[Test-Equipment] HP-606A Calibration question

[Barry]

> You will probably find the other bands also have a 
> calibration problem. Its probably the dial position. The 
> dial is held in place by a clamp with four screws. Access to 
> the screws is gotten by removing the main tuning knob, there 
> is a large opening under it. Start by approximately 
> centering the dial in the range of rotation, that is, set it 
> so that the overlap on each side is about equal. Then set up 
> the calibration for one band. Note the error. Move the dial 
> slightly one way or the other and make a note of the 
> direction. Again, align that band. If the error is smaller 
> move the dial a bit more in that direction, or, obviously, 
> if it gets worse, move it the other way. Continue this until 
> the calibration comes in all over. There may still be small 
> errors but they should be well within the specs, probably no 
> more than half. Once the dial is set for one band it should 
> be good for all. The top band may need some adjustment of 
> the coil if you find its out of range. The coils on the top 
> band are essentially air wound thick wire held in place on a 
> plastic former with coil dope. If the dope has hardened up 
> over the years the coil can become loose and move relative 
> to the slug or the coil spacing can change a bit. The coil 
> can be stretched or compressed a bit to bring it in. The 
> slug should be in about the half-way point. Once this is 
> done the band should calibrate fine. Note that the same 
> treatment may be needed on the amplifier side. Coil dope AKA 
> Q-dope is hard to find now but airplane glue will work 
> satisfactorily. The coils should be cemented in place once 
> you have them adjusted. Don't close things up until the 
> cement has thoroughly set to insure that the coil is still 
> in adjustment.
> I used to know how to make coil dope, its something 
> like polystrene dissolved in xylene but I am not sure.
> 
> The dial slipping procedure is tedious but not 
> difficult.
> 
> BTW, you have confirmed to me something that I couldn't 
> remember, namely whether the tuning capacitors were ever 
> bent in new units. In my 606A they were severly bent at the 
> high end and I thought that was wrong. Generally plate 
> bending is a no-no on any multi-band device. It turned out 
> that the stators were out of alignment and I think someone 
> tried to compensate by plate bending. The stators are 
> clamped to the frame with a single bolt at either end (or 
> side depending on how you look at it). I had to remove both 
> caps to re-align the stators and unbend the plates. The 
> trouble with plate bending is that once done, it can never 
> be completely undone. Nonetheless, I got my generator to 
> meet specs. While removing the caps may seem like pretty 
> deep disassembly its actually not too difficult because of 
> the excellent mechanical design of the unit.
> 
> I don't know a source for the specific BNC connector 
> although there are sources for old -hp- parts. I think you 
> could probably straighten the shell well enough using a pair 
> of round nose pliers of the right size to push them out from 
> the inside. I've had success with this a few times.
> 
> Beware that the tuning caps are at B+ potential and 
> will bite if contacted.
> 
> For setting the oscillator and amplifier current you 
> can measure the voltage drop across R-9 and R-15 (with an 
> isolated voltmeter) rather than disconnecting the leads and 
> using a milliamp meter.
> 
> 
> --
> Richard Knoppow

Richard,

What you say makes sense.  It's like fitting the dial to the "curve" of the capacitor.  I should have realized that 
since the dial markings are not angularly linear, then there's a curve that has to match somewhere.  I originally set 
the dial plate to the center (approximately equal overtravel on both ends), but apparently this is not where it 
belongs.

Thanks for the pointer on the high range.  That range is way off and I cannot adjust it to where it needs to be.  
Perhaps, though, after I adjust the dial plate, it might come into range as well.  That might just be a good indicator 
of where to start this process (getting it closer to the high range's calibration marks might bring everything else 
into calibration as well).  I think the coil dope is still intact so perhaps they are still where they should be.

Yes, I was using a metal screwdriver to break the trimmers free and accidentally shorted the shaft to the frame.  It 
blew the B+ fuse.  At least I can use my plastic screwdriver now that the trimmers are free to turn.

I can probably straighten the BNC connector as it is easily removed from the front panel.  I don't have any round nose 
pliers but I think I can insert a steel rod and form it against a softer surface.

Thanks again,

Barry - N4BUQ