Dual Rectifier Adapter

What happens when there is no more stock of 6H6 dual rectifier tubes, but plenty of 6AL5 tubes?  This situation clearly calls for an adapter.

Take a base from a dead tube and remove the tube by breaking it and de-soldering the leads.
Take a tube socket from an old TV chassis and wire the leads to match.

The result is a convenient adapter that can be applied to a classic radio without making any modifications to the vintage equipment.

6H6       6AL5
  2              4
  7              3
  5              7
  3              2
  8              1
  4              5

FT-8900r repair - pre-driver

This particular Yaesu FT-8900r came from a repeat customer of the Cly Institute.  He delivered the bare board for the repair saying to change the final transistor, and even supplied the correct part.  The process was done, but that did not cure the problem, there was still no output on transmit.

With the now fully re-assembled transceiver, the debugging process started by stepping back from final transistor gate to discover where the transmit signal was being lost.  It didn't take long to find the gate of the pre-driver transistor had the transmit signal. This meant that the pre-driver was not functioning.  Surprisingly pressing down on the chip re-established output.  This turned into an easy fix by re-sweating some solder under the chip.  In our experience at the Cly Institute, the RoHS solder they are using today is pretty poor for higher vibration applications.  We only use Lead solder for repairs trusting in its age old reliability in soldering applications.

This would have been the end of the repair story, however with the transmitter set to HIGH output, the final stage began to ring, causing a tone on the received audio, and likely some spurious emissions.  It had to go back to the bench for investigation.  In the process of replacing the final transistor, the chip capacitors had to be removed surrounding it.  This was the likely culprit that one, if not all were overheated and no longer performing their designed task.

The original capacitors were rated 50pf at 500vdc.  They were not ceramic, and were likely heat-damaged during the process of replacing the final transistor.  New ones were only a eBay order away.

The areas circled in red are the ones that were providing trouble.  The solder joints around Q1137 were an issue.  I had to add some serious heat to this transistor to get it re-flowed, but trying to keep the body cool by holding a cold metallic tool on the top of the chip.

Note the new ceramic capacitors around the final transistor Q1134 in the picture above.  These are much higher quality than the original capacitors.  They can take a good bit more heat and should be more stable throughout their lifetime.

The radio was held in transmit attached to a dummy load for an excessive time.  It did not overheat on high, and it did not drop power.  I listened to it through the radio I keep in the shop, and it did not oscillate or produce any spurious tones.  Its time to box it back up and return it to the customer.

Lionel J-38 restoration better than factory

A recent sale of equipment from a local SK presented the opportunity to purchase a Lionel J-38 straight key.  I had been using a JJ-38 Japanese-made key, which was functional, but not nearly as classic as an original.  I snapped up the J-38 despite the tarnish.

The J-38 was designed to be used by the Signal Corps.  This example is missing the bar across the back along with two of the binding posts.  The shorting bar was designed to be closed for listening mode, and open for sending.  For the modern ham, this feature is convenient for tuning up the finals in a tube amplifier by closing the switch and adjusting the tuning and loading controls without having to hold the key down.

The ugly mess you see here is the result of years of laying in a box unused.  Each fastener is brass and can be brought back to a high luster with the right application of elbow grease and Mother's Polish.  The first part is getting the components clean.  For this simple soap and water is enough.

The key is carefully stripped down.  Be very careful not to misplace the insulator parts.  The left side of the key is insulated from the cast base.  There are fiber washers and collars which must go together in the right order.  

The first pass is a scotch-brite pad to remove the top layer of dirt and oxidation.  The second pass is a wet sand with 2000 grit wet sand paper.  This will dull the surface slightly, but the third pass of Mother's Polish brings the brass to a high luster.  The final step is a spray finishing wax like Prestone or Maguires mist.  "The Lionel Corporation" is clearly cast into the frame, along with the stylized letter "L".  This model is particularly nicely styled with the Lionel logo right into the shape of the plate that makes up the bottom contact of the key.  This part was particularly hard to polish evenly.  I just kept at it until I was satisfied by a mirror shine.  Its not always about elbow grease when it comes to Mother's Polish.  Just let the chemicals do their work until the cloth turns black.  Shift to a clean spot in the cloth and wipe away any excess.

The fasteners can be placed in the chuck of a drill, spun at high speed against the polishing cloth to get the best uniform shine with the minimum of effort.  The jam nuts can also be handled the same way by letting the drill chuck grip the shoulder on the inside part of the nut.

The shorting bar was easy to polish after removing a large layer of oxidation.  It has a mirror shine to it.  When re-assembling be sure to put a small drop of oil on the collar of the bolt that retains it.  This insures smooth operation so that the fastener doesn't bind and start to back out of the base.

The finished product is one that any ham can feel proud to display and use on the operating table of the shack.  No J-38 looked this good right out of the factory and into the hands of a Signal Corp Trainee.  This example needs some appropriate cloth-covered wire and a 1/4" plug to fit into the key input of the radio.  I always recommend tinning the wire so that it doesn't fray when inserted into the binding posts.  Also a short piece of shrink tube at the end of the wire keeps the cloth insulation from fraying as well.

The nickel finish on the Japanese key is fine, but the brass is so much nicer.  The knurled nuts are larger on the Lionel and much easier to grasp.  The fulcrum points on the Lionel are actually points.  The ones on the JJ-38 are just squared off and have to be kept very loose in order to keep from binding up.  Here a side by each photo exemplifies the beauty of the original Lionel key vs the Japanese-made key.

73 ES GUD DX de N3FIX dit dit

Surface Mount repair - Lead Cut Method

The subject this morning is a USB to CAT CI-V interface cable.  Someone (not me) plugged it into the wrong 3.5mm port and blew the chip up so badly that the case was deformed due to the heat.  The chip was obviously bad, there are very few other chips on the board, so I just ordered a new chip.

Some folks don't have a hot-air desoldering tool for surface mount components.  So how does your average Plugger of ham get a multi-pin surface mount chip off the board without damaging the board?  When you know you have a ready replacement chip there's an easy way to remove it from the board.  Don't try to unsolder every lead and try to preserve the chip.  You will get frustrated.  Just clip the leads off with your best fine clipping tool or EXACTO knife.  Tip the chip up and clip the remaining leads.

I have a simple general use soldering iron as well, it gets a LOT of use.  I don't file my tip down.  I take it out anneal it in a and hammer it down to a fine point on the anvil.  The act of hammering it to a point makes the tip hard again.  I find it lasts a lot longer this way.  You will need a sharp tip on your iron to do this properly.

This is what makes it easy, just take the hot soldering tip and wipe it across the lands of the board.  The clipped off leads will stick to the iron and they will just be left behind when you dip the iron's tip in the cleaning sponge.  Easy!

Once the chip is off then using a set of helping hands and magnifying glass, putting the new chip in place is simple (provided your hands are steady and your eyesight is good).  The lands should be clean and only a tiny amount of solder is required to make the connection.

None of us are getting any younger, so using a eye loop and a magnifying glass in conjunction can be helpful too.  Hope you find these tech tips helpful.  de N3FIX at the Cly Institute for Radio Repair.

FT8 Wigi-Digi Survey

Amateur Radio - Receive Antenna Relay Box

Some older transceivers don't have a separate Receive Antenna Input jack.  A Receive Antenna can be a beverage, e-field probe, or other active antenna.  The advantages of using one antenna with lower noise on receive and a tuned antenna on transmit are obvious.

Since my IC-746 does not have this feature, I needed to construct a simple relay box.  The box would have three coax connectors, a connection to the rig for the send and power, and also a power output to source my active antenna.

The theory of operation is one that takes into account the safety of the transceiver and the active antenna.  The failsafe state is TX antenna position.  If the circuit fails to power up (or the fuse blows), the TX antenna will stay in circuit.  Likewise, if the circuit fails to power up, the active antenna will not get any power.  Only when the rig powers the relays will the active antenna attached to RX be connected and powered up.  The HSEND output from the radio likewise provides a safety.  It disengages the RX active antenna power through the Rp relay, and then subsequently drops out the Rt relay so that the rig may transmit into the TX antenna.

Here are all the parts on the table ready to assemble.  I chose an aluminum 6x4x3 BUD box since aluminum is much easier to work with.  I also have two 12 volt relays, one small one to switch the loads and one large one to switch the RF.  I kept the RF leads as short as possible, and also used shielded cable between the radio and the relay box.

The coax connectors were placed at a certain height so the relay would be very close to them.  Keep in mind that the general purpose relay that was employed in this project is not going to be good for anything above HF frequencies.  If I could have sourced an economical coaxial relay, that would have been better.  This would not work very well as a relay box for using your SDR as an separate RX radio.  (That may be a project for the future.)

The fuse protects the rig's ACC2 jack from excessive current draw.  The switch disables the operation of the relay box if the receive antenna is not desired.  The indicator illuminates when the RX antenna is in circuit and powered up.  The lamp goes out when the rig goes into transmit.

The wiring was done point-to-point to keep the leads short.  The control and power cable goes out the back bottom of the enclosure through rubber grommets.

The result is good.  The relay switches between RX and TX antenna when the rig is keyed and the switch is up.  When the switch is left down (in bypass), the RX antenna is not connected at all and all signals go through the TX antenna.

The final touch was to put some magnetic feet on it, so it sticks to the top of the radio.  Then apply the labels.

Amateur Radio - WARC band fan dipole

Welcome back to the Cly Institute for Radio Repair subsidiary of the Imp Barn. The institute wants to be capable on as many bands as we are licensed to operate on.

The WARC bands are three portions of the shortwave radio spectrum consisting of 30 meters (10.100–10.150 MHz), 17 meters (18.068–18.168 MHz) and 12 meters (24.890–24.990 MHz). They were named after the World Administrative Radio Conference, which in 1979 created a worldwide allocation of these bands for amateur use. The bands were opened for use in the early 1980s. They can sometimes be ignored by ham operators, but possess good opportunity for DX under the right conditions. My manual tuner works HARD to make my transceiver happy on these bands with my existing equipment for very poor efficiency, and very few contacts.

In researching the availability of antennas for these bands I found very little. Verticals are available from the usual sources, but the cost is prohibitive. (I didn't want to include 60m in this design either since my radio doesn't do 60.) The bands are nice and narrow bandwidth with little need to strive for obtaining wide bandwidth capability in a design. I normally run a commercial "fan" dipole which Alpha-Delta refers to as a "parallel" dipole for 80, 40, 20, 15, and 10 meters. What was needed was a simple wire solution. I was inspired by an article by W4DAN for this fan dipole design. The solution was simple, create a fan dipole for the WARC bands using first principles where the calculation is 468 / freq in Mhz = total length in feet for a half wave dipole.

 To reduce interactions between elements, I spaced them 6 inches apart. This may be excessive, but works fine. The center is an old 1:1: balun I found at a hamfest.

With the longest element of just over 23 feet in the center, the next longest on top and the shortest on the bottom.  A Dacron rope makes up the difference between the 17m and 12m element to reach the last spacer.

30m just over 23 ft

17m just under 13 ft

12m just over 9.5 ft

Here's a shot at dusk before the tuning process got fully underway.  We did all this work by flashlight in the dark.  This has few advantages, but at least the neighbors don't stare.  Its SCIENCE folks!

When tuning this antenna, I put the center up on a thin bamboo pole supported by my son's wooden swing set, and supported either end so that I could reach up at the end and grab it.  After getting the wire in hand I could walk hand-over-hand bending the bamboo pole down to reach the end of the element for tuning.  This was rather more like an Inverted-Vee arrangement which will result in slightly shorter lengths and will be ideal for mounting where there are no high objects to tie to.  At the recommendations of my elmers, I started with the 30m elements and tuned them to under 1.5:1 SWR.  Progression was to adjust 17m and then 12m elements.  I noticed little interaction between those elements while tuning.  I did jump back and forth once between 17m and 12m to get the tune just right.  The bamboo pole worked well for a temporary tuning setup.  A final mounting location is yet to be determined.

Using my VK5JST analyzer, we were able to get the tuning reasonably close.  I discovered that a simple technique to keep me from cutting too much off the elements.  It didn't seem to affect the tuning and I would encourage others to take advantage of this trick to enable you to re-tune an antenna in its final installation for perfect matching.

I folded the element back on itself and used a cable clamp to secure it.  The loop can be adjusted easily by loosening the cable clamp and re-tightening.  The element wire in the loop didn't seem to matter much, but I kept it to a minimum without too much wire involved in the loop simply for fine tuning.

Good high quality T-B ty-wraps were used to keep the spreading spacers taut with the 30m elements, and with the spreader near the feed point to keep everything aligned.  The ty-wraps can be adjusted slightly if needed but provide a good solid way of keeping the spreaders in place.  This is what Alpha-Delta uses, so why not!

Catch you on the WARC bands!