Sony vFET Illustrated build guide

[Benji90]

many thanks!

 

[Botte]

You may need to increase R34 and R35 to get them to bias correctly as the VGS is higher on the Fairchild parts.

 

[Benji90]

another quick question. ztx550 appears to be obsolete. what can be used as an alternative? Many thanks

 

[Benji90]

Couls simply ztx551/451 be used instead? From what I can gather from the data-sheet they are almost identical

 

[Dennis Hui]

Yes you can.

 

[Peppe]

The brackets must be flat against the heatsink with thermal grease and torqued properly to ensure maximum thermal transfer.

What would be the appropriate torque value for bracket-heatsink coupling?

 

[6L6]

Enough to get the interface flat. No more than you can do a screwdriver tip by hand.

 

[Peppe]

I have now tested DC voltages across the test points and compared to the 2nd chart in Pa's documentation. Most values are OK, except the ones below.

G-T18 This may initially read very different than 0. If so, make a small adjustment to P3 and set until it reads +/- 1.0v

G-T18 is 5V in one channel and only increases turning P3. The other channel is 1V.

Q5 and Q6 are Toshiba parts. Should I decrease R34/35?

G-T19 , G-T20, G-T17, G-T16 The suggested voltages are very rough. Within 3-4 volts is fine.

Here both channels differs more than 4V:

G-T19 = +22V (instead of +12V)
G-T20 = -22V (instead of -12V)
G-T17 = -17V (instead of -10V)
G-T16 = +19V (instead of +10V)

How critical are those values at this stage?

 

[Peppe]

Ignore my post above. P1 and P2 were not in the middle position. 😗

 

[Benji90]

I'm in the process of building my unit. I wanted to ask if there's been, among the many units build, any failure ( primary or secondary) of the vfets ( without building mistakes) to understand what could be the potential expected life of the amplifier and if it would make sense to try to acquire some extra vfets as future replacements.
Thanks
Benjamin

 

[Dennis Hui]

I haven't followed all the discussions of this project, but I don't recall seeing mentions of vfet failures; I personally wouldn't worry too much about it.

Also Papa has commented in the past that the Sony devices are pretty rugged.

While generally it's a not a bad idea to have spare devices around, but please be mindful of the fakes out there.

Have fun with your build.

Dennis

 

[WBS]

There have been no failures that I'm aware of. Just follow the build guide exactly and you shouldn't have any problems. If I can do it, just about anyone can!

 

[Benji90]

Thanks guys!