[Hammarlund] update HQ-180 issues

[Rodger Singley]

Bob,

The RF gain control has two sections, one controls cathode bias for the RF amp and the other controls cathode bias for the second IF stage.  I believe this pot is probably a reverse log taper and will likely be somewhat difficult to find now.  It is quite possible someone replaced this in the past with a wrong taper pot.  Other possibilities are a tube issue in one of these controlled stages or someone substituted a different tube type.  In practice I am not sure you are ever going to need fine control of the RF gain control and normally it can be set at maximum gain.  I have several of these family member receivers, a HQ-180 along with HQ-170, HQ-170A, and HQ-170A VHF ham band versions of the HQ-180 and I don't recall needing to reduce RF gain on any of these.  They all have good all mode AGC systems.

Can you better describe how the audio sounds bad?  One fault I found in a HQ-180 I restored was a bad audio "couplate" Z2 that had a leaky internal capacitor and was allowing positive bias on the output tube audio grid.  With volume set to minimum check for DC voltage on the output tube audio grid.

Another reason for poor audio with the HQ-170/180 series is misalignment of the low IF.  This alignment is critical and given the selectivity at 60Khz. poor alignment will result in very poor operation.  Make sure that your signal generator is accurately placed on 60 Khz. for the alignment.

The HQ-170/180 receivers were never meant to be high fidelity receivers and although these are some of the best "battle conditions" vintage receivers when interference is tough even in the widest mode AM fidelity is quite restricted.  I used a HQ-170 with my Ranger/Desk KW for quite awhile and it did a very nice job with AM under rough conditions.  I now use a Hallicrafters SX-88 with that station but I sometimes miss the easy sideband selection on AM provided by the HQ 170/180 receivers, the SX-88 requires a slight retuning to choose AM sideband to avoid interference. One of the most versatile Hammarlund setups is a HQ-160 coupled with a HC-10 sideband adapter.  The HQ-160 is the predecessor of the HQ-180 and has a final IF of 455 Khz., the HC-10 is effectively the final converter, 60Khz. IF, AGC, detector, and audio section from a HQ-170/180 receiver and the combination allows better fidelity when conditions permit by using the HQ-160 audio output while using the interference fighting capabilities of the later models, albeit with lesser fidelity, when conditions are bad.  

I have a slight preference for the Hallicrafters approach to selectable sideband receivers (used in the SX-96, 100, 101, 115, 117 family) since only the bandwidth and not the passband position is changed in the selective IF.  Hallicrafters uses either low or high side injection in the final converter to choose sidebands while Hammarlund changes both width and passband offset direction in the low IF which is a bit more complex and in practice doesn't allow perfectly identical response for the sideband chosen. The choices in the Halli system allow a little more fidelity with the widest choice of 5 Khz. which is the equivalent of 10 Khz. with conventional dual sideband detection.  But both approaches provide good performance under trying conditions.  If my SX-88 had the later selectable sideband approach of the later family members it would be the near perfect vintage receiver :)  Heathkit borrowed the Hallicrafters approach when designing the RX-1 Mohawk.

Rodger WQ9E

-------- Original Message --------
> From: Robert Sauvan <rsauvan at beyondbb.com>
> Sent: Wednesday, December 17, 2014 7:40 AM
> To: "jdteske at verizon.net" <jdteske at verizon.net>,  hammarlund at mailman.qth.net
> Subject: Re: [Hammarlund] update HQ-180 issues
> 
> Thats interesting. Before I replaced the Hayseed cap, the RF gain acted 
> as I described in the previous email but now it is worse. I am going to 
> put a meter on the pot to see what it might be doing. If I need one, not 
> sure where a replacement can be found but may have to start looking. 
> Just one of my couple of issues Im trying to work out for now.
> 
> Thanks-Bob-W0YBS
>