Vfet / SIT Amplifiers

@kitr 
thanks for sharing and I am not surprised. The B-3s along with its vfet family produce very engaging listening experiences when in working order.
Get those B-3s fully restored, bump the bias up to 50-60mv. if you like them so much now, you will love them even more after.

@sonetduo

Since the last time, I've bought C-1, B-2, Hitachi HA-500F and Sony TA-N88.

I reckon, that the Hitachi and the Sony won't be any better than the B-3s, but I wonder if the C-1 will somehow enhance the sound.

The Hitachi and the C-1 are on the way. The B-2 and the Sony don't work, but they should soon.

Well, it's time for an update.

The B-2 is fixed and working like a charm. Sound-wise, it's very similar to the B-3. I fancy the B-2 more than one B-3, but two B-3s are definitely better than the B-2. Two B-3s have a tad better soundstage and are a tad warmer.

@kitr, you are starting to build a vfet geat collection that is quite impressive. Congrats on your recent purchases!
Any of the gear you called out can be repaired if the vfets are still OK, with C-1 being the most difficult to repair out of the rest.
Restoring them to proper order, is quite a different thing than just getting them to work again.

I am glad you got the B-2 to work again and thanks for sharing your listening impressions. Depending on how the B-2 was restored / repaired, will determine if it would sound noticeable different than the B-3 or B-3 x 2/ BTL mode. Key aspects of the B-2 restoration are the choice of bulk caps replacements and how the selector assembly is addressed. B-3 is simpler and does not have the selector assembly issue B-2 has. In BTL mode the B-3s might sound different to you but will have difficulty driving any difficult loads (below 6 ohms). That is not the case with a B-2. The warmer sound and soundstage of B3 in BTL mode might be a matter of speaker marching as the vfets of the B2 and B3 are technically the same and the circuit design is also mostly similar. I found that I actually prefer the B-2 over the 2 x B-3s in my system, and I did extensive real time A/B listening with no variables other than the amplifiers, so I guess is a matter of system synergy??

additional observations:
If the C-1 you bought was listed as non-functional, if it is one of the units sold at the auction site in JP recently,
CAUTION on who you take it to for repair!
Do not take it to the corner tech / shop for repair or you will be sorry. You must make sure that you specifically ask the tech if he has experience with this unit...not with other Vfet units, but specifically with the C-1. Otherwise you will be sorry. The AK forum is full of such stories where a "tech with 30+ years of experience" takes on the job, just so that he returns the unit to the owner with fried unobtanium small vfets. C-1 has multiple types of small vfets, some only used in this unit and nearly impossible to source if gonne bad. You will find one person in the US that still works on these, one in Canada and a couple in Europe. Amp8 in Japan would also take on these units.

The TA-N88 uses a pulse lock PSU that has the tendency to self destruct....which takes out a vfet or two. Hoping that is not the case and that yours can be repaired.

For the Hitachi, there is no service manual or schematic available. Someone on a JP forum back-engineered the schematic but use that at your own risk as I do not believe it is fully accurate or complete...I couldn’t find the link at the moment.

Good luck with all your units. I hope you get them properly serviced and restored so that they provide you with sweet vfet musical bliss for the next 40 years!

@kitr Pass labs keeps spare SIT output devices for warranty repairs.. 
being that these SITs are built to military spec and can handle extreme conditions, according to pass labs support… I doubt there will be too many issues.