Re: HP 180A scopes - anything I need to know?
Mr Bungle,
These are nice scopes with a particularly good tube.
The trigger is good but must be set up properly.
The usual 50Mhz timebase (1821) plug-in uses tunnel diodes. See notes elsewhere on the Forum. But particularly do not try testing with an ohmmeter/Avo. It will destroy them.
The 100Mhz TB (1825) uses ECL for the trigger, which again must be set up carefully. Remains stable provided the power rails are absolutely stable.
The HP180A main frame and also HP181A storage version use little stabilizer neons for each rail, which with age begin to fluctuate enough to stop the trigger working, however much you re-set it. This model also has no overload limitation other than blowing a fuse. So keep a stock of fuses to hand when you start fault finding.
The HP180C and 180D use the now usual zener differential transistor pair on one rail, and all the other rails draw off it. Much better, and it also has electronic overload protection.
I did consider modifying my HP180A power supply to the 180C/D version, but it effectively means a new board.
However Philips suggest on their PM3262/PM3266 family of scopes a modification to replace such neons with a zener/transistor combination. It can fit on the board.
Circuit attached. It is preferable to using a high voltage zener as the temperature coefficient is vastly better and comparable to the neon. Neons replaced from GI,Hivac or Mullard are: the 83v ones V83R4,Z82R7, ZZ1000,8228. For 103v - V103R2. For 116v - V116R2.
You have to change the resistor chain which feeds the transistor base for each voltage, as noted.
Other points. As Humber888 says, the handle is "famous". Replace with a metal strap at once.
All HP scopes seem to use discrete semiconductors which can be replaced up to the 75Mhz models. (PI 1801,PI 1808, 1804 4 channel and scope HP1707).
The 100Mhz models (PI 1805,1809 4channel, scopes HP1740, HP1741) use integrated circuits which are quite irreplaceable.
I have a note of the commercial equivalents of the transistors in these scopes. There is one germanium type as well, usual vhf switching, for which comparable can be found.
For a design introduced in 1966, they seem reliable. Most parts are commodity and similar still are available.
The HP182A is the large screen version and the the HP 184A is the fast storage. Both use the later 180C/D zener power supply.
wme_Bill
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