Heathkit HW8 toroid wire

[Endckr111]

Hi
I’m probably going to replace the output toroid coils on my Heathkit hw8, and just need confirmation that the coil wire used in original coils was in AWG.
I have noticed in a few topics on this subject show #26 & #28 wire, and I presume that means AWG.
I could convert over to SWG, but would rather go for AWG to keep things original ect
If someone could confirm I would be most grateful
Mark

[David G4EBT]

All of the inductors were supplied in the kit ready wound, so the only way of knowing the original wire gauge would be to measure the thickness of the wire with say digital callipers. The inductances are however all stated on page 14 of the full 87-page manual, which can be found here to view or download FOC:

https://www.vintageshifi.com/reperto...W-8-Manual.pdf

26 AWG is: 0.0159” 0.404mm
26 SWG is: 0.0180” 0.457mm

28 AWG is: 0.0126” 0.320mm
28 SWG is: 0.0148” 0.376mm

Hope that helps a bit.

[Endckr111]

Thanks David for that info, I shall take some measurements, and compare them
One other thing, I know replacing same number of turns on new cores is the way Togo, but I’m going to rewind on 67 mix toroids, so I was just wondering what would be the best way to check each value after winding ect, iv an LC meter, but frequency isn’t that high more in audio range, ok there are some expensive meters out there, just wondered if there is another way of measuring, maybe something in the home brew department?
Mark

[Ed_Dinning]

Hi Mark, you should be aware that you need to check the diameter on the bare wire. as modern wire is often double coated (best for mains primary use) whereas the older wire may only be single coated.
That said, slight wire diameter differences will make little difference to the toroid. The grade of material used could make a large difference to its inductance value.

Your LC meter may not read very accurately on this toroid due to the L/R ratio, you wouls be better using a proper bridge (Marconi TF 2700 etc)

Ed

[Ian - G4JQT]

Absolute wire diameter is not too important, something close is quite adequate. I guess you've read of the tx LPF inductors changing value with heat, I had that happen on one band of an HW-8.

If you can, measure the inductances and compare with the manual before you start. Any that are a long way off can be rewound on new cores, and adjust the wire spacing for the right inductance with an LCR meter.

I've worked on seven HW-8 rigs. They don't compare with modern stuff, but nevertheless great little rigs that when properly aligned and with a few minor mods preform very well.

Attached is an article about them I wrote for Practical Wireless covering the important stuff to consider. It's not the final version, but it's near enough.

Ian

[Endckr111]

Thanks Ed and Ian, much appreciated, now Marconi! Well would be nice to have! If I can find one I shall endeavour to purchase one or similar! Totally agree with you those cheap LCR meters are just no good for this type of work.
Thank you Ian for your hw8 article, a good read indeed! Plenty of things to check out
I guess I should give the HW8 a quick test on air, before I do anymore work on it! Seems to be putting out a reasonable output at present, see how it goes!
Thank you again for your input
Mark

[kellys_eye]

If the inductance is known then ISTR Micrometals have tables to indicate the required number of turns for each ferrite type - indeed I have a simple program (Windows) that permits the various values to be entered and thus reveals the necessary 'missing' parameters (turns, max gauge that will fit, inductance etc). I'm sure it's still available online somewhere. I'll see if I can find it....

[Endckr111]

Thanks everyone, as Ed suggested earlier I might just have a Marconi TF 2700 to hand, price not to bad, but reading up it goes upto 1 kc/s, using onboard frequency, anything high requires external source
So question is, should I get it, and then figure some way to increase frequency for testing out theses newly wound toroids, there’s also the possibility the Marconi TF 2700 needs restoration work! How feasible is that? So your advice please
Cheers
Mark
Mark

[Ed_Dinning]

Hi Mark, the TF2700 is a pretty rugged device, slide wires may need cleaning and re-lube but that is about all.

You are measuring inductance, not impedance, so the frequency will only make a small error in the actual reading.
Note when using this bridge it is best to adjust the balance and loss balance controls together to get the best null. Increase sensitivity and re balance,

Ed

[Endckr111]

Cheers Ed, from what Iv read up, seems it would be agood investment to have, always seems to have good reviews, and fairly accurate, so I am going to make the move and get it! I’m sure I will be back here with a few questions! Once Iv open it up! I gather the ganged pots can be iffy but replacements are possible from a company in wales
Many thanks again
Mark

[kellys_eye]

Although not the same as the (much simpler) version of program I have for calculating toroidal inductors this version seems to show a lot more detail:

https://miguelvaca.github.io/vk3cpu/toroid.html

[Station X]

Originally Posted by Endckr111

Hi
I’m probably going to replace the output toroid coils on my Heathkit hw8, and just need confirmation that the coil wire used in original coils was in AWG.
I have noticed in a few topics on this subject show #26 & #28 wire, and I presume that means AWG.
I could convert over to SWG, but would rather go for AWG to keep things original ect
If someone could confirm I would be most grateful
Mark

Can't you just measure the diameter of the original wire with a micrometer?

[Ed_Dinning]

Hi Mark, you can indeed run it at different frequencies and all that is explained in the handbook, but accuracy suffers if you go too far away from the nominal 1KHz.
Handbook also gives details of adaptor units so caps can be measured with high voltages on them as well as inductors with DC in the windings. This is very useful when you must make these measurements.
There is also a facility to use an external standard so you can accurately match 2 parts

I have used these setups with success and one day I'll build them into a small enclosure

Cheers, Ed

[Endckr111]

Cheers Kelly’s eye, looks good once you get to grips with it, very comprehensive! Good for doing initial calculations ect
Cheers Ed for your input, just had a peek at instructions and those extra bits of kit, have to say a lot of it I’m having trouble getting my head round! At first glance! Think I will definitely need some advice once it’s up n running, of course give it the once over first! Caps are ancient!
Cheers
Mark

[Endckr111]

Well I’m glad to say, I have may hands on a Marconi TF2700, pretty neat piece of kit for its age! But on closer inspection, theses caps are looking a little worst for wear, dated 1962 on a few of them.
I have to hand, most of the required electrolytic values, except new ones have a slightly higher voltage, double in some cases, is that going to cause any issues with the function of meter, Or should I obtain some lower voltage caps?
Your thoughts please
Mark

[Radio Wrangler]

Electrolytic capacitors:

The voltage rating is just that, a voltage level to be sure you don't use it above. If you do, the life expectancy comes crashing down. It's not an instant death-sentence, but over a number of units, you'll come to regret it. Canny designers try not to go above 80% of rating.

Less well know is that some (not all) will tend to depolarise (forget how to be a capacitor) if run with too little DC bias across them. Good practice is to try to keep it above 10% of rating. You don't have to, but you'll get better reliability.

Dust-Iron toroids:

1) These are iron powder, not ferrite and have quite different properties.

2) The familiar ones 'T50-2' sort of thing are made by Micrometals inc. of Anaheim California (Think Disneyland) but were sold into amateur radio circles by Bill Amidon of the distributor Amidon Associates inc of Otsego street Hollywood. Bill's catalogue has type numbers not quite the same as Micrometals' catalogue, but clearly derived.

3) The different mixes are good over different frequency ranges. They also give quite different inductance factors.... usually quoted as an 'Al value' in nanoHenries.

4)Find the Al value of your core, count the turns. Multiply Al by the number of turns squared and you should get a result very close to what you'll measure. If you change core size or material, use this backwards from the inductance or turns count, then use forwards with the new Al value to find the new number of turns.

5) This fools many people! You can only have whole numbers of turns on a toroid. A wire goes through the hole so many times and that's the number of turns. People argue about half turns and etc, but you can't use a winding without something in the outside world relating one end to the other. This unavoidably completes that turn. It may look partial, but it cannot be.

6) Inductance goes up as turns squared, because each turn induces not only into itself, but also into all the others, and the others all do the same. Work out the combinations and the induced voltages add up proportional to turns squared.

David

[Endckr111]

Thanks David, very well explained! The inductor ferrite cores will be done very shortly, on new mix, I’m hoping once this meter is up n running it will help me out!
Cheers
Mark

Careful with toriods, most leak a bit of filed and so a winding covering only a bit of the core will have less inductance than one evenly distributed. Magnetics has been described as electrics done with carbon rods in salt water, nothing conducts very well and nothing insulates very well either.

[David G4EBT]

For information Mark, (if you don't already know), there is an active well-established Heathkit 'HW8' User Group, (established in 2008), where there is a wealth of information about all aspects of the HW8. You might wish to take a look:

https://groups.io/g/HW8

Hope that's of interest.

[Endckr111]

Hi David, thanks Iv just taken a look at the hw8 site, plenty of info there, and just found a link regarding replacing toroids!
Thanks again
Mark