Against my better judgment i purchased a TA-5650 on ebay. Predictably, half the VFETs are dead.
I'm pondering my options here...
opinions/suggestions welcome
I'm pondering my options here...
- since the 5605 has 4 devices per channel, would it be possible to modify it to run of a single pair per channel? Presumably this would mandate the use of a somewhat lower voltage in order not to overload the remaining devices. I'd then get a VFET amp somewhat equivilent to the 4650 that i could at least listen to.
- Alternatively i could just sell the remaining good VFETs and recover my cost and either scrap the rest of the unit, or potentially modify to use standard MOSFETS just to avoid destroying a nice 70s amp if that is possible
- And the last option... obtain more VFETS. I Don't suppose anyone has a set of 4 going spare? 😀
opinions/suggestions welcome
All your options are valid.
There is little difference between a 4650 and a 5650, but rebuilding is hmm... a accurate job.
If bought on a virtual market, travel to the seller and check the fets before the deal. That's the only way for guarantee.
Selling a broken dream is an option. I consider mos a mishap. There is a unit with a 'Quad main amp inside'...
I own three 4650's (one in duty, one in service, one tampered with, maybe beyond service), and one 5650 (in service).
But all the 20 fet's ok (also in the tampered one!), with different ranges. What am I going to do with the tampered one?
There is little difference between a 4650 and a 5650, but rebuilding is hmm... a accurate job.
If bought on a virtual market, travel to the seller and check the fets before the deal. That's the only way for guarantee.
Selling a broken dream is an option. I consider mos a mishap. There is a unit with a 'Quad main amp inside'...
I own three 4650's (one in duty, one in service, one tampered with, maybe beyond service), and one 5650 (in service).
But all the 20 fet's ok (also in the tampered one!), with different ranges. What am I going to do with the tampered one?
On further inspection the amplifier board has clearly got quite toasty in it's life. lots of shrunken plastic sleeves on caps and oxidized tabs on the to220 parts. It would be quite a bit of work to bring it back, not something i want to embark on unless i know the results would be good with just half the vfets. If it came to trying to bring it back without any vfets at all it i'd probably put an ESP P3A in there or something (it can join the ta-f3 waiting for a p3a retrofit 😀 )
Your tampered unit sounds like a spare for if/when the others fail! 😀 unfortunately given the lack of new vfets there is no way around the situation where somewhere, somehow a unit has to die when the fets die.
I briefly considered looking at modern vfet designs with PCBs available that would make use of just the 4 remaining vfets, but dislike them all, poor performing single ended/ no feedback abominations IMO.
Your tampered unit sounds like a spare for if/when the others fail! 😀 unfortunately given the lack of new vfets there is no way around the situation where somewhere, somehow a unit has to die when the fets die.
I briefly considered looking at modern vfet designs with PCBs available that would make use of just the 4 remaining vfets, but dislike them all, poor performing single ended/ no feedback abominations IMO.
Do both: sell the ok vfets and use the carcass for exploration with that ESP.
In short: any combo jfet/mos/bjt) can make a triode output compound - power vfets (P/N ch) are possible again for next to nothing.
In the Pass section, various single ended designs are promoted.
Given the fact you have two working pairs, a full complementairy unity gain buffer is an option. A high voltage drive is needed though.
But that is not what makes the vfet sound! Such a buffer has the sources joined as the output, whereas the 4650/5650 has the drains joined as the output. And that, and that only, makes that extra dimension in sound reproduction, alike vacuum triodes.
I've posted some contributions on this issue, but not yet possible to disclose it (dragging lawyers issue).
In short: any combo jfet/mos/bjt) can make a triode output compound - power vfets (P/N ch) are possible again for next to nothing.
In the Pass section, various single ended designs are promoted.
Given the fact you have two working pairs, a full complementairy unity gain buffer is an option. A high voltage drive is needed though.
But that is not what makes the vfet sound! Such a buffer has the sources joined as the output, whereas the 4650/5650 has the drains joined as the output. And that, and that only, makes that extra dimension in sound reproduction, alike vacuum triodes.
:O sounds too good to be true! presumably such a solution requires a spesific drive circuit and wouldn't lend it's self to a direct replacment of a failed vfet in an unmodifyed sony
I might just sit on the working ones... just in case a TA-F7 turns up in a local charity shop or somthing 😀
....
well i can dream lol
It can be made of a jfet as input, and a enhencement mos objt to make it a vfet. Thus, when selecting the proper Vth, it nears a J18/K60 but extra power components must be added for the larger current (Darlington/Sziklai).