[Test-Equipment] Hewlett-Packard 606A Redux

[Richard Knoppow]

     Some time ago I posted here asking if the tuning 
capacitors of the 606A were ever adjusted at the factory by 
bending. No one had a definite answer but I suspected that 
no multi-band oscillator, regardless of application should 
be adjusted this way. I can now pretty much answer the 
question: it should not.
     After examining the generatore carefully I found what 
probably caused someone to do the plate bending, the stators 
were out of alignment. I have no idea of how this could have 
happened but the generator is some forty years old and may 
have been treated badly. In any case, I found that the 
tuning caps could be removed much more easily than appears 
at first. I removed them, straightened the bent outer rotors 
as best I could and aligned the stators to get them centered 
and parallel. The rotor blades are not perfect because the 
metal is thin and the ends were bent to an extreme but they 
are very close to being straight. After re-assembling 
everything and doing a careful alignment I found that the 
frequency calibration was within less than half specs at 
maximum deviation, not too bad:-) I also re-tuned the 
amplifier and found that the tracking was pretty good. I 
checked this by simply testing the peaking of the trimmers 
at a couple of places on the bands. Aligning also brought 
output regulation into specs, actually much better than 
specs, its nearly flat all over and within a fraction of a 
db out to 65Mhz.
     I will not go into detail in this post but will 
certainly answer any questions if asked. I also had to 
restring the drive cable and learned a couple of tricks. 
Note that there are two drawings in both  the 606A and 606B 
manuals showing the string wind, one is in error and the 
error was carried over to the later manual. The _correct_ 
drawing is the one showing only the cable. It is the 
relative position of the cable on the drive pulley which is 
shown wrongly on the more complete drawing. If strung this 
way it will pull itself off the pulley.
     Note that dial calibration can require slipping the 
dial. The dial is held by a clamp which is accessible when 
the main tuning knob is removed. There are four screws 
holding the clamp. If the calibration is way off check to 
see if the dial is approximately centered between stops. 
Slipping a bit from this position can improve things 
markedly but it should not have to be moved very far. Again, 
I will go into detail if anyone is interested.
     I worked for -hp- for ten years, mostly on microwave 
and RF equipment but simply don't remember ever working on 
many 606's. Perhaps someone else in the shop got them. I 
remember many other instruments in great detail so its a bit 
of a puzzle.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com