|
Tubes Asylum Questions about tubes and gear that glows. FAQ |
|
|
|
Tubes Asylum Questions about tubes and gear that glows. FAQ |
|
In Reply to: Saga?? posted by HiFiBlues on April 2, 2001 at 11:45:32:
Dear Hifiblues,My saga is in the archives from January. First I put orange globe Amperex 6DJ8's into the 6922 positions. These came out of my preamp, which I had upgraded to some low noise tubes. I neglected to adjust the voltage rails, which I only found about later.
Next I bought two "matched" quads of Svetlana KT88's from a vendor who was supposed to be reputable, mentioned well by the vendor I bought the other tubes from. When I put them in, there was an immediate increase in dynamics, bass, and midbass, compared to the ARC supplied Svetlana 6550C's which were only about 6 months old at that point. I had retubed in the summer.
The trade was a decrease in clarity, especially in the upper midrange. It was certainly different, but not everything I was after. When I opened the amp after a number of days to check bias, it only came up to 124 on one channel. So I called Leonard at ARC. He said that I needed to adjust the rail voltages, something usually to be done by an experienced technician, but I was game with my handy voltmeter, and went at it. Well, something was wrong with the 6DJ8's, because the voltages were all wacky and would not come into line. The voltages varied a whole lot as I switched tube positions, which is what you need to do to help bring it into line. At one point, I shorted across a resistor next to one of the KT88's, but everything seemed to be okay after replacing the fuse. When I switched power tubes around to see if that had an effect on bias, two resistors went off like a firecracker next to a tube, probably the one I took out with the short.
So in this state of discouragement, in over my head, I sent the amp to ARC. I did not send the Amperexes because I had determined that there was something wrong with some of them. For a preamp they may have been fine, but the loading in the power amp required a tube that could take more abuse.
ARC tested the KT88's I sent them. The match numbers were 306-121, 310-118, 310-119, 318-116, 321-119, 324-116, 326-110, 335-115. Look at your old ARC tubeset. The match numbers on the tubes will read within one digit for each number within a quad. ARC will only use tubes if they are this closely matched.
Since my amp was in the shop, costing a fortune for Fedex, I decided to go for the Mk3 upgrade. One reason was that they highly recommended it. Another was that it got rid of the 6922's in favor of a Sovtek 6H30, which is where ARC is taking all their new designs. Look at the Ref2Mk2. The Sovtek 6922's were grainy and restrained on the highs, whereas these new tubes are not. Also, it would not allow me to tube roll, Sovtek making the only one.
Now that it has broken in a month, I can say that it is truly worth it. It has the dynamics and bass punch that the KT88's gave the Mk2, but also has a clarity and purity across the board that it did not have before.
The tube dealer took back the KT88's, minus a charge, minus the shorted tube, which was fair. He thought the limitations that ARC placed on power tube matching to be unreasonable. I can only say that if I had had a well matched set of very good quality 6DJ8's, and the same for the power tubes, it may have worked fine. But I'm not taking chances anymore with my amp. This escapade cost me a lot of money.
Talk to the people at ARC. They are the people who know their equipment best, no matter what anyone else might say. They have been down the road with many different tubes and many different designs, and also know most of the tube vendors you will deal with.
Good luck.
Bob
This post is made possible by the generous support of people like you and our sponsors:
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2025, Audio Asylum, all rights reserved ]
