Tank Coil Calculation

[W9ZSL]

Scored this coil assembly and heavy-duty band switch so I could ditch the low-power rotary inductor shown in the photo.  Now.  I know how to calculate the inductance of the wire end of the coil but the tubing and ribbon calculations have me stumped.  I suspect I'll probably have to remove some of the 16 turns on the wire end because similar coils like the AirDux 195 only have 12.  Any suggestions?  I know I'll need help when wiring it as far as determining taps, but for now I'd like to know the TOTAL inductance of this thing.  Thanks!
Mike
W9ZSL

[Pete, WA2CWA]

Calculate each coil separately and then add them.
You can use this coil inductance calculator to get in the ball park: http://www.66pacific.com/calculators/coil_calc.aspx

[W9ZSL]

Doesn't the gauge / diameter of the wire / tubing / ribbon effect the final total?  The wire end is no problem but what about the tubing for instance?  Does the same formula apply?

[W4AMV]

Hi Mike,

A lot of work in this area. Yes, the mutual coupling modifies the prior formula (Wheeler formula) and the mutual is driven by wire gauge (diameter).

Try this, see the formula at the bottom of the page:

http://www.microwavecoil.com/Design%20Guides%202008.pdf

Or do a search under solenoid inductance calculator with thick wire. Have used the above with good accuracy.

[Pete, WA2CWA]

Doesn't the gauge / diameter of the wire / tubing / ribbon effect the final total?  The wire end is no problem but what about the tubing for instance?  Does the same formula apply?

The diameter of the coil is measured from the center-to-center of the wire on each side of the coil so the diameter of the wire is taken into account. Look at the diagram. The ribbon coil would probably skew the calculation a small amount.

[W9ZSL]

I'm not too concerned about the ribbon.  In any event, this should definitely get the job done! 

[W4AMV]

I believe Wheelers formula is based on a close wound solenoid, yes the diameter is taken into account, but if the turns are spread, the calculation is off.

I attached a simple xls file. Please check for errors! You can put the other formula in there as well and compare. All units are in inches.

[Jim, W5JO]

See if this will help you

[W9ZSL]

Thanks Jim.  This looks exactly like Air-Dux but has no markings what so ever.

[KD6VXI]

On lower bands,  the interconnect ribbon / strap is negligible.

As you get up there (17 meters to 10), I found the length of strap IS enough to throw the Q off.

What I do is:  set Ctune for the calculated amount,  subtracting Cstray and Cout.   Then,  set Cload l so to the calculated value.

Run a VNA into the antenna jack,  relay keyed and all hv and screen / control grid voltages off.  With the calculated load resistor across the tube anode to ground,  set the tap on  inductor,  installed in place,  for 50 ohms on the VNA.

Your operating Q is where it's calculated at,  not some arbitrary value.

Again,  this plays more in  higher bands,  where Lstray is a significant part of the tank circuit.

--Shane
KD6VXI

[Jim, W5JO]

Thanks Jim.  This looks exactly like Air-Dux but has no markings what so ever.

It is Air Dux.  No one else made anything like it.  I built a 4-1000 amp using the 195-2 back in the early 70s.  I used the information on that page to make all taps and it worked first time.

I have a couple more sheets with calculations and information for Pi network design that covered a lot of the Air Dux stock but didn't scan it.  It is faint and would be hard to read, but if you want it, I can try.

[WD8BIL]

No need to remove any turns. Just wire the switch in a shorting mode.

[W9ZSL]

Jim, did you design your amp or find it in QST or a handbook?  It would be interesting to see how you tapped it , where and how it compares to the Orr. 

The 1962 Orr Handbook also has an amp using one of these and it gives all the instructions for tapping.  I don't have any test equipment except for multi-meters, but I can use that for starters.  Right now my project #1 is the resurrection of that Heathkit AT-1.

[N2DTS]

It should not be critical.
I make all my coils out of copper tubing and have a bunch of different ones.
I plug them in on Banana jacks and tried different ones on different bands and they all seem to work about the same. The tuning and loading points change, but power output, efficiency and dip all are about the same if its in range of tuning.
I suppose the actual Q is all over the place, but it does not seem to matter much over a wide range.
I can even plug in my 80 meter coil for 40 meters and tune it up and it works fine, same power out, same current on the final, no harmonics noticed.

Some people over think things sometimes but you just have to be in the ball park.

[Jim, W5JO]

Jim, did you design your amp or find it in QST or a handbook?  It would be interesting to see how you tapped it , where and how it compares to the Orr. 

The 1962 Orr Handbook also has an amp using one of these and it gives all the instructions for tapping.  I don't have any test equipment except for multi-meters, but I can use that for starters.  Right now my project #1 is the resurrection of that Heathkit AT-1.

I designed and built it myself using the sheet that I posted along with the other sheets that I have that I did not post.    Look closely at the directions on the 195-2 paragraph, then follow the directions contained in the table.  Each point on the diagram of the coil (A, B, C, etc.) will give you the inductance at that point.  You choose the capacitance for the input and output of the tank based on that value.  They are all pretty much standard values.

I have a 21st edition of the Orr book and it contains about  the same information on the sheets I have.  Everything was based on a Q of 12 and was AB1 as I recall.  I had a BC 610 HV transformer and a lot of capacitors to filter it.  I followed construction practices I learned from my mentors and applied them.  If your switch is a shorting type, you are in luck, if not you will have to do some adjusting of the taps.  Not a lot of fun.