[Test-Equipment] HP-606A Calibration question

[Richard Knoppow]

----- Original Message ----- 
From: "Barry" <n4buq at knology.net>
To: <test-equipment at mailman.qth.net>
Sent: Monday, May 25, 2009 8:00 PM
Subject: [Test-Equipment] HP-606A Calibration question


> Hi,
>
> I'm new to the list and have been working on cleaning and 
> calibrating my "new" HP-606A.  I read a thread on this 
> list a month or so ago about a problem these generators 
> can have where they are out of calibration towards the 
> center of dial (discussion about bending the fins of the 
> tuning cap, etc.).
>
> I set the end points on mine and am seeing this quite 
> noticeably.  In fact, on the 530kc - 1800kc range, it 
> jumps out of calibration almost immediately upon moving 
> away from the upper endpoint.  Here's what I just 
> measured:
>
> Dial - Actual
> 530 -  530
> 600 -  601
> 700 -  710
> 800 -  820
> 900 -  933
> 1000 - 1040
> 1100 - 1147
> 1200 - 1250
> 1300 - 1352
> 1400 - 1460
> 1500 - 1561
> 1600 - 1655
> 1700 - 1735
> 1800 - 1800
>
> Is there a recommended fix for this?  I don't plan on 
> bending the tuning cap (it is pristine from 1968) and will 
> rely on a counter for accuracy anyway, but would like to 
> have the dial a lot closer to calibration over the entire 
> range if possible.
>
> Also, does anyone know a source for the BNC panel mount 
> output jack?  Mine has taken a slight hit and has a flat 
> spot on it.  I don't quite see this style of connector 
> anywhere (it has a threaded ID on the rear that accepts 
> the threaded plug and that includes the female brass 
> connector part).  I'd like to replace this if possible.
>
> Thanks,
>
> Barry - N4BUQ
>
    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
Los Angeles
WB6KBL
dickburk at ix.netcom.com