Threshold FET repair story.

[Renehc]

Hello

(At first I wrote this in another thread, but it might belong in its own, I believe. )


I just took my "new" Threshold Fet nine to service, and I would like to share my experience.




Regarding the technician:

I have some questions.. I really did not like how this started when I at first, gave him the FET. First of all he where a bit careless when taking it out of the original box from march 1987, "scraapiing" it along his table (..not the box) as if he "just" thought it was a cheap piece of PA equipment.. grrrr. So I told him to "be gentle to my babe - looks like ALL new, you see sir? He looked at me like a dog who did not understand the words of his master... So then, I asked him to open it up (so he could see what was actually inside) - which he did not do, he was already a bit angry at me... As he said, "I`ve been in this business for 25 years, been servicing B&O, (while pointing his fingers at the "certificate" hanging on the wall next to him), "I know what I am doing".

I was/and am a bit worried, because he did not seem to mind the goal of good sound......

I went away from his shop and he called me an hour later, he told me what was wrong: it needed new (maybe output!?) transistors I believe 7 of them and a.. ehm relay (danish: relæ)?!

I told him that Jon Soderberg from the old High End company "Threshold" (he did not know about Threshold.. I think: PA look-a-like for him.. you know), said that I should change the capacitors also.... He told me, "I looked at them and they look fine" (I DONT know if he did any measurements of them, because his answers where like... "I know what im doing" - but he should do that right?)

- He told me that he could get the RIGHT transistors, and I was amazed..... As far as I know it is not possible to get these anymore, and therefore you need to find alternatives to 2N5566 as an example - any respond to that?

- When changing/upgrading transistors, will it be normal TO MATCH them, if you are a technician? .. Do you normally buy "matched transistors", so that all of the new transistors are functioning perfect as they should?

- How about this relay? Do they come in a variaty? Will "this one" be better than "this one"? Well im sure he knows what he is doing, but again, im not sure he has this thing, "sound", calculated with it... I just dont know...


A quick note to everything I wrote:

... I believe he got my point in the end, when I told him I wanted to have this repaired as good as new, and sound was important to me - and that is why I had a lot of questions when I was at his shop.
If he took that seriously, maybe he did go the extra mile(!)


Before everything gets done by him on monday/tuesday i think, maybe I can reach out to him with good questions made by you... with the RIGHT questions that this technician understands


ADDED PICTURES:

Pictures:

IMG-0991 — imgbb.com

IMG-0989 — imgbb.com

IMG-0990 — imgbb.com


Regards..

 

[Zen Mod]

take it to another tech

 

[diyiggy]

if staying with this odd tech...

- I will not worry too much about the relay choice first (but indeed some are better for audio purpose but you're not sure Threshold chosed them for that but people here can't answer without knowing the former model and its spec)

- transistors : is it that so fragile in a Pre ? You may ask if they are the exact reference or just "compatible" chosed from equivalent datasheet list (not the same brand & not exactly the same spec : it works but may waste all the efforts of the sounding design as you guessed). Worst case, ask him to give you the former parts to have the reference for a futur sota refurbishment to sold it (and to test it after but it's may be also a honest guy)

- There are some vintage hifi gears forums where you may ask about Threshold, your model & whether transistors matching about it.

- You should try the service manual if exist to have all the circuits specs and parts list

-You could shoot a picture of inside to know about the caps (brand, if top is bumped or if some linked (main power caps).

- You indeed try an enthusiast audio tech or a a DIY hifi club; here is certainly a good place to ask but also forums of your country !

- You may try to buy a DVM, good soldering station and ask the very good reliable techs & engineers here able to help you.

hope that "roadmap" helps for your project.

 

[Zung]

Yeah, look for another tech.

You didn't say what's wrong with your preamp, so I can only answer your specific questions:

1. Capacitors: you can't tell their conditions just by looking at them, so the tech is wrong. But then again, what the Threshold guy said is only a precautionary advise: old cap's are not necessarily bad: I've got a McIntosh tube amp from the 60's, and the original cap's are still good as new: capacitance, Q factor... I have replacement cap's ready to be fitted, but I see no point in doing this, nearly half a century after.
2. Transistors: the 2N5566 are hard to find, but yours may not be dead at all: it takes some effort to kill them, lightning for ex. The others TR are not difficult to find or to subs. Regarding matching, the 2N5566 are dual's, sort of pre-matched; the rest are not that critical. If you're really fussy, maybe you want to pay the tech to match Q10 & Q11, the output Tr, if he has a tester.
3. I don't see a relay in the service manual

Since this is DIYaudio, maybe you should consider doing it yourself, but start with something you don't care for, like one of the cheap Chinese kit.

 

[diyiggy]

If that one Threshold FET One Series Two Preamplifier: Beautiful Condition, Only One Owner. | eBay


look at the last picture...


should be not that hard to fix... yellow caps:leave it, no chance their value changed.

 

[Zen Mod]

oh yeah - and move this thread to Pass Forum

some info here , as well : Treshold Treasure …… while Papa was there : FET 9 | Zen Mod Blog

 

[elwood625]

I had a Threshold FET 9 and an S300 amplifier for over 20 years. My house was hit by lightening which took out everything plugged into 110v EXCEPT the S300. Worked perfectly, the FET 9 had a ground hum which required two new capacitors to fix, total cast $50 (2003 dollars). My FET 10Pe section required new capacitors in the power supply after over 27 years of ownership, constantly on, no on-off switch.
These things are incredible, I agree with Zen Mod, find someone else to work on it, HURRY!

 

[GaryB]

. . .I have some questions..

I went away from his shop and he called me an hour later, he told me what was wrong: it needed new (maybe output!?) transistors I believe 7 of them and a.. ehm relay (danish: relæ)?!

- He told me that he could get the RIGHT transistors, and I was amazed..... As far as I know it is not possible to get these anymore . . .

- When changing/upgrading transistors, will it be normal TO MATCH them . . .

If you look at the service manual for the FET 9 that Zen Mod linked, you'll see that the output transistors are MPSA42 and MPSA92 bipolar transistors. These are still in production. And bipolar transistors don't need to be matched. So if the problem with your FET9 is the output transistors then your tech could be on the right track. The relay also isn't critical.

Regarding replacement of the electrolytic capacitors, I recommend that for any older piece of electronics. But your tech is right that it will work just fine with the older capacitors. It's easy to change these out, so I'd suggest you take on that job yourself when you get the preamp home. Listen to it first - if you like the sound then you might not even bother. But it probably would benefit from changing them.

Good luck!
---Gary

 

[diyiggy]

Hi elwwod625,

Do you remember the model & brand of the lytic caps int it please ?

I saw a purple one which seems an Elna. But what about the blue ones ? Elna as well ? It was from Ebay picture but perhaps those lytics were already swapped...

Ahahaha maybe it's just a relay or the main separate powersupply

 

[GaryB]

Do you remember the model & brand of the lytic caps int it please ?

I saw a purple one which seems an Elna. But what about the blue ones ? Elna as well ? It was from Ebay picture but perhaps those lytics were already swapped...

I've owned quite a few different Threshold preamps including an FET one series II, like the one in the ebay listing, an SL10, and the FET10. The brand of caps in the later preamps like the FET9 and the FET10 was different from the ones in the earlier ones (SL10 and FET one).

The original power supply caps in the FET one were Mallory 2000uf 75v caps. The smaller blue electrolytics were labeled "Instrument Devices", which is a brand that I don't know much about.
If you want to upgrade the smaller caps in your preamp, I'd use something like the Elna RFS Silmic II caps which are available at Digikey and Mouser.

---Gary

 

[diyiggy]

Thanks Gary B.


Nah, nope the Silmic II... please...

 

[Renehc]

take it to another tech

yeah.. I should at that time.

I talked to him on the phone yesterday, and he really softened.. I believe he understands a bit more what it means to me..

He thought that he could get the 2N5566 transistor, I told im "maybe impossible", and since he found out that this is the case, he saw he caught me wrong in the first place - this is good.

 

[Renehc]

- I will not worry too much about the relay choice first (but indeed some are better for audio purpose but you're not sure Threshold chosed them for that but people here can't answer without knowing the former model and its spec)

- transistors : is it that so fragile in a Pre ? You may ask if they are the exact reference or just "compatible" chosed from equivalent datasheet list (not the same brand & not exactly the same spec : it works but may waste all the efforts of the sounding design as you guessed). Worst case, ask him to give you the former parts to have the reference for a futur sota refurbishment to sold it (and to test it after but it's may be also a honest guy)



- There are some vintage hifi gears forums where you may ask about Threshold, your model & whether transistors matching about it.

- You should try the service manual if exist to have all the circuits specs and parts list

-You could shoot a picture of inside to know about the caps (brand, if top is bumped or if some linked (main power caps).

- You indeed try an enthusiast audio tech or a a DIY hifi club; here is certainly a good place to ask but also forums of your country !

- You may try to buy a DVM, good soldering station and ask the very good reliable techs & engineers here able to help you.

hope that "roadmap" helps for your project.

First of all, I am NO technician (I wish I were).


Relay:

Thanks - Thats good to hear.


Transistors:

Jon Soderberg said that 2SK174 can be matched to form a new pair. So I am thinking (with my lack of knowledge) that I could use the 2N5566 in the phonostage section, and use as the replacement for the faulty one, and then use a paired 2SK174 in the phonostage - possible?
The reason: I dont use the phonostage much, if not at all.


I should try and find a Danish forum - absolutely. (Jon send me hear, because of your expertise - and that there was a forum for "Pass".)

There seems to be some danes her also - I could ask

Thanks for your reply diyiggy.

 

[Renehc]

Yeah, look for another tech.

You didn't say what's wrong with your preamp, so I can only answer your specific questions:

1. Capacitors: you can't tell their conditions just by looking at them, so the tech is wrong. But then again, what the Threshold guy said is only a precautionary advise: old cap's are not necessarily bad: I've got a McIntosh tube amp from the 60's, and the original cap's are still good as new: capacitance, Q factor... I have replacement cap's ready to be fitted, but I see no point in doing this, nearly half a century after.
2. Transistors: the 2N5566 are hard to find, but yours may not be dead at all: it takes some effort to kill them, lightning for ex. The others TR are not difficult to find or to subs. Regarding matching, the 2N5566 are dual's, sort of pre-matched; the rest are not that critical. If you're really fussy, maybe you want to pay the tech to match Q10 & Q11, the output Tr, if he has a tester.
3. I don't see a relay in the service manual

Since this is DIYaudio, maybe you should consider doing it yourself, but start with something you don't care for, like one of the cheap Chinese kit.

The problem:

There are a constant hizzing noise (not that loud).
There are some louder popping/hizzing noises, every two minutes or so, its quite sporadically.


The capacitors:

Hmm.. I should as him again whether or not he took measurements of them, and ask him to do it if not.


The 2N5566 transistor:

The technician told me that it was dead.
I will ask him to save the old parts.

What is Q10 & Q11? (sorry... )

It sounds interesting! Can I do this you think? - when I say that im a salesman, yes?


Thanks for your reply

 

[Renehc]

If that one Threshold FET One Series Two Preamplifier: Beautiful Condition, Only One Owner. | eBay


look at the last picture...


should be not that hard to fix... yellow caps:leave it, no chance their value changed.

It a FET nine. I will try to post pictures. I tried before but it did not workout well.

Thanks!

 

[Renehc]

Pictures:

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

 

[Zung]

... It sounds interesting! Can I do this you think? - when I say that im a salesman, yes? ...

Normally, engineers are not allowed to talk to salespersons; but since I'm retired, I'll make an exception, just this once

... There are a constant hizzing noise (not that loud)...

That could be the 2N5566... Was the preamp silent before, and then this happened or has it been always like that? Anyway, you can replace them with LKS389 (dual) or matched LSK170 or matched 2SK170 if you can find the genuine ones.

... There are some louder popping/hizzing noises, every two minutes or so, its quite sporadically...
...

That could be the cap's in the power supply frying. I would use the opportunity to replace all of the electrolytics; refer to the service manual, that'll be C1, C2, C7, C8 in the regulated power supply, and C1, C2 in the universal supply. Follow Nelson Pass's lead and use Elna Silmic if you can.

The 2 points above make me think your tech is not such a meatball after all, even though a long record of servicing B&O stuff is more a liability to me .

... What is Q10 & Q11? (sorry... )...

These are the output transistors in the phono stage schematic and the high level schematic in the service manual.

And yes, you can do it, but first get some practice on some stuff you don't care about. You also need to invest in a good soldering iron, like the T12, about $50, and a good DVM, about $20 (do a search) plus some hand tools like pliers & screwdrivers.

 

[Renehc]

Hope this one works.... Here goes!

Pictures:

IMG-0991 — imgbb.com

IMG-0989 — imgbb.com

IMG-0990 — imgbb.com

 

[Renehc]

oh yeah - and move this thread to Pass Forum

some info here , as well : Treshold Treasure …… while Papa was there : FET 9 | Zen Mod Blog

Already moved it once.

Can the whole thread be moved maybe?

 

[Renehc]

I had a Threshold FET 9 and an S300 amplifier for over 20 years. My house was hit by lightening which took out everything plugged into 110v EXCEPT the S300. Worked perfectly, the FET 9 had a ground hum which required two new capacitors to fix, total cast $50 (2003 dollars). My FET 10Pe section required new capacitors in the power supply after over 27 years of ownership, constantly on, no on-off switch.
These things are incredible, I agree with Zen Mod, find someone else to work on it, HURRY!

Its a nice piece for sure - a keeper.
Think I will try the ELna Silmic ones. Just have to be more sure about which ones specific and all before telling the tech....

And... the Tech:

Its better, he understands my problem now, and seems like he wants to do it right, letting me find the right parts, for the sake of good sound.

Regards - and thank you.