Is the 7189 a mil spec version that is more rugged and lasts longer?

Can take more heat?

My guitar amp uses them upsides down and I want something that won't get
toasted right away.

kevin g said:

Is the 7189 a mil spec version that is more rugged and lasts longer?


Dunno about the MIL spec, but the ratings are a bit higher.


Can take more heat?


More or less.


My guitar amp uses them upsides down and I want something that won't get
toasted right away.


The EL84M (Sovtek) is said to be a good replacement, but I'd increase
the value of the screen grid resistors a bit, or insert them when they
aren't present.
Can't tell you anything about their sound in a guitar amp, however.

The ordinary current production EL84 won't last very long in a 7189
design.

--
Sander de Waal
" SOA of a KT88? Sufficient. "

in article , kevin g at wrote on
4/21/05 3:03 PM:

Is the 7189 a mil spec version that is more rugged and lasts longer?

Can take more heat?

My guitar amp uses them upsides down and I want something that won't get
toasted right away.


It kinda depends upon plate voltage, among other things. The 7189 is rated
for a higher plate voltage.

Good old NOS EL84s usually can withstand higher plate voltages than current
production EL84s and against new production 7189s.

By the same token, some new production EL84s will get red plates when
operated in older circuits that pushed the limits of the NOS tubes.

My experience with 7189s is that current production Sovtek and Tesla aren't
anywhere as hardy as the original 7189s.

You might look at the Russian 6P14-EV. Works fine in apps where the 7189 is
called for, is cheap, and is readily available, and should sub for an EL84
too.

Jon

The Russian 6P14P-EV, made by Reflektor, IS the tube that Sovtek sells as
EL84M. The EV suffix means it should be a long-life, vibration resistant
version. It is probably the toughest EL84 still in production. According
to its CCCP data sheet, it can take 500V on the plate and 300 on the G2. In
order to improve its life, it has already been suggested to change or add G2
resistances and to check the bias and the balance among the PP pair.
I'd add that ventilation could be improved: it is to be noticed that cold
air must get in, but hot air must get OUT. This is trivial, but often
ignored by people designing air intakes in electronic units...

Ciao

Fabio


"Jon Yaeger" ha scritto nel messaggio
...
in article , kevin g at wrote
on
4/21/05 3:03 PM:

Is the 7189 a mil spec version that is more rugged and lasts longer?

Can take more heat?

My guitar amp uses them upsides down and I want something that won't get
toasted right away.


It kinda depends upon plate voltage, among other things. The 7189 is
rated
for a higher plate voltage.

Good old NOS EL84s usually can withstand higher plate voltages than
current
production EL84s and against new production 7189s.

By the same token, some new production EL84s will get red plates when
operated in older circuits that pushed the limits of the NOS tubes.

My experience with 7189s is that current production Sovtek and Tesla
aren't
anywhere as hardy as the original 7189s.

You might look at the Russian 6P14-EV. Works fine in apps where the 7189
is
called for, is cheap, and is readily available, and should sub for an EL84
too.

Jon

kevin g wrote:
Is the 7189 a mil spec version that is more rugged and lasts longer?

Can take more heat?

My guitar amp uses them upsides down and I want something that won't get
toasted right away.
Let me clarify, all apologies. The guitar amp uses two EL84 class A and
they are upside down. Personally I prefer when tubes are right side up
not sideways or upside down. Don't know if it alters tube life but it
seems to me a tube should be right side up. Being these two EL84 are
upside down I was just wondering what substitute I could put in there
place that is a little more hardy a tube.

I know people talk about tone, but at the levels I play my tone is going
to come from the preamp tubes, so my concern with the two output tubes
is longevity, endurance.

I currently have a pair of old stock LORENZ branded that I was told are
mullard re-lables and as a backup pair I have an old set of miniwatt
EL84 have some life left in them that came from a relatives old console
stereo they were getting rid of. But I'd like to start looking for a
new pair now that there is no urgency. Thanks.

kevin g wrote:

kevin g wrote:
Is the 7189 a mil spec version that is more rugged and lasts longer?

Can take more heat?

My guitar amp uses them upsides down and I want something that won't get
toasted right away.
Let me clarify, all apologies. The guitar amp uses two EL84 class A and
they are upside down. Personally I prefer when tubes are right side up
not sideways or upside down. Don't know if it alters tube life but it
seems to me a tube should be right side up. Being these two EL84 are
upside down I was just wondering what substitute I could put in there
place that is a little more hardy a tube.

If you are cooking EL84 too fast then probably you are
asking too much from the tubes.
I suggest you set the amp to 4 ohms but use an 8 ohm speaker.

There is some data on 7189 at
http://www.mif.pg.gda.pl/homepages/f...106/7/7189.pdf

This indicates the Pd is 13.2 watts, about only 1.2 watts more than any EL84
and the theoretical benefit of using 7189 seems unlikely to be realised in
practice.




I know people talk about tone, but at the levels I play my tone is going
to come from the preamp tubes, so my concern with the two output tubes
is longevity, endurance.

I currently have a pair of old stock LORENZ branded that I was told are
mullard re-lables and as a backup pair I have an old set of miniwatt
EL84 have some life left in them that came from a relatives old console
stereo they were getting rid of. But I'd like to start looking for a
new pair now that there is no urgency. Thanks.

Try 7189 by all means if you want to.

But there is a limit that tubes can take for long periods
of severe overload so enjoyed by musicians.
Tubes can take ths bashing because when they become saturated the
grid currents charge up the coupling caps and the tubes become biased for
class C operation and the dissipation is limited during severe
overload.

Also check that the idle dissipation is below 12 watts **for each tube**

You have a class A amp you say, and that means both tubes will be
dissipating say 12 watts sitting there doing nothing.
But often the bias voltage applied to the grids is the same,
and the bias current vary because tubes are not matched,
so one tube has 30 mA, the other 40 mA, so
if Ea = 350v, then one tube dissipates 10.5 watts and the other 14 watts
and the hotter one is on the brink of thermalling out.

If there is a bias balance pot for nulling the hum, use it, since it should
keep your tube currents equal and hence the dissipation
which shouldn't be more than 11 watts per tube in a class A EL84 amp.

The class A power at clipping, sine wave, is about only a tiny 10 watts.
The big sound you hear is the grossly oveloaded class A amp desperately
trying to force a 20 watt square wave through your speaker.
So increasing the load the tubes experience by using a 4 ohm tap instead of
the 8 ohm tap for
an 8 ohm speaker should reduce the wear a little, but only slightly
reduce the percieved sound levels.


Patrick Turner.