18-05-2013, 02:15 PM
Just for reference, ignoring fwd voltage drop non linearity in diode etc: V average out from a half wave rectifier = .318 of peak AC in, so for peak AC in multiply by 3.144
Lawrence.
Lawrence.
PW 1986 High Impedance MOSFET Voltmeter
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18-05-2013, 02:15 PM
Just for reference, ignoring fwd voltage drop non linearity in diode etc: V average out from a half wave rectifier = .318 of peak AC in, so for peak AC in multiply by 3.144
Lawrence.
18-05-2013, 04:39 PM
The peaks on half wave rectifiers are the same voltage as the ones on a full wave circuit. Average voltage without any capacitance would indeed be half that of a full wave circuit.
I have a valve volt meter and it has two diodes in the AC probe with two signal wires and earth.
18-05-2013, 06:27 PM
(18-05-2013, 12:59 PM)Joe Wrote: One thing I am wondering about a bit is the AC Probe. Yes Joe - your circuit is correct. I found a feedthrough cap among my bits and bobs, so I checked the capacitance and it is 1,000pF. I don't suppose for a moment that it would make any difference to substitute that with a small 1,000 pF cap (eg, polystyrene or whatever), as I don't think feedthroughs are that easy to find these days. I've finally completed my meter after a lapse of 28 years, and am working on the probes now, so when they're done I'll post some pics (at some future date!).
Regards, David.
BVWS Member. G-QRP Club Member 1339. 'I'm in my own little world, but I'm happy, and they know me here'
19-05-2013, 01:11 AM
The two diode probe circuit would require a three pin probe connector so it is less useful here.
You can still have a look at it if you want to. The two signals go to both inputs of the amplifying device so it could be done if you are building from scratch. http://golbornevintageradio.org/forum/sh...p?tid=3358&pid=33981#pid33981
19-05-2013, 11:32 AM
Link to a description of an AC half wave diode probe, looks more or less identical to the one Joe was on about.
http://n5ese.com/rfprobe1.htm Lawrence
20-05-2013, 07:31 PM
Finally finished my meter!
It works fine on AC and DC and is accurate when compared with other analogue and digital meters. The probes were a bit fiddly to make, notably the AC probe as for the 'business end' I used a piece of 1/4" diam rod in which I drilled one end (on the lathe) to accept a short piece of 1/8" diam brass sharpened to a point for the probe tip, soldered into the 1/4" brass rod. At the other end, I turned the 1/4" rod down to a thinner diameter and drilled a hole in the end to accept the feedthrough terminal so that it could be soldered into that end and the BAT85 diode and resistor attached. I've attached a few pics - not much more I can say really except that I'll probably fit an LED to show when it's on.
Regards, David.
BVWS Member. G-QRP Club Member 1339. 'I'm in my own little world, but I'm happy, and they know me here'
20-05-2013, 07:42 PM
You wait twenty-seven years and then two come along together.
Nice job, as always. - Joe
20-05-2013, 08:22 PM
Proper tidy job David, no excuse for servicing valve stuff now....
Lawrence. |
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