Good Finds at the "Firecracker"

[KC4VWU]

Found some good repairable jackbar coils. I don't know the ratings right off, but I would suppose the larger ones would handle full snot. Parts list is just about complete now.

Phil

[WQ9E]

Nice find! 

Seems like not many people want to fool with link coupled output so it is getting easier to acquire these coil sets.  I have 3 link coupled rigs (a homebrew, Halli HT-19, and Globe Champ 175) and these generally stay on 1 band so the plug in coils are not a nuisance.  It would be fun to see a home movie of a 30's era contest op changing bands with a HRO receiver and a multi-stage HB rig with plug in coils.

[k4kyv]

I think my speed record for changing all 5 coils in the HF-300 rig, retuning and running out to the tower to reset the antenna tuner and back to the operating position, was just a little over 2 minutes.

Now, it would take me longer because I am a little out of practice.  I have 3 separate active transmitters, and keep one tuned for each of the bands I usually operate, so to change bands I just turn on the rig that is tuned to the band I want to get on.

I still have to run down to the tower (actually walk; I am not as physically agile as I used to be) to change bands or QSY across a major portion.  Soon, I'll be able to use the reversible motor and worm drive to QSY remotely, but will still have to go to the tower to change bands until I come up with a way to rotate the selector switch by remote control with foolproof reliability.

[W3SLK]

Was this the Firecracker in Harrisburg,PA?

[Opcom]

I do not mind the idea of changing coils but since I am not used to it, I worry there could be an accident with the voltage some day because I change frequency frequently. Even with an interlock, stuff can happen.

[WQ9E]

I still have to run down to the tower (actually walk; I am not as physically agile as I used to be) to change bands or QSY across a major portion.  Soon, I'll be able to use the reversible motor and worm drive to QSY remotely, but will still have to go to the tower to change bands until I come up with a way to rotate the selector switch by remote control with foolproof reliability.

Don,

What is your switch layout (number of positions, degrees between, continuous or stopped rotation)?  I saw a vintage Navy coax switch at a recent hamfest that used a hefty 28 volt gear head motor to rotate the attached N type RF  switch and had a separate keyed switch section and selector cam that controlled the motor rotation.   The owner was demonstrating it and it very surely and accurately selected the proper connector.  A design like this might be the ticket but unless you are married to the actual switch some heavy duty relays would be a lot easier to implement.

[k4kyv]

What is your switch layout (number of positions, degrees between, continuous or stopped rotation)?  I saw a vintage Navy coax switch at a recent hamfest that used a hefty 28 volt gear head motor to rotate the attached N type RF  switch and had a separate keyed switch section and selector cam that controlled the motor rotation.   The owner was demonstrating it and it very surely and accurately selected the proper connector.  A design like this might be the ticket but unless you are married to the actual switch some heavy duty relays would be a lot easier to implement.

Here is a photo of the switch (Fig. 1).  The total length is about 15".  It is 5-pole 10 position, with 5 identical ceramic wafers.  I cobbled it together by disassembling several large ceramic switches similar to what is shown in Fig. 2, and then re-assembling the parts.  Some of the mechanical parts were fabricated from an old 1/4" thick rack panel and stuff already in the junk box.  The shafts of the two sections would not line up precisely; one or both were slightly eccentric, and the assembly would bind at certain positions.  I cured that by linking the shafts together with an Oldham coupler removed from a junked-for-parts T-368 master oscillator unit. The kind of switches I used for parts is shown in Fig. 2. Since the switch has 10 positions, there is 36° of rotation between positions.  Actually the switch is only 9-position, since the 10th slot is occupied by the wiper contacts on the wafers.

The purpose of the switch is to select which one of five separate tuners the feed line from the shack (either coax or open wire) feeds into, and which one of three of those tuners feeds into the open wire line that goes to the dipole or which one of two tuners feeds the vertical tower. This will use up 5 positions and 6th position will connect the line from the shack directly to the open wire line to the dipole, bypassing the tuners altogether. The remaining 3 positions will not be used.  I may remove all unused contacts from the switch wafers to make the switch easier to turn. The separate tuners are all adjusted to frequency using five individual bread-slicers ganged together and rotated using a reversible DC motor and worm drive assembly.

One method I have thought about would use a large diameter wheel with a worm drive.  I once had just the thing, an 8" diameter wheel with worm gear that was used in a broadcast transmitter to operate the plate voltage rheostat.  I have a bunch of micro-switches with the little roller assembly, so I believe I could fabricate a cam assembly to use with the switches to turn the switch. Unfortunately, I let the BC transmitter worm drive mechanism go about 20 years ago.  Another example of why one should hold onto unique one-of-a-kind items for which one can think of no immediate use.

The switch requires quite a bit of torque to rotate manually, but this could be greatly reduced by removing the indexing springs and lever mechanism, if I can come up with a remotely controlled configuration that does not need mechanical stops.

This switch didn't cost me a penny, since I had all the parts on hand and did not have to buy even a single screw or washer.  But I have worked on it for several hours almost every day for over a week, so if I paid myself a reasonable wage, I would undoubtedly have several hundred dollars invested in it.

To use relays, I would need at least 5 heavy duty DPDT relays with wide spacing between the contacts.  The cost would undoubtedly be prohibitive to purchase brand new ones, and I don't think I have seen a total of that many of the kind of relays I would need, at hamfests in my whole life.

[WQ9E]

Don,

How about driving the switch through a small TV rotor or other 1 to 2 RPM high torque source.  Use a connecting shaft that is either spring or flex rubber coupled providing a little bit of slippage to allow the the detent selector in the switch to provide the proper indexing and one additional 36 degree indexed wafer to drive a set of 10 LED's to indicate the contacts selected.  You might be able to depend upon the indicator if you use an antenna rotator drive but the lights would provide a sure and more convenient indication.

[WD5JKO]

I still have to run down to the tower (actually walk; I am not as physically agile as I used to be) to change bands or QSY across a major portion.

Don, That walk to the tower might be good for your heart, especially if it is a vigorous one. Seems that many of us OM's don't get much exercise these days. We got to do something since many XYL's don't appreciate being chased around the house after exiting the shower. 

Jim
WD5JKO

[KX5JT]

"We got to do something since many XYL's don't appreciate being chased around the house after exiting the shower.  "

But some DO! 

[KC4VWU]

This firecracker fest was at Salisbury, N.C. Did anyone else make it?

Phil

[k4kyv]

Don,

How about driving the switch through a small TV rotor or other 1 to 2 RPM high torque source.  Use a connecting shaft that is either spring or flex rubber coupled providing a little bit of slippage to allow the the detent selector in the switch to provide the proper indexing and one additional 36 degree indexed wafer to drive a set of 10 LED's to indicate the contacts selected.  You might be able to depend upon the indicator if you use an antenna rotator drive but the lights would provide a sure and more convenient indication.

I have thought of that.  I use a similar motor to rotate the tuning capacitors. I am not sure if the stock detent spring and cam would work satisfactorily, however.  The cam uses v-shaped notches, but the upper points of the Vs are cut off so that there is a small flat spot on top of each one.  This makes it easier for the roller to pass over, but sometimes the contacts don't settle in exactly at TDC until I manually wiggle the control lever.  This was the way those switches were designed, but the springs and detent levers could be removed and a better detent mechanism outrigged. Actually, I would prefer some kind of servo system if I could come up with a design and the needed material were available.

The idea of led's to indicate the contacts selected is probably not the most practical solution.  I have looked  through literally hundreds of switch wafers of a wide variety of construction in my junk box, and every one of them is indexed at 30 degrees, regardless of the number of actual contact positions. Apparently, 30° is the universal standard for rotary switch indexing and my 36° ones used to make up this switch assembly are oddballs.

The other problem with 6 to 9 LEDs is that each one would need a separate conductor back to the control point.  I think a better solution would be similar to what I am using to indicate the capacitor settings; a pot or (correctly indexed) rotary
switch with fixed resistors, to feed a specific voltage back for every contact selection.  For example, position 1 could be adjusted to 1 volt, position 2 to 2 volts, etc, and a 0-6 DC voltmeter at the control  point would directly indicate which of 6 positions is selected, and unused contacts would show up as zero volts. That way one pair of wires would do the job.

The idea of using a TV antenna rotator sounds good, until you look at the prices of TV rotators these days.  I haven't seen a used one at a garage sale for years.  It's been so long since most people have used a rotatable rooftop TV antenna that 99% of them are undoubtedly rusting away in a landfill. And don't even think of buying a light-duty ham antenna rotator.  I wish I had one for my rotatable receiving loop, but I think even the smallest TV rotator would take up too much room in the space available in my antenna dog-house.

[WQ9E]

Don,

The old Alliance units (offset mount, meter readout with directional bar on top from the 50's/60's) are a common hamfest and garage sale item here.  Maybe the rotors were more common here in the Midwest or people held onto them longer but they are easy to find.  I used one with my 2 element quad when I was newly licensed.

My idea of using the LED indicators was you could use a smaller contact centered within the contact range of the main contacts to show accurate closure.  Since this is a low current/low voltage contact you could make your own switch wafer out of printed circuit board material. 

I have an old DC powered coax switch here (also Navy surplus) that I will dig out and take a photo of the mechanism; perhaps that will give you some construction ideas. 

[k4kyv]

Since this is a low current/low voltage contact you could make your own switch wafer out of printed circuit board material. 

I had thought of doing just that, just letting the main switch indexing do the work. I have seen pieces of commercially built equipment that had a switch wafer etched right on the main circuit board with the rotary contact mounted on little standoffs.

I have an old DC powered coax switch here (also Navy surplus) that I will dig out and take a photo of the mechanism; perhaps that will give you some construction ideas. 

Thanks. That might be helpful.

I'd bet that over  the years I have passed by several pieces of military or industrial surplus equipment at hamfests that contained just exactly what would have done the trick, but I didn't have the specific use for it in mind at the time.

[K5UJ]

Those are some nice looking coils you got there at the hamfest.  I'm glad to know these things are available because I just joined the link coupled tank club and some of the coils I got have been damaged.  They may be fixable with good old JB Weld.

Rob

[k4kyv]

I wouldn't use JB Weld.  It has fillers mixed in with the epoxy, and I'm not sure they are RF transparent or have good dielectric characteristics.  Try 2-ton Crystal Clear Epoxy.  It takes it a long time to set and harden, but it holds very well and as far as I can tell, is an excellent RF dielectric.  Besides, being almost 100% transparent, it looks better on ceramic or plastic.

[K5UJ]

Rats.  I used JB Weld to repair a porcelain shaft decoupler    Well I'm glad I learned about it before I used it on anything else. 

[k4kyv]

I wouldn't worry about that.  A shaft coupler is not right in the middle of the high intensity rf field of the coil like the insulation is that holds the link and coil itself together.

Another thing to beware of is using iron, steel or any other ferrous metal in the hardware associated with the rf circuitry, or anything that carries considerable current of any variety.  Brass is the preferred material, but aluminium is OK too. Copper would be best, but I have never seen nuts, bolts and screws made of pure copper other than split bolts used for splicing electrical wiring. Ferrous hardware can be a problem at 60~ a.c.  I had a problem with a flaky pair of 866s in my medium voltage power supply.  It turned out that the nuts holding the wires to the tube socket terminals were of steel.  I happened to touch one, and received a 2nd degree burn on my finger.  I replaced the steel nuts with  brass ones, and immediately the voltmeter registered proper filament voltage at the tube socket, the connection stayed cool to the touch and those 866s never sputtered at me again.

[NE4AM]

The black filler in JB Weld is Iron Oxide - yeah, the stuff will stick to a magnet.  Depending on where you use it, it may be OK - but never near the coil in a VFO circuit! 

73 Dave

[K5UJ]

okay, thanks for the information on JB Weld.  I'll get some clear epoxy and go to work on those coils!  Also Thanks Don for the advice on steel hardware.  I would have probably never thought of that myself and would have gone ahead and used s.s. nuts and bolts on the RF junctions if they were the only things I had.

Rob

[k4kyv]

The black filler in JB Weld is Iron Oxide - yeah, the stuff will stick to a magnet.  Depending on where you use it, it may be OK - but never near the coil in a VFO circuit! 

That filler must be powdered iron or some alloy of iron.  Iron oxide (rust) is red, not black, and is not attracted by a magnet.  I don't recall the exact physics and chemistry of it, but when iron atoms combine with oxygen, they lose their magnetic properties.

[K5UJ]

I got me two tubes of Devcon 2 ton clear crystal epoxy and went to work on two of the B&W TWL jack-bar split, link-coupled coils I got.  The coils are held on the porcelain banana plug bars with a sort of plastic air dux coil holding material B&W used.  this plastic has cracked, fragmented, deteriorated and is falling apart.  Maybe the coils were stored in an attic or something for years.
When I started slathering epoxy on them with a Q tip the material went to pieces on me.   I had the coils hanging upside down from file cabinet drawer handles with paper spread out on the floor under them.  I cleared off the broken old material and I think I have enough epoxy on them to hold them.   

I went looking for them for sale used on-line and only place I could find was $urplu$ $ale$ where they had the 80 meter one for around $100    Glad I already got that one.  In fact, I'm in pretty good shape.  I have 160, 80, 20 and 15.  Probably will never use the high band ones.  I wouldn't mind having 40 and was thinking I might be able to add on to the 20 meter one to make it a 40.  But, I'll probably only use the rig on 75 and 160 with the signal shifter. 

[KC4VWU]

Rob, It's best to cut some replacement strips out of Lexan to replace those old plastic ones on the coils. You know how the older plastics of those days holds up. If I can ever get the Dell back up, I have a copy of a nice article on coil winding I'll send you; it really works great and produces a nice piece. I wonder if a nice thick piece of phenolic material could replace the ceramic jackbars? I may try to homebrew a couple.

Phil 

[K5UJ]

okay Phil thanks!

Other big news:  Mystery solved--guess what guys, I don't have a HB 813 rig after all.   It turns out the rig I got is an Eldico TR-1:

http://www.rigpix.com/mischam/eldico_tr1.htm

[k4kyv]

Epoxy will stick to the old coil insulating material OK.  Most of them used what was called cellulose acetate.  It is not thermoset not thermoplastic; you may notice that heating it just makes it turn brown like wood, but it doesn't melt.  More recently manufactured coils were made of polystyrene or some other thermoplastic material.  It doesn't usually self destruct like the older material, although UV destroys polystyrene.  I learnt that the hard way when I used polystyrene rods to make open wire spreaders.

Cellulose acetate shrinks over time.  I have actually seen it cause the ceramic plug bars to break in two.  It turns sort of an amber brown, like old paper, and eventually turns into a powder.  It loses its dielectric qualities as well; I have had the insulation to heat up and a time or two burst into smoke or flames while the transmitter was in use.

Epoxy sticks less well to plexiglass, but I  have had it to work OK.  Best to use plexiglass cement, which is nothing but ground up plexiglass mixed with a solvent to achieve the consistency of model plane glue.  You can buy the solvent in pure liquid form, and use it to "weld" plexiglass together.  If done right, the repaired part is just as strong as the original.

Epoxy (without filler) is said to be an excellent rf dielectric.  There was an article in QST several years ago about making air core coils and moulding the strips of insulation round the wire using liquid epoxy.  I forget exactly how they  made the moulds, but I know there are certain materials that won't stick to epoxy.  I once worked in a factory where they used some kind of liquid teflon solution to coat pieces they didn't want epoxy to adhere to, and it worked 100% perfectly every time.

I have repaired old coils using clear epoxy many times, and if the original stuff isn't so far gone that the rf heats it up, the repair seems to last a long time.