2. amps-preamps
  3. 1198420632

first tube rolling: expert advice needed - take 2

Annoyingly my first thread that went under this header has disappeared. Apologies to everyone who had contributed and put a lot of thinking into this.

Here is the plot again: I had bought a second hand Unison Research Unico SE hybrid integrated amp with two Electro Harmonix 12AU7A in the pre-amp section. Very fine in musical terms, the amp caused an unacceptable (in my solid-state biassed opinion) amount of hiss and slight traces of hum coming from the speakers in silent parts. I had assumed this was caused by (perhaps defective) tubes. Not knowing where or what substitutes to start searching for, I have had the benefit of Audiogoner's advice and finally acquired a pair of NOS tubes at Machmat in the Netherlands, namely:
Tesla ECC802S unused NOS (virtually the same as Telefunken's ECC802S, I have been told, picture: see my "Guests" system).

Here is the good news: Am I glad I tried this! I am getting a cleaner and more saturated sound, as if creases had been ironed out; bass appears more finely detailed (tried this with different speakers with reproducible results)
And here is the bad news: The hiss is still there, perhaps even more disturbing than before because the music is better. Guess I'll have to have the amp inspected and probed (hope I haven't been "had"). Anyway, if it doesn't work out with this machine, I'll be looking at a full valve integrated from Unison (I do like this sound).

One tip I gladly pass on (not just to the Europeans): Mattijs de Vries of Machmat sure is someone to rely on!
http://www.machmat.com/index.htm

Finally one question to the experts: Is there something like a burn-in procedure I should observe or time I must allow for with unused NOS?

Thanks in advance and regards
Karel
karelfd
jorgeparrapuppy
257 posts
 
Karelfd: I'll have to second Mechans' take on the
SS pre and tube amps set up. I've got that set up as well,
using mono tube amps and get absolutely fantastic
results.

good luck!
fihigh
4 posts
 
Karelfd,I have experienced the same problem that you have.I tried different tubes,speaker cables,interconnects,power cords,Spikes,cones everything you could imagine.It was only after placing a tubed preamp with a separate power supply in my system did i achieve silence.Of course nothing goes well for the audiophile, although silent I didn't care for the sound of the new preamp.
Good Luck
adcom00
12 posts
 
I just can't agree with you guys.I have a tube pre(BAT VK-30) and SS monoblocks(PSE's) and I have absolute silence in the silent sections.I also have Tesla's in my pre.
slates
35 posts
 
I had some serious hiss as well a while back, I later found that my 6922 pre-amp tubes had very little gain in them. I bought them from a reputable tube dealer, and I paid large for matched sections, matched pairs and high gain. I now own a tube tester and it makes life alot easier. Out of 8 EH6922 Gold Pin only 5 were showing good
EM and Gm tests , 3 of the tubes were showing "REPLACE" in Em and below the Gm acceptance grade.I decided to test my findings and bought a bunch of Tesla E88CC for a great price.
I bought 24 tubes and totally did the nines on testing them,I found 8 really high scoring tubes, and decided to test them in my pre-amp, and in conclusion I was right, the hiss disappeared.I did receive a full refund for my
EH6922 Gold pin, and never bought tubes from that outfit
again. My pre-amp and amp take a total of 22 tubes, it just made sense to have my own tube tester, to think I was going to spend my money on an AC line conditioner, it would have improved nothing, if you have bad tubes.

Thanks
rodman99999
6,130 posts
 
Hello Karelfd- It certainly sounds like "tube rush" the way you describe it. The least little noise put out by a tube in your pre-amp will be magnified exponentially. Contact Kevin here: (http://www.upscaleaudio.com/view_category.asp?cat=44) He very closely screens every tube that passes through his operation, and has tubes that are designated for pre-amp use. Very knowledgable on tube equipment and possible problems. OH- nothing manufactured today even comes close to the Telefunken ECC802S(regardless of what you may be told otherwise). No one can afford to put that much effort into precise/quality manufacturing techniques nowdays. Now if EAT or KR were to manufacture a copy.....
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