I have been given a Hammarlund HQ-100A Communications Receiver. Has the Clock option and 'most' of the wiring looks original. I am only starting to assess whether it is worthwhile to refurb. So far so good.

It has been converted to 240v with an Aussie made transformer feeding the 5YE rectifier. Some-one has added a fuse holder, but it is short circuited with fuse wire ...... . Audio output transformer has been changed and 'Calibration' switch added ...... and another circuit, as yet unidentified. Something has chewed at several components and there is the usual dirt and cobwebs and dribbles of ????? ......

First on my list of "TO DO"s will be a new power cord, earth chassis and a couple of X1Y2 safety caps, check out the 240v transformer and associated circuitry .......

A month or so ago, some-one mentioned Hammarlund radios ..... cannot find the Post or remember who. If anyone has any experience with these radios I would appreciate their advice etc..

The idea if you have not got it is to get a circuit, then you can see what does not belong. If it never was fitted someone may have added a BFO to get sideband?

Rectifier will actually be 5Y3. Do not run it sideways.

5Y3GT ...... yes, mistyped it.

No 'sideways' .... must remember that when powering it up. I often do that with equipment so I can get at top and bottom circuits. Is this a construction issue???

Have the circuit and Operators Manual.

BFO is there as part of original circuit.

Thanks,
Ian

There is a warning in the valves data sheets re it & probably 80. The filament sags and will short & there is only one position it can be run in, sideways. Un-powered no problem

We really need more data on the mod and perhaps a photo of the bits. I just sorted out a Philco BC221N frequency meter. It has a 1MHz crystal calibration Oscillator. I wonder if they put something like that in, hence the calibration SW.

Whatever happened to tuning to WWVH & WWV? These are still handy for checking Sig Gens & such.

There might be some info here?

http://antiqueradios.com/forums/viewforum.php?f=5&sid=cce8600e5c4d18d7db4d9878e21da278

Marc

Hi Marc,

Had a quick look at that web site and yes, it has heaps of good stuff.

Traced out the wiring for this mod that I cannot identify as yet. A photo wouldn't show much; a metal casing about 4 to 5 cms, grounded to chassis, 6BA6 valve on top, 100.000kc crystal stuck into the top, and a Trimpot. Wiring disappearing into this box is ..... 6volt power, switched high voltage power, switched connection to antenna input.

Cannot get into the metal box as yet. I am now thinking that this mod maybe 'factory' as it is a very neat job and the associated wiring is included within the wiring loom.

Originally, I thought that it might be a clock frequency 'adjustor' ...... 60 Hz to 50 Hz. Although it is located directly below the clock, there is no connection to the clock.

I will be taking refurb slowly as I think that it is worth doing properly.

Cheers,
Ian

Update: - found it ...... a pentode crystal calibrator .... also found a circuit for it on a later model Hammarlund. This stuff is mostly new to me ......

I just downloaded the user manual / schematic too familiarise myself with this radio. While not state of the art it is a quite decent communications receiver that should perform very well. The RF, Converter and IF valves are modern high gain types.

The manual gives a good chassis layout picture so based on your description, the extra box is a later addition. The added "calibration" switch is the vital clue, it sounds like a crystal calibration oscillator has been added to the radio. It's a simple but very useful addition. The crystal will be running at 100 kHz and producing harmonic multiples at every 100 kHz when switched on. i.e. a tone (or null) will be produced at 100 kHz, 200 kHz, 300 kHz etc. This allows the operator to calibrate the tuning scale accuracy against the calibration (or marker) oscillator. You can then set the receiver very accurately to a specific frequency instead of having to search around at the expected frequency and hoping to find the signal you want.

Modern receivers with crystal referenced PLL oscillators and digital readouts have no need for such things!

Rather fits what I suspected it may be and why. Things like my Yaesu are digital & basically the readout is a frequency counter. Its accuracy is handy for hetrodyning (Zero beating).

The metal box is logical, it will act as a "Faraday cage".

I have one counter I built in 1979 & a Fluke, one uses them to set the rough old Signal generator, rather than their dial. All the old generator has to have is good modulation & be reasonably stable.

Marc

Hi TV Collector,

A couple of questions for you, or anyone else who understands this stuff .........

This radio goes all the way to 30MHz. Will this crystal calibration oscillator produce harmonics this high???
If this oscillator had some audio modulation, then I would be expecting to hear a Tone every 100kc?
If no modulation, do I expect to hear 'beating' as I sweep the radio through the various harmonic frequencies?
An S meter? I'm guessing that the meter works off the AVC?? So why is it called an S meter??
Q Multiplier? Is this similar to Q of a resonance circuit? ie higher Q gives narrower frequency/selectivity but higher output etc??

... maybe this stuff will make more sense when I get this radio working. Unfortunately, it is going to have to wait awhile before I can make a serious attempt at getting it running.

Got my other Sansui running also (AU7500)...... intermttent fault in power supply Pass transistor .... found suitable replacement in my 'junk' box .....

Cheers,
novice

One does not use modulated signal for 'zero beating' nor does one have it "on" when trying to calibrate the signal generator with a frequency meter.

The signal coming together (hetrodyning) will create their own audio, which disappers enirely when the signals null This is virtually the same the Wartime frequency meter, in operation

Marc

This radio has many RMC Z5U ceramic disc caps. Not sure if they are original.

Is anyone familiar with the quality of these caps?? For example, are these caps are usually reliable??

Are their general operating capabilities suitable to this type of radio?? ..... with respect to stability etc??

Chers,
Ian

I did a quick Google search and it appears RMC brand capacitors are quite old so they may well be original to the radio. Z5U series capacitors are a standard grade of ceramic cap so are OK in non critical applications. Ceramic capacitors tend to be quite reliable, so if the radio was build with them, I'd leave them alone.

I was having a closer read of the manual and Hammarlund had an optional crystal calibrator available for these radios so the one fitted to your radio may be factory fitted. Search for Hammarlund XC-100 for more info.

To answer your other questions,
Yes, harmonics from the calibrator should extend up 30 MHz but the amplitude will have dropped off considerably.
Hopefully I'm interpreting this correctly. Looking at the XC-100 manual, the Cal oscillator is an unmodulated 100 kHz oscillator injecting a signal into the antenna input and designed to beat against the beat frequency oscillator frequency. The idea is that you tune to for example, 1 MHz and with the Cal on, adjust the tuning until the two oscillators are "zero beating" against each other. Then you know the receiver is set to 1MHz exactly regardless of what the dial reading says.
The S-Meter is named after the S unit for signal strength. It's amateur radio terminology.
Your right about the Q-Multiplier. It's a way of increasing the "Q" of the tuned circuit thus increasing it's selectivity. The manual has a section that explains it's function.

Thanks TV Collector. Found and downloaded a couple of manuals ......some good bedtime reading.

Cheers,
Ian