Monday, July 17, 2017

Ode to Heakit QRP Radios

There is no doubt about it, the Heathkit HW-8 is one of the most popular QRP radios ever made. Additionally, it also holds the record for the most modified QRP radio in history (so far). 

My love affair with the Heathkit QRP rigs started in early 1970s when I built my first HW-7. Stationed at Lajes Field in the Azores, I found the challenge of QRP invigorating using a 5BTV Newtronics vertical. My first QSO using my HW-7 was a ham in Scarborough, Ontario Canada. 

With one ear on the AFRTS broadcast of Super Bowl VII and the other attuned to the 20m CW band, I called "CQ" and was rewarded with a VE3 who came back. After a short rag chew I let it be known that I was running about 2 watts of RF output power. At which time the VE3 station stated that was impossible as I was a solid S-8/9 on his meter! I sent a picture of my QRP station along with my QSL card. A couple of weeks later I received his QSL and a very nice note stating that he was going to look into this QRP stuff! Welcome to QRP!

The HW-7 followed me to Tinker AFB, OK in late 1973. For FD 1974 I took the HW-7 and a dipole antenna, battery, and a small table out into the bush near Lake Thunderbird. It was then I found out how REALLY bad the receiver was in that rig! I made one QSO and decided that between the HW-7's receiver and the man-eating mosquitoes it was time to go home! 

In late 1979 I was re-stationed to RAF Mildenhall, UK (G5CSU) which was a god-send for my QRP efforts. In 1979 I retired the 7 in favor of the new HW-8.  In addition to the HW-8 I also had a Ten-Tec PM-3A in the shack. My first QRP QSO was with Colin Turner, G3VTT, one of the charter members of the G-QRP Club. The station was about as bare bones as you could imagine....PM-3A fed into a chain link fence behind my off-base house in Bury St. Edmunds. This first QRP to QRP QSO was the start of the most fascinating tour of my USAF career. 

Over the years I sold/traded several HW-8s but still kept my devotion to the "8". About a month ago I managed to procure a HW-8 (and a modified HW-7) from my long time buddy, Mike Bryce, WB8VGE, with the idea of holding on to both of them. The "7" needs some TLC. The "8" seemed ready to go out of the box. 

After shoveling out the shack so I could actually find my way to the ops bench, I put the new "8" on the air for the last two days of the 13 Colonies special operating event over the 4th of July. With a very intermittent operating schedule I managed to work a total of 7 of the 13 colony stations all on CW at about 1W output to wire antennas. 

Thankfully my HW-8 waited until the end of the 13 Colonies event before dying. I was having a lot of difficulty in tuning the rig up on 80 meters. The auto ATU I was using was buzzing and clicking away happily but I was not getting a good match. All of a sudden I noticed that the thru-line bidirectional watt meter was showing no RF output, BUT the meter on the HW-8 was showing RF output! I tried re-tuning everything and setting the ATU loose in the tune mode. No output! 

Found out a couple of VERY interesting things while troubleshooting the defunct HW-8, to wit:

  1.  The PA transistor (2N4427) died due to parasitic oscillations. The original transistor is very hard to find. However, a 2N3553 will work as a replacement for the 2N4427 Hw-8 PA. Although  not  a perfect replacement it does work with the added feature of slightly more RF output. If you have similar issues with your HW-8 PA, be sure that the ferrite bead is on the BASE lead when you install the replacement.
  2.  The new power output (as measured by two separate QRP watt meters) is 2.5W output on 80M, 2.25W on 40M, 2W on 20M and 1.0W on 15M.
  3. Another "sub" for the stock PA is a RCA SK-9645. I have two of them but haven't tried them yet. 
  4. In my travels around the Internet I discovered a site that has compiled a complete listing of all the replacement devices and their commercial equivalence. Heathkit part numbers are unique to Heathkit. This cross reference is a godsend for those of us trying to repair/restore 40 year old gear with parts made from "Unobtanium"! Try:  
  5.  Additionally someone had been all over the inside of that rig. Nothing Earth shattering, but the PA has been removed, and none too gently, I might add. The PCB traces are all messed up, but thankfully I have a high-end de-soldering station and got the bad PA out. Putting the new device in was a bit awkward, but I now have RF output and it is on freq w/apparently no parasitic oscillations.
  6. The 36V Zener was, in fact, dead. Put a new 36V 3W Zener in the rig with no problems.
  7. I found that the TX/RX relay was not closing when I went into TX mode (apparently some cold solder joints)! Methinks that this was the initial problem causing no load on the PA, which most likely took it out.
  8. I didn't notice that the relay was not closing during the 13 Colonies event since I was wearing some high-end head phones and they mute a lot of the outside noise.
  9. I am awaiting the KC9ON TX/RX relay mod kit and will install it and permanently get rid of that relay. The relay pins on the bottom of the PCB were very badly soldered. I am thinking of going over the entire PCB and re-heat/flow all the connections.
  10. The dial cal was off by over 10 kHz so I tweaked L9 to move the VFO up about 10-12 kHz as an immediate measure. Once I get some additional info not included the manual I received (like the schematic and tune up illustrations) I will do a complete alignment of the radio and then perform the mod to the VFO to reduce the tuning range to 125kHz.
  11. Speaking of L9....I have a very bad microphonic problem, all centered around the L9 area pf the PCB. I have re-heated the case lugs and the contact points on the PCB. It curried the majority of the problems but I still have some work to do to get rid of the problem. 

That is about it for now in my pursuit of restoring this HW-8. In addition I have two HW-7s and two Argonaut 509s in queue for restoration. I will detail the procedure here on the blog. 

Vy 73

Rich K7SZ

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