[Hammarlund] HQ-150 Question

[Richard Knoppow]

    I was in a bit of a rush before and forgot the arrangement of tuning 
capacitors for main tuning and band spread. The main tuning cap has two 
sections, I forgot the details but I think both are used for some bands 
and the others used individually to give three ranges of capacitance. 
There are three bandspread sections. It is likely one of these, main or 
bandspread, is causing the trouble. The usual variable cap problems, 
rubbing plates or dirt in the cap. If its only one section it may be 
responsible for the problem on only one band. You may be able to find 
the problem with a visual inspection. Another way is to run a sheet of 
typing paper between the plates of the suspected sections. It will 
either clean out whatever is in there or indicate if  the spacing is 
wrong due to a bend plate or something of the sort. Canned air may also 
help.
    Inspect the sections of the capacitor for spacing. My memory is that 
all sections of both the main tuning and bandspread cap are on the same 
shaft. The rotors of both should be centered in the stators. If they are 
not centered they can cause intermittent shorting problems and will 
spoil the calibration of the dials. They can be centered by tuning to 
the low end of any range and adjusting the bearing screws for maximum 
frequency. The capacitance of a symmetrical air spaced cap will be 
minimum when its centered. The frequency will go down on either side of 
the center. However, the problem you describe is more likely to be 
3between the plates or a bent plate. If one plate is bent you can 
probably straighten it with gentle bending with a needle nosed pliers.
    That's all I have at the moment, I hope its helpful.
    If the HQ-150 is like its earlier relatives its a very good receiver.
    BTW, the famous Hammarlund variable crystal filter was introduced on 
the HQ-120-X (X means it has the crystal).
    The handbooks on BAMA do not show pictures of the capacitor gangs 
but there IS a pic in the advertising brochure there. Not exactly high 
rez but may be of help. This is exactly the same arrangement as used in 
the HQ-120-X and HQ-129-X so if you can find pix of those it may be of 
help.
    The wipers can be cleaned with Deoxit, the ball bearings can be 
lubricated with light grease, even petroleum jelly (Vaseline) is OK but 
use the non-medicated kind. Apply with a toothpick.

On 7/29/2024 5:57 PM, Dan Martin via Hammarlund wrote:
> Have an HQ-150 here with a very noisy high band, 18-31 mHz.  Only the highest frequency band. No others. Lots of loud pops, snaps, and crackles while rapidly tuning up and down the band. LO signal on scope shows sharp variations and spikes in amplitude up and down corresponding to the snaps and crackles. Noise is main tuning cap movement driven. Radio sits quiet on a fixed frequency. Try tuning around and it gets real noisy fast.  I could post a video w/audio if this system could take the bandwidth.
> 
> I have rotated in several 6C4’s (oscillator) and 6BE6’s (mixer) without change. I’ve put in place the 6C4 and 6BE6 from my excellent performing HQ-140, to no avail.  I’ve cleaned, Deoxited, and even used metal polish to a shiny mirror gleam the C1 cap wipers and contact disks. No change. I’ve preemptively replaced C89, C6, and C29 caps without change. All associated resistors in and around osc. grid circuit check OK. Pin voltages of mixer and osc. OK. I’ve checked and tightened the screws mounting the cap sub-assembly to the chassis.
> 
> Have simply run out of ideas and need help and comments.
> 
> I have worked on HQ-140’s/150’s extensively and currently have one of each. These are excellent radios and among my very favorites. Treated right and aligned well the single conversion HQ’s are wonderful.
> 
> Comments? I’m dead-ended. Need more ideas.
> 
> Thanks in advance.
> 
> Dan
> WB4GRA

-- 
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998