Print

[W1VT]

I need an english version of his 9:1  info.   As is,  all that I can figure out is he used 1.5mm  wire.   I can't figure out what type of core was used, or core OD,  ID, and height.

If a photo of the finished unun is available, and some are, you may be able to use the wire dimension to estimate the other dimensions.

Zak W1VT

[LZ1HD]

Hello Jim VE7RF, I manage to translate the text from the dg0sa.de site by marking and copying the text and then pasting it into google translator. As far as I know, all the transformers described in this site are made with toroids from Wurth Elektronik with material 4W620 - it is with permeability 620. For your case, I think the 200 watt version of this transformer is suitable. Only one place in the description is marked with the number of the toroid and it refers to a 1: 1 balun, I guess the 1: 9 transformer is made on the same core. It is 7427015 Mfr. No. the dimensions are: 40.6/27.4/15 in millimeters. Looking for a Fair-Rite replacement, I think it is 5943018601, Mouser have such in stock.
At the beginning of the description on the site are listed the materials used. For 1: 9 transformers, a copper wire with a diameter of 1 mm (AWG18) is indicated and required length 1.5 m (150 centimeters).

Veselin LZ1HD

[KU3X]

Jim,
Here is my 9 to 1 (50 ohm to 450 ohm) UnUn.

https://drive.google.com/file/d/16EbXf_5if1cShfYMPJDhZnf9YqhrFuww/view

Sorry for the quality.

I made it on an FT 140-43 core. Two of the wires are #18 enamel wire. The center wire is #20 teflon insulated wire. The reactance on the high bands is pretty good. It's the wire's impedance that is mostly causing the elevated SWR on the higher frequency. You could experiment with a different center wire or just change the spacing a tad. I don't think by shunting a capacitor across the input will correct the problem? Try it anyway. At least this gets you a lot closer or maybe even usable for your needs.

As mentioned by other's, "Keep those lead lengths short. " Run coax to the UnUn and place the UnUn close to the input resistor.

Barry, KU3X

[VE7RF]

Tnx to both LZ1HD..and also KU3X for the info.   We will proceed with caution.  It appears the spacing between the 3 x windings is key to lower swr on 10m.... at least on dg0sa's version.   Anything has to be better than  3:1 on  10m.

[KH6AQ]

If the grid capacitance exceeds ~20pF the SWR will begin to rise at 20MHz. The magnitude of the grid capacitive reactance then exceeds the 450 ohm swamping resistance.

What tube(s) are being used?

[VE7RF]

If the grid capacitance exceeds ~20pF the SWR will begin to rise at 20MHz. The magnitude of the grid capacitive reactance then exceeds the 450 ohm swamping resistance.

What tube(s) are being used?

See  post  #14

[KH6AQ]

It looks like it would take more than a 450 ohm swamping resistor to drive the 8281 tube thru a 1:4 unun above the 40 meter band.  At 5 MHz the grid Xc is -J450 ohms.

4CX15000A Datasheet: https://frank.pocnet.net/sheets/140/8/8281.pdf

Cin grounded cathode: 160 pF

[VE7RF]

It looks like it would take more than a 450 ohm swamping resistor to drive the 8281 tube thru a 1:4 unun above the 40 meter band.  At 5 MHz the grid Xc is -J450 ohms.

4CX15000A Datasheet: https://frank.pocnet.net/sheets/140/8/8281.pdf

Cin grounded cathode: 160 pF

Relax,  the amp now runs like a  swiss watch.....  (+73dbm)   Your maths are way outa whack. 
At  2.21 mhz,   160 pf =  450 ohms of  XC.
At  3.84 mhz,   160 pf =  259 ohms of  XC
At  5 mhz,   160 pf =  199 ohms of XC
At  29 mhz,   160  pf  =  34.3 ohms of  XC.

At  2.21 mhz,   32.4 uh  =  450 ohms of  XL
At   3.84 mhz,   10.75 uh = 259 ohms of  XL
At  5 mhz,        6.35 uh  = 199 ohms of  XL
At  29 mhz,      .188 uh  = 34.3 ohms of  XL

The  variable coil in parallel with the 450 ohm globar, cancels out the tube C....leaving just the  450 ohms...which is matched to 50 ohms with the 1:9 un-un.