How expensive are replacement V-fet's?
- Thread starter Onebean
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Arm and a leg and a left gonad. If ..! big if..,you can find a serviceable pair. ie. With the same rank codes
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No. I don't think so..I am familiar with B-1 and B-2 Yamaha. And I won't work on either one.
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it will cost as much as another donor amp would cost and will be as hard to find as hard is to find a donor amp.
not I
NO, they are different not interchangeable among brands or without serious modifications.
clinic-audio
all on YAMAHA untill 1990
Hello Onebean
I assumed they were both using the same Vfet. not at all ! :
-YAMAHA made units with his own semi-conductors (V-FET small transistors and output power transistors. For B2 , B3, there are in TO3 package , for B1 they are MD18 package) and there is not substitutes .
- SONY made his own semi-conductors (IC's and V-fet ) and there is not substitutes.
- NELSON PASS used SONY V-FET
You can find some "NOS" on the auctions sites but there is no way to test them before to pay !
I'm looking at an amp, and the seller says it has distortion in one channel.
What make you think that the "problem" is coming from V-FET ??
I assumed they were both using the same Vfet. not at all ! :
-YAMAHA made units with his own semi-conductors (V-FET small transistors and output power transistors. For B2 , B3, there are in TO3 package , for B1 they are MD18 package) and there is not substitutes .
- SONY made his own semi-conductors (IC's and V-fet ) and there is not substitutes.
- NELSON PASS used SONY V-FET
You can find some "NOS" on the auctions sites but there is no way to test them before to pay !
I'm looking at an amp, and the seller says it has distortion in one channel.
What make you think that the "problem" is coming from V-FET ??
@clinic-audio I just assumed the worst. Is a Vfet either working or dead? Can bad Vfets cause distortion that gets worse as the volume goes up? The seller says the problem is related to one channel, the other channel is fine. I just don't want to buy a boat anchor.
clinic-audio
all on YAMAHA untill 1990
OK , I understand but I think that this is not coming from a V-FET but without the unit in front of me it is really difficult to know .....
What is the brand of this unit ?
If there is no brand on it , post a picture of the V-FET package , there is name on it and references
What is the brand of this unit ?
If there is no brand on it , post a picture of the V-FET package , there is name on it and references
only partially accurate.
Yamaha SB recommended Tokin 2sk180 as a direct replacement for 2sk77. The details of the SB stop there as to what rank or other specs the Tokin must have to substitute the 2sk77.
UnitedSiC makes power J-fets not V-fets.
Sadly, I was told they cannot be used in the place of V-fets.
guessing is the best you will get here without additional details.
some of the integrated amps, this one in particular do have issues in the pre-amp section. The first thing I would do (now that the owner has powered it up already) I would disconnect the pre-amp to amp bridge and test the amp separately. That should narrow down the root cause, between the amp and pre.
This amp needs to go on the bench of someone that understands v-fet amps, but sadly not too many ppl would touch it. Without too much detail, are we talking about the amp that just sold at the auction site last week?
Nope, I watched that one sell, but didn't jump in.
Is this a project you would take on if I can acquire the unit? Do you have a goto tech for vfet work? I need another broken amp like I need another hole in my head, but that doesn't seem to be slowing me down.
I searching for some common sense to forget about vfets all together. Are they really worth the effort?
slimecity
Super Member
The best thing you can do is look out for another unit to hope that it has some good VFETs in it.
The Sony amp you have, and the 4650, had some poorly designed circuitry in that if something went wrong, some/all of the VFETs died. Hence getting "parts units" can result in many dead VFETs in them also.
Any on sale on ebay are likely to be fake, ie: dont buy from China. NOS stock comes up now and then, but rare as hens teeth.
Thats only the first part of the problem - as mentioned above, VFETs in these amplifiers need to be of the same rank, or at least 2-3 ranks close to that rank. So you need to find (a) working VFETs, and (b) the ranks need to match.
Due to the above mentioned circuit flaws - if you lucky enough to find replacement VFET's, you need to modify the existing 5650 circuit to keep them alive.
Most techs dont like going near these due to these risks. Those who know about VFETs are also quite old these days, so there is much less practical working knowledge around as well.
The next best thing you can do, is put your amplifier aside and have a little cry. These VFETs really have become the holy grail. I know through bitter experience.
The Sony amp you have, and the 4650, had some poorly designed circuitry in that if something went wrong, some/all of the VFETs died. Hence getting "parts units" can result in many dead VFETs in them also.
Any on sale on ebay are likely to be fake, ie: dont buy from China. NOS stock comes up now and then, but rare as hens teeth.
Thats only the first part of the problem - as mentioned above, VFETs in these amplifiers need to be of the same rank, or at least 2-3 ranks close to that rank. So you need to find (a) working VFETs, and (b) the ranks need to match.
Due to the above mentioned circuit flaws - if you lucky enough to find replacement VFET's, you need to modify the existing 5650 circuit to keep them alive.
Most techs dont like going near these due to these risks. Those who know about VFETs are also quite old these days, so there is much less practical working knowledge around as well.
The next best thing you can do, is put your amplifier aside and have a little cry. These VFETs really have become the holy grail. I know through bitter experience.
