sunray

The Lindapter items Simon and I have referred to are actually structural devices and designed to support horizontal structural beams: https://www.lindapter.com/application/gc31 So should be suitable for the situation I've used the Unistrut fitting you linked to on numerous occasions but I wouldn't dream of using them vertical, they rely on clamping against a relatively flimsy box and may appear very solid when installed but then loads applied may easily alter the shape of the strut. Think about what happens to the shape of a round pipe when bent. Agreed, I have used gravlocks vertically but only for light duty; couple of patt23/PAR 64 LEDs etc however always with additional fixings/safeties in place.

I have drilled and tapped columns, and for that matter horizontal beams too, but under coordination with a structural engineer in writing before I started and continued inspection/checking during works. I wouldn't do anything less and quite honestly for a moving item weighing 4KG I'd personally be looking at using at least 2 of those arrangements. All of those I'd recommend have unfortunately retired/got too unhealty or as seems to be happening too often; passed away. I used to work for a nightclub light and sound company and their attitude was 'just whack it up' and seeing others works I fear that is a too common approach these days.

Obviously drilling the column would be a brilliant solution but not one I'd recommend without a structural engineers sayso. The thing with these is; despite seeing it done on a regular basis, I wouldn't be comportable relying on one fixing onto the each edge of a column. However if the there were 4 clamps I think it would be a different matter. Those clamps are only £1 to 2 ( I haven't purchased any for a number of years so don't know how prices have changed) so in my view £32 seems excessive for a piece of angle with a few punched holes. However I believe Tom's Gravlocks would be a more appropriate fitting but still the doubt about the suitability for a vertical column. A quick search for Lindapter comes up with a selection of fixings, such as https://www.lindapter.com/application/gc33 essentially a plate with holes with the correct spacing and clamp blocks doing the work, this plate happens to be an 'L' bracket:

Those Doughty brackets are an expensive way to purchase a couple of LINDAPTER fittings (and a length of angle iron) I've often seen them used on vertical beams with a pair of half couplers and length of tube, Personally I'd be a little uncomfortable and would be happier with a plate with 4 or even 6 fittings.

Judging by the unfinished state of the building any trade could have left something undone.

If it is a length of unistrut, I've regularly seen M6 or M8 studding drop rods with only square washer and plain nut holding a unitrut to support ducting. the theory being when the weight of the duct is installed then the nuts are adjusted for level and a locknut added. The second stage all too often seems to be forgotten. Of course if it is Unistrut that has fallen it could easily be a piece missed (or incorrectly installed) by any of the other contractors; Ceilings, Electricians, Plumbers, Sprinklers etc in no order other than alphabetical.

Personally I'd rather have food.

Hopefully a picture speaks a thousand words. Half wave rectificationwith 2 diodes in series with one reversed. No current can flow in either polarity: Solution: reverse the load: I recall this problem cropped up a lot of years back on some model railway points motors where different manufacturers opted for the opposite polirity and therefore incompatible.

Going back 25 years I was in this position, a mobile disco CO-OP brought in 4 with blown bulbs, they were 1*15" 400W, 2*12" 250W, 4* tweeter (3" ?) all Celestion & 4*piezo. Marron carpet & grill covered. The tweeters and piezo were protected by 2 festoon bulbs (2 tweeters and 2 piezo per bulb IIRC). Luckily they had more similar speakers, I wired one of their good bulbs in series with all ratings of festoons available from an automotive outlet and did a simple comparison on a variable supply measuring the voltage across each bulb. 12V 18W was the closest match. I used to keep a stock of 24V 45W bulbs for Bose 802's (then 12V 12W when the 45's became unavailable) where so many used to come in but they are a very different beast.

Indeed. In 1969 I used a valve amplifier (ECC81 & PL84) and loudspeaker robbed from a record player, LT & HT PSU's from physics dept, headset from language lab for comms between MD (Known as organist) and lighting. I soon added c/o switch to isolate LS and enable Foster DF1 microphone to talkback to MD. used for 2 plays a year apart. After leaving school I joined a little theatre club and installed the same system into there for use between SM/sound position to lighting but knocked up a basic PSU, changed the PL84 to EL84 and the C/O switch to PTT button and used the LS as the talkback mic. I did 2 plays there as lighting op and left it in place. About 10 years later I went to a show and it was still in place and lit so I assume being used.

I've done this several times with a half coupler or hook clamp and 1/4"W bolt, 2 penny washers, nut and wing nut As mentiined adding a ball joint will make things much easier

If it's a 6th form college there are likely to be technical students with contruction abilities. Look on this forum for blueclone.

This sort of sleeving makes a good multicore https://www.ebay.co.uk/itm/175821632523?var=475224440614&itmmeta=01HVMD1FW5CW4TMA1EKRXBBY9V&hash=item28efc9340b:g:8XEAAOSwaxBktPWf&itmprp=enc%3AAQAJAAAA4O83tJaNvCmVhFZdXqXoVTLD5OAq6aCfYLqo1hbc2tgFXN%2FqVQVFdJvosaVxeYzcCeR8uwqiFGe8%2BF2oFUkwAJSjSGpzjqV8hAFzBOeI6z2EFntnMKxr43Lf5xEoInaS4PxXBY8IVA1H%2BLO3eqmfty9ZPtTzmDWJaLNJHLjDIcx19cX2j68Y1hq%2F0ITC5HZSodc3PO%2FVzvyu%2BeepxQZ4ppDgGZjqrKDPzU94ffRdx9BOpY1Vii1Tq8wZH7aHNSucMhy0nP1R09HFbZPpPFJRYKh8hMQ3BXQA5SjXZyZTXjCD|tkp%3ABFBMsv6Fjd1j I often position radiomic receivers nearer to the source rather than run long aerial cables. Bear in mind you will require a working space of at the very least the length of any loom you make, I've found it's easier to draw the sleeving onto the bunch of cables rather than pull them into the sleeve in which case you require twice the length. The longest I've done has been 50m, that requires at least 3 people but the end result is worth it.

I have no problems with the operation if they are individual & isolated, however to date I've only encountered them in groups of 4, 6 etc and so far only a common pin, I made up a cable just a couple of weeks back, DB25 (with only one common) to 4x 8 pin Din (with one common each) which is typical of what I've come across and until now assumed it's standard..

How does that work?