[ARC5] [BoatAnchors] Programmable Osc. Booster : Western Electric 227B

[Roy Morgan]

On Nov 7, 2014, at 11:19 PM, David Stinson via BoatAnchors <boatanchors at theporch.com> wrote:

> While the programmable oscillators we've been discussing will push the receiver fine, driving the transmitter 6L6 power
> oscillator takes a little more "push."   I built a simple Class-D MOSFET stage with a 4:1 autotransformer UNUN output.  It drives the set well.
> Here's the circuit:
> 
> http://home.netcom.com/~arc5/oscbrd.jpg
> 
> One "kink":  the toroid I used was a "junkbox" find….
> Anyone know how to classify an unknown toroid?

Here are my suggestions:

First, gather data from the manufacturers.  See links below.

- If you have a Boonton RX meter or Q meter, use that
- If not, you can lash up a signal generator and oscilloscope or even just an RF detector probe to do some measurements.
- A grid dip oscillator can be very useful to test for resonance

To guess as to the material in the toroid:
- wind some turns on the thing - taking up 2/3 of the circumference and somewhat spaced from each other
- with your dipper or signal generator and scope and some test capacitors, find a resonant point 
- calculate inductance, then calculate the inductance-turns factor (the AL number)  from that

uH = (AL * Turns^2) / 10000

- then refer to published specs to guess the material you have

To test loss:
- Make a transformer with the unknown toroid: two windings of equal number of turns, each a bit less than half the circumference
- With the signal generator and scope, see what frequencies the thing will pass.  Find low and high frequencies where loss increases above mid point.
- Refer to published curves to guess as to the material.

> If not, what toroid do you think would work as well?

Quite possibly the type 61 material would work.  It is supposed to be useful from about .2 mc to 15 mc.  (Type 43 material us useful at higher frequencies and is used in noise suppression beads and toroids.)

Some of many many references out there on the Web:

From Micrometals, Inc, a manufacturer, 
-their home page with iron powder materials data and lots of other stuff:
http://www.micrometals.com/
-a technical treatise on losses:
http://www.micrometals.com/appnotes/appnotedownloads/chfsdltw.pdf
- at their application notes page, 
http://www.micrometals.com/appnotes_index.html
see especially these two:
1) Iron Powder Cores for High Q Inductors
2) Iron Powder Core Selection for RF Power Applications

The ARRL Handbook has quite a lot of information on toroids, their uses and characteristics.
My 1998 Handbook has a section “Component Data” with a subsection “Inductors and Core Materials”.  You’ll find much useful data there.  Note that powdered iron materials from Micrometals may be color coded, where ferrites are not.

The well known source: Amidon Associates:
http://www.amidoncorp.com/
-their specifications page is:
http://www.amidoncorp.com/specs/
- description of many of the standard materials:
http://www.amidoncorp.com/product_images/specifications/2-02.pdf
-and the specs for many common type materials are at:
http://www.amidoncorp.com/product_images/specifications/2-05.pdf



There are many calculators on the web that help you design toroid inductors - these can be used backwards to figure out what you might have in your hand.  
Use google with: "toroid calculator"
It is pretty hopeless to guess what is offered at a hamfest vendors table unless the type material is available.


Hope this helps.

Roy



Roy Morgan
RoyMorgan at alum.mit.edu
K1LKY Since 1958