That's great thanks dave appreciate the explanation a bit wiser to its working now !!

I'm guessing this is for a linear.

The ones I built had the voltmeter in the linear.

The PSU was always separate, even if in the same box, but especially when it was external, I wanted to know the voltage at the PA.

All the linears I made had a regulator down to 24V, then from that regulators for 15V and 12V to supply relays, bias and control circuits.

I did also use some DC power meters (intended for use on RC and lipos) which gave me the voltage, current and power being drawn from the PSU on a 2X16 LCD display, which was the most useful solution, as it also helped see the efficiency on various bands.


Edit

Found it very quickly, surprising as I have been using them for many years, and certainly haven't bought one for 3 years or more

https://www.ebay.co.uk/itm/255460495878 ... %3A2047675

I take them out of the box, and mount them in the amp, and the SWR RF power meter has the same 16X2 display, so it looks neat.

Note the reason those simple two wire type only require two wires (but have a minimum voltage they will display down to, ie they don't do 0 to 100 volts, often that minimum is 4 to 5 volts), is because they derive their running power supply for the onboard electronics and display direct from the measured voltage over their stated range, which as long as it is within the stated limits internally regulated down to a constant lower voltage for running the onboard electronics and display, normally about 3 volts DC, and the same two wires also supply the as measured voltage to be displayed.

https://www.ebay.co.uk/itm/154598588628?
Add a 7824 regulator in supply line.
This one comes with the shunt as well for current, and does not appear to come from the land of the balloon.

Thanks so much guys the advice is always very much appreciated.

Cheers could be just the thing It's for an eltek powepack 2 50v psu to power a LDMOS HF linear just want to keep an eye on output voltage of the psu

I have used Eltek flatpacks (still have a new unused one somewhere), and yes it works fine on them.

I used the Eltec supplies on 1-1.2 kW amp modules, but for the later 600W modules I used a Chinese supply, more conventional, and shorter although fatter.

Is it an amp you are building, or a commercial one?

What protection does it have?

I mounted a protection circuit and one of those meters in a small box between a PSU and the amp, just needed one wire from the amp to cut the DC supply in case of over current, mismatch (which covered wrong filter selected as well as output mismatch), over drive and over temperature.

That was between the time I was using built in supplies and the time I decided I wanted the PSU hidden under the table. Later ones had the meter and cut out in the amp box, so that the main supply stayed on, and just the supply to the PS block was cut, meant I could have a reset button instead of cycling the mains power if the protection circuit tripped.

Amp is the DXWORLD HF/6mtr version. Says accepts between 48 to 53.5 volts which suits the Eltek fine. Again just want to keep an eye on the pau output as no protection on the linear If things should go wrong . Saying that do these supplies poss have protection circuits to prevent it going over the max voltage ?

Will probably just buy that unit you linked to as I must admitt I like the look of it.could I run it with the same eltek psu that I want to measure its voltage output ? No worries if not would just power of a seperate psu .

They might have over voltage protection, many do, but if unsure you could always fit a suitable retro on the output rails "crowbar over voltage"" clamp down device, but that's another kettle of technical add on fish!
Just stick a voltage regulator between the PSU limited adjustable output rails and the supply input of the voltage reading/displaying device, that way you know its being constantly fed well within its ball park working voltage supply range consistently, as opposed to whatever you set the output rails to.
They are simple three leg TO220 devices, input voltage leg, ground/negative leg, and stabilised output voltage leg, add a decoupling cap on input and output pins to ground/negative and away you go, correctly selected supply voltage for the digital meter voltage display concerned.

Perfect thanks again,