[Hammarlund] HQ-129-X Question

[Richard Knoppow]

-----Original Message-----
>From: Roy Morgan <k1lky at earthlink.net>
>Sent: Nov 28, 2010 11:07 PM
>To: hammarlund List <hammarlund at mailman.qth.net>
>Subject: Re: [Hammarlund] HQ-129-X Question
>
>
>On Nov 25, 2010, at 2:45 PM, Carl wrote:
>
>> Thats a good possibility but it would also affect GC which is where  
>> its
>> aligned.
>>
>> The BS cap could be out of alignment, it has to be exactly centered.
>
>Carl said "centered".  Not "fully open".  Do I remember that unlike  
>many bandspread arrangements, the HQ-129 is aligned with the  
>bandspread capacitor HALF MESHED when the main tuning dial (and  
>bandspread dial) is/are set to the appropriate set point?  If so,  
>maybe someone has changed the relationship between the bandspread dial  
>and the capacitor.
>
>Many radios are set up so the bandspread dial is at its upper  
>frequency, the bandspread cap is at it's lowest capacity position, and  
>the logging dial is at 100, and the main dial is set at the upper end  
>of the section of the band to be spread.  Often this is at the upper  
>end of the ham band as it was at the time of design/manufacture.
>
>Worth checking.. don't rely on my (possibly feeble) memory here.
>
>Oddly, a TMC GPR-92 I have here uses frequencies above the ham band  
>edges, e.g. 4.1 mc for 80 meters.  Maybe they accounted for MARS use.
>
>
>Roy
>
>
>Roy Morgan
>k1lky at earthlink.net
>K1LKY Since 1958 - Keep 'em Glowing!
>
      I think there is some confusion here about what is meant by "centered". So far as the tuning capacitors it means that the rotor plates must be centered exactly in-between the stator plates rather than being at the mid-capacitance position. I don't know about all receivers but, at least for the HQ-129-X the specified band spread position for calibration of the main dial is at minimum capacitance, which is at 200 on the logging dial. In fact, the calibrations for the ham bands goes beyond their limits a bit. 
      A note about capacitors: If the rotor is not centered both the capacitance at any position of the rotor will be wrong and the rate at which the capacitance changes with rotor position will be wrong. If the stator is tilted with regard to the rotor it becomes even worse. In many receivers the tuning capacitors are made with the stators separate from the rotors so that they are adjustable in manufacture. The HQ-129-X is one of these as is the SP-600-JX. The HQ-129-X capacitors are made so that the tuning unit is the capacitor frame. It is quite rigid. The rotors are mounted to it on a shaft with a single thrust bearing at each end, the back bearing having a loading adjustment to take up any end play. The stators are mounted on ceramic plates, each section, i.e., antenna, RF, and oscillator, being separate, the main tuning and band spread caps being made in the same way. The stator plates are fastened to the ceramic plate with clamp screws through the plate from the bottom. In turn each plate is fastened to tabs on the tuning unit with screws at diagonally opposite corners. It is likely that each assembly was carefully adjusted for parallelism and centering at the factory. 
     The main tuning capacitor has two sections for each function, that is six sections total. One of each section is used for the lower two bands, the other, which is smaller, is used for the upper four bands. There are three ganged band spread sections for each function, each of different value. The largest is use for 80 and 40 meters, the next is used for 20 meters, and the smallest for 10 meters. This is a very elaborate arrangement done probably to minimize electrical losses and to eliminate the need for a complex system of padding and trimming for the band spread. I would guess that the tuning unit was quite expensive to make since it would have involved a lot of skilled hand work. It is a very impressive assembly. The result is a quite rigid mechanism which is relatively free of microphonics. The tuning drive is by means of a large plastic disc, which is also the dial. This is driven by a friction pinch wheel mounted on a shaft actuated directly by the tuning knob. This shaft also has a flywheel on it. The dials drive the capacitor through a reduction gear with a spring-loaded  anti-backlash gear. The whole being directly connected so that there can be no slippage of the dial in relation to the capacitor. When adjusted and lubricated correctly this is a very smooth mechanism with no play or backlash. A somewhat similar arrangement, but without the reduction gears and flywheel is used on the SP-100/200/400 series of Super-Pro receivers. Hammarlund seems to have had the magic touch with making extremely smooth feeling tuning mechanisms. 
     I investigated the capacitors in my receiver for mechanical mis-alignment. I can find no sign of it and it appears that it would be very unlikely that it would simply drift out of position. Also, no one has bent any plates. The latter is almost always a disaster when applied to multiple band devices. BTW, it should _never_ be done to SP-600-JX capacitors or you will ruin the capacitor. OTOH, the stators do seem to get out of alignment on these receivers but can be re-centered by removing the capacitor and adjusting the clamps for the rotors. 
     Adjusting the plates on a HQ-219-X would entail a lot of work; it would require removal of the entire tuning unit since the screws that clamp the ceramic plates to the sub-chassis and the screws that clamp the rotor plates to the ceramic mounting plates are both accessible only from the bottom. This would be a mess to do and I am not about to undertake it for a relatively minor problem; for one thing, I am not at all certain I could improve things and could make them a lot worse. 
     The overall construction and design of this receiver are very impressive especially considering it was a moderately priced one, Hammarlund's "economy" model, at least in comparison to the contemporary Super-Pro, which was, in its day, the most expensive receiver on the market (the RCA 88-A was probably as expensive, I've never seen a retail price for one). Its interesting to speculate on what such a product would cost to make now. I have seen figures on much simpler devices, and the cost was astonishing. Consider even more elaborate receivers, particularly the Super-Pro with its extremely elaborate tuning unit and such equipment as the National NC-100 and NC-240 series with their sliding turrets. 
     BTW, the HQ-129-X is temperature compensated and does not seem to drift much. There is a single ceramic compensating cap in the oscillator section of the tuning unit, perhaps there is some other mechanism in the coil structure. Whatever they did seems to work well. 
     I have a number of questions about the receiver, for instance, if the panel paint was changed during production, mine looks darker than it does in the advertising photos and some contemporary photos on the Internet. I think mine is a late receiver, it has all white lettering. It would be interesting if anyone had a serial number list, but I suspect that has been lost.