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1. [Amps] filament voltage question (score: 1): Author: TexasRF@aol.com; Date: Wed, 27 Oct 2004 12:34:22 EDT; I am looking for some advice on adjusting the filament voltage on a TH347 tetrode used in my 1296mhz cavity amplifier. The TH347 is a directly heated cathode tube. Due to a long underground run for t; /archives//html/Amps/2004-10/msg00447.html (8,687 bytes)
2. Re: [Amps] filament voltage question (score: 1): Author: R.Measures <r@somis.org>; Date: Wed, 27 Oct 2004 11:28:56 -0700; Gerald -- The 8169 amplifier on my Web site has N.O. relay contacts across a 6-ohm resistor in series with the filament-V adjustment rheostat that's in series with the primary of the 9v, 43a filament; /archives//html/Amps/2004-10/msg00454.html (10,268 bytes)
3. Re: [Amps] filament voltage question (score: 1): Author: "Jim Smith" <jimsmith@ispwest.com>; Date: Fri, 29 Oct 2004 05:47:41 -0700; I'd install a buck/boost transformer to correct the problem with voltage drop rather than working around it, which may lead to still more complications. Jim Smith, KQ6UV I am looking for some advice; /archives//html/Amps/2004-10/msg00503.html (9,921 bytes)
4. Re: [Amps] filament voltage question (score: 1): Author: Tony King <amps@w4zt.com>; Date: Fri, 29 Oct 2004 09:26:32 -0400; An easy solution would be to obtain one of the small variable transformers (I have a couple I bought on Ebay) and put it in the filament transformer primary so you can make the necessary minor adjust; /archives//html/Amps/2004-10/msg00504.html (10,877 bytes)
5. Re: [Amps] filament voltage question (score: 1): Author: R.Measures <r@somis.org>; Date: Fri, 29 Oct 2004 06:58:32 -0700; Tony -- The problem with 0 - 115% variable transformers is that it is not necessary to be able to adjust the filament V more than +/- 8%. A rheostat does the job nicely. On Oct 29, 2004, at 6:26 AM,; /archives//html/Amps/2004-10/msg00505.html (11,682 bytes)
6. Re: [Amps] filament voltage question (score: 1): Author: Colin Lamb <k7fm@teleport.com>; Date: Fri, 29 Oct 2004 08:34:16 -0700 (GMT-07:00); It seems that the sag can be used to compensate for the increase in voltage due to back bombardment. If you set the voltage at 6.0 volts, for example, and the filament voltage drops under the load of; /archives//html/Amps/2004-10/msg00506.html (14,422 bytes)
7. Re: [Amps] filament voltage question (score: 1): Author: Radio WC6W <wc6w@juno.com>; Date: Fri, 29 Oct 2004 08:45:57 -0700; Hi Gerald, TH347 heated <snip> voltage tube life that Yes, standby time counts! current Not necessarily. One could build a simple primary side regulator using a suitably heatsinked power FET, as the; /archives//html/Amps/2004-10/msg00507.html (9,005 bytes)
8. Re: [Amps] filament voltage question (score: 1): Author: Tony King <amps@w4zt.com>; Date: Fri, 29 Oct 2004 13:52:33 -0400; That's a good point Rich. In any case, a minor adjustment to the primary will bring the filament right to where you want it. I'm a firm believer in step start for filaments on expensive tubes as well; /archives//html/Amps/2004-10/msg00509.html (8,566 bytes)
9. [Amps] Filament Voltage Question (score: 1): Author: "Jim Garland" <4cx250b@miamioh.edu>; Date: Tue, 22 Apr 2014 09:19:04 -0600; I was reading the data sheet this morning on the 4CX3500A and noticed the filament requirements are 5V@90Amps. It occurred to me that I've never understood why so many tubes with indirectly heated ca; /archives//html/Amps/2014-04/msg00186.html (7,408 bytes)
10. Re: [Amps] Filament Voltage Question (score: 1): Author: Radio WC6W via Amps <amps@contesting.com>; Date: Tue, 22 Apr 2014 08:28:25 -0700 (PDT); Hi Jim, That tube employs a DIRECTLY heated filament. Two good reasons for low voltage in this case: High voltage operation would require thin elements that would be mechanically fragile. Current dis; /archives//html/Amps/2014-04/msg00187.html (8,721 bytes)
11. Re: [Amps] Filament Voltage Question (score: 1): Author: "Joe Subich, W4TV" <lists@subich.com>; Date: Tue, 22 Apr 2014 11:33:55 -0400; Perhaps because the low voltage, high current filament is more physically rugged? 73, ... Joe, W4TV On 4/22/2014 11:19 AM, Jim Garland wrote: I was reading the data sheet this morning on the 4CX3500A; /archives//html/Amps/2014-04/msg00188.html (7,576 bytes)
12. Re: [Amps] Filament Voltage Question (score: 1): Author: "Jim Garland" <4cx250b@miamioh.edu>; Date: Tue, 22 Apr 2014 10:09:28 -0600; A note from WC6W pointed out that the particular tube in question, a 4CX3500A, actually uses a directly heated cathode, although I'm not sure that makes a lot of difference (except that the filament; /archives//html/Amps/2014-04/msg00189.html (9,617 bytes)
13. Re: [Amps] Filament Voltage Question (score: 1): Author: "Fuqua, Bill L" <wlfuqu00@uky.edu>; Date: Tue, 22 Apr 2014 17:37:04 +0000; Thinner and longer filaments also have more inductance. 73 Bill wa4lav Hi Jim, That tube employs a DIRECTLY heated filament. Two good reasons for low voltage in this case: High voltage operation woul; /archives//html/Amps/2014-04/msg00191.html (9,379 bytes)
14. Re: [Amps] Filament Voltage Question (score: 1): Author: KA4INM <ka4inm@gmail.com>; Date: Tue, 22 Apr 2014 14:02:02 -0400; Hi Jim W8ZR Garland: A note from WC6W pointed out that the particular tube in question, a 4CX3500A, actually uses a directly heated cathode, although I'm not sure that makes a lot of difference (exce; /archives//html/Amps/2014-04/msg00192.html (10,000 bytes)
15. Re: [Amps] Filament Voltage Question (score: 1): Author: peter chadwick <g8on@fsmail.net>; Date: Tue, 22 Apr 2014 20:33:08 +0200; Jim, In a directly heated cathode, i.e. a filament, the higher the filament voltage, the greater the induced grid swing caused by the filament voltage. If you had a 100 volt heater and the grid retur; /archives//html/Amps/2014-04/msg00193.html (13,022 bytes)
16. Re: [Amps] Filament Voltage Question (score: 1): Author: Bill Turner <dezrat1242@wildblue.net>; Date: Tue, 22 Apr 2014 11:40:55 -0700; ORIGINAL MESSAGE: (may be snipped) REPLY: There is another issue too: With a directly heated cathode (filament), there is an unintentional bias across the filament. Whether using AC or DC, one end of; /archives//html/Amps/2014-04/msg00194.html (8,544 bytes)
17. Re: [Amps] Filament Voltage Question (score: 1): Author: "Jim Garland" <4cx250b@miamioh.edu>; Date: Tue, 22 Apr 2014 13:13:26 -0600; Good point, Bill. I hadn't thought of that, but that's obviously a consideration for VHF/UHF tubes with directly heated cathodes. Jim mechanically fragile. in a high voltage _________________________; /archives//html/Amps/2014-04/msg00195.html (10,957 bytes)
18. [Amps] Filament Voltage Question (score: 1): Author: John Lyles <jtml@losalamos.com>; Date: Fri, 25 Apr 2014 23:39:25 -0600; When direct heated filaments of thoriated tungsten (usually 1-2% thoria) have a lot of hours of operation (thousands), they become brittle and easy to break. Older tubes are much more prone to shippi; /archives//html/Amps/2014-04/msg00223.html (10,918 bytes)

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