Sorry for the delay,I am the caregiver for my Dad.
Trying to help the same friend from this thread https://www.diyaudio.com/community/threads/threshold-s-300-repair.372868/
I gave the information received from the thread above to him. Since then, he has contacted me stating that the right channel of the amp stopped playing. So, he took it to a local tech who told him that the output transistors are toast. So,he has been trying to call Jon to talk about the repair of it.
Trying to help the same friend from this thread https://www.diyaudio.com/community/threads/threshold-s-300-repair.372868/
I gave the information received from the thread above to him. Since then, he has contacted me stating that the right channel of the amp stopped playing. So, he took it to a local tech who told him that the output transistors are toast. So,he has been trying to call Jon to talk about the repair of it.
I just had a stock front end of a Threshold amplifier repaired by him. However, I had already partially diagnosed the problem which may have made it a quick easy fix for him.
Did the tech explain how he came to the conclusion that the outputs are fried? The problem that I had was a very high DC offset caused by the JFET pair on the front end. I didn't test the channel to see if it still amplified a signal it as the offset was 10vdc but I believe the channel was non-functioning. There is also a Tantalum cap which is known to cause issues.
A stupid check is to check the two fuses for the channel that is bad
Did the tech explain how he came to the conclusion that the outputs are fried? The problem that I had was a very high DC offset caused by the JFET pair on the front end. I didn't test the channel to see if it still amplified a signal it as the offset was 10vdc but I believe the channel was non-functioning. There is also a Tantalum cap which is known to cause issues.
A stupid check is to check the two fuses for the channel that is bad
Jon's Threshold repair is a labor of love and not his day job. The day gig frequently keeps him away and occupied. He is however very reliable.
I fully understand being busy and the need for rest.😉
The tech didn't mention how he came to the conclusion that outputs are fried but, he did say that everything else was fine. I taking that to mean that the front end is functioning okay. The tantalum capacitor and fuses is something I will inform him about.
I myself have no doubts about Jon's integrity. I trust Gary and Nelson's recommendation of him wholeheartedly.
The tech didn't mention how he came to the conclusion that outputs are fried but, he did say that everything else was fine. I taking that to mean that the front end is functioning okay. The tantalum capacitor and fuses is something I will inform him about.
I myself have no doubts about Jon's integrity. I trust Gary and Nelson's recommendation of him wholeheartedly.
I believe someone was selling the transistors that were most likely used in that amp. I will PM you and for the information to you.
Hello folks, I am still here working hard to keep old equipment up and running. I have had quite the drama with keeping my .net web site, so recently went to onbizmap.com and facebook. Visit that if you would and help it get moving. I get many scam calls, please leave a good message.
Hi Jon,
I am a Forte 4A owner and would like to know what is the best way to contact you for repair request? FYI, the NSC-NPD5566 chip need to be replaced and I have a hard time finding one. Hope you can help.
I am a Forte 4A owner and would like to know what is the best way to contact you for repair request? FYI, the NSC-NPD5566 chip need to be replaced and I have a hard time finding one. Hope you can help.
Yes indeed they are hard to come by. I have a few in my reserve stock. you can contact me via vintageamp@surewest.net
Thank you both Jon and Nelson for your quick replies. I will reach out to see how I can buy the chip from either of you.
Good morning,
I should repair my Threshold T50.
I'm looking for NPD5566 chips.
Can anyone help me find 2 pairs of NPD5566 ?
I should repair my Threshold T50.
I'm looking for NPD5566 chips.
Can anyone help me find 2 pairs of NPD5566 ?
Qualcuno può aiutarmi altrimenti sarò costretto ad abbandonare un amplificatore al quale sono molto affezionato.
Very often the FET is mis-diagnosed as the failure point. The symptom of a bad fet is very high distortion with DC offset or DC offset with not signal and the fuses do not open. If the fuses open when power is applies, the FET is most likely not the problem. That failure mode would point toward output devices.
In my case the fuses do not open when power is applied. The output devices have been checked and they all appear ok