Hi Robert Many thanks for the clarification re the reference, I wasn't intending to be nitpicky it was just that your comment about the Weston cell was what started me on the struggle to retrieve the meter from where it was nesting, so I was paying it a bit more attention that I might have done otherwise......pain is quite good for focussing the attention:-) Thanks too for the warning re the switch wafers, that was something I hadn't considered. Fortunately the wafers themselves were ok in this instance and the jammed switch was down to the grease in the mounting bush drying out and becoming "gummy". A couple of very small drops of three-in-one from the end of a cocktail stick between the front of the bush and the circlip on the shaft, plus a bit of patience, and all was fine again. Regards Nigel GM8PZR In a message dated 07/08/2013 12:55:40 GMT Daylight Time, robert8rpi@yahoo.co.uk writes: Hi Nigel, I just re-read my post and I wan't very clear. I was trying to say that the 803B has a Weston cell reference. Jammed switches are often caused by the readout drums shrinking and seizing on the shaft :-( . Watch out for the switch wafers, at least on the higher accuracy units they were impregnated with silicone oil to reduce leakage. Standard waferes may not be up to specification. Regards, robert G8RPI. ________________________________ From: "GandalfG8@aol.com" <GandalfG8@aol.com> To: volt-nuts@febo.com Sent: Wednesday, 7 August 2013, 11:10 Subject: Re: [volt-nuts] Fluke differential meters Hi Robert Your comments reminded me that some years ago I bought a Fluke differential voltmeter and a hernia inducing struggle through other equipment to reach it down from a shelf just confirmed it's an 893A. I must admit I was more interested in the case when I bought it, sacrilege I know but at least it looked too nice to take apart so did remain intact, and I'm much more inclined now to leave it that way:-) Component markings suggest this one dates from around 1984 and it uses the same style blue plastic switch wafers in the Kelvin-Varley divider that later became notorious for failing on the Redifon 551 HF receiver. There are, or were, some references on line to repairing the switches in the 551 and I have seen the wafers offered for sale from time to time, I seem to recall they were also used in one version of the RS components "make-a-switch" kit. As far as I can tell from the manual though and unless I'm missing something, which isn't entirely unkown:-), the voltage reference consists of a pair of zener diodes rather than a Weston cell. Either way, I've just discovered one of the switches is jammed, the wafers look ok and I don't recall it being jammed when I bought it so not sure why yet, but there goes what I already had planned for today:-) Regards Nigel GM8PZR In a message dated 07/08/2013 07:37:44 GMT Daylight Time, robert8rpi@yahoo.co.uk writes: Hi Joe, The 893 is worth having as a working instrument. The older ones are collectibles (possibly) or a source of parts. The Voltage reference is a Weston cell which will be well past it's expected life. In particular these meters have a Kelvin Varley voltage divider. This can be used without the meter section working, possibly recased. The plastic switch dials/drums do tend to crack or warp due to srinkage of the plastic though. If theK-V dividers switches are worn out, they are still a good source for precision matched resistors. Perhaps not spot on value but all the resistors in a decade will be very close in value. These can be used for voltage dividers and Hamon resistor units (google Hamon resistor and see http://conradhoffman.com/HamonResistor.html). They may not look much but are high performance. There are other precision resitors in these units Take care when removing them, don't apply any force or stress to the resistor body as this can affect their performance. Robert G8RPI. ________________________________ From: Joseph Gray <jgray@zianet.com> To: Discussion of precise voltage measurement <volt-nuts@febo.com> Sent: Wednesday, 7 August 2013, 6:00 Subject: [volt-nuts] Fluke differential meters The local surplus guy has at least three different differential meters that have been collecting dust for decades. I have borrowed two of them (so far). The first one is a Fluke 893A and is solid state. Although it appears to work, it fails the very first of the performance tests. Now that I have a full manual, I'm going to look at this a bit closer. The second one is a Fluke 803B (I think. There is no label on it). It has tubes. I am slowly bringing it up on a variac before messing with it. I plan to open it up later and take a good look. I'm not sure what the third model is, but it looks like it may be an even older Fluke. It is on a high shelf and I haven't gone over there to lift it down yet. I'll probably do that later this week. At the moment, I'm just playing around with this gear and learning a few things. In the long run, are these things worth having? Joe Gray W5JG _______________________________________________ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there. _______________________________________________ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there. _______________________________________________ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there. _______________________________________________ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.