Hammarlund HQ-129X crystal filter issue

[KC2TAU]

I've been working on aligning the crystal filter on my Hammarlund HQ-129X and I've run into a bit of a problem.

For the entire time I've owned it the filter has always acted as an attenuator rather than a filter. I took it apart,replaced the old silver micas for new and carefully cleaned the crystal. I put everything back together and it still does not seem to function properly. The crystal is supposed to be in the neighbourhood of 455kc but I'm seeing a sharp resonance around 468kc which seems more than a ways off.

My method is to inject a signal generator to the 6K8 mixer grid cap,set the crystal selectivity to its sharpest setting,make sure the phasing control is at half mesh and then sweep to find the peak using the AVC(s-meter)to find the peak. When the peak was found at 468kc I then turn off the crystal filter and align the other IF cans for maximum s-meter reading.

The radio itself is very sensitive and sounds good. The crystal filter attenuates the signal by about 1 1/2 s-units at position three but by position five the attenuation factor is somewhere around 4 s-units. I don't really hear a narrowing of the passband,either. The phasing control acts such that sweeping the phasing control from the center towards 10 causes for an increase in signal strength whereas sweeping it towards 0 causes a significant "notch" dip at position 2 and a little bit past position "0" when tuned to an AM station.

I'm not sure if the crystal is bad but I've looked online for replacement quartz(or otherwise)455kc crystals and have come up empty. I'm not entirely sure what the matter is with the unit.

[W7TFO]

The rock might be from a post-war SP-400, they used a 465 KC IF. 

Or, it might have been shaved a bit and the IF strip realigned for that freq, hoping to 'make it better'.

Believe me, I've seen every kind of travesty foisted upon these radios over the years.  Most involved drills and snips.  ouch!

I have plenty parts BTW.

73DG

[KC2TAU]

Yeah,I think having a second unit would be nice just to have a reference. It's a bit hard knowing where to start when you don't know where square one is or what it looks like.

[WQ9E]

My check for the crystals in these filters is to connect it between my signal generator and scope (hot lead from generator to one crystal pin, scope vertical to the other, generator and scope lead grounds tied together).  As you slowly tune the signal generator through the crystal frequency you will see a very sharp and pronounced peak with a good crystal while a degraded one will have a very broad peak and lower peak.   

As I recall the crystal was standard issue in the HQ-129X unlike some of the Hallicrafters receivers.  Is the holder marked with the frequency?  It could have been ground to a higher frequency as noted by a previous poster but if it shifted on its own it probably has much lower response than it should. 

A good source for IF filter crystals for these older radios are the FT-241 series that often show up at hamfests and on ebay.   I have used these in several receivers that were missing the filter crystal.  Channel 46 in the 2 digit series or channel 327 in the 3 digit series will have a fundamental frequency of 455 Khz. and a couple of channel numbers either side will also work fine.

[KA0HCP]

KC2TAU

Hi, I've got an HQ-129 too, but it's waiting to be refurbished.

If I may offer my comments...

-Your brief description of your method does not match the last two steps of the alignment procedure in the manual (page 15-16).  There is also a prior step that affects signal strength at the crystal.

- Have you done a full alignment first per the manual?  Using the  internal meter to detect the peak of the crystal is not adequate.  An oscope is necessary in order to see the "maximum amplitude, symmetry and pattern coincidence".  (great  phrase).

-If you have been doing the alignment based on signal peaks, it is possible to have the signal misaligned or non coincident.

The radio condition sounds encouraging to me.  I think it just needs a bit more tweeking.   

Cheers, Bill

[Jim, W5JO]

My check for the crystals in these filters is to connect it between my signal generator and scope (hot lead from generator to one crystal pin, scope vertical to the other, generator and scope lead grounds tied together)

It is best to put a 10 K resistor in series with the hot lead.

[WBear2GCR]

I passed ur info along to someone who has some parts for the rig - they should be emailing you if they have not done so already...

                       _-_-bear

[Tom WA3KLR]

I've re-aligned the crystal filters on 2 HQ-120X's and the WWII evolution of the HQ-120 - the RBG.  My dad had a HQ-129X.  In every case the crystal filters were not working properly.  I’ve been wondering if perhaps the factory was not even sending them out properly tuned.  It is a matter of critical alignment involving a sweep generator signal.  

The symptom is that as soon as the broadest position is turned on, the bandwidth appears to be in a narrow CW bandwidth.

When the filter is properly aligned, just as the manual shows, the first few positions do allow AM signals to be received.  A heterodyne can be notched out well with the front-panel phasing adjustment as long as the offending carrier is not within a couple kHz.

I have photos of the filter adjustments and I’ve always wanted to document the process but very little time for ham radio the past 2 years.  There is a variable capacitor inside the filter case that needs to be adjusted also.  As I recall I drill one or two holes in the left side plate to be able to tune them. (Plate removed first.)  I don’t recall if I had to take the whole filter can out for this but I did remove and reinstall the can in at least one receiver.

The peak in the crystal must be found and all the i.f. coils aligned to that frequency.  If the crystal is really at 468 kHz or so the i.f.s will probably tune here ok, but the tracking at the bottom end of the broadcast band may be a problem.

My intent is not to tease people here, but I can help, but can’t do it right now.  Perhaps in the coming week or so.

In the meantime here I think I can add the photo I took as part of the documentation I have wanted to create on the Hammarlund crystal filter re-alignment.  The photo is from the left outside of a rack-mount version of the HQ-120X.  The actual filter can is behind the rack-mount bracket.

[KM1H]

The rock might be from a post-war SP-400, they used a 465 KC IF.

The SP-400 is 455, The SP-200 and WW2 versions is 465.

The 129X manual is confusing and a sweep system is far from mandatory for good performance. Read the WW2 Super Pro manual, it gives excellent instructions for a field alignment and the 120X and RBG manuals are good also.

Maybe Ive been lucky but Ive never had a problem with a Hammarlund filter unless the crystal is sluggish and a cleaning has always fixed that. Ive rebuilt dozens of 120X, 129X and a few RBG receivers and own 2 ea 120X, 129X and a RBG.

Carl

[KC2TAU]

That sounds like the exact opposite symptom of mine. When I switch the crystal filter to the most broad position I can hear a slight narrowing of the bandwidth but switching to the subsequent selectivity settings produces no audible decrease in passband,just a reduction in received S-meter and audio level.

The variable capacitor you speak of is the phasing control,correct?

I'm not sure if the crystal is really resonating there or if there is something else amiss in the module but that is where I'm seeing the peak. It's relatively sharp too. This week I'm going to head over to the W2SZ shack where I have access to an 8640B and my Tektronix 531. I'll be able to provide a more useful report and tell you what sort of signal level I'm throwing into the radio in order to get a certain reading on the s-meter. In short I'll be able to give much more detailed information. I'll also be able to take a look through the scope at the filter response as I feed the generator through it.

That phasing cap padder is your addition,right? Other than that my filter module looks exactly the same.

Bear - They have! Thank you!

KB4QAA - The reason why I did not have done an alignment according to the book is due to the confusion created by reading the manual's text. Where does one connect the oscilloscope to in order to observe the waveforms? I am also unfamiliar with synchronizing an oscilloscope to a signal generator. I'm assuming this is done by passing the output of the generator through an auxiliary output and feeding it into the scope so that you have a reference image to compare to? I have heard many people using the method I used to good success. Some people even align receivers using their ears but that requires experience. I also prefer to use lab equipment just to double check my instincts.

WQ9E - Does the crystal in question need to be tested out of circuit?

[Tom WA3KLR]

In one HQ-120X I have, the last owner had removed the filter crytal and installed a series chain of Murata ceramic filters.  I was lucky to find a 456 kHz FT-243 crystal in my junkbox!  The original de-Q'ing resistors for each BW position had been removed and the manual does not show the values.  But the RBG military manual has resistor values documented.  Perhaps they are not the same values as the -129 but is a start and I installed the RBG values.  You could play with these values.

[Tom WA3KLR]

No, the sweep alignment padder is not the front panel PHASING control.  The padder I am talking about is adjusted from the side and is normally not acessible.  It is not depicted in the schematics!  Obviously they did not want hambones playing with it, but it has been over 60 years since it left the factory.

It goes across the bottom of the secondary of the first transformer to the output side of the PHASING control differential capacitor. It is essentially across the one side of the PHASING differential capacitor.

This is why you must remove the left side panel of the filter can and make a hole over the padder area, re-install the cover, and adjust it during the sweep alignment.  During the sweep alignment the front panel "PHASING" control is set to dead center.

[W7TFO]

The rock might be from a post-war SP-400, they used a 465 KC IF.

The SP-400 is 455, The SP-200 and WW2 versions is 465.

Au contraire,  SP-400 is high (465KC), the HQ-120/129's are low (455KC).

73DG

[KC2TAU]

No, the sweep alignment padder is not the front panel PHASING control.  The padder I am talking about is adjusted from the side and is normally not acessible.  It is not depicted in the schematics!  Obviously they did not want hambones playing with it, but it has been over 60 years since it left the factory.

It goes across the bottom of the secondary of the first transformer to the output side of the PHASING control differential capacitor. It is essentially across the one side of the PHASING differential capacitor.

This is why you must remove the left side panel of the filter can and make a hole over the padder area, re-install the cover, and adjust it during the sweep alignment.  During the sweep alignment the front panel "PHASING" control is set to dead center.

I was talking about the adjustment on the side of the module. There is a variable capacitor on the front of the radio that controls the phasing. On my HQ-129X there are only two slugs,top and bottom,but no phasing padder. I was asking if the padder was your addition as my HQ-129X has holes for two slugs on the side and that is it.

[KC2TAU]

[duplicate post]

[WQ9E]

WQ9E - Does the crystal in question need to be tested out of circuit?

I test it out of circuit.  This gives you the clearest indication of the operation of the crystal itself.

Like Carl I have not been using the sweep alignment method.  I have two HQ-129X receivers and the crystal filters responded well to a typical receiver alignment.

Oddly enough, I have recently acquired two not quite as vintage pieces of gear that use a single crystal filter in conjunction with the SSB filter for CW.  I thought it was a bit odd when I found this circuit in a 1968 Hallicrafters SR-400 "Cyclone II" but then I noticed that Yaesu did the same thing in my 1965 era FR-100B.  In both receivers it does provide a very useful benefit for CW.

[KA0HCP]

'TAU

- "External Trigger" is the usual Oscope function used to synch with an external device.  Just a lead from the signal generator output to the external trigger port on the scope.

- I would connect the Oscope to the crystal filter output for the alignment.

[KM1H]

Au contraire,  SP-400 is high (465KC), the HQ-120/129's are low (455KC).

73DG

Since you obviously dont own one I suggest you try reading the manual.

[Tom WA3KLR]

Michael,

The padder acessible from the  left side of the crystal compartment is factory installed, but there is no hole in the cover to re-tune it.  It is a 1.5 - 5 pf trimmer.  It is not shown on the HQ-120 and HQ-129X schematics.  It is shown on the RBG schematic.  Perhaps it was regarded as a trade secret at the time.

Have you taken off the left side cover and found no such trimmer?

I regret not taking a photo of the inside of that compartment when it was open.  

Anyone out there with a HQ-120X, RBG, or -129X right now with the cabinet off, that can take off the crystal filter left cover and photograph the guts?

[KC2TAU]

Hello Tom,

The inside of my crystal filter module looks as such. Sitting below the crystal and the selectivity switch is the front panel phasing capacitor and nothing more.

http://img823.imageshack.us/img823/6133/dsc06880t.jpg

[Tom WA3KLR]

Michael,

It's very interesting that your set does not have the additional padder.  I just looked in my HQ-120X folder and I have zeroxes from an original HQ-120 manual on the crystal filter and the photo of the crystal filter can is taken from the right side; no additional trimmer seen.

Anyhow here is some data on 2 HQ-120X receivers I re-aligned and their bandwidths:

Both have the additional padder.  Receiver 1 (S/N 7745) is the one which had no crystal and I put in a FT-243 456 kc crystal and had to add the de-Q'ing resistors per the RBG manual.  Receiver 2 is a restored stock rack-mount HQ-120X.

       6 dB bandwidths, kHz.

        Rx 1   Rx 2 S/N 10259
OFF   3.7    3.5
1       4.0    2.3
2       3.4    1.5
3       2.5    0.9
4       0.7    0.14
5      0.25   0.065

Reviewing this old data on receiver 1, I'm surprised to see that the bandwidth in position 1 is greater than the OFF position.

My main intent for receiver 1 is AM use.  If I were a CW guy, I would probably prefer receiver 2's values.

[KM1H]

Id prefer #1 for CW of which I use a lot. Even 250Hz will ring a lot and going wider is often better.

Even on the various riceboxes here I prefer the cascaded 500Hz filters to the 250's.