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Hafler NOS MOSFETS

R

rmaiers

New Member
Has anyone bought the Hafler NOS MOSFETS being advertised on the Bay? I have Hafler DH-200 and DH-500 power amps that I intend to keep a while and am wondering if I should pick up some of the NOS Hitatchi MOSFETS as it sounds like they are getting hard to come by.
 
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Don't panic. You shouldn't have any problems with mosfets in yours Hafler amps, if used properly, for next 20 years. Better to check the condensers. And if you'll ever need a new mosfet I suggest you to take Exicon from Profusion, even better than Hitachi.

LIX
 
Thanks for the advice. I did have the Hafler DH-500 checked out by a Hafler qualified technician about a year ago and he said it met or exceeded all specifications and the DH-200 doesn't have any issues as far as I can hear even when pushed. Does it make sense to start replacing parts when there are no problems?
 
Yes it makes sense. How old are your Haflers - 30 years? What is the life of a condenser - 10 years? New ones much less. After 30 years it is almost impossible that every condenser in an amp is still good. I'm not saying that I didn't see amplifiers of this age when I decided to not touch anything, but it happens very very rarely. There are many more of them, which worked fine until yesterday and today they are completely blown. Leaking capacitors and bad solder joints usually cause such disasters. And I don't know of a professional technician who is willing to spend hours and check all solder joints with a lens and check all condensers. Usually they connect an oscilloscope, check the clipping level, sometimes they check for a possible oscillation and maybe distortion. That's it, done. Let me explain in other words - would it make sense to you driving a 30 years old car with oil and brakes never changed at maximum speed on a highway?

LIX
 
Agree with Lix to get the aging components out of the circuits. I've got dual Haflers (P500 and DH200) but have updated the driver boards and the power supplies in both.

As for the MOSFETs on eBay, I'd not touch them until I got word from some of the respected restorers that post here at AK that they are for real. I fully expect them to be marked as Hitachi but really are not. I certainly am not going to risk one of my amps with them.

Cheers,

David
 
He was asking about MOSFETs... answer is still no, what benefit would he gain by replacing those when they're still working?

John
 
jdurbin1 said:
what benefit would he gain by replacing those when they're still working?

John
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Soldering practice and used spares instead of new spares if he did buy a set. Otherwise, as some have stated before: if it ain't broke don't fix it.*

*we all have our opinions about condensers/capacitors that is a little bit different from the blanket statement about repairing working units.
 
dshoaf said:
As for the MOSFETs on eBay, I'd not touch them until I got word from some of the respected restorers that post here at AK that they are for real. I fully expect them to be marked as Hitachi but really are not. I certainly am not going to risk one of my amps with them.
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David, can you elaborate on your suspicions?

The seller is Sound Values - the same folks who bought out Hafler and Dynaco's back stock. They have a large number of NOS Hafler parts for sale. If anybody's sitting on original Hitachi MOSFETs, it's them.

I have no affiliation other than being a satisfied customer for other NOS parts from them. I would think that buying from them would be a pretty good risk.
 
IF it is SV then I'd be more inclined to purchase as long as they're sold in matched pairs needed for the amps. I, too, have picked up some of the cosmetic parts I needed for my Hafler gear.

I assumed that we were talking about an Asian vendor of some sort. Shows you that I _should_ actually check out the OP's comments before starting to type - and making assumptions.

Cheers,

David
 
Thanks for all the good responses. It is nice to know there are so many vintage Hafler owners out there that are knowledgable about the equipment and willing to share what they know.
 
If you care....

You can look for a thread on my DH-500. I replaced the differential amplification transistors because the DC offset was over spec, and while I was in there, I also redid every cap in the amp, except for the two big ones. Those are also on the list for replacement, but I just haven't gotten to it yet....

Anyway, recapping the DH-500 is a piece of cake....:thmbsp:
 
Thanks! Can you direct me to your DH-500 thread. I have been thinking about replacing the differential amplifier transistors because of excessive DC offset.
 
Dh/p500

If you go to hafler's website the manual is available.
had downloaded it before.
the p500 is close in design to my SCS 2450a
used the hafler info to base some of my diagnostics.
other than a schematic cannot find any tech information on it.
note: the Hitachi mosfets dont have to be match for nchannel/pchannel pairs.
But do have to match gain on all nchannels and gain on all pchannels
have to have matched sets
example the qp113/2sj56 p channels have to match gain and the qn113/2sk176 n channels have to match gain
the d/p500s should have 3 pair of 2sk176(qn113)/2sj56(qp113)
the q numbers are Hafler's numbers for the Hitachi 2sk176/2sj56
also the older Haflers without drain(emitter) follower resisters have match marks printed on the cans.
if the sets are not matched the one with the most gain will hog current and run hotter than the rest, on that rail. possibly fail, short
have had used trannys with the same mark not match.
you cannot check gain on mosfets the same way as regular bi polars.
so if you are buying NOS see if they are matching gain, if they are worth buying they will now what are asking about or state that they are matched
 
I've also wondered about these MOSFETS becoming unobtanium and looked at these packages on ebay. However, I've heard others agree with lixaudio that you'd have to be doing some crazy stuff to need to replace them...
 
I would suggest getting a few to squirrl away, once sound values runs out, the will be VERY hard to find, have been for years.

The Exicon parts mentioned above tend to oscillate in the haflers from what I have heard, and are not recommended for replacemet use.
 
bharper said:
The Exicon parts mentioned above tend to oscillate in the haflers from what I have heard, and are not recommended for replacemet use.
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I read that in Sound Values sales literature. It's not that I don't trust them to be the authority on Hafler, but since they have an interest in clearing out Hitachi stock, I'd be interested to hear what other parties have had to say on the subject.
 
hafler dh 500 the treasure

analog addict said:
You can look for a thread on my DH-500. I replaced the differential amplification transistors because the DC offset was over spec, and while I was in there, I also redid every cap in the amp, except for the two big ones. Those are also on the list for replacement, but I just haven't gotten to it yet....

Anyway, recapping the DH-500 is a piece of cake....:thmbsp:
Click to expand...

hy ilike to ask you about the big yellow cap sprague ,idont remenber the value of it , but if ichange for new ones or better quality ones , each one you sugest ? thanks very much ! ifix my hafler in the way to musical concepts , i have the intuition to open up again and dont ask me how , ijust spray to the inputs ,clean the fuses and that it . the amp was overheating ,cutting off ,and switch was flashing ! thermal issues ! luck my ibeen listen 5 or 6 hours of music and trying 5 or 6 diferent preamp ,to find out thr better match , ken basic 2 soudcraftsmen cx 4000 , the superphon revelation , onkyo 301 ,and p3300 onkyo also , any sugestion ? thanks pwilson :music::thmbsp:
 
I did contract work for Sound Values (Valves) during the acquisition of the Hafler stuff. I talked to the president of S/V a couple years ago when he came across a large stock of mosfets from the factory. I'd bet S/V's mosfets are legit.
 
Sorry.....

rmaiers said:
Thanks! Can you direct me to your DH-500 thread. I have been thinking about replacing the differential amplifier transistors because of excessive DC offset.
Click to expand...

This thread got away from me. It's discussed in the other current DH-500 thread, but at the risk of being redundant, look here.....
 
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