DIY kits 70W SSB linear HF Power Amplifier For YAESU FT-817 KX3

[Dudley]

Hi, this is one of those Chinese kits that came with no instructions. I have found some help on the internet but I can't seem to work out how to wind the transformers and inductors. This is a link to the only article I could find https://pa-11019.blogspot.com/2016/11/diy-kits-70w-ssb-linear-hf-power.html. The other query is that the physical item has 4 inductors and the circuit diagram only appears to have 3. Any help in this matter would be greatly appreciated

 

[rjenkinsgb]

Have you noticed that the large output transformer is constructed from two separate "sleeve" type cores, side by side?

 

[Dudley]

Many thanks for the reply. Yes I have but the problem is how are they wound? although it says turns are .5/2turns and 3/.5 turns on the diagram they have centre tap and that I can't comprehend with the information I have

 

[JimB]

Have a look here:

A fragment copied from Solid State Design for the Radio Amateur, published by the ARRL.


Does this help?

JimB

 

[Dudley]

I think it does I'm a bit busy at present but feel when I have a bit more time I may well be able to relate this to my problem. Not sure st present how to do Half a turn, if you could throw some light on this it would really help Many thanks 73's

 

[Ylli]

I suspect the 0.5 turn relates to half the winding. I think the input transformer should have 2 turns on the primary and the output transformer should have 3 turns on the secondary. But you could always experiment.

 

[JimB]

Half a turn, if you could throw some light on this it would really help

The concept of half a turn through a toroid is a bit weird.
With toroids, if the wire passes through the hole, that is one turn.
A fractional turn does not (cannot) exist.

Refer to the pictures in my attachment.
In the case of this transformer, there are two ferrite cylinders mounted side by side.
Brass tubes pass through the cylinders.
At one end, the tubes are joined together with a flat conductive sheet. Either a piece of brass or a piece of circuit board material.
This end connection is a centre tap.

The other ends of the tubes are joined by a piece of circuit board material, but the copper is cut so that the tube ends are not connected.
These two ends connect to the collectors of the PA transistors.

We now have our "half turn".

To make the "Three turn" winding, enamelled copper wire is passed through the inside of both tubes several (three?) times.
This makes the connection to the antenna etc.
Don't forget the lowpass filter. This amplifier WILL make some horrendous harmonics without one.

JimB

 

[Dudley]

Thanks everyone for your help however if anybody ha particular experience with this linear amp your comments will be welcome