Appreciate your content here. I've become obsessed with antique and new Pi Wound RF coils ever since subjecting a big one to a ZVS output and was amazed to see big phat arc. Yes, it was very expensive.... I just had a brain storm and i bet yall will like it... Fishing reel could be used as is or modified to wind Pi. There's nothing like the real thing.
Great topic! Your presentations are very welcoming, and I like how you set a older radio booklet or magazine next to the project at hand. Well done and very informative!
You CAN make pi winding chokes. David J. Gingery wrote a book on how to "Build a Universal Coil Winding Machine", that describes the device. Such coil winders were once sold by Allied Radio and Lafayette Radio. When using a GD meter to measure the resonant frequency of the choke you need to use the lightest coupling. Otherwise the mutual inductance of the GD coil with the choke under measurement will throw the GD oscillator off calibration. That's why the GD measurement didn't agree with the test oscillator. Then there is also the effect of the parallel resistance you added that loads down the coil, and the resistor also has some inductance in it. I built a clone of the Heath HD-1250 and I added a sampling output from the MOSFET amplifier to which I can connect a frequency counter, so I can get more accurate readings. You may have more than 470pf across that home made choke, you don't have any way of measuring the distributed capacitance across the windings.
Well done Michael - very very informative. Having issues with a second hand homebrewed VFO currently and thanks to video will check the chokes very carefully. Looking forward to future updates on the TX.
Those multi pi chokes are not as perfect across a wide range as we all thought. They are a compromise and all have resonances and suck outs that can surprise the experimenter. Thanks for watching.
Lately I have been playing with the inductors found in old ATX power supplies. These can be purchased cheaply 10 for 10 dollars in 1mH, and they self resonate around 1 MHz, so useful maybe up to 5 MHz. There are usually a couple in any ATX supply that can be rewound to hit 100 uH to 4 mH if you use fine enough wire. they are the short black ones that have a bobbin style, finer wire and shrink over them. The ones with mini ferrite rods and a few turns of heavier wire and plastic molds were low Q and low value, so not really too useful at RF.
Good stuff. I'm selecting inductors for a tuned input. Settling on toroidal type. At 15:17 it sounds like you suggest the plate choke pictured was designed to not function in 11m. Would like more on how the grid dip meter works. Thanks for posting.
Very informative thank you for posting this. I can use this to assess my home-made IF transformer designs. I also have a winter project to built a coil winder that can do universal and honeycomb, sort of a micro-controller controlled version of a Gingery mechanical coil winder. Again, thanks for sharing this, I hope your project does well. Cheers,
9:23 Aka 'Natural Frequency' 28:28 I once read in Popular Electronics, or such magazine (30 yrs ago) how you could use a capacity meter to measure an unknown inductance, using a factor-constant to convert Farads into Henries
I did not touch on Toroid cores. So I had a few small Type 77 Amidon cores and I wound about 100 turns of #28 on one and it came out to 6.15 mH. So there is another approach.
I have built several mini-whip circuits and binocular cores of Type 73 material were used for the 470uH chokes in the bias-tee circuits. You can get about 15 turns of 30AWG wire-wrap wire on a BN73-202 core and I think this will give you around 1 mH of inductance.
Cores are also excellent and the good old Type 43 or better 77 or 75 work great. One or a few in series of the little Bobbin cores like RLB0608-102KL work good for many radio projects.
Neat coincidence...taught one of our General Class upgrade courses today including components, L and C, and the license manual topic strays into parasitic effects and self-resonance. Why those two topics are in that license class I'm not sure...want to see students' eyes glaze over? ;-) Anyway, got some great screenshots for adding to my slides for the next course...hopefully make SR more understandable for them from a practical view. TNX Mike! 73 - Dino KL0S
Hi Dino, Really wish I lived in your area then I could come listen to your talks. I really should start working on getting my license for real! Cheers!
@@vincei4252 Howdy Vince, wow, thanks for the nice compliment! When you get started if there isn't a class being held locally there are some pretty good YT series for all three license classes...check out W4EEY for example. 73!
@@PapasDino Thanks for the tips. Looking forward to getting certified to make sure that the black helicopters and SUV's don't turn up to my house after building a couple circuits :-)
Real pain to find then outrageous $$". Like Calrad Japanese vernier dials in small, medium and (impossible to find) large 3". All less than $2 or $3 except last dial which was about $8. Just a few years ago in 1975.
The old scavenged junk verniers are what I look for and when I see some at a ham flea market, I just buy them. I have a box. Typically I pay 10 bucks for a good one.
Good Question Scott. They look similar, but alas, no. There is no ferrous content in the rod, and thus there are no magnetic field intensifying effects. Rather there would be Q reducing losses. Carbon does make a good resistor!
If you can find a miniature choke that has a value of say 1 mH, try it! Most are ferrite loaded however, so be careful of resonances if you want to use it broadband.
Have you made a video on winding your own IF transformers, especially for older tube-based radios? I'm toying with the idea of setting up an Arduino-based winder that can count the number of turns and evenly distribute the windings.
Wow that is impressive. The early IF transformers were tuned with trimmers and the coils were on forms with no ferrite. Most of the modern transformers in the 40's-50's fail because of the Silver Oxide Disease on the plated caps not as much with the windings. I have never attempted winding transformers, but I do have a manual coil winder gathering dust that I may bring out of hiding.
@@MIKROWAVE1 Haven't actually made it yet, just starting to plan out how to make one. I figure it'll be something like what's shown in the middle of this page: www.angelfire.com/electronic/funwithtubes/winding_if_transformers.html I remember seeing a video where somebody made one using the plastic body from a cheap mechanical pencil as a wire guide, clamped to a stepper/servo motor to move the wire back and forth along the form. Should be a neat project for making RF chokes/transformers.
and now the 3D printer would be a good solution! !! Really believe me! how and what i want myself i can make it simple and fast I can print everything as I want. the rubber pads can be plastic discs and even discs with a slot in it. I have already printed various spool shapes , buttons Desire Asjes you name it. a 3D printer is the golden TIP here! please note!!! I don't print everything!!! sometimes other material is also good to use! PVC pipe for example! Friendly greetings from The Netherlands! Rob.
Great info! Never was good at math. Could and have done winding coils but never bothered doing chokes. You could have stopped the video to answer your cricket cell phone. Might have been a call from the sex band, eh? Ya really got me with that one! I see that others who like this video did not want to touch that one! lol
Good video. 👍🏻 First time i ever heard about these coils were from just MW1 and i just didnt got it to work well when i tried making my own, so i hope i will pick something up from This video. Power supplies for tube circuita in the next video? ☺ Ps. Btw, you should advertise your Paypal so people can donate.
Hi, in the diagram at 8:38 why have the Antenna RF Choke? It is a high impedance to RF so what's the purpose of it? The circuitry around it is AC coupled from the plate so .... what is it for?
Excellent question. What would happen if the .001 coupling capacitor failed and you had your hand on the antenna? Now the 400V of B+ would give you a shock. The choke's job is to be a DC protective short to ground thus protecting you and hopefully blowing the fuse! So yes it is useless to the circuit itself!
@@MIKROWAVE1 Thanks for the response. I was staring at the circuit and sure enough the only reason I could come up with is if the capacitor failed short, however, then what? Obviously if the choke has wire of sufficient gauge then there's a chance of stopping everything in its tracks - I didn't think of that. Thanks for the explanation!
Great question! The scope probes certainly have an effect. Even the best 10:1 will have around 10 pF of capacitance. So the idea is to measure at a point other than across the choke, or if you do have to, swamp the capacitance with a much larger capacitance - like the 470 pF and add the 10 pF into the equation. On the SRF test circuit, we measure across a 150 Ohm resistor, so the effect is small. But you probably could add another series resistor at the end of the generator lead to attach to the choke and do even better to isolate the capacitance issue.
