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-   -   Vintage amps to repair? (https://www.diyaudio.com/forums/solid-state/227810-vintage-amps-repair.html)

ORNJ 14th January 2013 06:30 PM

Vintage amps to repair?
 
Hey guys, I found alot about tube refurbishing and repair but not SS amps.

I was wondering if a good approach would be to look for some good older, vintage SS amps for repair for a low cost option to higher power?

If so, what amp manufacturers should I really be looking at? I know McIntosh and Marantz are popular but I would take anything at this point as I am trying to just get into audio design and repair.

I would prefer SS amps as well because my system is for music and movies so it would better to have SS than tubes for me.

I know the MC2105 seems to be very popular old McIntosh but I really am at a loss.

I was going to build an F5 until the heat went out in the car and now I am looking for another job so I think it would be better to look at doing some restoration work instead of starting from scratch.

indianajo 14th January 2013 08:24 PM

I like Peavey's and Dynaco's. The schematics are available on line. The parts are US code mostly and datasheets can be downloaded. Even the private label peavey parts, there is an interchange to OEM number list. The Peavey CS800s and CS800x and the dynaco ST400 and ST410 have good sound specs, and the CS800s sounds great when the power supply is not tripping the breaker (14 years old, needs e-cap probably).
Salas tutorial to refurbishing old amp is here http://www.diyaudio.com/forums/solid...de-manual.html
Look around old musician resale shops as well as the usual suspects craigslist ebay. I got a PV-1.3k blown up (not transformer) for $55 and a CS800s (input resistors toasted) for about $100. Dynaco ST400's are going for about $300 working, unrestored.
Older CS800 amps don't have as good sound and lack the speaker protection circuits of the x & s suffix. Nor do I expect a lot soundwise out of the PV=1.3k. The PV1.3k and Dynaco ST400 lack effective speaker protection, I'm installing it now in the PV-1.3k. The dynaco ST120 has sound issues and blows OT's a lot unless the heat is managed better, but is extremely easy to fix. The ST120 can't blow up a speaker until it shorts a 100 v cap in series with the speaker. Great feature, especially if your speakers cost more than the amp. I've upgraded my ST120 to sound like the CS800s with a djoffe bias board and fans, see this thread:http://www.diyaudio.com/forums/solid...de-manual.html

chicks 14th January 2013 08:51 PM

Lots of well-built amps out there worthy of re-capping and bringing back to life, like this Kenwood Supreme 600 (if you can find one):

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Another option is to just re-use the chassis, power transformer, and possibly the heat sinks, with completely new DIY boards inside.

ORNJ 14th January 2013 09:13 PM

I guess a good question would be are there any brands that I should make sure to avoid entirely?

I know there are a few McIntosh models to avoid, though I am not sure of which, but I heard that the first couple of models when they started going to SS designs are not very good.

Ed Holland 14th January 2013 10:47 PM

From experience, amps with complex DC servos can be tricky for the beginner or intermediate - e.g. my Adcom GFA 585 and it's relations - capacitor electrolyte all over the sensitive areas of a circuit board can really upset things...

I recently revived a Dynaco ST400 - not too hard to bring back to life, plus there's a lot of interesting resources on the internet due to interest in these products. That helped me choose appropriate output device replacements and learn about common problems and their solutions.

It's always worth investing in the service manual, especially if one intends to keep the amp, so that is perhaps the basis of another tip: search and see if reprints or copies of these are available before you buy.

Build an 8 Ohm dummy load with some big resistors; get a Variac and know when and when not to use it.

Good luck - there's plenty of fun SS gear out there to play with.

Ed

djoffe 14th January 2013 11:17 PM

As Indianajo suggested, Dynaco Stereo 120's are plentiful, and have lots of room to work on them. Lots of folks like them dead stock, some add some more microfarads here and there, maybe do the TIP mod...(shameless commerce warning) I sell some kits that change out original amp modules and power supplies (do as little or as much as you like) at Update My Dynaco.

If you're pretty skilled a Dynaco Stereo 400 could be a great value. I just bought one that I restored and am keeping for my own, but the fellow I bought it from had 2 more for sale.

ORNJ 15th January 2013 03:27 PM

djoffe, that was goign to be my next question to see if there was a way to improve them...I am glad to see there are kits!

How does going the route of repairing vintage amps compare to the approach of building an F5? It seems to be cheaper but is there any other benefit to building from scratch that I need to consider?

djoffe 15th January 2013 04:09 PM

It really depends how much you want to personalize what you do, and how much time you have.

Refurbing an old amp avoids most of the mechanical and construction issues. That's good or bad, depending upon what you're equipped to do, and what you like to do.

The F5 looks like a neat design...Nelson Pass of course, does nice work! A quick look around the net shows people selling parts and boards. I'm sure other people reading this thread could provide a good collection of links that would allow you to collect everything you need to build...case, switches, power supplies, heatsinks..It can definitely be a lot of fun, and a lot of work!

An alternative (warning: shameless commerce plug)...is my product, the Akitika GT-101. It's a complete amplifier kit...everything collected in one kit...you just add solder and labor.

Akitika GT-101

Any of these options can be very rewarding, and a lot of fun!

chicks 15th January 2013 04:34 PM

Depends on you skills. I enjoy soldering, but have no skill or tools for building a great-looking chassis, so resto-mod was the route I chose for my latest project, a Dynaco SCA-80Q.

djoffe, had I known about your Dynaco boards, I might have tried them, but found Michael Renardson's MJR7 board, which nicely fit the single-rail requirement on the Dynaco's existing transformer, and is an exceptionally well-document design.

I love the way vintage gear looks, but this particular Dynaco had old dried out caps, and a 1960's design with super hot resistors and very high (by today's standards) distortion. So, it still looks great externally, but has much better specs, and should last a very long time.

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djoffe 15th January 2013 04:54 PM

Nice work, and nice pics! What kind of camera are you using?

Update My Dynaco


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