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Quad 606

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Lee in Montreal
Senior Contributor 200+

Joined: 22 Aug 2009
Posts: 203

PostPosted: Thu Jan 14, 2010 12:07 am    Post subject: Quad 606 Reply with quote

I bought a $100cdn cosmetically mint Quad 606 with one channel popping fuses whenever it was powered. Visually there was no burn sign on the PCBs and suspected the output transistors to be bad. Therefore I purchased 25 units MJ15003G transistors. Both driver transistors were burned and took out two output transistors. So, I changed the drivers and the output transistors, all 6 of them. I also changed the drivers on the other board.

Put everything back together and am delighted. The stock 606 sounds warmer and fuller than even an updated 405. Next step will be to change a few caps on the boards and upgrade the four 6,3k F power caps to 10k F units, or even 15k F units if possible.

One word of wisdom I would like to share about the so-called legendary transformer hum that is the mechanical vibration heard around the amp, not at the speakers. No need to swap transformer if it happens. Basically, the problen is much simpler than people think. The heavy transfo is mechanically insulated from the chassis by a top and bottom layer of foam. Over the years, that foam has thinned and dried out. Most likely there's a lot of black powder and desintegrated foam in the casing. Not being dampened anymore, the small oscillations from the transfo are mechanically transfered to the casing. What I did is simple and took 20 minutes. First I removed the transfo, cleaned up the old foam from the transfo, casing and supporting brackets. Even using thinner to remove any remaining glue from the brackets. Then I applied a few sections of new foam strips. Brand new suspension, good for another 15 years.

The 606 is a wonderfully designed object. Top and bottom covers are cast heatsinks. Big central power supply with four caps on top, and amp boards on each side.

The full rack as of January 2010 - Top to bottom

Technics SL1100a
Kube 200
Cambridge D500se
Technics SU-9070
Hafler DH500
Quad 606
Quad 405
Quad 405
Sony ST 88

Kef Calinda - since 1979
Kef Cantata - since 2009
Kef 105/2 - since 2009
Evo 105/2 - in the build
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Senior Contributor 200+

Joined: 07 Nov 2004
Posts: 275
Location: Toronto, Canada

PostPosted: Tue Feb 02, 2010 4:05 am    Post subject: Reply with quote

Very nice.

You should conduct listening tours for those of us within (long) driving distance. Smile
Sometimes I lie awake at night, and I ask, "Where have I gone wrong?" Then a voice says to me, "This is going to take more than one night."
-- Charles M. Schulz (as Charlie Brown)
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