F5 bias

[AudioSan]

hello i have 2pc 225VA transformers in my F5. and a bias of about 1.72A(cviller's dual output's) and the transformer(only one ch yet) is nice and cool. about 32C.
anyone have an idè of how much i can crank the bias with those transformers? heatsinks is also nice and cool. maybe 37-38C ambient is about 22-23C.
rigth now bias is 1.72A. DC ofsett -0.4mV- +0.4mV

 

[Zen Mod]

up to 50W per mosfet

 

[AudioSan]

50W pr mosfet on a 225VA?
thats 200W. i don't want to boil the transformers

 

[Bksabath]

225 VA is not much to go on as it is the voltagge time current
so what voltagge is it?

If it is split secondary at 18 and 18 V 225 divided by 36 = 6.25 A total
Or you can take max 3.125 A out of each secondary

Papa reccomend a 3 to 1 margin so in respect to that you are already taking out enough.

rest is again realy meaningless as what size heath sink?
and ofset again got nought to do with it as it all down on how carefull you are when tweaking the pots.

If you go Papa class you need bigher trafoss

 

[Bksabath]

Still mighty Zen is right
50 W on each mosfet is max that is the given trought
Boiled trafoss irellevant we have them for breakfast

 

[Zen Mod]

I meant you wrote one 225 Watt-er per channel

so - if using original F5 schm , where you have 2 mosfets per channel , that means you're still in ballpark - 100W power consumption per 225W iron

 

[AudioSan]

225VA pr ch. 4 mosfets pr ch

 

[AudioSan]

yes it is 2x18V transformer. so +/-22-23V no itd 1.72A bias. and the transformeris at about 32-34C witch is about 80W i think it will have no broblem with at least 120W.
BTW. it sounds fantastic. i just love it. but it's too cool

 

[AudioSan]

here it is

 

[AudioSan]

the whole thing

 

[Zen Mod]

that's cheating - 2+2 mosfets per channel

so - crank them , up to 50% of iron power

 

[bobodioulasso]

You may also need more capacitance in the PSU as ripple will increase when drawing more current.

 

[AudioSan]

it's 6x12.000uF pr.ch.
ZM: hehe. thats not cheating it's spreading the heat
will do

 

[bobodioulasso]

Which is not a lot.
A stock F5 needs 30mF per channel rail.
You may have to double this i you double the current.
Let's see.

 

[gadut]

nice build, can't wait to start mine anyway which one is better configuration, CCCC R CC or CC R CCCC ? but it's for my aleph30 with 2pcs talema 2x18V 225VA and 12pcs 15.000uF, so each channel will be supplied by 90.000uF which already exceeds aleph30 design which is 60.000uF per channel

 

[jacco vermeulen]

=> C-R-CC =>

 

[AudioSan]

nice build, can't wait to start mine anyway which one is better configuration, CCCC R CC or CC R CCCC ? but it's for my aleph30 with 2pcs talema 2x18V 225VA and 12pcs 15.000uF, so each channel will be supplied by 90.000uF which already exceeds aleph30 design which is 60.000uF per channel

i also have some aleph30 boards
have to build them soon

 

[AndrewT]

24 off 15mF for two channels could be arranged

CRCLCCCC per channel per rail

 

[gadut]

go go go..wouldn't aleph30 better due to single ended configuration? my preliminary research on articles

 

[AudioSan]

Which is not a lot.
A stock F5 needs 30mF per channel rail.
You may have to double this i you double the current.
Let's see.

it's not double current. more like 30% rise.
ripple is 3.59A eatch cap.