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1. [Amps] Small transformer evaluation (score: 1): Author: Vic K2VCO <k2vco.vic@gmail.com>; Date: Sat, 01 Sep 2012 13:37:10 -0700; Some of you will remember that I was wondering about utilizing a small Philco power transformer (model 45-7011-7) for a screen supply. It puts out 380-0-380 vac plus 5 and 6 v for filaments. I have h; /archives//html/Amps/2012-09/msg00002.html (7,903 bytes)
2. Re: [Amps] Small transformer evaluation (score: 1): Author: "Bill, W6WRT" <dezrat1242@yahoo.com>; Date: Sat, 01 Sep 2012 13:55:36 -0700; REPLY: You should not use a choke input filter for a screen supply except for constant carrier modes such as FM or RTTY. When the screen current varies as with SSB and CW, the varying current through; /archives//html/Amps/2012-09/msg00004.html (7,372 bytes)
3. Re: [Amps] Small transformer evaluation (score: 1): Author: Vic K2VCO <k2vco.vic@gmail.com>; Date: Sat, 01 Sep 2012 14:18:46 -0700; I switched to capacitor input and changed the load to 5300 ohms. Now I am getting 438V and 83 MA. I stuck a fuse on the transformer just in case and I will let it run for a while. It is noticeably wa; /archives//html/Amps/2012-09/msg00005.html (8,449 bytes)
4. Re: [Amps] Small transformer evaluation (score: 1): Author: Vic K2VCO <k2vco.vic@gmail.com>; Date: Sat, 01 Sep 2012 14:20:58 -0700; It's going to feed a transistor regulator. I'm sure it will be a capacitor filter because of the voltage. Some of you will remember that I was wondering about utilizing a small Philco power transform; /archives//html/Amps/2012-09/msg00006.html (8,563 bytes)
5. Re: [Amps] Small transformer evaluation (score: 1): Author: "Bill, W6WRT" <dezrat1242@yahoo.com>; Date: Sat, 01 Sep 2012 16:51:36 -0700; REPLY: A transistor regulator is ok, but my personal preference is for a high power zener diode (or two in series). Adjust the resistor feeding the zeners so the idle current through them is about 12; /archives//html/Amps/2012-09/msg00007.html (8,269 bytes)
6. Re: [Amps] Small transformer evaluation (score: 1): Author: "Bill, W6WRT" <dezrat1242@yahoo.com>; Date: Sat, 01 Sep 2012 16:51:45 -0700; REPLY: That is the best measure of a transformer's power capacity, IMO. Heat is the enemy of transformer insulation and the lower the heat, the better. My personal rule is if it's too hot to keep you; /archives//html/Amps/2012-09/msg00008.html (7,378 bytes)
7. Re: [Amps] Small transformer evaluation (score: 1): Author: "Jim W7RY" <jimw7ry@gmail.com>; Date: Sat, 1 Sep 2012 17:55:48 -0700; Why not just lift the negative end of the HV bleeder with zenner diodes? If the plate voltage goes away, so does the screen voltage. I hear that screens don't make very good plates? 73 Jim W7RY Some; /archives//html/Amps/2012-09/msg00010.html (9,408 bytes)
8. Re: [Amps] Small transformer evaluation (score: 1): Author: "Jerry Kaidor" <jerry@tr2.com>; Date: Sat, 1 Sep 2012 20:44:06 -0700 (PDT); I hear that ** When I was in high school, I built an SSB transceiver from IIRC a QST article. Or maybe the ARRL Handbook. Whatever, I had somehow forgotten to connect the plate of one of the tubes. S; /archives//html/Amps/2012-09/msg00012.html (8,403 bytes)
9. Re: [Amps] Small transformer evaluation (score: 1): Author: "Bill, W6WRT" <dezrat1242@yahoo.com>; Date: Sat, 01 Sep 2012 19:11:32 -0700; REPLY: That will work, but it requires some very high power bleeder resistors. For example, if the HV is 3 kV and your screen requirement is 400 V at 80 mA, the total power dissipated is 208 watts in; /archives//html/Amps/2012-09/msg00013.html (8,747 bytes)
10. Re: [Amps] Small transformer evaluation (score: 1): Author: Vic K2VCO <k2vco.vic@gmail.com>; Date: Sat, 01 Sep 2012 20:39:35 -0700; Interesting idea. Nominal screen current is 35 mA and voltage is 325. Current goes negative in zero-signal state so the regulator has to deal with that. I want to be able to vary screen voltage for e; /archives//html/Amps/2012-09/msg00016.html (9,627 bytes)
11. Re: [Amps] Small transformer evaluation (score: 1): Author: "Carl" <km1h@jeremy.mv.com>; Date: Sun, 2 Sep 2012 11:53:20 -0400; A resistor from screen pin to ground will take care of the negative current by supplying a constant bleed. Calculate what is needed based upon the actual negative current without the regulator in pla; /archives//html/Amps/2012-09/msg00018.html (11,234 bytes)
12. Re: [Amps] Small transformer evaluation (score: 1): Author: "Bill, W6WRT" <dezrat1242@yahoo.com>; Date: Sun, 02 Sep 2012 12:35:40 -0700; REPLY: What Carl says is true if you are using a transistor regulator which can not supply negative current. If you have a simple zener (or two) you don't need a separate bleeder. The zener(s) will s; /archives//html/Amps/2012-09/msg00022.html (9,061 bytes)

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