Another YouTube channel worth a look - Page 1
Forum section: electronics / general

author: icon
author_rank: Regular Contributor
timestamp: October 20, 2012, 09:14:21 pm
content: HiI'm addicted to the videos of this chap called Andy Davies, whose channel is calledAndyDaviesByTheSea. He does a lot of stuff about old radio equipment and test equipment, but even if that doesn't sound like your cup of tea give it a go anyway - it's fascinating. There's a recent video about him fixing a Telequipment scope (which is how I found him). He says "It smelled like a selenium rectifier packing up, if you know what that smells like". Priceless. He also makes forays into horology, which appeals to me no end. I admire his ability to make things out of the contents of a junk box without thousands of pounds worth of tools. I don't think he has a piece of test equipment made in the last 20 years. Makes me feel like a charlatan.Anyway, check him out.CheersJohnModerator: Added link

author: PeterG
author_rank: Frequent Contributor
timestamp: October 20, 2012, 10:39:13 pm
content: I found him a while ago, he makes very interesting videos.Regards

author: ablacon64
author_rank: Frequent Contributor
timestamp: October 21, 2012, 12:51:32 am
content: Didn't know about it, just subscribed! Thanks for the tip!

author: BalticLab
author_rank: Regular Contributor
timestamp: October 21, 2012, 04:54:59 am
content: An old-timer, must me great. Just subscribed. Thanks for sharing that with us.

author: G7PSK
author_rank: Super Contributor
timestamp: October 21, 2012, 09:12:54 am
content: Just looked at the link, and watched No.53. I would like to see Dave measure 2KV with a fluke, just shows how good the old AVO's were

author: SeanB
author_rank: Super Contributor
timestamp: October 21, 2012, 09:39:00 am
content: I checked the output of my insulation tester with a cheap DVM, that I can get cheap if it did not survive. 1053V on the 1000V range. Meter input impedance was measured as well, 10M on the insulation tester ( actually 5M indicated, but there is a scale factor to the 1000 and 250V ranges) which agrees well with the quoted spec for the meter and the tester.

author: M0BSW
author_rank: Frequent Contributor
timestamp: October 21, 2012, 12:21:01 pm
content: Quote from: icon on October 20, 2012, 09:14:21 pm.Thank you for the link, As a fully licensed radio amateur myself, i can relate to Andy , and his videos are brilliant, I got a few to watch

author: M0BSW
author_rank: Frequent Contributor
timestamp: October 21, 2012, 12:22:10 pm
content: Quote from: G7PSK on October 21, 2012, 09:12:54 amI was offered one of those and turned it down how dumb was I Arghhhhhhhhhhhhhh

author: G7PSK
author_rank: Super Contributor
timestamp: October 21, 2012, 01:55:18 pm
content: Quote from: M0BSW on October 21, 2012, 12:22:10 pmThe scope or the AVO. I used to have a similar scope and still have the AVO which is still a good meter. I have a couple of DMM but if I think there might be large transients or I want to measure HT I roll the AVO out best meter ever produced bar none to my mind. A proper mans tool.(For many things but no good for teeny weeny weedy electronics)ps. my tongue was so far in my cheek for that last bit I may never be able to make adjustments again.

author: M0BSW
author_rank: Frequent Contributor
timestamp: October 21, 2012, 04:18:54 pm
content: Quote from: G7PSK on October 21, 2012, 01:55:18 pmI'm looking on E-Bay at one now , I intend to correct the mistake I made, as my Transceivers are all high voltage Yaesu FT101 ZD, Kenwood 820, 820s, 520s, big voltage boys.

author: IanB
author_rank: Super Contributor
timestamp: October 21, 2012, 04:50:10 pm
content: A handy trick for anyone who might occasionally want to measure a voltage like 1.8 kV which exceeds the DC V range on a multimeter. If you have two meters, put them both on the 1000 V DC range and connect them in series when taking the measurement. You will now have a 2000 V range. Add together the readings on each meter to get the total voltage.

author: Unknown
author_rank: Unknown
timestamp: October 21, 2012, 06:06:20 pm
content: Assuming the input impedance is the same. What happens in the case of an overload? CAT III 1000 V standard overload test is an 8 kV transient, so lets assume 16 kV for 2000 V (no idea if there's actually such a thing as CAT III 2000 V, let alone what the test conditions are). The MOV in one of the meters will start clamping the transient. This essentially shorts the inputs of that DMM, and puts almost the full transient across the second DMM, which might catastrophically fails since it suddenly gets to dissipate twice the voltage transient it was designed for.This assumes the meters were properly designed, like the Fluke 27 that Dave recently reviewed. I wouldn't even trust some random cheap DMM which skimped on safety features, eg. Uni-T, to handle its rated transient, let alone twice that.

author: IanB
author_rank: Super Contributor
timestamp: October 21, 2012, 06:17:27 pm
content: I was going to add a comment at the end of my post that such techniques should only be used for low energy electronic circuits on the bench, but then I removed it because I thought such a thing would be obvious. It is clear to me that if you have to measure 2 kV DC in an industrial setting where high energy transients might occur then you will of course have appropriate (safe) instrumentation and training available to you.It is of course best to use two similar or identical meters so that the voltage is divided roughly equally between them, otherwise one meter might go over range.

author: SeanB
author_rank: Super Contributor
timestamp: October 21, 2012, 06:25:08 pm
content: The meters in series works for analogue meters where the input is totally resistive well into overload, but is not good on a digital meter where the input impedance can be modified by overvoltage protection or by other protective methods like a PTC fuse.Of course the analogue meters must be the same make, model and mod state, otherwise all bets are off.

author: Unknown
author_rank: Unknown
timestamp: October 21, 2012, 06:50:34 pm
content: Or you could use a proper resistive high-voltage probe, which is much more likely to be purely resistive well beyond the max. voltage. Shouldn't cost much more than another multimeter. Of course these are usually only designed for low energy circuits.

author: IanB
author_rank: Super Contributor
timestamp: October 21, 2012, 09:54:18 pm
content: Quote from: SeanB on October 21, 2012, 06:25:08 pmI'm really failing to understand the concern here. If you overload a single DMM on the DC V range, you may damage the meter. If you now put two meters in series each on the DC V range, you run the risk of damaging two meters. OK, that's slightly more painful than damaging one meter, but presuming you use two similar meters and keep the total voltage in range the risk is minimal.A second use for this trick is to get more digits of precision when measuring lower voltages. For instance if you have two 4000 count meters and you want to measure 5 V, you could have 5.00 V on a single meter, or 2.498 V + 2.502 V on two meters in series.

author: Unknown
author_rank: Unknown
timestamp: October 21, 2012, 10:10:14 pm
content: The bang might be larger (four times as large in the worst case of one meter completely shorting and the other behaving as a resistive load seeing twice the voltage). Granted, the risk should be quite small as long as you have decent meters and stay within their limits.You get more digits of precision with two meters in series, but accuracy may be worse if the offset error (+ n digits) dominates, since you double this offset error.

author: EEVblog
author_rank: Unknown
timestamp: October 21, 2012, 10:17:26 pm
content: Quote from: G7PSK on October 21, 2012, 09:12:54 amWhy would I, I've got a Tripplett that can measure 6KV.I wonder if the old AVO's survive an 8KV 2ohm transient?Dave.