Sunday August 25 1996 08:06, John Allen wrote to All:
JA>         As an absolute newbie to the world of tubes I am looking at an
JA> S.G.JoLida Integrated amp/pre-amp advertised in Audio Advisor. It is a
JA>  Model #SJ502A, rated at 85 WPC and driven by 2 matched pairs of
JA> Russian 6550s with two 6DJ8s and two 12AT7s. The specs look good and
JA> the listed price is $999 (US). They have two lesser models running
JA> from $699 to $850 at 50 WPC and 65 WPC. However neither of these
JA> models utilize the Russian 6550s.
JA>         I have large full range speakers that are very sensitive, a
JA> large listening area absent any side walls of note with a cathedral
JA> ceiling. I listen to classical, new age, female vocal, chamber music,
JA> string quartets and soft rock mostly. But would also like to be able
JA> to fire up my 60s hard rock every once in a while.
JA>         1. How long should you expect to get out of a set of tubes?
This all depends directly upon how hard the tubes are driven. What I mean by 
this is the internal DC voltage of the amp and the biasing of the amplifier. 
The Jolida must be running the tubes at about 550-570 VDC to be getting their 
claimed wattage. This means they must be using the Russian Svetlana Mil-spec 
tubes. The pre-amp section can be run at a lower voltage, so they should not 
be as likely to age as fast as the output tubes. I have seen small signal 
tubes still working in some older amps after well more than 30 years. Ya just 
can't run 'em too hard.
JA>         2. How long should a tube unit be allowed to "warm up"
JA>            before playing?
As long as you want. It takes time for the transformers to reach a 
equilibrium point. It takes usually about 30-60 minutes. All the warmup IS 
strictly temperature related.
JA>         3. Do the "tube covers" (look like little tube sweaters)
JA>            actually increase tube life?
The consensus is that they do not. But they do provide some damping of the 
tube body. Helps lower the noise floor. Tubes are terribly sensitive to 
vibration.
JA>         4. What things are tube amps/pre-amps sensitive to/about
JA>            that might cause them NOT to play at their optimum?
They are sensitive to impedance mismatching, bad physical placement (noise), 
AC power noise and AC polarity. The reason they are sensitive to AC noise is 
because they STEP UP the AC instead of stepping it down. For instance, at 
120VAC, all you get is a 370 volt sine wave. The jolida needs about a 600 
volt sine wave to rectify down to about 550 VDC. Thus the noise sensitivity.
JA>         5. Are tube units more or less sensitive to vibration and
JA>            should extraordinary effort be put into their isolation?
YES!!  Turn up a tube amp (listening via the headphone socket for maximum 
protection and effect) and listen to the noise as you gently tap the tubes 
with a fingernail.
JA>         6. Can a tube amp like I described be placed in an enclosed
JA>            (no back) entertainment center without overheating etc
JA>            or - - must they be in the open air due to heat? (I have
JA>            often seen them called "space heaters").
Tube amps generally dissipate a minimum of 1.5 watts of heat for every watt 
of rated output. All the time. Do not get any finger grease or the like on 
the tubes, as this reflects the heat back into the tube and shortens their 
lifespan.
JA>         7. Am I nuts for even considering getting into tubes?
They are fun toys. They are a plasma/voltage type device and can thus react 
to a signal change very quickly and accurately. (no mass!!) Transistors have 
mass. they cannot do the really high frequency stuff. All radio transmitters 
are tube based partially for this very reason.
JA>         I would also appreciate thoughts and suggestions on the
JA> S.G.JoLida integrated amp mentioned above. The smallest of the three
JA> amps got some good ink in Stereophile recently, but that does not
JA> substitute for real people experience. Cheers, John
The impedance curve of your legacy speakers would have to be very linear and 
benign, otherwise frequency anomalies will result. Dips below 6 or so ohms 
will give tube amps trouble. Look for something very high powered for these 
beasts. Little guys will do, but not very well.
I originally bought my Monitor Audio 952MD's for their extremely even and 
benign impedance curve. They are almost flat, between 7 to 10 ohms. A 
fantastic match for tube amps, with their 90db efficiency.
Take one home on a trial run, is the best advice. They will do some things 
that will amaze you. But they may run out of steam due to the impedance of 
the Legacy speakers.
Oh, yes, the impedance of the load, as in the impedance of the CD player, or 
what ever you hook up to it may cause some flatness and high frequency roll 
off. As a bonus, this will cause distortion as well. Flabby bass is also a 
concern with tube amps. No real current is the problem here. It's the 
impedance of the speakers coming back to haunt you. The amps will tend to 
'flatten out' under high load (high volume) as the power supply in them gets 
drained. HUGE tube amps are the only solution to this problem.
I fixed this problem once by dicking around with one ( a little 15 watt per 
channel Dynaco SCA35 intergrated) and ended up with a power supply 
capacitance 30 times it's original size. It had a custom rounded gloss black 
faceplate, line filtering, silver teflon wiring, Mallory Viper capacitors, 
Rubycon Black gate capacitors, a damped chassis, separate DC low impedance 
filament voltages for each channel, all Holco resistors and polypropylene and 
polystyrene caps, Alps brand plastic film potentiometers, and no tone 
controls. All in the original box. Oh yeah, copper binding posts, VandenHul 
RCA input jacks and matched New Old Stock Telefunken 'diamond' tubes. They 
have great output transformers. People buy them just to rip the transformers 
out and make better amps around them. It took months to get the thing right. 
And I very stupidly gave it away for $750. It was so much work, I don't think 
I'll ever do anything like that again. I had basically designed, tested and 
voiced an amplifier (even though I worked around an original base circuit)
It just wiped the floor with my customized (about 6g's) transistor amp. 
Pretty humbling, I tell you.
The guy who has it, swears by it, and won't give it back.
Ken Hotte
> Netmail: 1:249/146    Email: ken.hotte@serpents.crp.kingston.on.ca   <
... Really ??  What a coincidence, I'm shallow too!!
--- GoldED/2
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