A. The Main Charactor 6C33C
The 6C33C
has only one equivalent: 6C18C.
The 6C18C
is an early version of 6C33C, might be used as drop-in replacement.
The 6C18C
is very good tube, in some instances is better sounding then 6C33C but in may
experience the 6C18C has a large percentage of faulty tubes.
Among
fifteen new 6C18C that I used 5 of them were discarded immediately due to the
pins shortage, 2 of the “good” tubes failed a few hours after they were heated
and one of the surviving failed in a few month when it was subjected to
shaking.
In
contrary, the 6C33C is very reliable; among 60-70 tubes that I have burned I
had only one that was defective. (1.42%)
Things you should know and do about 6C33C, it is getting more popular in 2023. Mainly because of the clonning of GRAAF GM-20 OTL/OCL Amplifier, I guess.
<6C33C Survival Guide>
1)
A
new 6C33C has pins cover with something that I call “white shit”.
I
have no idea what it is, perhaps some solidified oil or paraffin.
Anyhow
it should be scrubbed out before you use 6C33C for a first time.
If
you do not clean up the “white shit” from the pins then it will short the
lifespan of your 6C33C tube socket
2)
There
are six 6C33C tube sockets (ordered from worst to the best)
A.
Chinese
Ceramic
B.
Russian
Plastic
C.
Russian
Ceramic
D.
Russian
Exotic (with side handles)
E.
American
Johnson
F.
Japanese
Exotic
Each
of them works fine but the best sockets will last longer.
The
Chinese sockets will die after 1-1.5 year of heavy use and generally it
is a good idea to replace a new 6C33C right along with replace of the tube
socket.
The
American sockets might last for years and the Japanese socket
where pins hold by a full cylinder might last for a near a life-time.
3)
The
6C33C tube sockets should be mounted at well ventilated location with nothing
closer to the tube then ~ 2-3 inches. Out of chassis mount is highly advisable,
but if the in-chassis mount use then punch necessary holes to crated natural
air-convention or use forced cooling.
4)
The Filaments should use AC.
The
filaments wires should be 16ga or larger.
The
wires to the socket’s leads should be soldered with high temperature solder.
5)
If
forces air use then do not cool down tube but cool down tube socket.
6)
6C33C
should be use with fixed bios only.
If
you feel that in your amplifier 6C33C sounds better with automatic of
Semi-automatic
bias then ether you are in a strong need to perform a lobotomy over your
reference point of your amplifier is a piece of crap to begin with.
7)
Biasing
resistor that goes to the 6C33C grid should be the best possible quality and
has value less than 100K.
8)
The
multi-turn precession attenuator that sets up you 6C33C’s bios should be also
very high quality.
9)
The 6C33C bias supply lines are very critical for 6C33C’s sound; even the proximity to the ground of the negative bias wire is
auditable. Use transmission line techniques to set up that line.
10)
Although
the 6C33C marked for 60W plate dissipation and some of them will care even more
with no problem still made for yours an absolute rule: the maximum plate
dissipation of 6C33C is 50W, with recommended plate dissipation 40-45W for a
full tube and 30-35W of a half tube.
11)
The
half 6C33C sound better then a whole 6C33C, the half 6C33C sound 30000 times
better than one 6C41C.
12)
Set
up proper operational parameter for your 6C33C. The proper operational point
will be the properly of your plate load, type of acoustic system you use and a
few other factors. Still, with all things considered your 6C33C should
experience power clipping by currant and by voltage at the SAME time.
13)
Generally
look for 180-210V on 6C33C’s plate and 180-230mA of plate current for a full
6C33C. still, the paragraph above (#12) should be denominating rule
14)
The
6C33C has HUGE inconsistency of parameters when it is new, so huge that it is
impossible to measure the tube in order to determine how much of cathode
emission left or what mutual conductance would be is. The only possibility with
such inconsistency of new parameters is to monitor how the parameters were
changed for a given tube.
15)
Make
bias supply available from minus 50V to minus 120V
16)
Generally
the signs of the 6C33C dying are (in case the tube still operates
properly):
a)
Appearance
from time to time mechanically sounding loud “ping” through loudspeaker.
b)
The tube’s
getter loosing it’s gloss
c)
Change of
bias voltage more than 50%
d)
Tube is used
over one year in amplifier that works dally.
e)
Too small
amplitude of “start up gap” (more about it later)
Since
the tube is dirt cheap ($5 in Russia) it is advisable to replace the 6C33C each
yeas or what the above mentioned effects show up.
17)
All
6C33C have different gain. Gain of 6C33C is the only parameters that
should be matched. If you have 3 of those tubes on a row with the same gain
then you are incredibly lucky and you should stop play with your amplifier and
should become a stock broker.
18)
When
a well worked 6C33C starts in your amp the filaments should be pre-burn for
=>2 minutes.
19)
Do
not apply a signal that would exceed more than ¼ of class A1 to a “cold” 6C33C.
The 6C33C stops become “cold” ONLY AFTER 30-40 minutes of burning by its cruise
plate currant (I call it “Hot Mode”). Practically it means that you should not
play your 6C33C amps too loud for the first half hour, particularly if you have
low sensitively loudspeakers of too large listening room.
20)
When
6C33C start with none-regulated power supply then it has the “start up gap”.
The voltage is higher than cruise plate voltage and the currant is lower. With
time, when the plate current hits up the tube the voltage drops and the current
raises to it references cruise values. Usually a worked 6C33C reaches its 95%
of cruise currant within 10 minutes.
21)
Use
the 6C33C “start up gap” to monitor the life cycle of 6C33C. If your cruise
current is 220mA then a worn 6C33C might start at 200mA and then within 10
minutes reach 220mA. A newer tube will start at 150mA and then within 10
minutes reach 220mA.
22)
When
you take as brand new tube, then heat it’s filaments up for 2 minutes and start
the amp with 20mA on plate. In 10-15 minutes the plate current will rise to
150mA – let it be this way. Burn the tune for another 3-6 hours with
100mA-150mA and then consider it ready to be use at full power.
23)
Violation
of proper pre-heating rules and application excessive grid current to “cold”
6C33C lead to overheating of anode. Once anode was overheated it will have
tendency to be more susceptible to overheating in this tube. A properly
pre-burned tube, running “Hot Mode”, with fix bias and in class A1 is
absolutely indestructible and perfectly thermo-stabilized.
24)
It
is advisable once a 6 moths to inspect the 6C33C’ filaments pins for the sights
of corona, partially if your use not American trapezoid tube sockets buy
Russian and Chaise triangular sockets. It worth also, if you have nothing else
to do, once as 6 month to listed the balloon of cold 6C33C with juts applied
filaments voltage with a stethoscope. A present of corona on the filament’ pins
will, sound like a very light buzzing.
25)
Keep
the power supply impedance that drives 6C33C as low and you can.
That
is all that I have atop of my mind. Properly-used 6C33C is truly a problem-free
tube with opportunity to have excellent sound if it is appropriately used in
amplifier.
So,
I was disappointed with moronic myths that audio people invent about this tube
and to address that stupid audio-prejudicial folklore I have put together that
“6C33C Survival Guide”.
