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1. [Amps] Alpha Seventy HV Meter Readings (score: 1): Author: "Paul Christensen" <w9ac@arrl.net>; Date: Thu, 12 Jan 2017 16:09:21 -0500; I've recently acquired an air-cooled version of the Alpha Seventy amplifier. I notice that HV reads about 500V low when comparing it to a Fluke DMM with Fluke HV probe. The supply is the same as my v; /archives//html/Amps/2017-01/msg00243.html (7,747 bytes)
2. Re: [Amps] Alpha Seventy HV Meter Readings (score: 1): Author: MU 4CX250B <4cx250b@miamioh.edu>; Date: Thu, 12 Jan 2017 14:24:09 -0700; To compute the value of the bottom resistor in the divider string, don't you need to compute the parallel resistance of the bottom resistor and the resistance in series with the 1mA panel meter? Pres; /archives//html/Amps/2017-01/msg00244.html (8,395 bytes)
3. Re: [Amps] Alpha Seventy HV Meter Readings (score: 1): Author: "Paul Christensen" <w9ac@arrl.net>; Date: Thu, 12 Jan 2017 17:29:52 -0500; Jim, In addition to the five series 1 meg resistors from HV+, there's a 6th resistor, a 15K 1/2W in parallel with the panel multimeter. However, the 15K resistor is across the multimeter only when th; /archives//html/Amps/2017-01/msg00247.html (10,585 bytes)
4. Re: [Amps] Alpha Seventy HV Meter Readings (score: 1): Author: MU 4CX250B <4cx250b@miamioh.edu>; Date: Thu, 12 Jan 2017 16:44:57 -0700; I think you're half right! Yes, the divider string results in a voltage that is a fixed percentage of the voltage at the top of the string, e.g, 5V versus 5000 V. However, you'd need a high impedance; /archives//html/Amps/2017-01/msg00250.html (10,201 bytes)
5. Re: [Amps] Alpha Seventy HV Meter Readings (score: 1): Author: "Paul Christensen" <w9ac@arrl.net>; Date: Thu, 19 Jan 2017 14:12:17 -0500; Here's a quick update. The math worked and the replacement resistor value of 550K results in a HV reading of 4KV. This matches a Fluke DMM with HV probe. The new HV meter divider string is now 4.55 M; /archives//html/Amps/2017-01/msg00273.html (10,914 bytes)
6. Re: [Amps] Alpha Seventy HV Meter Readings (score: 1): Author: MU 4CX250B <4cx250b@miamioh.edu>; Date: Thu, 19 Jan 2017 14:45:52 -0700; Paul, your method of measuring internal resistance of the meter is just fine, though it's easier just to use a DMM and measure the resistance directly. I imagine you have a fluke DMM and these normal; /archives//html/Amps/2017-01/msg00274.html (11,665 bytes)
7. Re: [Amps] Alpha Seventy HV Meter Readings (score: 1): Author: Bill Turner <dezrat@outlook.com>; Date: Fri, 20 Jan 2017 00:06:05 +0000; I'm glad your meter is reading correctly now, but one question remains: Why did it read wrong in the first place? From your description it seems like the meter circuit was designed wrong by Alpha in; /archives//html/Amps/2017-01/msg00275.html (7,947 bytes)
8. Re: [Amps] Alpha Seventy HV Meter Readings (score: 1): Author: "Paul Christensen" <w9ac@arrl.net>; Date: Thu, 19 Jan 2017 20:55:32 -0500; I must be the only person who didnt know the Fluke DMM can source exactly 1 mA. If I read the manual in the past, it probably didnt register. Not sure if the internal source is regulated as the batte; /archives//html/Amps/2017-01/msg00276.html (14,871 bytes)
9. Re: [Amps] Alpha Seventy HV Meter Readings (score: 1): Author: Bill Turner <dezrat@outlook.com>; Date: Fri, 20 Jan 2017 09:57:17 +0000; That still doesn't explain the original error. I see two possibilities: 1. Alpha designed it wrong in the first place. or 2/ Some component changed value. So, which was it? Or was it something else?; /archives//html/Amps/2017-01/msg00277.html (16,675 bytes)
10. Re: [Amps] Alpha Seventy HV Meter Readings (score: 1): Author: "Paul Christensen" <w9ac@arrl.net>; Date: Fri, 20 Jan 2017 08:05:30 -0500; I'm confident in the original Alpha electrical design (but see last paragraph). The math works in their favor and my Alpha 70V/77Dx amps report accurate HV. So, I can't reach a conclusion until sour; /archives//html/Amps/2017-01/msg00278.html (18,530 bytes)
11. Re: [Amps] Alpha Seventy HV Meter Readings (score: 1): Author: Jim Garland <4cx250b@miamioh.edu>; Date: Fri, 20 Jan 2017 06:21:06 -0700; I've not looked at the Alpha 70 circuit, but from the discussion it appears that the HV is measured by putting a 1 mA meter in series with a high resistance voltage divider, with a shunt across the m; /archives//html/Amps/2017-01/msg00279.html (18,472 bytes)
12. Re: [Amps] Alpha Seventy HV Meter Readings (score: 1): Author: "Paul Christensen" <w9ac@arrl.net>; Date: Fri, 20 Jan 2017 09:00:44 -0500; appears that the HV is measured by putting a 1 mA meter in series with a high resistance voltage divider, with a shunt across the meter to give the correct calibration. " In the case of the Alpha 70; /archives//html/Amps/2017-01/msg00280.html (10,424 bytes)
13. Re: [Amps] Alpha Seventy HV Meter Readings (score: 1): Author: John Watkins via Amps <amps@contesting.com>; Date: Fri, 20 Jan 2017 08:15:47 -0600; Guess I will have to read the manual for my Fluke 77 and see if also has the 1 ma source in the low range. I do have a meter or 2 that I want to check. I have used the variable resistor method also.; /archives//html/Amps/2017-01/msg00281.html (21,017 bytes)
14. Re: [Amps] Alpha Seventy HV Meter Readings (score: 1): Author: Bill Turner <dezrat@outlook.com>; Date: Fri, 20 Jan 2017 16:13:23 +0000; I don't have the 70x schematic before me, but if it is like most modern amps, ground is not B-. HV should be measured from B+ to B-. not from, B+ to ground. Check your schematic. The difference is no; /archives//html/Amps/2017-01/msg00282.html (9,507 bytes)
15. Re: [Amps] Alpha Seventy HV Meter Readings (score: 1): Author: "Paul Christensen" <w9ac@arrl.net>; Date: Fri, 20 Jan 2017 11:50:06 -0500; Bill, The Alpha 70 series definitely connects the HV meter return to chassis ground and not B-. As designed by Alpha, it must be that way, since the multimeter is shared with several other functions; /archives//html/Amps/2017-01/msg00283.html (10,171 bytes)

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