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
Indeed yes an unused tube requires some use to get the emmiting plates boiling off electrons in a steady equilibrium while the recieving plates acquire a coating of of oxidation. The filment wire burns in etc.
That said, let me warn you that totally black silence with tubes is a rare commodity indeed. If you press your ear to the speaker almost any tube will yeild a slight hiss. It should not be pronounced and will not get better with use. In fact hiss is more often associated with aging tubes (not old as in old stock, but with usage). If you really want total silence you will have to forgoe the splendor of tubed equipment, and return to solid state.
Being a tubophile myself, I highly prefer the glorious dimensionality (a neologism?), transparency and tone my tube preamps AND tube amps give me. I simply ignore this shortcoming and choose the quieter tubes I have.
Hiss is frequently tube related Hum rarely. Iwould suspect some other element for hum problems. For instance the well known ground loop.
A very good alternative is the opposite of the common belief that a tube pre and solid state power amps yield the essential tube amp sound. Use a totally solid state preamp of course the best being the one you like and can afford and then buy tube power amps. Alternatively an all tube integrated, which I'm heading toward BTW will be just as good in many cases. That way you will really hear how good tubes are, at least to some of us. Don't even use a hybrid pre in this manner it must be a good entirely solid state unit. I am not kidding. This phenomena is well described by my old buddy and respected audiogon member TRELJA on his website. I don't know if the Audiogon censors will allow my to tell you what the site is so e-mail me on the side.

My Mono bloc tube power amps are great BTW, but I had a once in a blue moon opportunity, to aquire a truly special integrated. There is a current review of these puppies on 6 Six Moons, Opera audio/Consonance Cyber 800 mono block amps. I may well keep these. I like them that much. The integrated is a Jadis DA-60, which, it seems is being replaced by the DA-88s. These amps are mucho dinero, approx. $10-12K+ new and rarely come up for sale used. I assume, knowing the amp fairly well, that it is because, the owners hold on to them.

Note: Consider the fact that, I am/was an old friend to the current importer/distributor of Opera Audio of North America.

BTW, I had 2 tube rolling topics deleted. For reasons that elude me they think the topic is inherently contentious and will result in a flamethrower contest. Honestly I don't see why this topic, which some people, may have strong opions about, is any different than any other post that makes it???? I will try again, last time they said I have to mention a specific piece of gear. Why? I don't know.

Hi Mechans, good to hear from you again. With regard to the hiss I hear, it's not the phenomenon you describe I'm afraid. I can actually hear it from a few meters away, definitely too much if you ask me.
Interestingly, you mention Jadis. I first heared my Well Tempered table with Jadis gear and was mightily impressed. Eventually, things would take another turn and, in honesty, I am perfectly satisfied with the Tidal amps in my main system. For the second system Jadis seems indeed too expensive (I have seen one or the other used but even then it's a lot of $$ and I'm becoming wary of some offers after what I'm experiencing with my Unison), but I'm seriously considering an all tubes alternative.
As to my deleted thread, apart from opinions on one or the other dealer, I only saw people of the same conviction exchanging thoughts. To me this thread held a lot of information and introduced me to a fascinating new field. Too bad it had to go.
Mechans,

I am having this same problem with my Unison Unico. Have you had any luck in reducing the hissing?

I too can hear it from meters away.
I guess the question on the Unico was actually addressed to me. I have been swapping cables, experimenting with isolation bases and moving the unit to different places in the apartment but never succeeded to get rid of the noise. Hooking up different speakers however made a huge difference. With Lua Con Fuoco Mk3 (4 Ohm impedance, SPL rated around 89db) the hiss reached the annoying level I described. With Chario Constellation Cygnus (4 Ohm, SPL 87db) the level was at a point that I could probably live with: audible in 1m, ear at the height of the drivers; to me that is, a friend told me he barely noticed anything in the ambient of a living room at daytime. I had been intending sending the Unison to the distributor for examination whether there was a defect after all, but I didn't get that far since the guy I mentioned bought the amp and the speakers from me.

Meanwhile, I got myself a Unison S2K tube integrated rated at 2x15W (an enormous difference in terms of output from the hybrid Unico SE with its 2x130W) that I'm driving the Lua with, and guess what: dead silent. I have also hooked up a couple of Zu Druid Mk4 (rated at 101db), again: silence. The S2K sports 2 ECC802S (I use NOS Tesla with EAT Cool Dampers) and 2 KT88 (presently the original Sovtek - with my fingers itching to try EAT KT88 Diamond Valves, ridiculously expensive but reportedly as good as NOS Genalex).

I'm not stating that the problem with the Unico was reducible to speaker sensitivity (there may be other tech specs that complete the picture) and I cannot be sure whether there wasn't an inherent defect on top of it (the lottery with buying used gear). But in my case the speakers made all the difference.
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!