGINAL MESSAGE: REPLY: Excellent point. It is a well known law of geometry that multiple small objects have larger surface area than a single object of the same total volume. It stands to reason th; /archives//html/Amps/2009-12/msg00123.html (8,289 bytes)
26. Re: [Amps] Advice (score: 1): Author: "Gary Schafer" <garyschafer@comcast.net>; Date: Sat, 5 Dec 2009 11:04:46 -0500; There is no free lunch. While it may seem like you could get by with less air flow it doesn't follow. A pair of tubes will require twice the air flow at the same back pressure as a single tube. Tubes; /archives//html/Amps/2009-12/msg00124.html (9,644 bytes)
27. Re: [Amps] Advice (score: 1): Author: "Carl" <km1h@jeremy.mv.com>; Date: Sat, 5 Dec 2009 11:50:41 -0500; True, BUT a pair of 3-500's require less air than a single 3-1000Z assuming the use of the Eimac plastic sockets and the same RF output. And, the pair of 3-500Z can use axial air flow and no chimney; /archives//html/Amps/2009-12/msg00125.html (9,901 bytes)
28. Re: [Amps] Advice (score: 1): Author: Jim Barber <audioguy@charter.net>; Date: Sat, 05 Dec 2009 10:28:52 -0800; Here's a question from another angle: Say I use two 8877's instead of one (with proper cooling and whatever else is required) and run 1500W PEP output SSB, would the two tube version run more hours t; /archives//html/Amps/2009-12/msg00126.html (8,948 bytes)
29. [Amps] Advice (score: 1): Author: Dennis OConnor <ad4hk2004@yahoo.com>; Date: Sat, 5 Dec 2009 11:54:49 -0800 (PST); Yeah, I'll take that... Absolutely, the two tubes running at ~750 watts each will outlast by a sginificant margin (your lifetime) a single tube running at 1500 watts... You are not beating up the ox; /archives//html/Amps/2009-12/msg00128.html (7,430 bytes)
30. Re: [Amps] Advice (score: 1): Author: "Carl" <km1h@jeremy.mv.com>; Date: Sat, 5 Dec 2009 15:15:05 -0500; That would be true if the only criteria is filament emission. However, a single 8877 is loafing at 1500W and is not really a good example. Now, if you want to compare a 3-500Z at 900W to a pair at 12; /archives//html/Amps/2009-12/msg00129.html (10,230 bytes)
31. Re: [Amps] Advice (score: 1): Author: Paul Decker <kg7hf@comcast.net>; Date: Sat, 5 Dec 2009 21:26:22 +0000 (UTC); When I was writing the original reply I was thinking more along the lines of different tubes for example a single 8877 requires more airflow and has more back pressure than two 3cx800's. Agreed, two; /archives//html/Amps/2009-12/msg00131.html (8,939 bytes)
32. Re: [Amps] Advice (score: 1): Author: "Gary Schafer" <garyschafer@comcast.net>; Date: Sat, 5 Dec 2009 16:39:36 -0500; The chart that I am looking at says: 8877 requires 35 cu ft at .41 back pressure. A 3CX800A7 requires 19 cu ft at .5 back pressure. Two of those would require 38 cu ft at .5 back pressure. 73 Gary K4; /archives//html/Amps/2009-12/msg00132.html (10,236 bytes)
33. Re: [Amps] Advice (score: 1): Author: Roger <sub1@rogerhalstead.com>; Date: Sat, 05 Dec 2009 17:05:36 -0500; I could easily run the legal limit with one FU728F, 8877, or 4CX-1500B but with a pair of them still running the legal limit they will take a little more volume, but not require near the back pressur; /archives//html/Amps/2009-12/msg00133.html (10,004 bytes)
34. Re: [Amps] Advice (score: 1): Author: "Gary Schafer" <garyschafer@comcast.net>; Date: Sat, 5 Dec 2009 17:11:10 -0500; Paul, sorry I missed your second paragraph. Air flow needed depends on how much power is being dissipated. If you divide the airflow by the dissipation rating of the 8877 as an example 35/1500 = .023; /archives//html/Amps/2009-12/msg00135.html (12,162 bytes)
35. Re: [Amps] Advice (score: 1): Author: Paul Decker <kg7hf@comcast.net>; Date: Sat, 5 Dec 2009 23:25:39 +0000 (UTC); Hi Gary, The point of the second paragraph was that with a pair tubes operating under their specificed dissipation rating require less cooling then a single tube operating at or above its dissipation; /archives//html/Amps/2009-12/msg00136.html (12,614 bytes)
36. Re: [Amps] Advice (score: 1): Author: Ron Youvan <ka4inm@tampabay.rr.com>; Date: Sun, 06 Dec 2009 02:07:38 +0000; < There is a broadcast station that has kept a set of finals in stand bye, running at mildly reduced filament voltage, not dark heat, for something like 30,000 or 40,000 hours... Had the tubes tested; /archives//html/Amps/2009-12/msg00140.html (7,748 bytes)
37. Re: [Amps] Advice (score: 1): Author: Ron Youvan <ka4inm@tampabay.rr.com>; Date: Sun, 06 Dec 2009 02:22:54 +0000; I assume these values are at the maximum power dissipation, running a tube at reduced power dissipation allows operating at reduced cooling effort, so two tubes splitting a given amount of dissipati; /archives//html/Amps/2009-12/msg00142.html (8,321 bytes)
38. Re: [Amps] Advice (score: 1): Author: "Gary Schafer" <garyschafer@comcast.net>; Date: Sat, 5 Dec 2009 23:57:34 -0500; Hi Paul, I didn't mean that I didn't understand the 2nd paragraph but that I didn't read it. I just overlooked it when I read your first post with it. I do think that you have the cooling requirement; /archives//html/Amps/2009-12/msg00147.html (14,141 bytes)
39. Re: [Amps] Advice (score: 1): Author: Paul Decker <kg7hf@comcast.net>; Date: Sun, 6 Dec 2009 05:11:00 +0000 (UTC); Hi Gary, I don't know if it's a linear relation. Perhaps a typo, but on page 13.19 of the 1995 handbook, it says 12 CFM at 0.09" back pressure for two 3cx800's operating at 400 Watts dissipation ea; /archives//html/Amps/2009-12/msg00148.html (14,604 bytes)
40. Re: [Amps] Advice (score: 1): Author: "Joe Subich, W4TV" <lists@subich.com>; Date: Sun, 6 Dec 2009 00:40:46 -0500; The current Eimac data sheet gives the cooling requirements at sea level as: Anode CFM Pressure Diss In. Water -- 400 6 0.09 600 11 0.20 800 19 0.50 However, the original (1983) Eimac data sheet for; /archives//html/Amps/2009-12/msg00151.html (18,197 bytes)

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