Vfet / SIT Amplifiers

Does the N-7 suffer from the diode issue as the Sony's intergateds did?

Hello PR,
Actually there are a few vfet connoisseurs in France....but I agree that  vfet units are so exotic and very much extinct...unless you find a vintage unit and have it properly restored.
Nelson Pass has some newer offerings, but those are becoming rare as well. 

I agree with you about the using a different preamp and not the one in the ta-5650. The Lampizator is in a different class and I am not surprised you like it so much. I am aware of Lukasz and his creations, but I do not own any yet.
About the ta-n88: I agree it could be a bit too transparent but it is a good preamp, nonetheless for those that like that level of transparency. If you have not had it serviced yet, that could also be a reason why it might sound "dry/sterile". Also, if not serviced, your unit could experience PSU failure (some zener diodes in there are ill-fated) that could take out the transformers.

@kitr,
Yes, the TA-N7 has the veractor "diodes" / death diodes, but it also suffers of problems with fusible resistors. The thermal runaway of those fusible resistors is horrible and over time they drift substantially from the original value. When they drift past a certain point, they will take out a vfet or two.
Also, the BJTs in the final stage need to be replaced as they are also known to fail.
Net, Net, while the TA-N7 does not have the death rate of the n4650/n5650, it needs to be restored nonetheless. The problem is that there are very few techs that fully understand vfet units and even fewer who would take vfet units for service or restoration. This is valid for all vfet units.
Depending of where you are located (I mean on which continent) I could point you to someone qualified to service your units. 

Yes, my Sony V-fet is full restaured with nichicon and VD1221 have been changed by 1N4148😉

The "bias" must be lowered to 45mv for the ta-4650 and 55mv for the ta-5650.