Heathkit HW-7

Early this year I purchased a HW-7 from Paul, W0RW, of HF Pack fame. I had been looking for a HW-8 or HW-7 because I drooled over these kits when I was younger and never really thought to pick one up until I started selling a lot of my old ham gear I did not use anymore. I wanted a project to use and not one to sit in a closet.

I have been having a blast modifying the HW-7 for field and home use. I probably will not pickup the HW-7's little brother, the HW-8, as one project radio at a time is enough.

My, new to me, HW-7
While there are several modifications listed for the HW series of radios but most of the information or I should say "how to" revolves around the HW-8 radios. This is a problem for me, while I can solder and do some basics without detailed instructions I make a lot of mistakes and most of the time I am lost.

I will attempt to talk about modifications I have done to my HW-7 and will try to document them the best I can so others may follow.

My HW-7 is SN 04502 and I have no idea how many were made. I think it was built around 1973 which would had been the time I was beginning my fascination with radio. In 1976 the ARRL Operating Manual had a picture of two hams on top of Mount Whitney using a HW-7, a couple of 6 volt batteries and a dipole during Field Day. That image was burned into my brain and probably influenced me towards QRP, simple radios and taking them to the field.


I do not know how WA6VBA and K6JTH did during that Field Day (I doubt they did very well with a dipole 12 inches off the ground) but I sure did admire them for doing it.

Unfortunately the ARRL Operating Manual for that year and subsequent years was lacking a level of enthusiasm for field operations and trail radios.

Now that I am having fun with Summits On The Air my goal is to modify the HW-7 to be somewhat deployable. I think it will be fun to do a "vintage" SOTA activation with a radio 40 years old.

I have done very little to the HW-7 since I received it but I did add LED lights (I thought green was appropriate) to light up the dial and relative power scale at night as I thought that may come in handy.

LED mounted in the side of the Relative power Scale

LED Mounted above the frequency dial
The LED wire routing
The LED is really just too simple. The hardest part was drilling the holes. I just took the power from the switch and added the appropriate resistor and the LEDs. It really is just that simple. However, if anyone wants details just let me know.


The next modification is an Audio Amp that is offered by KC9ON for the HW-8 (he has instructions for the HW-7 on his web site as well). Here is a link HW-8/7 Audio Board.

The kit and instructions
Built and ready for testing and install
You really cannot go wrong for less than 10 dollars, shipped.

Audio amp board installed

The Heathkit Speaker the HW-7 now uses
I also built the Elecraft AF-1 audio filter (case is by W8FGU) and it works great with the HW-7.
Elecraft AF-1 and W8FGU case
However, it is a little big to haul up a SOTA summit so I built the NEScaf offered from the New England QRP Club and I am also very please with it. I housed it in a child's puzzle tin from the dollar store that cost, you guessed it, one dollar!


The NEScaf will join me on HW-7 / Rockmite deployments as it is light and compact. It works very well. I decided to not add it to the internals of the HW-7 I can also use it with other radios I take to the field.

Up next will be the break-in circuit modification. I would also like to add a RIT but feel that it is a little out of my league so I am open to guidance and/or advice.


19 May 2014

I have returned from Dayton without spend hardly any money which was great. During Dayton I was emailing KR7W, Rich, another HW-7 guy and mentioned the problem I was having with the relay. When using a keyed it was acting as if the relay was not able to keep up transferring power. In fact I decided to do the QSK mod but had not done it yet because it was a little more than I want to do to the radio. Rich came up with a solution and that is to replace R-14 with a 4.7K Ohm resistor vice the 47 Ohm resistor.

Here is his email to me:    "I finally figured out and fixed the QSK issue with the Antenna Relay in my HW7.

R14 in the keying circuit is the wrong value.  It is wrong on the schematic and labeled wrong on the 7's printed circuit board. (but the schematic does show the proper voltage reading of 6 volts).  I've not seen this issue in any of the mods I've read about and is not in the HW8 Handbook which includes updates from Heathkit."

He continues with:      "R14 should be 4.7K ohms, not 47K.  With the wrong value... Q8 is biased to not saturate when the key is down... which in turn causes Q9 to not go into saturation to place a full 12 volts across the relay coil.

On my HW7 had 4.6 volts across the relay coil which made it operate very slowly.

The HW8 uses the same keying relay and circuit... and it's schematic shows the correct resistor value."

New resistor in place

Expanded view

Schematic

I also had about 4.5 volts across the relay coil so I decided to make this mod before I did anything else today and it works like a champ. Rich is also right in that it is not listed anywhere else. I looked. Rich will post his mod to the Heathkit Forum and hopefully get the word out. If you would like to see Rich's other mods please check here.


This modification saved me a lot of work and time. I hooked the Heathkit keys up to the HW-7 and it worked like a champ. The HW-7 is almost ready to be taken up to a SOTA summit.

72 Frank K0JQZ

4 comments:

  1. Great info on HW-7. I have one too.

    My problem with the HW-7 is that after transmitting, the receiver seems going deaf for a while, and sometimes the station has moved away to a little off frequency than it was.

    Due to this problem, I have lost some contacts in the middle of QSO.

    Another problem is that I cannot use any Power Supply to the HW-7 due to hum. When it is powered by battery, the hum disappears.

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  2. Hi there from a cold and wet Wales UK just acquired a untouched HW7 what headphones can I use on the radio at the minute I would like to keep it as original as possible but after a little playin around I intend to modify it in what order would you say the mods should be carried out. Many thanks for you site always makes interesting reading. Dave c G0NVF

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    Replies
    1. I use an audio amp and a healthkit speaker. I really do not like wearing headphones. Thanks for reading. 73

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