Opinions on Graaf Amps

Yes i have had the GM 200 OTL for about 2,5 years and ive heard the GM 20 as well , i sold it off after i listened 3 months to them on my new speakers with a diamond high frequency cone .
The smooth topend what i had with the graaf tube amp and i was missing with SS was merely a tweeter problem in my case , my highs are almost as sweet with ss as with tubes (zanden exepted ).
Further very good amps, spatial/dynamic as well , i sold them merely because they need new tubes once in while , and with the 32 in the GM 200 it will not be chaep, the bass is a bitt more rounded than with the krells but also beatifull , i rank them in the top of poweramps

Replacing the entire set of 32 tubes on the GM200 costs an extremely reasonable 500 Euro for a matched set from the factory (you really want to order them from the factory as close matching is absolutely necessary). This is hardly expensive, especially when considering that these tubes have a 10,000 hour lifetime. With idle power consumption of about 1000w this is not an amp that you leave on all the time so, assuming that you use the amp for 2 hours a day, every day, the tubes will last for 14 years. Spare sets can be ordered from the new distributor, Audio Analog in Italy.

The capacitors are relatively cheap to replace but if you are worried about heat affecting the capacitors, use the tube covers that Graaf supplies. The amp is not quite as pretty with them on as it is with rows of exposed glowing tubes (although it remains a truly stunning looking amp) but Graaf is effectively doing the same thing as Porsche does with its Turbo cars - Porsche puts a thin dimpled aluminum heat shield in the 1" space between the exhaust and the very thin rear plastic bumper to stop the extremely hot exhaust from melting holes in the bumper). The tube covers protect the capacitors and transformers from heat damage in a similar way. In fact, in addition to the covers acting as a heat shield, air convection currents will pull in cold air into the bottom holes on the covers and hot air will exit through the top, cooling things down even further on the rest of the amp. A bit counter intuitive - you would think that putting the tube covers on would make things hotter but they don't.

Hi,

My GM20 has just blown up for the second time this year, taking the driver of one of my Duevel Bella Lunas with it.

We're having some trouble fixing it and wondered if anyone has a service sheet with voltages and/or a circuit diagram?

I look forward to hearing from you, Zeb

PS Since it's spending more time being fixed than working these days I'm also interested in an inexpensive used amp that I could get for whilst it is being repaired. Ideally balanced, probably valve, maybe KT88s.

Zebshaw, likely the problem you are having has more to do with the power tubes than the amp.

A simple way to get greater reliability out of the tubes is, if you have a new set, put them in the amp and run it in Standby for about 2 days, and the bias up the amp and run it with either no music or very quietly for another day. This will double the life of the tubes and you will be far less likely to get premature arc-over failure!

We make fully differential balanced OTLs FWIW.