F5 power amplifier

[AuroraB]

Originally Posted by jackinnj

What is this thing that DIYr's have w beer?

It's for cleaning away all that blur from soldering smoke.....

[thanh1973]

Originally Posted by Samuel Jayaraj

Smyslow, thanks for your reply. So I assume that IRFP240/9240 outputs can be used safely without thermistors. However, I was looking at Patrick's (EUVL) schematic which shows rails of 16 volts and he did mention 4Amps bias with Toshiba devices.

I wonder where the 'sweet spot' lies for each of these device pairs when used in a balanced F5: 2SK1058/2SJ162, IRFP 240/9240?

You can have 4A bias but you need to parrallel output devices.
4A is too much for a single pair.
Keep the dissipation under 50W per device.

[Samuel Jayaraj]

Parallel devices may not be the best for low level sonic resolution. So it is better to keep the bias down to 1.6 amps per side (3.2 amps for balanced F5). But it is so challenging and difficult to decide between the stock F5, balanced F5 and Cascoded F5. Ofcourse one could build all and then decide but I simply don't want to add to all the unused stuff lying in my rented workshop. Simply can't get rid of the ever increasing pile. Plus it will be such a shame to scrap any version of the F5!!

[thanh1973]

Maybe make one channel point to point.
Try every version, and then choose the one you like best.

[mstr]

Originally Posted by jackinnj

What is this thing that DIYr's have w beer?

... the beer bottles are intended for proper cooling of the output devices, if anything goes wrong

[thanh1973]

Originally Posted by mstr

... the beer bottles are intended for proper cooling of the output devices, if anything goes wrong

Or worst case scenario would be to put the fire out.
Just make sure it's not high strength beer otherwise instead of putting out the fire you'll probably burn the house down

[maxlorenz]

Hi Mstr,
Thanks for sharing your nice photos and congratulations.
I am intrigued...how the sound compares to the analog rig, left superior corner on the third photo?

[mstr]

Hi maxlorenz,

well, that´s a little bit difficult to say, because the valve amp needs to be serviced, and I haven´t powered it up since 2007. So blind tests between both are not possible, BUT: even if I cannot do direct comparisons, the F5 is definetly much better, especially at low frequencys (the EL34-Amp lacks a bit auf defined bass) and the most convincing fact is that the F5 has much more resolution and better tracability of the soundstage.
Hard to find the right words in english, but I would say the F5 also has more silence, everything sounds more relaxed, and I dont miss anything in the frequency response of this amp.
So, in short words: after first listening sessions with the F5, I never ever spent a thought about repairing the tube amp.

best regards, Michael

[gaborbela]

Hello
I would like to ask some (help) opinion about a high power F5X with out cascode using multiple power mosfet.
It is possible to use 3pair power mosfet / channel powered from 24V rail power supp. based on the the attached schematic ?
I like these simple schematic (unfortunately it is hard to read any value of the components) any way probably with 24V rail would need adjust most of the resistor values .
In case someone interested for a high power F5X please let me know .
We could make some plan together ,I do not have the skill to modify the schematic to a high power verizon .
I have 14PC 2SK1528 & 18PC 2SJ200 matched Toshiba mosfet , JETs , a 20-0-20VAC 1.5KVA Plitron toroid & monster heat sink (enclosure) over 25lb.
I would like to use these to build a F5X instead a high power F5 .
The (enclosure) heat sink was design for a Aleph2 but I like the X topology better. I have a Aleph X , I like the sound of the X so much , it would be great a high power F5X .
Thank for any advise or help .
Greets

[thanh1973]

If you do the x version you won't really need 3 pairs on each half (2 pairs per half will do), unless of course you want to bias greater than 6A (3A per half).
It is very straight forward to do.
Go for it

Tell us what bias and rail voltage you are intending on using.

The only thing that might be a bit tricky could possbly be adjusting dc offset