F5 power amplifier

[bobodioulasso]

Am i wrong to see, in Nelson's Pdf, for 110v operation, the equivalent of 2 parallaled thermistors in serie with two paralleled primaries?
If so, one thermistor for 220v operation and the ratio 1/2 is as suggested by Andrew.
The value is halved.

[Nelson Pass]

That's how it goes.

[Sisyphism]

Wow, that was interesting.

Back to my power supply:
I'm still not sure if that will be good to use
with two transformers with 225VA each.
Does this matter how big those transformers are?

I mean 300VA is not the same as 450VA.
That is the reason why i asked about calculation.


I can not post pictures at this moment.
But i would like to put in this new schematic.
The schematics i posted are not ok, sorry for that.
500 Downloads

Thanks to Andrew and all the other good guys around,
and of course to the Oracle.
This forum is very impressive.

[bobodioulasso]

I use one cl60 per 250va/220v transformer. It s working fine.

[Babowana]

Originally posted by Sisyphism


I mean 300VA is not the same as 450VA.
That is the reason why i asked about calculation.

The sizes of the transformers are just scale of their sizes, and the bigger the better in handling the amount of current.

Meanwhile, the actual current on the primary side is depending on the actual current on the secondary side (load current) and the turns ratio of the coils, independent of the transformer size. If you are going to apply the similar bias current and the similar total filter capacitance as the original F5, one CL60 is enough on the primary side when you are going to use 220-240VAC main. But, when you are going to use 110-120VAC main, you want to use two CL60s because the primary current will double up, compared with in case of 220-240VAC main.

You do not believe in the primary currents mentioned as above . . . ? Go to the drawing in post#4646 and see the fuse sizes--1.25A for the 240VAC main and 2.5A for the 120VAC main.

Happy diy!

[jacco vermeulen]

Originally posted by Sisyphism
really

Hope you realise that the constant power draw of an F3 channel is 100W, and the F5 does 60W.

A General Electric CL60 thermistor handles 4.5W dissipation.
The thermistors in the F3 power supply are loaded with about half an amp of current.
If you calculate the Ro value at that current with the X-Y trick, it follows that the thermistors are running at 20% maximum continuous rating, as Babowanabanana and moi would say.
The Oracle has been loading his semis and passive parts at 25% or less since way back to the Threshold days.

Your 15 Ohm Siemens B57237S series thermistors are loaded with a constant draw of something like 0.267 amp in your schematic.
If you calculate the corresponding resistance value of the thermistor with the k-n numbers at that current, roughly the same as the X-Y numbers of the CL60, you'll end up with a dissipation of some 0.6W each.
The B57237S handles 3W constant dissipation, so they run at 20% MCR as well.

[Renron]

Beginner question if I may.
What is the purpose of the // capacitor between the thermistors on the 120Vac PS? If it were in series, I'd guess DC blocking.
Thanks,
Ron

[udailey]

I think it has to do with supressing those nasty 'turn on' pops.
Uriah

[Sisyphism]

Now you are talking.

Thank you jacco vermeulen.

So both schematics i posted would work.
Since F3 draws more Power, it would not work for both channels.

[nicoch58]

can try power the F5 with two 120VA 15vac r-core from seletronic ?