F5 Turbo Builders Thread - Page 637

nikwatt · Yesterday, 10:46 AM

F5 v_1

nikwatt · Yesterday, 10:53 AM

scheme v1 from guide

cubicincher · Yesterday, 01:27 PM

Hello Nicola,

you use a 600 VA toroid with secondaries of 2x25V~.

After the bridgerectifier and capbank you will 'land' anywhere around +-32,5 V?
(25 V ~ x 1,3 = 32,5V - rule of thumb/ could be a bit higher?).

The voltage rating at 35V of your caps (15000uF / 35V) seems a bit low for me.
Not a lot of headroom! In other words - close to none. I would have used 50V
types minmum to have a safety margin.

Greets
Dirk

nikwatt · Yesterday, 08:00 PM

Ok....I have other caps
Kermet 15000 40v

verticalmammal · Today, 05:45 AM

When I'm using the cascode voltage formula to determine desired resistance values for R25-28, what cascode voltage am I actually shooting for in my F5Tv2 build? Maybe shooting for just under 24V? Using the lowest suggested value of 4.75 across the board I get 16V of cascode voltage. Is that where I want to be or should I look at possibly dropping the resistance of R25,26? Or perhaps I'm misunderstanding something?

Thanks again!

Bfpca · Today, 01:24 PM

Most people seem to aim at between 11 and 16 volts. I don’t think it is super critical. You are lowering the voltage on the input Jfets to a safe level and also reducing the power consumption, so the jfets run cooler.

6L6 · Today, 02:43 PM

Just make the cascode resistors all the same so your cascode voltage is approx 1/2 the rails.

verticalmammal · Today, 04:26 PM

Quote:

Originally Posted by Bfpca

Most people seem to aim at between 11 and 16 volts. I don’t think it is super critical. You are lowering the voltage on the input Jfets to a safe level and also reducing the power consumption, so the jfets run cooler.

Quote:

Originally Posted by 6L6

Just make the cascode resistors all the same so your cascode voltage is approx 1/2 the rails.

4.75 across the board for 16V on the nose it is then.

Are y'all sick of hearing me say "thanks again" yet? I hope not, I still have a few more parts to source before I start building

Seriously, I hugely appreciate your help.

AudioSan · Today, 07:18 PM

16V is a nice place to lande. I don't agree with some others that the voltage is not important. Well, the voltage alone is not. But combined with the current they draw, it makes up the power dissipation. And thats the important factor. Keep it way below the limit.

Yesterday, 01:27 PM	#6363
cubicincher diyAudio Member Join Date: Mar 2016 Location: Hechingen, South of Germany	to nikwatt #6360 Hello Nicola, you use a 600 VA toroid with secondaries of 2x25V~. After the bridgerectifier and capbank you will 'land' anywhere around +-32,5 V? (25 V ~ x 1,3 = 32,5V - rule of thumb/ could be a bit higher?). The voltage rating at 35V of your caps (15000uF / 35V) seems a bit low for me. Not a lot of headroom! In other words - close to none. I would have used 50V types minmum to have a safety margin. Greets Dirk

Today, 02:43 PM	#6367
6L6 diyAudio Moderator Join Date: Oct 2010 Location: Denver, Colorado	Just make the cascode resistors all the same so your cascode voltage is approx 1/2 the rails. __________________ Illustrated Build Guides - Pass F4 - Pass B1 - Pass F5 - Pearl 2 - O2 HPA - Hagerman Bugle 2 - Pass Aleph J - Me at BAF'13 -Pass F5Turbo - BA-3 Amp - BA-3 Preamp -F6- -AmpCampAmp -Me at BAF'18 -Me at BAF'19

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Today, 05:45 AM	#6365
verticalmammal diyAudio Member Join Date: Jan 2021 Location: Hamsterdam	When I'm using the cascode voltage formula to determine desired resistance values for R25-28, what cascode voltage am I actually shooting for in my F5Tv2 build? Maybe shooting for just under 24V? Using the lowest suggested value of 4.75 across the board I get 16V of cascode voltage. Is that where I want to be or should I look at possibly dropping the resistance of R25,26? Or perhaps I'm misunderstanding something? Thanks again!

Today, 01:24 PM	#6366
Bfpca diyAudio Member Join Date: Feb 2007 Location: Nova Scotia	Most people seem to aim at between 11 and 16 volts. I don’t think it is super critical. You are lowering the voltage on the input Jfets to a safe level and also reducing the power consumption, so the jfets run cooler.

Today, 07:18 PM	#6369
AudioSan diyAudio Member Join Date: Feb 2009	16V is a nice place to lande. I don't agree with some others that the voltage is not important. Well, the voltage alone is not. But combined with the current they draw, it makes up the power dissipation. And thats the important factor. Keep it way below the limit.