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1. [Amps] SB-220 diode failure (score: 1): Author: John Adkins <w4kv@yahoo.com>; Date: Tue, 9 Aug 2005 10:05:52 -0700 (PDT); My sb220 cooked one of the diodes on the pc board a couple of days ago. I replaced the faulty one with a 1kv piv 2.5 amp substitute that was in my junk box. Resoldered the wires back to the pc board,; /archives//html/Amps/2005-08/msg00342.html (7,732 bytes)
2. Re: [Amps] SB-220 diode failure (score: 1): Author: "Will Matney" <craxd1@verizon.net>; Date: Tue, 09 Aug 2005 13:11:33 -0400; John, The first thing that comes to my mind is a bad zener diode. It controls the bias on the tube on transmit. On idle, there's a 120 Vdc source connected to it. If the plate current is ok on receiv; /archives//html/Amps/2005-08/msg00344.html (8,750 bytes)
3. Re: [Amps] SB-220 diode failure (score: 1): Author: "Mike Schatzberg" <cherokeehillfarm@earthlink.net>; Date: Tue, 09 Aug 2005 13:37:11 -0400; Hi John: As I recall, with zero bias voltage, that is about what the two tubes would idle at, with a blown zener diode. I would replace the zener with a string of decent diodes, to get the voltage su; /archives//html/Amps/2005-08/msg00346.html (9,718 bytes)
4. [Amps] SB-220 diode failure (score: 1): Author: John <w4kv@arrl.net>; Date: Tue, 09 Aug 2005 14:28:41 -0400; Mike-- Thanks for your comments. If it isn't too much trouble, do let me know the design of the bias supply board you mention. My inclination is to go ahead and get the Harbach board, since several o; /archives//html/Amps/2005-08/msg00348.html (6,758 bytes)
5. Re: [Amps] SB-220 diode failure (score: 1): Author: R.Measures <r@somis.org>; Date: Tue, 9 Aug 2005 13:09:04 -0700; If the zener is shorted, it can be replaced by 7, fwd biased, 1A Si diodes in series, mounted on a perfboard. If the resistance of V2's parasitic suppressor R is more than 30% high, odds are that you; /archives//html/Amps/2005-08/msg00352.html (9,109 bytes)
6. Re: [Amps] SB-220 diode failure (score: 1): Author: Gary Smith <wa6fgi@sbcglobal.net>; Date: Tue, 09 Aug 2005 13:27:53 -0700; My .02 on this: I would update the 220 with the Harbach rectifier mod. Have heard nothing but praise for his mods to the point he is sometimes overwhelmed with orders for them. To me, that speaks wel; /archives//html/Amps/2005-08/msg00353.html (8,494 bytes)
7. Re: [Amps] SB-220 diode failure (score: 1): Author: R.Measures <r@somis.org>; Date: Tue, 9 Aug 2005 13:57:31 -0700; The only problem that I have heard about is that his suppressors don't get hot enough at 28MHz to a decent job of suppressing VHF. Adding more L to L-supp would fix this. Richard L. Measures, AG6K, 8; /archives//html/Amps/2005-08/msg00354.html (9,731 bytes)
8. [Amps] SB-220 diode failure (score: 1): Author: John Adkins <w4kv@yahoo.com>; Date: Mon, 29 Aug 2005 09:43:30 -0700 (PDT); Thanks for the suggestions earlier this month regarding the SB-220. You may recall that after replacing a failed diode on the PC board, resting plate current was 0.3 amp instead of 0.120. The zener d; /archives//html/Amps/2005-08/msg00752.html (7,758 bytes)

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