Longevity of mosfet transistors, etc? My Soundcraftsman PCR800 amp

[Mark609]

I have an old 1987 Soundcraftsman PCR 800 amp that was used for many years to drive DIY subs and is now driving my Ascend Acoustic ELX towers. It sounds great, built like a tank and powerful. https://ampslab-spk.com/2018/09/30/soundcraftsmen-pcr800/

BUT, what kind of life can I expect from the components, specifically the mosfets and caps? Can I get the amp tested? Wonder if Amir would do it.

Thanks

 

[SSS]

Mosfets in metal case will last long when not overheated or otherwise destroyed by a defect on the driver chain side. Of course electrolytic capacitors can deteriorate over time and need to be checked for capacity and ESR as well defects and fluid/paste coming out. The big power supply caps can have reduced capacity due to aging and will then allow more hum on the voltage rails. IC legs can corrode and the socket contacts can become lose. So a check will be good and if necessary cleaning and readjust the socket contacts. If the pins of the big mosfet transistors are soldered then check the solder joints and re-solder it. Beware of electrostatic discharge and take protection. All what I wrote I had in practice at similar amplifiers I own and from friends when I restore them occasionally.

 

[Galway]

If you are concerned consider getting it serviced from a decent audio service technician. In the UK i like watching "mend it Mark" who does repairs and servicing to a good standard and does the calibrations to ensure its working to the designs it was made. Being a tech myself if I thought it needed a recap or the heat syncs being refreshed id do it myself. The biggest thing a non tech can do is ensure its not getting too hot and ventilation is good while its in use and you will be fine. If its got dust build up then blow it out and it should give you years of enjoyment. I would not be replacing perfectly good working parts and doubt any tech would be suggesting so, but a service might put your mind at rest.

 

[Redacted]

As a general rule of thumb the hotter something runs, the less long it lasts.
Not just silicon (which does wear out) but heat build in the unit will affect caps and more (per SSS above).
Poor layout of components still happens - I know of one guitar amp for example, that is famous for breaking down owing to big caps being millimetres from a valve.

 

[Panelhead]

I have restored a few amps in the past. The output transistors may be suspect. You can easily check each one. Most VOM will check transistors. After 39 years of irregular use they may have drifted.
I would replace the large filter caps. If not squeeze them. If soft replace. I
I had a couple Soundcraftsman units, one a big mother. If there is only a single pair you can get an idea of condition in circuit. If multiple pairs you may need to pull them to check.
I would eyeball the rectifiers.
Think through hole product development and availability has gone downhill. But output transistors, diodes, and filter caps have come a long way since the mid 80’s.

 

[SSS]

To check the output transistors they need to de-soldered and put out which I would NOT do. In this case the glimmer isolation pads need to be re-lubricated with heat leading paste. Also the simple transistor test of a digital voltmeter will not really work for power mosfet transistors. The only thing ist to test for shorts in a transistor. For bipolar junction transistors (these are the majority) a test will work. Especially with small signal transistors. If the amplifier works without big problems and delivers its rated power then the output transistors will be OK.

 

[Mark609]

Thanks for the thorough replies! Time to upgrade. I just don't have the drive to fool around with this old amp plus I doubt if parts are even available.

I've spent a lot of time checking out 2 and 3 channel amps. My final picks are the 3 channel Anthem MCA325 and Buckeye. https://www.buckeyeamp.com/shop/amplifiers/hypex/ncx500/3_channel

 

[SSS]

Thanks for the thorough replies! Time to upgrade. I just don't have the drive to fool around with this old amp plus I doubt if parts are even available.

I've spent a lot of time checking out 2 and 3 channel amps. My final picks are the 3 channel Anthem MCA325 and Buckeye. https://www.buckeyeamp.com/shop/amplifiers/hypex/ncx500/3_channel

You are welcome. If you cannot do the restoration work by yourself the labor cost to spend is probably not worth the amp. I had such a case but the guy paid for it.

 

[MarkELong]

Have one they are very powerful but I had mine serviced it developed a slight buzz in one channel. The guy that redid it said it’s a beast and and parts are still very much available . I use it now in a second system .

 

[DanielT]

I bought a Hitachi HMA- 6500 power amp a few months ago. I chose it because I liked the VU-meters and got it at a good price. It works flawlessly. It’s from 1980 and uses MOS FET transistors.

Temporary setup:


Tip: When, if, how, why, or why not:

Importance of replacing the electrolytic capacitors in any vintage gears

Quote from this part of the article below. In that link you can see how the values of the capacitors were measured and how much they deviate from spec/tolerance. The question is whether it is possible to generalize and say this: As one can see from the test results about 30% of all original...

www.audiosciencereview.com

 

[dfuller]

Big output FETs like that last a very long time. Long enough that I would consider them to be the things that determine the life of the unit, assuming no random catastrophic failures.