HQ-180A: Troubleshooting IF Chain

[KW4H]

After using my newly-restored HQ-180A for a while, it was clear that -- although the radio works -- it's rather noisy, the audio is a little bizarre (almost muffled at times, and a bit distorted), and sensitivity nowhere near what it should be.  To make a long story short, I was able to determine that someone has fiddled with the IF alignment in the past and left their mess behind.  Time to do an IF alignment.

The behavior I'm seeing is mystifying -- please see the attached schematic.  This is the 60 KHz IF section.  To align, all you do is put a VTVM on the product detector output, inject an unmodulated 60 KHz signal into the grid of the 2nd converter, and peak up T6/7/8/9/10/11 (maximum NEGATIVE voltage).  However, when I inject a 60 KHz signal into the 2nd converter the radio is deaf as a doornail.  I'm using a SG-85 and have jammed the signal level WAY up higher than necessary, and you can barely move the needle on the VTVM.  As called for in the instructions, this is with the radio in AM mode, the sideband control in USB, and the bandwidth in .5.  However, if you broaden the bandwidth and set the sideband control in "both", the 60 KHz signal becomes discernible.  At that point, and as an experiment, I looked for a peak with T6 and T7.  I could find a peak with T6, but T7 has no peak, but it tries to find a peak when you run the slug all the way to the top or bottom of its run.  Very odd and not what it should be doing.

As a next step, I injected the 60 KHz signal into the grid of V7.  This only left T10 and T11 to fiddle with.  Blammo!  The signal came through -- much better!  However, T10 and T11 exhibit the exact same relationship as T6 and T7.  I can find a 60 KHz peak on T10, but T11 behaves identically as T7 -- no real peak, but an increase in signal at the top and bottom of the adjustment.

Anytime I see something like this -- where two different stages are behaving in the same unusual manner, I always look for something in common.  In the case of the HQ-180A, what's in common are a bank of wafer switches, which Hammarlund annoyingly parked right over top of the IF section. 

Am I going down the right path with this, or have I wandered off course in diagnosing this?  Even considering the wafer switches, when I look at T11 and T7, I can't really see a reason why they would both fail to find a peak.  But I have more digging to do.

Appreciate any thoughts/advice.

Steve, KW4H

[WA2SQQ]

Again, I believe the videos on YouTuube cover the alignment. I think they were posted by k7pp

[W1NB]

It sounds to me like the capacitors inside both of the IF cans have gone bad. That will change both their shape and resonant frequency.

[K9MB]

I do not have a lot of experience with Hannarlund receivers other than aligning an HQ170 I bought, however:

If you Google Hammarlund IF transformer capacitor failure, you will find a lot of stuff about silver migration shorting the silver micas that Hammarlund used in their IF transformers.

It is possible that the 820pF cap in T11 is shorted if the circuit will not peak.
I think there are instructions on rebuilding these IF transformers somewhere.
Clip out the internal caps and put new ones outside, is what I would do.

Also, it is a good idea to always use the least signal you can and a scope is better with a good probe and a very small coupling capacitor to limit swamping.
If you do that and still cannot get a peak on T11, it might be time to think about the possibility of a bad cap in T11.
Others may have more experience, however, but I have 45 years of trouble shooting RF strips and these are just basic things.
Also, keep in mind that the generator for a 60khz IF needs to be accurate and stable. It is easy to get them way off and then nothing seems to work. A frequency counter may be helpful to make sure it is exactly at 60khz before you start cranking adjustment screws.
The alignment of these radios must be dome in a systematic sequence. Watch the videos made by real experts before you begin and make sure you have the necessary equipment to do the job. 73, Mike

Edit- Just realized that others had posted on this. Bad silver mica in IF Tramsformer is indeed the likely cause, but the other things are still important when aligning a narrow band LC IF filter like this. MB

Edit “- here is a link to a tutorial on repairing the Hammarlund IF transformers.
https://youtu.be/8mS6oEMdY7k

[KW4H]

Thanks all for the feedback.  Some notes:

I've watched most of K7PP's videos on the IF alignment and was in fact re-watching one and following along, pausing the video as I went along.  His videos are a must-watch for anyone needing to do an IF alignment on the Hammarlund.

The signal generator being off-frequency is immediately where I ran when this happened.  Unfortunately, the generator is spot-on and the fix for this isn't going to be so easy.

Digging into the IF cans of a HQ-180A is complicated by the wafer switches covering up virtually the entire section.  Has anyone here serviced a HQ-180A and had to pull those switches?  I'm trying to determine the best way to go about it.  I've serviced a lot of electronics over the years, but have rarely seen wafer switches so tightly embedded in the circuit you can't even figure out how it was built in the first place!

Steve, KW4H

[KW4H]

It sounds to me like the capacitors inside both of the IF cans have gone bad. That will change both their shape and resonant frequency.

Yep, it does sound like that.  However -- I have a duplicate HQ-180A from the same era as a parts unit, and to check into this I pulled T-6 off of it for inspection.  The capacitor is a dipped silver mica -- completely sealed.  The odds of those failing are extremely slim.  I'm back to examining the wafer switch assembly again.  Also, I stumbled across this video of how to deal with the switch assembly.  It's a HQ-170A, but the exact same process should apply to the HQ-180A.  Posting it in case others might find it useful:

https://www.youtube.com/watch?v=f7OhJAq0dlY

Steve, KW4H

[WQ9E]

The problem capacitors were in the earlier runs, not the HQ-180A, and the real problem with these caps is they are open construction of the interleaved mica and metal plates.  I had a HQ-170 that required replacement of these caps and it isn't silver migration but instead buildup of debris that becomes carbonized and conductive over time.

Most problems with capacitors in transformers are from this open leaf design.  For silver to migrate across the mica barrier edges, there has to be a high DC differential across the capacitor and in most of IF transformer applications the capacitors shunt the transformer windings so no significant DC appears across them.

Classic silver migration can be seen in some of the CE phasing type SSB transmitters and the fix for those is a large value capacitor in series that removes DC from the problematic precision type cap in the phasing network.  You can see the same issue with Tektronix 500 series lab scopes which use silver and porcelain terminal strips, in some climates (humidity and air pollution), silver will migrate across the insulating barriers in between tie points.

Rodger WQ9E

[K9MB]

The problem capacitors were in the earlier runs, not the HQ-180A, and the real problem with these caps is they are open construction of the interleaved mica and metal plates.  I had a HQ-170 that required replacement of these caps and it isn't silver migration but instead buildup of debris that becomes carbonized and conductive over time.

Most problems with capacitors in transformers are from this open leaf design.  For silver to migrate across the mica barrier edges, there has to be a high DC differential across the capacitor and in most of IF transformer applications the capacitors shunt the transformer windings so no significant DC appears across them.

Classic silver migration can be seen in some of the CE phasing type SSB transmitters and the fix for those is a large value capacitor in series that removes DC from the problematic precision type cap in the phasing network.  You can see the same issue with Tektronix 500 series lab scopes which use silver and porcelain terminal strips, in some climates (humidity and air pollution), silver will migrate across the insulating barriers in between tie points.

Rodger WQ9E

That is very interesting and informative. It points out the risk of quoting someone without having any personal experience in a matter. I was thinking chainsaw and you have provided reason to substitute a scalpel as the tool of choice in this problem. 😉

[KW4H]

That is very interesting and informative. It points out the risk of quoting someone without having any personal experience in a matter. I was thinking chainsaw and you have provided reason to substitute a scalpel as the tool of choice in this problem. 😉

The variety of responses is extremely useful in these situations.  Nothing is unhelpful and everything is a learning experience.  Have you noticed that with every passing year, the boat anchors are getting older and crankier -- and so are we!    And I'm about to get REAL cranky with this HQ-180A.

[WQ9E]

Michael,

I will never forget the capacitor problems with that HQ-170.  I picked it up at the Baton Rouge hamfest while I was officially down there for an academic research conference   I got it back to IL (interesting carry on luggage which was OK back in those pre 9/11 days)  and was almost finished with the alignment when one of my newly replaced resistors turned red and went up in smoke complete with a match sized flame, the first time I ever saw one of the then newer metal oxide resistors severely overloaded.

I found the problem in the IF can and fixed it and then checked the other IF cans and all of them in the high and mid IF sections showed signs of carbon tracks from those Rube Goldberg capacitors.  I suspect the humid location in its previous home in Louisiana had a lot to do with it.

Fortunately, even in those early sets the problematic caps are only in the first two IF sections and the 60 Khz. cans had regular caps even in early production HQ-170/180 rigs.

The next Hammarlund I picked up was a SP-600 and my luck was still running bad because it was one built with the contaminated potting tar in the chokes that becomes ever more conductive with age   That one got a replacement set of chokes from Hammond.  My next Hammarlund acquisition was a PRO-310 and fortunately it didn't have any weird problems.

I MUCH prefer the selectivity system used by Hallicrafters for its selectable sideband receivers.  Hammarlund does both selectivity and sideband selection by varying switched components in the IF chain which is a very complex system that never works perfectly.  Hallicrafters just changes bandwidth in the IF and sideband is chosen by using either high or low side injection to the final mixer resulting in a much simpler IF strip and perfect sideband setup which works beautifully for AM. 

With one of these Hallicrafters receivers, once tuned properly to zero beat, you can instantly switch between upper and lower sideband on AM without re-tuning and both sidebands sound identical.  The Hallicrafters system is often misunderstood because people assume the bandwidth is too narrow on AM since the widest position (except for the SX-88) is 5 Khz. but these receivers are intended to receive only one sideband at a time and the 5 Khz. position is equivalent to 10 Khz. bandwidth in a traditional AM receiver.

Heathkit copied this excellent system for their RX-1 Mohawk.  Note that Hallicrafters also did the right thing (which was also copied by Heathkit) in NOT applying AGC to the 50 Khz. IF system and unfortunately there are articles out there claiming this was a design mistake.  AGC should not be applied to a high selectivity tube type IF strip using L/C filtering because of the Miller Effect which results in changing tube capacitance as the gain is varied resulting in de-tuning the high selectivity IF strip as gain is controlled by the AGC system.  A properly aligned (and operated in the case of the RX-1 which means never run the IF gain near wide open) has all of the AGC control it needs via the RF and high IF stages.

I recently bought a badly abused and damaged Hallicrafters SX-111 which will be providing the donor parts for a project I have planned for a long time, a Hallicrafters equivalent of the Hammarlund HC-10 sideband/CW adapter.  I think using that as the "tail end" on my SP-400X will make for the perfect vintage AM receiver with beautiful audio and wideband selectivity direct from the SP-400X when conditions are great and the ability to dial in all the steep skirted selectivity you need while instantly choosing the sideband with the lowest QRM when necessary via the adapter.

Rodger WQ9E

[KW4H]

Hammarlund does both selectivity and sideband selection by varying switched components in the IF chain which is a very complex system that never works perfectly.

I've been attracted to Hammarlund for nostalgic reasons.  The HQ-180A was the first receiver I had as a kid (it was gifted to me by a family member) and is what I learned morse code on and did tons of SWL'ing.  That radio was destroyed in a move in the late '70s.  Now -- as a senior citizen and retired after 40 years of professional radio and electronics work -- I'm elbow-deep in restoring one that I picked up.  The IF system does seem overly-complex and a complete pain in the rear to work on.  I'll eventually get it done, but this has become surgery.

Last year I restored a National HRO-60 that looked like it had been pulled through the fence backwards.  A lot of that radio had to be rebuilt, and it's a decent performer, but was a WHOLE lot easier to work on than the Hammarlund.  It's my go-to boat anchor receiver at the moment.

Steve, KW4H

[KW4H]

Well -- after putting a great deal of thought and additional troubleshooting into this, I've decided the switch assembly has to come out.  There's simply no other way to test and evaluate the components below in the IF chain.  Most likely there are a number of drifted resistors under there, as I've found those throughout the unit.  I'm going to use the same procedure in the previously posted video link.  This has become a much longer process than I anticipated; however, the end result should be a well-performing HQ-180A for years to come.

Steve, KW4H

[KW4H]

Posting this so that others with HQ-180A's that may want or need to pull the wafer switch assembly blocking access to the IF chain might find the information in the future.  Per the attached photo -- looking from the rear of the underside of the chassis forward, you can see that the switch assembly is comprised of 12 switch banks.  Using a fine-point sharpie, mark them A through L, starting at the top left (A-B-C-D), and then going back up to the right-top, from the top-down (E-F-G-H-I-J-K-L).

Also attached to this posting is the complete inventory of the connections you will need to cut in order to remove the switch bank.  The inventory gives you the switch bank letter (A through L), the wire color as built by Hammarlund, and a wire number.  Each wire also has a "switch position" and "chassis destination".  Your orientation when using this is just as it shows in the photo:  the chassis upside-down, with the rear of the chassis toward you.  The front panel is ahead.  The "switch position" notations are indicated by hours on the clock, and whether the wire is soldered to a lug on the switch bank that's FACING you or on the BACK of the switch as you see it.  Finally, the "Chassis Destination" is given, and for the tubes it's the pin numbers.  For the transformers it's the transformer pins as you see them from the position in the photo -- again, that's with the chassis upside-down, with the rear of the chassis towards you and the front panel ahead.

You will note that two of the switch banks (C and L) have no wires going to the chassis to cut.

Those 12 wires are the ones you need to cut.  Once you cut them, remove the four screws holding the switch assembly frame to the chassis, and then pull UP and BACK to remove the switch assembly.  You have to pull back because of the switch rods sticking out of the front panel.  Do it gently -- it will play a little tug of war with you because of a couple of components on the chassis rubbing against the bottom of that L-bracket.  

I also believe I finally figured out how Hammarlund built that switch assembly.  It was most likely originally manufactured from the front to the back of the radio, installing the wafer switches in layers.  It must have been quite an assembly line!

73 - Steve, KW4H