Let's try this again, here you go.
Here ia a nice large image.
http://www.briangt.com/gallery/album01/AF3?full=1
Regards
Anthony
Here ia a nice large image.
http://www.briangt.com/gallery/album01/AF3?full=1
Regards
Anthony
Attachments
Hi,
I am about to modify an old set of Sugden p128, removing twin pair of 2sk225/j81 and inserting 4 pair of 2sk1058/j162 just like yours.
I had thought the extra capacitance of 4 pair would overload my VAS and intended adding in a pair of bjt drivers.
I see yours has no drivers.
Q what is the cascode type & do you expect it to cope?
Q what is the VAS quiescent?
Q Why are the gate resistors on N & P channel the same?
I am about to modify an old set of Sugden p128, removing twin pair of 2sk225/j81 and inserting 4 pair of 2sk1058/j162 just like yours.
I had thought the extra capacitance of 4 pair would overload my VAS and intended adding in a pair of bjt drivers.
I see yours has no drivers.
Q what is the cascode type & do you expect it to cope?
Q what is the VAS quiescent?
Q Why are the gate resistors on N & P channel the same?
spence said:
I am not sure sure, but as these MOSFETS were designed to be used in this configuration as pairs I assume it is not a problem The amp works very well, right channel is working great, the left channel may have a bad device, I have to take it apart and trouble shoot it.
Regards
Anthony
Banned
Joined 2002
I noticed the original Mosfets in the circuit are the K135/J50.
I cant imagine it wise not to use emitter R's, there is no way to select these Lateral Mosfets good enough to skip those.
From the Hitachi days i remember some who tried despite warning, in those days these Mosfets were US$10 the piece.
(the circuit resembles an elektor oldy).
The K225/1058/135 have equal Css, same goes for the J81/162/50.
Going from 2 to 4 pairs without other changes will not be an improvement, for one it will kill SR.
The SugdenP128 is nice, i fancied the brand alltogether.
I cant imagine it wise not to use emitter R's, there is no way to select these Lateral Mosfets good enough to skip those.
From the Hitachi days i remember some who tried despite warning, in those days these Mosfets were US$10 the piece.
(the circuit resembles an elektor oldy).
The K225/1058/135 have equal Css, same goes for the J81/162/50.
Going from 2 to 4 pairs without other changes will not be an improvement, for one it will kill SR.
The SugdenP128 is nice, i fancied the brand alltogether.
jacco vermeulen said:I cant imagine it wise not to use emitter R's, there is no way to select these Lateral Mosfets good enough to skip those.
From the Hitachi days i remember some who tried despite warning, in those days these Mosfets were US$10 the piece.
(the circuit resembles an elektor oldy).
I agree with Jacco, without source (emitter) resistors, the devices will not share current evenly, one MOSFET is likely conducting the majority of the current. You mentioned that you thought there may be a failed device in one channel... this could be why.
For my amp using SJ162/SK1058, 0.47R source resistors seem to do the trick, all the MOSFETS share current evenly.
Regards, Spence
Banned
Joined 2002
Banned
Joined 2002
One channel is working great, the other channel has given me problems since Day One. I can not retrofit Source resistors in the current configuration. I would have to remove all the devices for the boards and hard wire them PTP. I also am having some trouble finding replacement 2SK/2SJ devices. I bought these kits several years ago and have only just finished the amp. I have already moved on to finishing my Aelph 5 and then to fix my Rotel 1080. This project will likely sit for another few months before I even begin to think about stripping it completely apart to get the defective main board on the test bench again,
Regards
Anthony
Regards
Anthony
Coulomb said:One channel is working great, the other channel has given me problems since Day One. I can not retrofit Source resistors in the current configuration. I would have to remove all the devices for the boards and hard wire them PTP. I also am having some trouble finding replacement 2SK/2SJ devices. I bought these kits several years ago and have only just finished the amp. I have already moved on to finishing my Aelph 5 and then to fix my Rotel 1080. This project will likely sit for another few months before I even begin to think about stripping it completely apart to get the defective main board on the test bench again,
Regards
Anthony
Anthony,
Can you desolder the source lead on the MOSFET, bend upward, attach source resistor, and insert the lead of the resistor into the hole where the source pin was? Do you have a picture?
Also, make sure the resistors are ~ 5W, 0.47R.
I would not scrap your boards, the circuit looks good... just squeeze in some source resistors. Make it fit
http://tech-diy.com/ <--- where to get SJ162 / SK1058... they can even be ordered in matched sets. I never ordered from these guys, so caveat emptor.
Regards, Spence
spence said:
Anthony,
Can you desolder the source lead on the MOSFET, bend upward, attach source resistor, and insert the lead of the resistor into the hole where the source pin was? Do you have a picture?
Also, make sure the resistors are ~ 5W, 0.47R.
I would not scrap your boards, the circuit looks good... just squeeze in some source resistors. Make it fit
http://tech-diy.com/ <--- where to get SJ162 / SK1058... they can even be ordered in matched sets. I never ordered from these guys, so caveat emptor.
Regards, Spence
AndrewT said:
Thanks for the tips guys, I will definately grab some matched pairs for spares.
I have thought about your suggested implementation of the source resitor Spence, I am just not sure if it is achievable. I have attached a link to a photo which shows how the boards are mounted to the heatsinks. As you will see there is little space for a 5W resistor under there if it's profile is thicker than the transistors, maybe a Caddock, but not a Mills ot other axial device.
http://www.briangt.com/gallery/album01/DSC00178?full=1
Regards
Anthony
AR2 said:
Hello ARnot,
I have tried tirelessly to crack the mystical supply chain for these kits. The Manufacturer was a chinese company called Accoustic Fidelity, they were distributed by SME in Hong Kong. My local Asian parts supplier used to stock shelf loads of these kits for $150 CAD all parts included, though I did swap out some dubious quality parts.
I often wondered if a high end version was warranted, but with so much to build, why bother?
Regards
Anthony
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