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PostPosted: Sat May 20, 2017 2:39 pm 
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Location: *, ON, CA
I have done boards off total rebuild on a Scott 299D and a McIntosh 2505 for, for me, obvious reasons, I plan to keep them. For me that is the only way, vintage means many things, for some it is an iPhone 1. A careful inspection is a must and your investment in the sound of that piece. If it has a selenium bridge rectifier replace it. Many younger pieces just need a good cleaning, dust is the enemy, potentiometers need cleaners with a little spirits to preserve the wafer boards. Lastly the answer to your question, no, and some are very difficult to find. T fwiw


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PostPosted: Sat May 20, 2017 4:31 pm 
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I'd say, to me, it's not worth it to pull a cap to test it, even if I had an ESR meter rather than replacing it anyway. That would usually be matched pairs or more of modern high-quality caps, why wouldn't you do that and do it yourself? If you can read and use a soldering iron you can do it. You could also electrocute yourself, peel the traces off the board, accidentally screw something else up, do a really shitty job, ruin the finish on an irreplaceable piece of equipment, needlessly spend hundreds of dollars....


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PostPosted: Sat May 20, 2017 7:51 pm 
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It's best to have them all original, unless the original design and/or parts used were defective.
Different driver transistors affect the sound much more than different power transistors.
Any change to the signal path will affect the sound, to some degree.
It is possible to completely ruin the original sound quality, but it is also possible to improve greatly, depending on what exactly is done.
It's tricky, a form of art.


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PostPosted: Sat May 20, 2017 11:40 pm 
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Location: Victoria, BC, CA
mcgsxr wrote:
I just picked up a mid 80's Sugden P28 power amp. SS, Class A/B.

Having a local tech (Dan Santoni) go through it. The amp works, but I want to hang on to it for a long time, so spending some $ to have it reviewed and likely replace the capacitors feels right to me.


Dan did some work recently on my mid 80's Sugden A25 integrated. Sounds wonderful. I had a P28 with the matching C28 preamp, and the pairing was excellent sounding.


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PostPosted: Sun May 21, 2017 12:41 am 
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Location: Coquitlam, BC, CA
Trying to get fancy with the caps can lead to sound quality issues, absolutely. Some are designed for certain uses and I noticed a big difference between Elna Cerafines and Silmics for examle. My best advice is to do whatever you want to do, but if you have to ask then you probably aren't ready yet.


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PostPosted: Tue May 23, 2017 11:35 am 
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Location: Burlington, ON, CA
cyrus wrote:
mcgsxr wrote:
I just picked up a mid 80's Sugden P28 power amp. SS, Class A/B.

Having a local tech (Dan Santoni) go through it. The amp works, but I want to hang on to it for a long time, so spending some $ to have it reviewed and likely replace the capacitors feels right to me.


Dan did some work recently on my mid 80's Sugden A25 integrated. Sounds wonderful. I had a P28 with the matching C28 preamp, and the pairing was excellent sounding.


Dan's work was excellent on my P28. Very pleased with it now. Had all caps and the input rca's replaced. Sounds like the old A28B I had from 94-04. Great stuff.

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PostPosted: Tue May 23, 2017 2:29 pm 
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Hi mcgsxr,
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Re: Does old SS Gear always need all output transistors repl

No, not unless something nasty happened to them. Replacing outputs or drivers (any parts really) can get you into trouble big time. Your amplifier might oscillate with some transistors if they are a lot faster or slower than the originals. That and most people don't match the transistors, especially the diff pair. These must be matched if you want good sound. However, a "meter" or tester won't do this. You need to build a jig in order to match transistors.

If your amp changes it's sound with different drivers, either it is broke, or was broke. Please don't mess around with stuff that really does require training. Most technicians aren't trained by the way.

-Chris


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PostPosted: Tue Sep 19, 2017 10:49 pm 
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<If the transistors are shot the item is pretty much toast.>

Wow. Sorry, but I replace and upgrade transistors when they are bad on a regular basis along with upgrade caps, resistors, diodes, replace all incandescent lamps with custom DC-powered LED retrofits, etc. When the unit is finished, it sounds much better than when it left Japan 40-years ago. I do it every day. Throw your "unrepairable" "toast" my way.


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PostPosted: Wed Sep 20, 2017 2:43 am 
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Location: Sherbrooke, QC, CA
Does it surprise you that people who believe in break-in periods would subscribe to the notion that at any given point in time any component or part has expired?

Audio has been a bad joke for years enjoyed by total neurotics.

I think all equipment should have a "best before" date and be immediately sent to the rubbish tip beyond it.

:shock:


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PostPosted: Wed Sep 20, 2017 4:10 am 
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I am using a 30 year old British Fidelity amp that produces 135 WPC with the first 100W in class A, lots of heat.
It sounds very good IMHO and I don't hear any signs of degradation.
One thing that attracted me to the unit was the beautiful dual mono layout inside, twin toroials and 176,000 pF combined capacitance high end power supply caps. Also, high quality raised sand resistors.
The big caps look great, there's a bit of heat discoloration around one sand resistor that's not raised above the PCB as much as the others. The output transistors all appear to have good paste and contact with the heat sinks.
The parts are marked as specially made for Musical Fidelity and I am sure they are high quality and my ears tell me all is well. I doubt I could find better caps, and these ones seem to be fine. I'm not interested in removing/testing them.

I have recapped sound cards on pinball machines and am aware of how caps fail. Very comfortable desoldering and soldering but why would I mess with it ? Boredom?
Sounds like I am an exception here.

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PostPosted: Wed Sep 20, 2017 6:28 am 
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Location: toronto, ON, CA
deltalight wrote:
<If the transistors are shot the item is pretty much toast.>

Wow. Sorry, but I replace and upgrade transistors when they are bad on a regular basis along with upgrade caps, resistors, diodes, replace all incandescent lamps with custom DC-powered LED retrofits, etc. When the unit is finished, it sounds much better than when it left Japan 40-years ago. I do it every day. Throw your "unrepairable" "toast" my way.


When is a transistor "bad" other than when it has failed?


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PostPosted: Wed Sep 20, 2017 7:16 am 
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Break-in periods may be worthy of serious discussion, but I don't see what break-in periods have to do with the topic thread.

PBB wrote:
Does it surprise you that people who believe in break-in periods would subscribe to the notion that at any given point in time any component or part has expired?

Audio has been a bad joke for years enjoyed by total neurotics.

I think all equipment should have a "best before" date and be immediately sent to the rubbish tip beyond it.

:shock:


I also don't agree with the condition "If you believe in A, then you are a B."

I take it that the gist of this post should be something close to "output transistors don't expire". Or possibly, "really, really don't expire".

Please note that any comments to this moderation post are off topic and should be made only by PM.


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PostPosted: Wed Sep 20, 2017 7:42 am 
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I can't believe that some folks would replace outputs without any regard to their AC ratings. Of course, if you don't check for oscillation or instability, it could be called "fat, dumb and happy".

Just "recapping" a unit doesn't address some other issues, and often the parts used are not optimal for the application. I would love to see untrained people who do this for money thrown in jail, because the real techs have to clean up after them and it is all done on the customer's nickle. I have seen stuff run for a couple years that you would swear should have blown up right away!

As for replacing outputs "and it sounded better", hogwash. Not unless the original outputs were leaky or the beta had dropped a great deal. If you do properly match the outputs and install ones that will mate with the circuit (or adjust the feedback high frequency response), then yes. The amp section could sound better. Without a THD analyser and low distortion sine source, you can't make any claims as to whether something works better or not.

I guess some of this comes down to the customer too. If you leave your set with someone without proper equipment and actual training, well, that's pretty stupid. It takes a good first-hand knowledge of measured characteristics of parts before anyone is able to choose the proper ones to replace, or even identify the parts that could be replaced. This goes for everything including transistors, capacitors and resistors. There isn't any one "best type". It all depends on what they are doing.

Finally, in normal service, outputs and drivers do not really go bad. The odd ones can, but that is no reason to replace them. If someone didn't replace all the transistors that should have been after a failure, then the remaining transistors have probably changed beta, leakage and other characteristics. While this won't necessarily cause a later failure - it sure can. What it often will do is compromise sound quality. One common misconception is that the output stage can be made tougher by installing outputs rated at higher power, voltage and / or current. This is only very marginally true, but not true enough to matter. Replacing them for "better sound" is often a make-work project and a completely unnecessary waste of a customer's money.

deltalight, you scare me. Your grasp of components is clearly not good enough for you to do what you are doing, and it is those folks you do work for that pay for that. I guess everything looks easy and straight-forward when you don't understand a subject. You haven't a clue as to what is a proper substitute transistor or what constitutes an "upgrade" with output transistors. Do you even know how to match them, and have the equipment to do that?

-Chris


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PostPosted: Wed Sep 20, 2017 8:08 am 
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Transistors DO blow on a regular basis...on high usage motor controllers. I have all kinds of solenoid control replacement transistors for pinball machines and have replaced many. These are higher powered, low frequency switches. Great Plains Electronics is good for that stuff.

Audio transistors regularly blowing, probably not so much. They aren't controlling solenoids at up to 48V either. They are switching at high frequencies and much lower voltages. And at a level where they must be calibrated to optimally work with matching units.

Capacitors are limited by the seal and the film inside. The quality of the can too. Generic small caps probably do fail fairly quick relatively speaking. I don't think higher quality larger power supply caps quite so frequently. But again a lot of passive board components are truly made in the old Chinese spirit of "cheap comes first". I am happy to see some higher quality electronics now built there.

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PostPosted: Wed Sep 20, 2017 8:37 am 
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Audio transistors blow very infrequently unless they have been abused. What is this abuse?
    High temperature. Blocked ventilation or loose mounting hardware, poor mounting in the first place'
    Excessive current. Shorted load (wires), or full power at high frequencies
    Excessive voltage. Poor designs where the parts aren't rated high enough. Inductive kick-back will do this too
    Operation outside of the SOA. There is derating so you can't use a transistor keeping the power constant across volts and current
    Outside influences. That would be covered by lightening or drinks spilled inside.
For every 10 °C rise in temperature, reliability goes down by 1/2. Long term operation at high temperatures does degrade a transistor.

Other than that, transistors are normally very, very reliable and don't really fail due to age like some other components can. Of course, the wrong transistor cause oscillation and fail due to high temperature and high current.

The output transistors I stock are normally only used when a unit blows a channel, or the unit has the wrong type of output transistors in it.

-Chris


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