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 Post subject: Homebrew Hegehog Audio Interstage Transformer.
PostPosted: Oct Wed 18, 2017 8:01 pm 
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Location: Warkworth, Ontario, Canada.
For some time I had been playing with the idea of making a home brew Hegehog audio transformer.

As a guide I used the article “An Efficient Audio Frequency Transformer” from Radio News, July 1922.

A cardboard tube about 1 1/2 inches long with cardboard ends was used as the core. The primary winding was 4000 turns of #40 wire and the secondary was 14,000 turns of #41. This was sealed with cloth tape and shellac

The core of the transformer was soft iron wire lengths, as many as would fit,, shellac coated and bent around the the winding package. The transformer was inserted into a brass tube that had a copper mounting plate soldered to it.

The final turns ratio is 3:5 to 1. Primary resistance is 0.839K ohms and the secondary resistance is 4.70K ohms.

I have yet to try it in an actual radio. If successful a second transformer will be made to complete a restoration.

Image

Image

Ed.


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 Post subject: Re: Homebrew Hegehog Audio Interstage Transformer.
PostPosted: Oct Wed 18, 2017 8:18 pm 
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Location: Annapolis, MD
Nice looking work!!

for wire that small, your are living on the edge of having breakage issues during winding---what is your setup?

For me, the big issue is the spooler, including some kind of drag control. I'm about to build a new spooler to deal with this.

( I found one site recommending 42 gms winding tension for #41...that's only 1.48 oz.)

_________________
-Mark http://pixellany.com

"It's always something". --Gilda Radner (1946 - 1989)


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 Post subject: Re: Homebrew Hegehog Audio Interstage Transformer.
PostPosted: Oct Wed 18, 2017 8:59 pm 
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Location: S. Dartmouth MA 02748-1225 USA
Super nice Ed!

http://www.americanradiohistory.com/Arc ... 2-07-R.pdf

Page 57...

Marc,

A yoke of spring steel with felt pads and an adjustable clamp will provide proper friction. Another method is a hub on the shaft of the supply spool over which is a cloth braid that provides friction with a adjustable weight. There are commercial tension devices that use magnetics, internal magnetic shunts set the amount of friction.

IMHO use two friction devices, just enough on the supply spool to prevent "free-wheeling" and additional in the form of spring or weight loaded pressure pads.

I used a jacquard woven "sock" over spools of .001" nylon mono-filament and took supply off the end of the cop. I had 12 such cops in a large cardboard box and pulled 12 filaments festooned overhead to the Lessona winder that wound universal filaments on a braider bobbin turning at roughly 600 RPM. The bobbin would fill in about 5 minutes, enough for about a mile of braided. The Lesson had a friction grid the 12 filaments would pass before reaching the winder eyelet.

I spent considerable time 20 ya in a small textile shop. Saw many, many gimmicks for friction. Weighted flat braid and felt pads were the most common.

Chas


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 Post subject: Re: Homebrew Hegehog Audio Interstage Transformer.
PostPosted: Oct Wed 18, 2017 9:26 pm 
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Location: Warkworth, Ontario, Canada.
pixellany wrote:
Nice looking work!!

for wire that small, your are living on the edge of having breakage issues during winding---what is your setup?

For me, the big issue is the spooler, including some kind of drag control. I'm about to build a new spooler to deal with this.

( I found one site recommending 42 gms winding tension for #41...that's only 1.48 oz.)


I use a mini lathe that has DC drive as the power source. I find that the DC drive allows me to stop or change speeds almost instantly without the inertia of a belt driven larger lathe.

I use my fingers as a tensioner and guide for the wire. You develop a feel for the tension. The wire I use is on 5 inch diameter plastic spools with a smooth rolled edge. I lay the spool on its edge on a stand between my knees and let the wire come off that way. No need for fancy devices that can snag or cause the wire to break.

As for speed, the Hegehogs were wound at 800 rpm, my normal winding speed. I can go faster but I am not sure that my turns counter would be accurate higher. It is based on a magnet and reed switch.

Ed.


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 Post subject: Re: Homebrew Hegehog Audio Interstage Transformer.
PostPosted: Oct Thu 19, 2017 4:57 am 
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Hi, Ed, the coils pictured in the OP don't look to me like what you are describing. Unless they are tiny, the wire looks like 16 -18 ga, not 40 ga. And they appear to be toroidal wound. what am I missing here? Do you have pictures of the audio transformers you described?


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 Post subject: Re: Homebrew Hegehog Audio Interstage Transformer.
PostPosted: Oct Thu 19, 2017 3:44 pm 
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Location: Warkworth, Ontario, Canada.
Macrohenry wrote:
Hi, Ed, the coils pictured in the OP don't look to me like what you are describing. Unless they are tiny, the wire looks like 16 -18 ga, not 40 ga. And they appear to be toroidal wound. what am I missing here? Do you have pictures of the audio transformers you described?


Here is a picture of an original Hegehog audio from somewhere on the internet years ago. My thanks and apologies for its use to whoever posted it.

Image

Back to my original posting. The primary and secondary are wound on a coil form inside the transformer iron. What you see is not toroidal winding but 4.5 inch pieces of soft iron wire inserted inside the round coil and wrapped around the coil ends. The two ends meet under the brass tube casing forming the transformer.

The wire you see is 15 gauge soft iron. I would have liked to use a smaller gauge but I used what was available out here in the country due to shipping costs.

I hope this clears this up.

Ed.


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 Post subject: Re: Homebrew Hegehog Audio Interstage Transformer.
PostPosted: Oct Thu 19, 2017 11:07 pm 
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Ed Kraushar wrote:
I hope this clears this up.

Ed.


Yes, it does, thanks. Good job!


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