What is it? (Varipower CS48)
 

Came across this recently. It is marked Varipower CS48. A Google search revealed only one reference to a Varipower CS48 Voltage/Current calibrator on a Calibration Services provider site. The handful of other references look unrelated and I could find no other descriptive information, nor a circuit diagram.

The unit is powered by 7 C size 1.5v cells, in a 2 + 2 + 3 configuration. Two cells provide -1.5v-0-1.5v. The remaining 5 cells are arranged in series but ground is taken from between the 2nd and 3rd cell so as to provide -3.0v-0-4.5v.

Inside, the unit has four small circuit boards built on Verboard! I found the following semiconductors:

LM308N - x3 op amps
LM741C - op amp
2N2222 - general purpose transistor
ZN432T - unknown, possibly a voltage reference?

Also there is a heatsink mounted part marked as follows:

Lucas, England, DTI15 20 6536

Searching for the ZN432T found a reference on UTSource to a 'precision voltage reference', but the stock image showed ICs, however, since it is marked 'sample image' it may not be representative.

The Lucas part is in a gold case (TO46?) with the number as shown above. Not sure whether that's a 1 or I after the T. Is this another voltage reference? Anyone have any information on that part number?

I presume that the wire loop in the final image is a current shunt? That would perhaps explain the purpose of those two terminals.

If anyone has any further information about this instrument it would be greatly appreciated.

Re: What is it?
 

No idea about the unit but a ZN432 (no T) was an early Ferranti 28 pin DIL A-D converter - and I can't see what that would be doing in your machine.

Re: What is it?
 

I assume that ZN432T is a house-code equivalent of TL432 etc.? The TL431/TL432 series of precision shunt references were available in a slightly bewildering array of packages and pin-outs, hence lots of suffixes!

Re: What is it?
 

Sorry, my mistake its ZN423T, not ZN432T. If it helps, the device is in a TO18 case and can been seen bottom left on the board in the picture.

It would probably take a while to reverse engineer the instrument - there are lots of resistors on rotary switches - but I might give it a go at some point.

Re: What is it?
 

That makes more sense - it is another Ferranti device - but a 1.2 volt reference. There is a single data sheet here but I could not download it.

https://www.web-bcs.com/oem/fi/ZN423.html

Re: What is it?
 

Right-clicking download next to Datasheet (jpg) and 'Save Link As' did the trick for me. That's one piece of useful information returned. Thank you for finding and posing that link.

Looks like the company that made the meter movements, Sifam, is still around, although perhaps no longer in the UK.

Re: What is it?
 

Ah yes - that worked.
Could the Lucas device be a DT1520? That seems to be a silicon NPN transistor. Not much info but some pictures here.
http://www.wylie.org.uk/technology/s...ucas/Lucas.htm

Re: What is it?
 

Looks like a lab built prototype of something or other so probably a one off. You just need to have a play and see what it can do...

Re: What is it?
 

Thanks for that link again. The Lucas name did make me think of auto parts, but I wasn't sure whether the same company made semiconductors. I couldn't tell whether it was a 1 or an I and there is a definite space between the 5 and the 2, but that will probably just be the printing. DTI1520 does make sense and the part looks identical.

Could be a prototype, which might explain the Veroboard. The case is made from wood but is also laminated with Formica. It has a matching lid that attaches using a clasp on either side. Someone has evidently gone to a bit of trouble to finish it with a hard-wearing surface, perhaps protect it from grime and moisture? In the linked online article by Andrew Wylie, he refers to a Lucas Catalogue from 1965 that identifies the DTI1520 transistor. The presence of Formica would seem to be consistent with that time period.

The power cell voltages were scribbled on the wood inside and a sequence of numbers is hand written on the reverse of the front panel (see image). Not sure if that's a '7' or a symbol of some sort at the beginning? There is a serial number hand written on a patch of some kind of paint on the front plate which is so worn that it is only partially visible in the photo, but appears to read V905.911. There is possibly an '8' on the end (can just seem make it out on the paintwork but could be my imagination).

As to what it does, moving the switch to the 'batt. check' position moves both meter pointers to about two thirds. The Kodak batteries measure at 1.6 volt so appear to be quite fresh, so I guess someone used some pound shop batteries to test it and left them in. Switching to the 'On' position produces no output whatsoever at the terminals. I have tried various positions of the range controls and the BIAS control, as well as rotating the vernier.

I have worked out that N/R probably stands for Normal/Reverse, which would allow both meters top operate in a positive or negative direction, but I don't yet know what ZRA, marked next to a push-release rather then toggle switch, stands for. The meter on the left seems to register something on some positions of the left range switch. The right meter registers nothing.

Re: What is it?
 

Some sort of voltage/current calibration source?

Re: What is it?
 

Thanks, that seems to be the inference from the one solitary link I could find, but I couldn't confirm that. If it is, then it is currently no sourcing anything so will need further investigation. The Lucas transistor could conceivably be being used in the current circuit. Will have to delve deeper and reverse engineer I guess.

I wonder if anyone can tell me what these markings on the meter panels mean? I haven't really taken much notice of them before, but I think I have seen similar marks on another meter as well.

Re: What is it?
 

It's a constant current, constant voltage source test set. The switches at the top are normal / reverse output.

I've seen those Lucas transistors before but at the moment I cannot recall where.

Re: What is it?
 

DT1520. Medium power NPN silicon. 30V, 0.8W free air, 1A max, hfe 120 at 300ma. TO39. circa 1966 by Joseph Lucas.
I think of 2N3053 or BFY51 families. I can probably find some more data, but hardly relevant in this case.
SeeMos description looks right. But fancy a test set powered by batteries. Whenever I pick up battery powered test gear, it always seems to need new batteries and servicing. (e.g CT471 voltmeter)
wme_bill

Re: What is it?
 

"ZRA" - wild guesses:

Z = Zero
R = Reading or Resistance
A = Adjustment, Allowance, Automatic or Ammeter

ZRA: any combination of the above.

I've met ZRA= Zero Resistance Ammeter, but only in technical writing, never in reality.

Al.

Re: What is it?
 

Rather than a prototype, could it be some kind of restoration job/upgrade?

Re: What is it?
 

At the top of the unit there are two switched labelled "N/R": clearly an abbreviations. Possible candidates are:
Noise Reduction; Normal Range; Null Reference.

Al.

Re: What is it?
 

Well I guess that settles it. Its a voltage/current calibration source. Thank you for your views. Now I need to figure out how it works, and why there is no output.

Bill, thank you for the transistor specs. I have made a note in my log. I also wondered why it was designed to run on batteries as having them run low would presumably be a drawback. It also requires seven of them and I don't think they were particularly cheap back then. It was evidently meant to be portable as it is fairly small (11in x 8in x 5in) for the time and has a carrying strap.

Thanks for those suggestions. That term 'Zero Resistance Ammeter' is one that I was not familiar with, so I looked it up. A quick search indicates that such devices do exist and are used in conjunction with measuring galvanic current and corrosion without imposing a voltage drop, however I need to do some further reading to gain a fuller understanding. The switch is on what would seem to be the current function side of the unit, although the knob below is marked in mV as well as A/mA. The two leftmost probe sockets at the top are linked with that wire bridge shown in one of the pictures of my opening post which I assume is a current shunt. This would make sense given the indicated 5/16A range marked on the left-most socket. Could it be that the left (default) position of the switch provides a current source, while the spring loaded right position provides a Zero Resistance Ammeter function?

I am also curious what the 'S' positions might be? The rotary switch on the other side has two positions between the DC and AC functions, but they are blank and unmarked, so I presume 'S' must have a meaning. One rather obvious meaning might be 'source', but there is presently no output.

I will hopefully have time to investigate a little more tomorrow, or if not, then later in the week.

Re: What is it?
 

Thanks. I will bear these suggestions in mind. The way the switches are wired seemed to me to be reversing polarity, hence my conjecture that it might mean Normal/Reverse, but I will need to trace the wires to establish that for sure. Null Reference might also make sense for precision measurement. There are two zeroing controls with large pots on the underside present in the centre of the unit between the two meters.

I wish I could find some documentation but I doubt that the calibration house that lists this device would be willing to share....

Re: What is it?
 

The crossed-over wiring on the back of the switches says normal/reverse.

David

Re: What is it?
 

I missed a semiconductor on my first look. I found a diode, which I presume to be a zenner marked as follows:

STC Z2A30CF XD6

I couldn't find any data on it but I measured 1.1248vDC across it. If anyone has any information on the component in an old semiconductor guide it would be appreciated. I couln't find it in the Towers Transistor Selector.

Some other measurements made:

LM308N across v+ to v- reads approx 8v, except for one of the identical ‘meter driver?’ boards which needs to be investigated further.

LM741C v+ and v- reads approx. 8v and voltage appears only when the ZRA switch is moved to the right.

The Z2A30CF has 1.1248v across it when the ZRA switch is pushed right.

The Lucas DT1520 transistor tests good.
The ZN423T bandgap diode has 1.2584v across it.

Also observed was that two ‘tropical fish’ capacitors have cracked surfaces. I am not too familiar with reading these, but following an online guide I think they read 0.47μF (left - I see the middle band as blue but 0.46μF is not a standard value so might be violet?) and 0.1μF (right - assuming top band is brown). Both I think are rated at 250v (bottom band looks pale red?). I would appreciate it if someone could confirm though as they will need to be replaced.

I have taken photos of both the top and bottom of the square centre board and the ZRA board with a view to reverse-engineering them. Antech Calibration services has the instrument listed and reckon they had a quote request some time ago, but didn't think that they had any documentation, so no luck there.