Last night I examined the offerings at KRaudio in cezch,

http://www.kraudio.cz/

I have to say that price isn't everything with tubes, and
i can see that these east europeans are making the chinese look like
amateurs.
The chinese seem hell bent on making large numbers of items able to be
sold at
a medium price in the west rather than make small volumes of quality.

KR offer a 2yr warranty. Does anyone else offer that?

I once built a pair of mono 25 watters with 13E1 in about 1997.

The output tubes are about 1/2 way through their life and last year when
i
serviced them they measured exactly as well as when i made them 8 years
ago.
The gettering shows wear, since the owner uses them almost every day for
4 hrs
or more, but they make fine music OK.

But will a chinese 845 be OK in 7 years?????

It seems to me i have 4 tube choices for getting 50 watts.

I could use pairs of GM70, 845, or 211 and all need the same OPT
and can be run from the same 900V to 1,200V supply.

Or I could use the 1610 from KR, which is really a 4212E about 75mmdia
and 300mm high,
used in the Kronzilla amps from KR.

But apart from the chinese Shuguang 845, there is mabe Cetron, 845,
about which I cannot find out much,
and the KR.

To drive the 845, 150vrms is needed, so a choke loaded Svetlana or NOS
EL34 in triode
looks like a nice candidate because EL34 becomes a nice triode when
triode strapped,
and it has a µ that is much higher than a 300B, 2A3, etc.
I would only then need a 6SN7 ( or ECC32 or E88CC which I have ) as the
input triode.

What other triode with µ of about 10 could be used to drive 845?

Patrick Turner

Hello Patrick,

But will a chinese 845 be OK in 7 years?????

I doubt the thoriated tungsten filaments will
stand many years of daily on/off cycles, regardless
if they are Chinese or NOS RCA.

Oh, and don't forget to regulate the filament voltage
to at least +/- 3% or better, 1% voltage precision.
BTW, other than pure tungsten filaments, thoriated
tungsten filaments are _NOT_ allowed to be underheated
by, say, 5% to extend lifespan a bit.

Tom

--
The large print giveth, the small print taketh away.
- Tom Waits

Hi Patrick,

To drive the 845, 150vrms is needed, [...]

What other triode with µ of about 10 could
be used to drive 845?

Mu = 10? Trioded 6V6 of course!

http://www.tubes.mynetcologne.de/roe..._as_triode.pdf

Tom

--
A consultant is a man who knows 40 ways to make love,
but doesn't know any women.

Patrick Turner wrote:



What other triode with µ of about 10 could be used to drive 845?


5998 looked great on the scope.

http://www.nj7p.org/Tube1.php?tube=5998



Adam

Adam Stouffer wrote:

Patrick Turner wrote:


What other triode with µ of about 10 could be used to drive 845?


5998 looked great on the scope.

http://www.nj7p.org/Tube1.php?tube=5998

The data is confusing....

"""TriodePlate Voltage ................................. 250 V

Plate Dissipation ............................. 13 W

Characteristics and Typical Operation
Class A AmplifierPlate Voltage ................................. 110 V
Grid No. 1 Voltage Derived from Cathode Bias Resistor
........................ 105 ?
Amplification Factor .......................... 5.4
Plate Resistance (approx) ..................... 350 ?
Transconductance .............................. 15.5K µ
Plate Current ................................. 100 mA"""



The µ quoted above is only 5.4

The low Ra is also nice, but it doesn't need to be that low
and anywhere under 2k would do.

And the 5998 is a maybe a rare tube, so EL34 which is abundant
may be just what I need.

But thanks anyway, I had no idea the 5998 existed.

Patrick Turner.




Adam

"Patrick Turner" wrote in message
...
:
:
: Adam Stouffer wrote:
:
: Patrick Turner wrote:
:
:
: What other triode with µ of about 10 could be used to drive 845?
:
:
: 5998 looked great on the scope.
:
: http://www.nj7p.org/Tube1.php?tube=5998
:
: The data is confusing....
:
: """TriodePlate Voltage ................................. 250 V
:
: Plate Dissipation ............................. 13 W
:
: Characteristics and Typical Operation
: Class A AmplifierPlate Voltage ................................. 110 V
: Grid No. 1 Voltage Derived from Cathode Bias Resistor
: ....................... 105 ?
: Amplification Factor .......................... 5.4
: Plate Resistance (approx) ..................... 350 ?
: Transconductance .............................. 15.5K µ
: Plate Current ................................. 100 mA"""
:
:
:
: The µ quoted above is only 5.4
:
: The low Ra is also nice, but it doesn't need to be that low
: and anywhere under 2k would do.
:
: And the 5998 is a maybe a rare tube, so EL34 which is abundant
: may be just what I need.
:
: But thanks anyway, I had no idea the 5998 existed.
:
: Patrick Turner.
:
:
:
:
: Adam


don't actually fit the 10* question, but these are some great looking
tube pic's :-)

http://www.jogis-roehrenbude.de/Roeh...tellungen/BTB/
PX4n/PX4n.htm

(in german, tube made by Full Music, cn
cheers,
Rudy

I use a 6AH4 for driving an 845 and the mu is 8.

http://www.nj7p.org/Tube1.php?tube=6AH4GT

Try a triode strapped 6AU5 or both sides of a 6BX7 tied together, its mu
is 10.

http://www.nj7p.org/Tube1.php?tube=6BX7GT


Adam

Adam Stouffer wrote:

I use a 6AH4 for driving an 845 and the mu is 8.

http://www.nj7p.org/Tube1.php?tube=6AH4GT

Try a triode strapped 6AU5 or both sides of a 6BX7 tied together, its mu
is 10.

http://www.nj7p.org/Tube1.php?tube=6BX7GT

Adam

A 6BX7 is almost the same as an EL34 in triode, µ = 10, Ra = 1.3k
for one 1/2, so with both 1/2 tied together Ra = 650ohms,
although with only 10mA per 1/2 ra would be higher...

I wonder if the ppl I know have any?

At least the 6BX7 is a real triode......

Patrick Turner.

"Tom Schlangen" wrote in message
...
Hello Patrick,

But will a chinese 845 be OK in 7 years?????

I doubt the thoriated tungsten filaments will
stand many years of daily on/off cycles, regardless
if they are Chinese or NOS RCA.

Oh, and don't forget to regulate the filament voltage
to at least +/- 3% or better, 1% voltage precision.
BTW, other than pure tungsten filaments, thoriated
tungsten filaments are _NOT_ allowed to be underheated
by, say, 5% to extend lifespan a bit.

Tom


Hello Tom,

I notice when running some heaters from a regulated bench
supply that they draw several times theitr nominal current when
cold (at switch on)

Surely current regulation would be a better way to increase their
lifespan. What do you think?

Iain

Iain Churches wrote:

"Tom Schlangen" wrote in message
...
Hello Patrick,

But will a chinese 845 be OK in 7 years?????

I doubt the thoriated tungsten filaments will
stand many years of daily on/off cycles, regardless
if they are Chinese or NOS RCA.

Oh, and don't forget to regulate the filament voltage
to at least +/- 3% or better, 1% voltage precision.
BTW, other than pure tungsten filaments, thoriated
tungsten filaments are _NOT_ allowed to be underheated
by, say, 5% to extend lifespan a bit.

Tom

Hello Tom,

I notice when running some heaters from a regulated bench
supply that they draw several times theitr nominal current when
cold (at switch on)

Because the heater has a positive tempco of resistance. It therefore
takes more current when cold because the heater resistance is lower.
This also helps it warm up more quickly than if the current was
limited.

Surely current regulation would be a better way to increase their
lifespan. What do you think?

Accurate voltage regulation is the best method actually.

Graham

Iain Churches wrote:

"Tom Schlangen" wrote in message
...
Hello Patrick,

But will a chinese 845 be OK in 7 years?????

I doubt the thoriated tungsten filaments will
stand many years of daily on/off cycles, regardless
if they are Chinese or NOS RCA.

Oh, and don't forget to regulate the filament voltage
to at least +/- 3% or better, 1% voltage precision.
BTW, other than pure tungsten filaments, thoriated
tungsten filaments are _NOT_ allowed to be underheated
by, say, 5% to extend lifespan a bit.

Tom

Hello Tom,

I notice when running some heaters from a regulated bench
supply that they draw several times theitr nominal current when
cold (at switch on)

Surely current regulation would be a better way to increase their
lifespan. What do you think?

Iain

The current draw is high when cold but soon as T rises the R rises.
But you are right that having current regulation would be nice
so as to slow the rise in T a bit but I have no idea if that extends the
tube life.

I worry that daily on/off cycles may indeed shorten TT fils life;
KR Audio warrant their tubes for 2 years though, even the 4212E that
they make.
I assume they allow say 1,000 cycles of turn on/off during the 2 years.
2 years is also 17,520 hours.

Cathode technology is the heart of good vacuum tube operation for a a
prolonged period,
and I just don't see any reports that ppl are using Chinese 845 after
5,000 hrs.

Patrick Turner.