F5 power amplifier

[tinitus]

I wouldnt take any risks with those expencive Toshibas
I have just bought Renesas, so I have the same worries
I have decided to keep it at 28V or 30V, with sligthly higher bias

Neither I have decided on the thermistors yet
Just a thought, but have anyone ever considered matching the thermistors
How accurate are they
Could the thermistor actually cause imbalance
Could that be one reason why people think it sounds better without

[gaborbela]

I purchased thermistor before just 200R for another project. I selected them in the store from 160R to 220 it was everything there .
It took me at least 20 min. to find 4 piece 200R.
I will go with 36V rail (3 pair per channel , must work) , probably with lower bias. Some people built Aleph4 only 3 pair power mosfet . Aleph4 running over 45V rail. 3 pair have to take the heat with the right size heat sink!!!
I just don't know if someone built F5 with out current lim. and with out thermistor.
Is to long to read all .
If is OK with out thermistor , I do not want to use them .
From Renesans you get Lateral mosfet or Vertical .
Someone already tried lateral verizon but in these circuit doesn't work.
Greets

[tinitus]

I think your Toshibas are laterals too
I believe Renesas bought the Toshiba patent

Yes, it have been done without limiter and thermistors
There have been several reporting not to set nias too high without
Bias seem to get unstable at a certain point
I might suspect that more efficient cooling and/or heat transfer would improve on this

With raised voltage you need to cacode the Jfet
It have been showed how, some posts back

[gaborbela]

Hello
Yes I go with cascode . My Toshiba mosfets are Vertical .
Renesans bought the Hitachi patent .
I know because I built similar amp like F5 with Lateral mosfet . The Profet .
It is a great amp !
The reason I want to try F5 .
Be careful if you get Lateral mosfet those are no good here !
I also have 10pair orig. Hitachi lateral but with Lateral mosfet F5 does not working !!
Greets

[gaborbela]

I posted the wrong pict.

[Zen Mod]

boyz

maybe - before throwing any amount of money or energy in it - is wise to re-read Papa's pdf few more times ?

just one thermistor per rail ; it's temperature sensitive input jfet's drain resistor , nothing else .

go back in thread and look for several already made F5s with laterals in output

if I remember - jackinnj made at least pair of them

[gaborbela]

Thanks Zen
I have to tell the truth I didn't read the tread all the way .It would take days!!!!!!!!!
All I remember right at the beginning someone tried with 3 pair lateral but to him didn't work to him .
To him the power mosfet(s) heat up very fast .
I do not want to mislead nobody .
If already was sucsesful built with laterals that great news .So go on and build it .Don't forget Renesans lateral 2SK1058 /2SJ162 only 7A .
I prefer laterals over vertical mosfet . Of course not from Renesans , Exicon much better even the orig Hitachi better to my ear .I tested them in my Profet amp .
But now is to late , I made my PC board layout to use the Toshiba vertical mosfet .
I think Toshiba is not bad either .Of course they are very expensive but I already have them .
Thank one more time Zen

[sekess]

Originally Posted by westend

It will be polished just like the backplate and sinks. I just can't stop listening to start on polishing, again .

Hey westend,

Are you polishing the aluminum by hand? I hand polished aluminum for an amp build about 2 years ago -- it took for ever and it was hell.

How did it go for you?

Steve

[bobodioulasso]

Originally Posted by jackies

My fellow DIYers and especially bobodioulasso , I'm sorry to bother you with my n00b-tastic PSU questions, but the more I think about it, the more I'm concerned. Anyhow, I'm trying to use a transformer from an Adcom GFA-1 amp, I measured 66v on the secondary, and thinking if I can get two separate +/- 22v supplies for my 2 channels of F5 amp respectively. Would it work like this, with a center tapped winding, as opposed to two separate secondaries?

Aren't your two grounds at different potentials?
...You need two separate secondary windings, i think.

[bobodioulasso]

See post 485 from Jackinnj.
Lateral mosfets having a negative tempco thermistors can be avoided.