Hammarlund HQ170 Restoration

 

 Although I refer to this exercise as "restoration" I intend to do the minimum amount of work to get this old receiver running tolerably well. I remember trying it out many years ago when I first acquired it and was surprised how sensitive it was and how quiet was background noise.

The first step was to lug out my 240/110 volt isolation transformer for which I paid £1 at a street auction donkeys years ago but when I plugged it in the was a dull thud and a cloud of smoke smelling like burnt rubber. After ditching the input and output cables and refitting with a new plastic covered output cable and adding an IEC connector on the front it worked a treat and the HQ170 dial lamps lit up.

Next, let's see exactly how the receiver performs..... most disappointing because after connecting an 80m dipole or a long wire all I was able to hear across its seven bands was a couple of very weak CW stations and a few weak teletype noises. I switched on my newly repaired Wavetek 2407 (with some trepidation... but it worked fine) and checked the receiver calibration and sensitivity (or as I was to discover: It's degree of extreme deafness).

During testing I found it very awkward to read the dials because the number of KHz between adjacent dial markings varies from band to band. I suppose that's something a user would get used to.

 The next day I spent a little more time on this receiver. As it uses an inconvenient tagstrip for the aerial I removed a wander plug socket fitted in the past by a previous owner, drilled out the hole slightly and fitted a BNC socket. That will provide a more reliable connection to my signal generator.

 I also noticed the 100KHz calibrator crystal wasn't gripped in its socket so I squeezed the socket and this was better. Once done I plugged in the set and connected my 80m dipole. Much to my surprise the set was now pretty sensitive and lots of signals were present on the 80m metres and above. All I can think is some valve pins may be making better contact than during the first test I did, perhaps disturbed by drilling out the hole for the aerial socket? SSB signals on 20m were hitting S9 +20dB on the S-meter, so not so much work to do as I first thought.

Before repeating a set of calibration and sensitivity checks now that the receiver's sensitivity is OK (initial tests on all bands needed some tens of millivolts to produce an S9 reading.. see later), I sorted out a discrepancy between the two dials. When the left dial was set against its cursor in its centre position I saw the right dial scales were out by about an inch. I eventually found an Allen key that fitted the grub screws and managed to twist the dial to match the one on the left.

Below; the results... only a little tweaking required on most of the bands, although 6m looks ropey.

 

 Dial reading MHz

Signal in MHz

 Signal in for S9

 Dial reading MHz

  Signal in MHz

 Signal in for S9

 1.803

 1.800

 64uV

 2.000

 1.993

 64uV

 3.513

 3.500

 15.7uV

 3.811

 3.800

 15.8uV

 7.008

 7.000

 15uV

 7.250

 7.240

 16uV

 14.000

 14.002

 30uV

 14.300

 14.304

 30uV

 21.000

 21.144

 40uV

 21.400

 21.558

 40uV

 28.000

 28.021

 22uV

 30.000

 30.056

 45uV

 50.000

 49.977

 428uV

 54.000

 53.976

 328uV

Before starting the tests I adjusted the S meter sensitivity to nearly maximum. Once I've completed alignment I'll set it to read S9 at 50uV which is the generally accepted signal strength for S9 on the HF bands. I turned the RF gain to full, selected AM and switched to "Both Sidebands" and Slot Frequency fully anti-clockwise. I left the Antenna tuning where it was but of course adjusting this for each reading may have improved the receiver's response.

While the signal generator was connected I also looked at the approximate settings of the IF amplifiers. With the 50MHz band selected a 100mV signal at the first IF of 3.035MHz produced the following...

The S-meter reading rose as the test signal increased in frequency with S3 being achieved at 3.03580MHz. As the frequency was increased further the S-meter reading rose then fell back so that S3 was achieved at 3.03587MHz. The average frequency being about 3.03584MHz. It should be 3.035MHz.

Setting the HQ170 to top band I checked the 2nd IF. I reduced to RF input to give me an S3 reading from 453.0KHz to 458.7KHz which corresponds to an average frequency of 455.85KHz. A peak reading was achieved at 455.2KHz. This gives a spread of -2.2KHz to +3.5KHz. Not too bad but could be better.

Twiddling the various controls told me a few things that will need correcting. First, the audio control doesn't increase the volume when turned beyond the third mark (I'll check for a positive bias on the 6AQ5 control grid or just replace the audio coupling condenser. I may also test the 6AQ5). Note: I later found that the design of the volume control circuitry is supposed, once reaching less than half-way, alters some of the parameters to improve audibility without making the audio any louder. I also found the background noise when switching between SSB Low and Upper sounds a lot different so the BFO frequency may not be on the correct frequency.

Although the product detector works well on 20m even with the RF gain at full, it needs the RF gain reducing for less strong signals on 80m to avoid distortion. The noise limiter inner pot isn't connected (in fact the circuit diagram doesn't show a pot here??) and, although the calibrator worked fine when I first turned on the receiver, the crystal socket still isn't very reliable.

Changing the AVC switch setting alters the overall noise level so there may be something leaky on the AVC line? In fact quite a lot of work to do to bring the receiver up to my liking.

I'll adjust the frequencies at the top and bottom of each band to match the dial calibration then repeat the sensitivity tests.. or should I initially check the IF tuning? Maybe confirm the IF tuning is correct first in case one or more of the settings is out otherwise I may need to repeat the local oscillator tuning? My best bet is to use my spectrum analyser to view the IF response shapes and centre frequencies, but maybe not as the manual seems to provide a recommended method based solely on twiddling against a meter.

 

 

 I looked at the HQ170 again. I tested the 6AQ5 output valve and found it was marked "Foreign" and gave me a reading of 80% on my AVO valve tester, so I checked its grid and found it sitting at only 6mV which is fine. The grid coupling component (above left) turns out to be a hybrid module carrying three capacitors and two resistors. Checking the 6AQ5 cathode I discovered its decoupling capacitor was a third element of the main aluminium can carrying the reservoir and smoothing condensers. Disconnecting the 40uF part gave me a reading of 60uF and an ESR of 1 ohm which is OK. HT read 263 volts and 243 volts at the reservoir and smoothing condensers.

The hybrid (above right) is used in the crystal calibrator circuit.

An observation before going further. The HQ170 uses a final IF of 60KHz. Because of this low frequency and because several stages of amplification are used, it is essential that circuits are not tuned by just peaking everything otherwise you'll end up with miles too much gain and a bandwidth really too narrow for comfortable listening to AM. I remembered this after carrying out the first IF alignment, then re-read the manual where it tells you the receiver settings for 60KHz alignment. I then recalled tuning up an early superhet from 1935 and finding it virtually unusable. Sometimes a user manual will tell you how to stagger-tune the IF transformers, but with the HQ170 the proper settings and peaking seems to work reasonably well. I did observe some double-humping when tuning across strong signals so I may return to the job but using my spectrum analyser.

I decided to investigate the small discrepancy in the 3.035MHz IF and found that adjustments are made via the bottom slugs in a pair of cans. Fortunately I found a suitable tuning adjuster in my collection of such things (see notes near the end of this page) and made a small correction. Then I found that there was an intermittent, apparently inside one of the two cans, which resulted in the extreme deafness I'd noted when first turning on the receiver. I jiggled the core in the top of the can and restored normal working, but that fault will need fixing.

I spent an hour listening to the various amateur bands and found the receiver to work very well. It has a double-sideband setting for SSB which I've not seen before and which produces very good results. A harsh LSB signal can sound much mellower in the double setting. Oddly the LSB/USB/Double switch affects AM reception. Maybe this a design feature?

After tuning around and listening for a while I noticed the right hand dial had slipped back so the marked band edges were now again an inch out. I wonder if one of the grub screws is loose but to check these means making a special tool because my only Allen key is too short and when extended goes in at an angle and is awkward to turn. The dials are coupled by a steel wire wrapped around pulleys. For the moment I don't think it advisable to carry out alignment until the dial slippage is fixed.

 

 
 

Below, the now defunct clock. This would have been designed to run on US 60Hz mains so would run slow on UK mains. Probably the best way to restore this is to ignore the switching arrangements at the rear, remove everything behind the face and fit a modern electronic unit, although finding a 24 hour type at a sensible price might be difficult. As I don't wish to leave the power on all the time the original purpose of the clock to turn on the receiver for 30 minutes before use is superfluous anyway.
 

 I decided to carry out more tests as I'd noticed a few problems. There are a couple of intermittent things, one of which is a rise or fall in background noise level. This is triggered by touching any part of the circuit near the 2580KHz crystal which is soldered in place below the oscillator valveholder. At first I thought it was something inside one of the cans then the crystal or a dry joint around the valveholder, but it seems to be a loose or shorting connection inside the transformer can.

I made a sketch of the pin wiring at the suspect T2 transformer can, unsoldered everything and unclipped the can from the chassis. A U-shaped spring with tiny teeth holds the can in place. The coil former looked a bit scruffy and I soon discovered it had been removed once before. There are three coils wired to six pins which are located in a ceramic base. At some time part of the ceramic material has been broken off and araldite now holds two of the pins in place. First, I cleaned off old solder then cleaned up the wire ends and resoldered all six wires. The thin wires to the coils looked bare in places so I fitted a paper sleeve inside the can to prevent a short. I also noticed two of the pins could be bent to touch the can surround so I fitted tape around the bottom of the coil to cover where the ceramic insulation was missing. Refitting the transformer seems to have now successfully cleared up that intermittent fault.

A really annoying thing is the manual for the set refers to transformers by their circuit reference number, but there isn't a drawing showing these numbers. The previous owner has marked the 60KHz cans but all the rest are anonymous, so I produced the drawing below.

Yesterday I peaked all the 60KHz transformers, thinking this was what was intended, then found the receiver gain was too high and the bandwidth switch settings were odd. I recall the slugs needed a lot of movement and thought this rather strange at the time so I then re-read the manual and found the stages need to be stagger-tuned and this is achieved by setting the receiver to AM, switching to lower sideband and 0.5KHz bandwidth and then peaking them all. Sure enough, once done I found the gain was manageable and the switched bandwidth control results sounded much better.

Nearly all the slugs in the various transformers require a hex shaped plastic trimming tool and most of these require the hex shape to be at the end of a necked section allowing the bottom slugs to be set from the top of the chassis. For some reason the exception to this are the three 455KHz transformers at the front of the chassis. For these I had to file a trimming tool from an old plastic knitting needle to match the slot in their slugs (see the note near the bottom of this page). I can now adjust the top slugs but those at the bottom won't adjust. Because of this the tuning of the 455KHz IF strip is about 1.5KHz too high.I suppose, if all else fails, I could add a little capacitance to bring down the setting?

I've also noticed that the RF from the final 60KHz IF strip is crackly. Looking at the output on a scope it's jumping around. Maybe a capacitor is acting up or there's a dry solder joint? I didn't get to the bottom of this problem and it's possible the set is so sensitive that it's picking up local electrical interference which is getting into the 60KHz IF strip and modulating incoming signals.
 

 

 

COIL

ADJUST-KHz

ADJUST-KHz

COIL

ADJUST-BAND

ADJUST-BAND

NUMBER

TOP

BOTTOM

NUMBER

TOP

BOTTOM

L4

395

T12

160

T1

455

3035

T13

80

T2

455

3035

T14

40

T3

455

455

T15

20

T4

455

455

T16

15

T5

455

455

T17

10

T6

60

60

T19

160

80

T7

60

60

T20

40

20

T8

60

60

T21

15

10

T9

60

60

T23

160

80

T10

60

60

T24

40

20

T11

60

60

T25

15

10

T28

60

 I can't stress too much to anyone contemplating an alignment that the correct tool types or exact equivalents are used. Hammarlund quote two types. One is a type 5097 which is a stubby flat blade used for T3, T4 and T5 and the other a type 8282 which is a hex shape on the end of a stalk. This enables the tool to adjust bottom slugs from the top of the set without interfering with slugs on the top. This isn't always easy and a bit of cautious jiggling may be necessary.

The hex tool type 8282 has a thickness between opposite flats of 2.54mm which I reckon is supposed to be a tenth of an inch. The length of the hex section needs to be around 10mm and the necked part about 2mm in diameter. A length of 100mm is OK. I had one of these in a cheap kit of alignment tools.

I filed a knitting needle to the exact fit for tool 5097 and it ended up 3.8mm in diameter with a blade width also 3.8mm and a thickness of 1.9mm. The length of the flat part need only be no more than 3mm to fit the slot in the slugs. The underside slugs need the tool to be no more than 3.8mm in diameter because the entry hole diameter is smaller than the top hole. If you use a 4mm plastic rod this needs to be reduced over about 25mm to reach the deepest slugs. A length of 100mm is OK.

 

 I found it a bit tricky to adjust the slugs because some were quite sticky in the threads. I suppose there's a chemical or oil that could be used to free them but I hesitated using anything in case it resulted in something nasty happening such as altering the basic coil inductance.

I spent a little more time on alignment once I'd made a decent 455KHz trimming tool and found one slug quite a way out. What had caught me out was the holes in the bottom of the cans are smaller than those at the tops and jamming the adjusting tool. Once I'd reduced the diameter of the tool the slugs tuned up easily. Finally, I was happy with results. During the job I'd noticed the controls for the BFO tuning and Slot Frequency which are both small variable condensers were slightly marred by protruding heads of the securing screws (are these original?) so I removed them together with their star washers and fitted countersunk types. Note that the two screws for the Slot Frequency need to be quite short otherwise they'll protrude too far and foul the condenser vanes.

Another tip concerns adjustment of the Slot Frequency coil. Mine was very stiff and was impossible to tune precisely. I discovered that if the pointer didn't quite line up to the zero mark the pointer can be pushed slightly to line up accurately.

The tuning mechanism is of fairly poor quality although it works well enough in practice. If you notice some backlash, this can be minimised by tightening the nut at the rear of the flywheel but at the expense of spin-ability. I don't know if a brand new receiver flywheel worked well enough to spin the dial, but I found that this isn't possible with a well used example. In practice a slightly heavy tuning knob is OK. Fine tuning can be carried out using the fine tuner which is ideal for tracking an SSB signal when either the station or the receiver frequency is drifting.

Below, waiting for a clean-up of the front panel, then I'll carry out a sensitivity check to see if there's been any significant improvements, then if all is well, fit the set back in its case and put on display. Before I did this, one of the controls had been annoying me. The Send/Receive?Cal switch had lost its positive ident. I found my box of ball bearings thinking one had fallen out of the yaxley switch but found it used only a bent metal wiper to engage in mouldings in the metal mounting plate. The wiper was no longer pressing down on the mouldings but I found an easy way to fix this. I tapped gently on the end of the metal wiper using a small hammer against a flat-bladed screwdriver and the wiper bent inwards, perfectly pressing against the mouldings. Now the control clicks into position.

 

 Here's a recap on receiver performance before starting realignment
 

 Dial reading MHz

Signal in MHz

 Signal in for S9

 Dial reading MHz

  Signal in MHz

 Signal in for S9

 1.803

 1.800

 64uV

 2.000

 1.993

 64uV

 3.513

 3.500

 15.7uV

 3.811

 3.800

 15.8uV

 7.008

 7.000

 15uV

 7.250

 7.240

 16uV

 14.000

 14.002

 30uV

 14.300

 14.304

 30uV

 21.000

 21.144

 40uV

 21.400

 21.558

 40uV

 28.000

 28.021

 22uV

 30.000

 30.056

 45uV

 50.000

 49.977

 428uV

 54.000

 53.976

 328uV

 And here's the results after realignment
 

 Dial reading MHz

Signal in MHz

 Signal in for S9

 Dial reading MHz

  Signal in MHz

 Signal in for S9

 1.800

 1.800

400uV

 2.000

 2.000

 400uV

 3.500

 3.500

 50uV

 3.800

 3.800

 67uV

 7.000

 7.000

 7uV

 7.300

 7.300

 7uV

 14.000

 14.000

 13uV

 14.400

 14.400

 10uV

 21.000

 21.000

 10uV

 21.600

 21.600

 10uV

 28.000

 28.000

 8uV

 30.000

 30.000

 11uV

 50.000

 50.000

5uV

 54.000

 54.000

 10uV

 The oscillator tracking is now perfect so I could make measurements at the dial ends. A few puzzling things.. why should top band sensitivity and 80m have dropped off? These two bands are in the double-superhet range whilst the others are all triple-superhet ranges, so it's possible one of the 455KHz transformers is now off frequency?

When I have time I'll use my Rigol spectrum analyser to see the shape of the receiver's response.

Before I did this I decided to remove the old mains lead which was a twin wire cable added by the last owner and instead fit an IEC chassis mounted socket. I then modified my 110 volt transformer by adding in place of its output cable, a US-style chassis mounted socket. This enables me now to use one of the dozens of IEC/US plug leads that came over the years with computer equipment. I also fitted to the rear of the receiver chassis, a phono socket wired in parallel with the loudspeaker screw terminals. I remembered to write on the chassis at the side of the new socket "110 V".

 If you missed it... here's a description of the HQ170 Receiver

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