Jadis DA60

When I picked the amp after its repair I was told that all the problems were my fault for using the wrong valves (Tung Sol 6550 reissues), and that the new Genalex KT88 reissuess could not run in my amp and would soon destroy it. And there woud be no warranty on the repair.

Without plugging the amp in I took it to David Peach of Peach Audio at Balmain in Sydney. He found that the heater voltage was set to 13.85V instead of the correct 12.6V (two KT88s in series), and there was a dry solder joint on a new cap.

I asked him to make the amp reliable and he designed and made the following changes:

· Removed the cathode fuses and instead fused the anodes as per http://www.audionote.co.uk/articles/tweak_fusing_valves.shtml

· Each pair of valves was previously cathode biased. Now every valve is cathode biased.

· He protected the output transformers from back EMF by installing shunting diodes.

· Changed the transformer taps from 4 Ohms to 8 Ohms to suit my speakers

· Reset the heater voltage

My amp is now back and sounds and works great. Peach Audio is highly recommended.

http://www.audionote.co.uk/articles/tweak_fusing_valves.shtml

Thanks for your responses.

I naturally always have a load connected.

I myself have wondered why the fuse does not blow to protect the amp. The tech at the one Jadis dealer in Sydney said:

"It is true that there is never enough current to go through the valves to "burn out" the output transformer as such. In the instance of Jadis DA60 each valve is protected by a 200mA fuse, which means that if a current of more than 200mA going through, the fuse will blow.This is the theory. But in real life if one of the valve develops a flashover inside the envelop, it may not be high enough current to burn the fuse but the spike will cause a very high voltage back EMF on the primary of the transformer, which adds on the over 470 Volts already there, can and will puncture the thin layer of paper separating the layers of windings between the primary and the earthy potential of the secondary of the transformer."

Does that sound reasonable to anyone?

The transformers are not warrented for life, however Jadis in France did cut me good deal, but having said that they are still expensive.

I quote an email from Jadis to me:

dear Sir
the DA 60 can work with all this kind of tube
after the choice is a question of personal taste
on my side I like the KT88 GENALEX because Ilisten a lot of jazz and voices I like the warm in the high frequency
for big orchestra the KT90 are more dynamic and have a very good control of the bass but the high frequency is less sweet
best regards

So I bought two matched hand matched quads of Genalex KT88 and supplied them to the Sydney dealer who is doing the repair (new output transformer, caps, resistors etc). They completed the rapair and returned the amp but have refused to give me a warranty on the work because they say the DA60 cannot use KT88s. They further say that in all likelihood that the KT88s will destroy my amp beacuse of the extra current draw and heat generated over 6550s.

When I drew their attantion to the fact that the recommendation to use KT88s came from Jadis, I was told by the boss that the their tech new better than Jadis.

So I fear that rationality has left the building and has been replaced with bluff, bluster and bs.

I welcolme any comments.
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