Wednesday, April 4, 2018

Gentlemen, start your engines..the OHR 500 is about to begin!

Stock Photo of an OHR-500 Station. Reminiscent of mine.

The venerable Oak Hills Research OHR-500; a five-band, QRP rig, senior member of the OHR stable of which came many noble kits. OHR was founded by the late, great Doug DeMaw, W1FB, and later passed into the hands of Dick Witzke, KE8KL, and lately Marshall Emm, N1FN. I know Doug by his exalted reputation the latter two gentlemen by their stewardship of OHR and from phone pleasant conversations in search of information re ailing kits.

I want to say this at the outset: just as these gentlemen are fine stewards of the QRP tradition, so are the products they represent. I have, in order, the following OHR products:

  o An OHR 100A for 40 meters sold to a ham in Nebraska.
  o A DD-1 frequency display for the above that also went to Nebraska.
  o A WM-2 that still resides on my bench and is used as a standard.
  o An OHR-500 built ans, sadly, sold off.
  o An OHR 100A for 30 meters given as a gift from K6BNC. (Still here.)
  o A DD-1 obtained at a swap meet and mate to the 30m OHR-100A.
  o The OHR-500 purchased through an eBay deal and subject of this writeup.
  o Another DD-1 from a WB6JDH clearance sale.
  o An OHR SCAF filter also picked up from the WB6JDH clearance sale.

As stated, I built one of these OHR-500s a long time ago and, when it was done, I fired it up and tuned across the band(s). Hearing nothing -- almost NO noise and only CW traffic -- I thought it was was numb. Of course, this was during the time I was building a lot of QRP kits that were peppered with NE602s and whose interiors were alive with the sound of phase noise and digital hash. It was also before the time when I did not understand nor test for receiver sensitivity. I would build 'em and put them on the air and let the chips fall where they may.

Also, about that time, I developed a love affair with the Elecraft K2 and realized that budgetary limitations would not tolerate owning and operating both. So, my OHR-500 went on the market and was sold with a nagging feeling of regret. As I become more knowledgeable, I wished I had kept it and, only now, was able to correct that mistake.

Here are some pics of the beast:

The radio arrived and it was immaculate with only two flaws: (1) the dial pointer was missing and (2) it did not work. But, with WB6JDH's gracious assistance, the unit was resurrected and put on firm footing. During this process it became apparent that the kit was built but never put on the air. Basically, we assumed this because the builder was immaculate and precise in his construction and there was no indication of the "golden screwdriver" ever being used on the radio. You know, no rework, mods or the like, etc.

We found that a couple of switches were wired backwards and there was a solder bridge on the underside of the receiver board (see below) that caused the side tone to be a no-op and would have precluded operation. I am guessing that the guy went through the whole process and, when completed and not working, put it away on the shelf figuring he would get to it another day. He probably then and lost interest and later sold it off.

Solder bridge corrected (scratchy joint in center)

It tuned up nicely and yields a peak of 7-10 watts on 80 through 20 meters and a diminished (but within spec) 3 watts on 15 meters. The filter is adequate but not as nifty as the variable filters on the OHR-100As. However, like he other OHRs, it offers a rock-solid stable VFO and good, sound ordinary workmanship with no glamor; just functionality. I always did like the fact that OHR radios had an abundance power to burn and you did not have to squeeze the bejeezus out of some overworked final transistor just to get it up to five watts. I would rather throttle a radio back than firewall it.

Happy to welcome it into my home and look forward to putting it on the air. The one thing I dread is programming up the companion DD-1 I got from Dick. Never could figure those instructions out!

Thursday, March 29, 2018

Norcal 40A 30A..that's "30" for tonight..

Posting WB6JDH's 30 meter mods for the 40A. These are more comprehensive than W0CH's mods and will be the ones we pursue on our builds. Stay tuned.

30 Meter Mods Per WB6JDH
(1) Install 8 MHz crystals
(2) T2 is wound as follows:
     Pri 2T
     Sec 17T
(3) T3 is wound as follows:
     Pri 18T
     Sec 4T
(4) C6 is 22 pF NPO
(5) C9-C13 are 470 monos or 470 C0G or 470 NP0 if they will fit
(6) L4 is 10 uH
(7) C14 is 47 pF NP0
(8) U2 same except X5 = 8 Mhz
    Pin 6 = 0.80 Vpp
(9) AGC Mute Circuit
     R4 is 4.7 MOhm
     R8 can be jumpered
(10) U4 Measurements:
      Pin 4 = 0.15 Vpp
      Pin 6 = 0.30 Vpp
(11) X6 is 8 MHz crystal
(12) L5 is 15 uH
(13) C35 is around 151 pF (see notes below)
(13) C38 is 68 pF NP0
(14) L6 is 24T
(15) Q5 Measurements
     Source = 1.0 Vpp
(16) T1 is wound as follows:
     Pri 13T
     Sec 3T
(17) R12 is 18-22 Ohms
(18) Q7 Measurements:
     Base 2.5 Vpp
(19) RFC1 = 15 uH
(20) L9 is 62T
(21) C52 and C53 are 1500 Poly
(22) Q8 Measurements:
     Source = 3.4 Vpp
     R23 on C7 side = 0.8 Vpp
     Rxvfo label = 0.8 Vpp
Regarding the oscillator circuit for U4, Dick was concerned because the drive to the base of Q7, the final transistor, was too low at 2.5 Vpp. At first, he thought it might be due to the crystal activity of X6 hanging off of pin 6. However, fishing through his stack of 8 MHz crystals and finding a substitution with more poop did not alter the drive that much.

Instead he proposed dropping the value of C35 hanging off of U4 pin 7 with something a little less than the 270 pF original. Dick tried a 150 pF NPO cap and reports that the power output for his 30m version was raised to just a shade under two watts. Recommend you try a temporary insertion until an optimum value is found. But be careful, however, as too low a value will swamp U4's oscillator.

Tuesday, March 27, 2018

Marking time with a Pixie..

Noticed that John Clements, KC9ON, who produces the outstanding aftermarket boards capable of reaching back in time and bringing the Heathkit HW-7s and HW-8s back from the stone age, has come up with some interesting products for the low-end Chinese kit market. These are principally his Pixie Switch which turns the $5 Pixie kit into a little radio capable of four channels.

John also offers a kit package including the Pixie kit and his switch and three 40 meter crystals: 7030 Kc, 7055 Kc, and 7110 Kc. The intent is to use the 7023 Kc crystal in the Pixie to round out the four frequencies. Intrigued, I sent off for several copies of the Pixie plus switch package, a couple of extra switch boards and a crystal pack. In addition to that, I got a Chinese Frog Sounds QRP kit off of eBay that should arrive sometime in the next decade.

Anyway, I gave one Pixie plus switch to N6VCW to keep him busy and, since I had some spare time waiting for NorCal 40A parts to come, I put the other package together. Here are some pictures.

Now, I am not sure if the kit works correctly or not. It seems to be constantly on transmit so I have to go back and debug the circuit but, for as simple as it is, I followed the parts placement diagrams very carefully. I am guessing I will have to review the circuit and double check the details. But, suffice to say, it was good soldering practice and seems to emit a clean signal. It hears quite well on 40m -- at least from my signal generator -- and the front end is as wide as a barn door. There's also the added bonus of being able to listen to KFI out here in Southern California on 640 Kc.

So an Collins 75S-1 or a Hammarlund HQ-180 it ain't!

Sunday, March 25, 2018

NorCal 40A 30A build starts at last..

O.K., this is really it! I am starting the NorCal 40A build -- except that I am building it for 30 meters since I already have a 40A in hand that I scored at TRW from a seller for a decent price. I tuned that one up and adjusted its output to 995 milliwatts so it could rightly work QRPp. Quite a few Qs for the few times it was used, actually. One of my faves was the Maritime Station at Bolinas Beach, KPH. The ham station 700 miles from my QTH, K6KPH, was worked twice and represented an exhilarating accomplishment for me.

Since then, I ordered a NorCal 40A form Bob Dyer at Wilderness Radio before he retired. That kit still awaits the soldering iron. But, in addition to the 40A kit and the KPC1 keyer and frequency enunciator unit, I ordered an additional labeled blue face plate for the original 40A as shown above.

Some time later, in conjunction with K7QO's QRP-Tech 25th Anniversary GOTA project, I ordered the boards form China (surveyed here) and am, as we speak, beginning the 30m effort in order to document WB6JDH's effort. By the way, visit Chuck's website here for additional notes and links to his videos. He has even kept notes on his assembly work that bear looking into. And, finally, the site has links to the videos he produced. Also, I did a page on these for convenience.

A couple of months ago, I had gone up to Dick's house to do some preliminary recon work..

..but had not dug into the project until now. Starting out without anyone looking over my shoulder, I had to take the bull by the tail, as it were, and look the problem squarely in the face. At first, I was going to build and test sections at a time but, after reviewing K7QO's videos on this, I decided to proceed with stuffing the "generic" (i.e., non-band-determining) parts and then do Chuck's basic tests before Dick and I got together to make notes on just how to get the radio on 30 meters.

When that is done, it will be written up here and constitute a rough tutorial on how to build the 30 meter version for anyone who has built a 40A before. So stay tuned.

Along the way, some discoveries and assumptions have been made. Basically:
  • Wayne Burdick of Bob Dyer apparently had a barrel of 0.047 disk caps that he used liberally throughout the kit. Standard 0.1 caps can be used in lieu of these.
  • Q1 is specified as a 2N4124 NPN transistor but, according to Jim Kortge, K8IQY, a 2N3904 is an acceptable substitute. (Note that a 2N2222 is not acceptable.)
  • An MVAM 108 is an acceptable substitute for the called for MVAM 108.
Further bulletins as warranted.

At first, I thought about laying out all the parts on a Styrofoam board to inventory them. But since the project was behind the power curve, I just stuck them into the board figuring that was as good a way as any to see what went where and what was needed. Guess the results can be rightfully described as "the porcupine".

Here's a few shots of the work to date.

UPDATE: See the picture below.

Monday, March 19, 2018

Astron Supply back in the land of the living..almost.

After a couple of family emergencies and a small cold/flu attack, this project was finally buttoned up. I reinstalled the charging ports and the meter. as you will see in the pictures below. However, this time, I added a diode and a fuse to negate my reverse-biasing and blowing the pass transistors to high heaven. Here's the screamingly simple circuit; no challenge here - except to install in the supply. Not great wiring, but it'll do.

Try not to be overwhelmed by the complexity of this circuit!

..and here's the pics.

And, no, I did not cut out a hole in the front panel. The steel is pretty thick and doesn't nibble readily. If I need to convert the supply back to "sorta stock" there are fewer/smaller holes to plug. Also, don't get nervous about the meter showing 14.01 volts. It reads a little high. The adjustment pot on the regulator board was set to 13.9 VDC whuich is a good compromise for running test radios and topping off my gel cells., back to the NorCal 40A project.

Friday, March 16, 2018

Spare to my needs: Paddles..

I am a pack rat and have a habit of accumulating stuff to the point of redundancy. Lately, I am girding my loins for an April-May foray into rejuvenating my Morse code [questionable] talents by way of the infamous CW Academy. In casting about the shack/clubhouse/workbench, I noted that I was overflowing in the CW paddle category and sought to disburse these who are desirous of same.

Of course, these are offered at a fair price but are in decent condition. Herewith a description, comments, and pictures.

This came to me many moons ago via the TRW Swap Meet and was my main weapon of choice for many years. When my father (N6ABV) passed away in 1992, I inherited his Bencher BY-2 (the chrome base model) and was using that. My BY-1 was stored lovingly (i.e., not out back in the garden near the water spout or near the septic tank overflow nozzle), has been cleaned and adjusted and is ready to get back into the game. As I was cleaning it and testing it, I was surprised at how really good it was -- in my opinion, as good as the BY-2. If space were not a premium and since I only have one code fist..

This paddle poses the question: was there a Code Warrior Senior? (No, there was not.) Anyway, I picked this up after one or two waltzes with the NorCal Paddle Kit released in 1997. Remember?

Those were actually incredibly marvelous little items given the price and -- with a little care -- the resulting product. And, except for the plastic paddles, they were also pretty rugged. No Italian $500 shack queen here, they could be taken out to the woods, ridden hard, and put away wet. But you had to take along a set of drilled out guitar picks just in case!

When Vibroplex came up with these, I got a set and, true to form, the plastic paddles gave up the ghost. Instead of some famous rocker's signature guitar picks, I used a thin piece of copperclad PCB painted black. To my wonderment, they were better than the thick plexiglass originals.

Here's the pictures:

Hope these go to a good home.

Wednesday, March 14, 2018

Beyond Astron Revitalization: Protection..

So we got here because the genius that I am thought it would be cool to re-purpose an Astron supply to charge batteries as well as provide power for radios I was checking out. Sadly, when the mods were done, I zapped the PS and launched the series of posts below to restore it to normal. Still faced with the prospect of making my contemplated mods non-lethal, I sent the following email to my dear friend and trusted resource, Dick, WB6JDH:

I finally got this beast squared away -- as in back to normal before I modded and zapped it. But I have a question regarding my mods and how to prevent a re-occurrence on the problem; Here is the product I am using to display the battery charging aspect of the PS:
As you can see, it has a schematic on the back of the device. Also, it is shunted for 20A -- hence the circuit shown above. However, I am not putting this "in series" with the whole power supply in order to have it show current draw as I am downright nervous about running an actual 15-20 amps through this meter; I am not willing to push it.

I will be using the PS to do two things:

(1) Power 12VDC radios that I am testing -- which I will do on reduced power and well under 15 amps.

(2) Recharge my gel cell batteries -- which draw only about 2 amps max.

The gel cells will plug into the front of the PS as shown below. The normal back post terminals will power radios being tested and the meter will be switched out of the circuit by the front panel switch.
So here's the question: is it sufficient to put a diode on the positive line to the banana jack in front to prevent battery back washing and protect against reverse polarization and frying my pass transistors as I did before? Or should I also add a reverse polarization diode across the lines as well?

Some guys on the repeater builder's site have described putting a diode of sufficient size across the C-E junctions of the pass transistors but I felt that since the battery charging part of the circuit would be switched in when used, that might be overkill.
Your faithful servant, etc.
Anyway, in preparation for Dick weighing in on this, I did some research and came up to the realization that merely slamming a diode into line solves the problem by incurs a 0.7 VDC drop and, in the case of the charger, would force me to run the PS at about 14.5 VDC to effect gel cell charging. This would, of course, might not be so peachy for the 12 VDC radios I want to bench test. So, in studying alternatives, I came across this video:

Now, the first and third methods are flat out unworkable as I want to keep it simple. The diode across the power leads with the fuse in line appeals to me as being a direct solution. The downside, of course, is the prospect of mounting a fuse somewhere. If it is inside the PS then I'd have to unscrew the case every time I sinned, But, then again, that would teach me a lesson.

This video explains a more sophisticated solution and I might consider that:

..stay tuned, still pondering.