The HP 5246L counter

ralph klimek 26-may-2009


this page created to pay tribute to a classic piece of Hewlett Packard test and measurement equipment


copyleft: the text and images, are mine, and I say you are free to do with them as you wish with the exception of commercial trademarks.

This item was found in a heap of hard rubbish that had been discarded by the chemistry department at Monash. When I chanced upon this junk heap  it had been raining solidly for about a week and this junk heap had got quite wet.  Underneath some real rubbish I found this HP frequency counter.  I do not need yet another counter, I allready have a very nice homemade unit and  a nice General Radio 7 digit counter with Nixie Tubes.   Here was a counter, a large rack mount device, but it had large Nixie tubes  and nothing looks more official than Nixie Tubes. I took it, really for the display tubes.  (I just want my ham shack to look like the centre 0f Global Domination too)

The office here is the usual dehumidified cube farm, and in one week, the dry atmosphere here had removed all traces of water from the insides and at that point I took it home.  I had to improvise a power connector, this old style of removeable power cord cannot now be found.  I powered it on, not really expecting anything usefull to happen, but I powered it on , at least so I could reassure myself that I had gone to at  least  this small amount of trouble.  

It worked !  Not only did it work,  it worked perfectly.   This equipment, from what I have been able to find out was made about 1963.   A more advanced  companion unit is described in the Hewlett-Packard Journal and has a price list as well.  The list price corresponded to what would have been twice the cost of a suburban Melbourne house in 1963 and as such I stood as much chance of owning  one as I had of becoming the King.  It was the sort of thing that major governments would purchase for weapons research and other such worthy causes.  

There you have it, biult in 1963 (I was in kinder, watching grainy newsreals of Project Mercury with this thing in the background!) it had seen years of service at Monash, and been left to the public abuse and the rain....and it just worked.  Thats nearly 50 years.

There were no integrated circuits back at the time this equipment would have been designed.  It is all discrete silicon and germanium transistors.  It can count natively to 50Mhz.  It can count to 3Ghz with the appropriate plug-in, which by good fortune was also found underneath some banana peels and ash tray contents in the dumpster.  The BCD counters drive an most amazing BCD to decimal nixies tube driver that consists of neon bulbs over a special array of cadmium sulphide photoresistive cells that perform the logical operation of converting a BCD pattern of Neons into a UNARY signal for driving the appropriate anodes in the Nixie tube.

There is one and only one integrated circuit in this unit. It is on the input preamplifier board and I can only conclude that it is a differential amplier, probably on of the very first ones.  The VHF/UHF prescalars plugins work on the principal of downconversion to something below 50Mhz which can be counted.  The internal 10Mhz timebase is fed to a step-recovery diode which generates a good harmonic comb. A tuneable cavity selects the required harmonic which is mixed with the input signal, the differance being counted.  A step recovery diode cost only $USD115 back then, a couple of months average wages.

The unit can supply data to a computer and be controlled by one through a parrallel BCD data bus which is brought out to the back. This must have seemed ridiculously far-sighted back then.

It must have seemed like alien technology back then, considering the state of the art in commercial and consumer electronic goods.


Here are some pictures. No manual seems to be available , allthough, manuals for the plugins are widely available.

HP 5246L counterHP 5246L counterassorted plugins
the black boxes are the Neon CdS BCD-unary  Nixie decoder/driversThis discrete logic works at 50Mhz ! It took till 1980 before 74x TTL logic could!a business-like but noisy fan
oven ensures excellent timebase stabilitybottom view of card busthere is one and only IC in this equipment.
Its on this preamplifier PCB, prabably a diff amp
only one slightly burned resistor
regulatorsI dont know what the relay doesbehind the plugin sub chassis
blank
internal test, I work !cool, l33t Nixie Tubes


If anybody out there has a scanned manual for this marvellous beast please let me know.







Mon May 25 17:49:14 EST 2009