Roender's FC-100 prototype and builder's thread

[den054]

I'm sorry if it is wrong place to ask or my question is silly.
Is it a good idea to turn 500VA 2x51V like this one into 4x24V by unwind a half of each secondary cut it and rewind back?
This idea is based on Mihai's post.

[AndrewT]

You might be able to identify the midpoint of each winding without removing the half winding.
See my previous posts describing the method.
Another unhelpful post?

[den054]

Thank you for reply!
If you mean that post than you mention toroidal trafo there. And it suppose the secondary has one layer. But I think 51V secondary is quite a lot for one layer windings..
So I suppose to add 10-20 windings for measuring V by wind and calculate number to unwind. Am I on right way?

[AndrewT]

I split a pair of dual 50Vac windings to create a 4 secondary 25Vac. No problem.

[atupi]

Finally i have in my hand 10 pcs of NJL 1302&3281. I used the schematic from Builders manual to measure Hfe and Vbe.
Vbe is very consistent between 0.610 and 0.614 V for NJL 1302 and between 0.623 to 0.627 for NJL 3281. (measured directly Vbe with Dmm while transistor was installed in the test rig).

Regarding hfe i have obtained for NJL3281 values between 110 and 115
and for NJL 1302 hfe is from 112 to 118.

What do you think are my values close enough? Also are my measured values close to what should be ?

Regards,
Adrian

[Rudi_Ratlos]

Adrian, the HFe values of your transistors look quite good, but I remember Mihai's advise to not use the NJL3 - series transistors,
since they have another type of compensation diode installed.
Find the description of the differences in Bob Cordell's book: "Designing Audio Power Amplifiers" on page 305.

The NJL4 - series would have been a better alternative!

If you want to stick to the NJL3 - transistors, build a compensation scheme like the ones Bob describes on the following pages.

Best regards - Rudi

[atupi]

Im looking to buy min 6pcb of NJL 0302 as i already have in my hand 10 pcs of NJL0281.
Adrian

[atupi]

Measured my 10pcs of NJL0281 i have:

Vf (diode)
0,503
0,510
0,510
0,509
0,509
0,509
0,504
0,507
0,506
0,507

Do you think i will be able to use 5 of them ?

[PeterLeest]

I think Roender called for 1/2w resistors, it is quite difficult to get 1/2w resistors for all the values wanted and also too big to fit into the PCB.

can 1/4w do the job? if not, which ones in particular need 1/2w?

[DRZ1]

Originally Posted by atupi

Measured my 10pcs of NJL0281 i have:

Vf (diode)
0,503
0,510
0,510
0,509
0,509
0,509
0,504
0,507
0,506
0,507

Do you think i will be able to use 5 of them ?

You can use them , the 3 0,509 on one side and the 2 0,507 with the 0,506 on the other side. They don't have to be matched side to side, just the ones in the same side.