[Fai C]

I see a local tube builder work on a tube KT120 and it belongs to the
KT88/6550 family based on what the web says. But it kicks out more
power than the 6550/KT90.

Some even says this tube capable more than 150W in push pull.

Is that really true??

[Phil Allison[_3_]]

"Fai C"

I see a local tube builder work on a tube KT120 and it belongs to the
KT88/6550 family based on what the web says. But it kicks out more
power than the 6550/KT90.

Some even says this tube capable more than 150W in push pull.

Is that really true??


** See:

http://thetubestore.com/tungsolkt120.html

Looks like a real brute.

Might be good in bass guitar amps that normally run 6 x 6550s and struggle
to give 300W.

$95 for a matched pair is nice price too.


.... Phil

[NX211]

On Jan 7, 6:28*am, Fai C wrote:
I see a local tube builder work on a tube KT120 and it belongs to the
KT88/6550 family based on what the web says. But it kicks out more
power than the 6550/KT90.

Some even says this tube capable more than 150W in push pull.

Is that really true??

Bought a pair of them about six months back and they work great. I
run out of plate current before they run out of the ability to produce
power.

[Fai C]

On Jan 7, 9:08*pm, NX211 wrote:
On Jan 7, 6:28*am, Fai C wrote:

I see a local tube builder work on a tube KT120 and it belongs to the
KT88/6550 family based on what the web says. But it kicks out more
power than the 6550/KT90.

Some even says this tube capable more than 150W in push pull.

Is that really true??

Bought a pair of them about six months back and they work great. *I
run out of plate current before they run out of the ability to produce
power.

They claimed capable over 700V, even 800V operating voltage. Is that
really true?

For a pair in push pull, it should be capable high power such as 100W
in UL!!

[NX211]

On Jan 7, 9:08*am, Fai C wrote:
On Jan 7, 9:08*pm, NX211 wrote:

On Jan 7, 6:28*am, Fai C wrote:

I see a local tube builder work on a tube KT120 and it belongs to the
KT88/6550 family based on what the web says. But it kicks out more
power than the 6550/KT90.

Some even says this tube capable more than 150W in push pull.

Is that really true??

Bought a pair of them about six months back and they work great. *I
run out of plate current before they run out of the ability to produce
power.

They claimed capable over 700V, even 800V operating voltage. Is that
really true?

For a pair in push pull, it should be capable high power such as 100W
in UL!!

I have 500VDC on the plates, 450VDC on the screens and about 85 mA
idle current. There's 200hrs + on them and they seem just fine. My
favorite tube is still the EL156 - but it's hard to beat the KT120
for the ability to produce power - especially at the price.

[Patrick Turner]

On Jan 8, 1:08*am, Fai C wrote:
On Jan 7, 9:08*pm, NX211 wrote:

On Jan 7, 6:28*am, Fai C wrote:

I see a local tube builder work on a tube KT120 and it belongs to the
KT88/6550 family based on what the web says. But it kicks out more
power than the 6550/KT90.

Some even says this tube capable more than 150W in push pull.

Is that really true??

Bought a pair of them about six months back and they work great. *I
run out of plate current before they run out of the ability to produce
power.

They claimed capable over 700V, even 800V operating voltage. Is that
really true?

For a pair in push pull, it should be capable high power such as 100W
in UL!!

My ancient 1960s copy of the british amateur radio handbook has a
schematic for class AB2 operation of one pair of TT21 which could make
140 Watts.
The TT21 was a KT88 with a top cap, which meant 800V could be used on
the anode. Screen voltage was flexible, but up to 600V for Eg2 was
allowed.
KT120 has octal base and no top cap, so if 800V is used for Ea, beware
arcing at the socket. But maybe high Ia ability without grid current
allows for a steeper load line to be used, ie, use of Ea = 600V with
lower load than used for KT88 etc may be better tolerated, without
cooking tubes.

But for more class A and hi-fi performance one could get more class A
because Pda could be higher with the lower Ea for class A1.

The KT120 should indeed be able to produce 150W from a pair, thus
doing the work of a quad of 6L6GC if you flog everything hard enough.
100W is possible from a pair of EL34.
6550, KT88 had Pda rating of 42W, KT90 raised that to about 50W, then
KT120 raises it to 60W, but the KT120 tube curves look very close to
KT88/KT90 etc. Seems like its no more linear than its smaller older
brothers.

I'm getting a few KT120 soon to try out, and then I will really know
if they are worth the extra dough.

Patrick Turner.

[Roger Jones]

On Jan 7, 6:28*am, Fai C wrote:
I see a local tube builder work on a tube KT120 and it belongs to the
KT88/6550 family based on what the web says. But it kicks out more
power than the 6550/KT90.

Some even says this tube capable more than 150W in push pull.

Is that really true??

How might these compare to the 7534 (E130L)? 7534's look a bit like
"large 807's"... top cap plate for high B+, but on an octal base.
They allegedly give an easy 60 watts with only 300 volts B+ but seem
OK to well over 500 VDC. Disclaimer: I have four, but have not used
them... yet. My planned "100 watt plus" PA project will be a choice
between 4 x 807 or 2 x 7534's, so far leaning towards the 807's with
about 550 volts (less cathode bias) on the plates from a big 510-0-510
power transformer and a CLC B+ filter. OPT "choice" is 1.9K P-P to 4,
8, 15, 250 and 500 ohms speaker/line - the only one I have that is big
enough!
Cheers,
Roger

[Phil Allison[_3_]]

"Fai C"

They claimed capable over 700V, even 800V operating voltage. Is that
really true?


** The plate supply can be that high, but the screen cannot - same goes for
EL34s, 6L6GCs and 6550s.

The safe limit for the screen supply is about 500V.

For a pair in push pull, it should be capable high power such as 100W
in UL!!


** To get 150W, the screen and plate supplies must differ by 250V or so.



..... Phil

[Fai C]

On Jan 8, 4:03*am, Patrick Turner wrote:
On Jan 8, 1:08*am, Fai C wrote:









On Jan 7, 9:08*pm, NX211 wrote:

On Jan 7, 6:28*am, Fai C wrote:

I see a local tube builder work on a tube KT120 and it belongs to the
KT88/6550 family based on what the web says. But it kicks out more
power than the 6550/KT90.

Some even says this tube capable more than 150W in push pull.

Is that really true??

Bought a pair of them about six months back and they work great. *I
run out of plate current before they run out of the ability to produce
power.

They claimed capable over 700V, even 800V operating voltage. Is that
really true?

For a pair in push pull, it should be capable high power such as 100W
in UL!!

My ancient 1960s copy of the british amateur radio handbook has a
schematic for class AB2 operation of one pair of TT21 which could make
140 Watts.
The TT21 was a KT88 with a top cap, which meant 800V could be used on
the anode. Screen voltage was flexible, but up to 600V for Eg2 was
allowed.
KT120 has octal base and no top cap, so if 800V is used for Ea, beware
arcing at the socket. *But maybe high Ia ability without grid current
allows for a steeper load line to be used, ie, use of Ea = 600V with
lower load than used for KT88 etc may be better tolerated, without
cooking tubes.

But for more class A and hi-fi performance one could get more class A
because Pda could be higher with the lower Ea for class A1.

The KT120 should indeed be able to produce 150W from a pair, thus
doing the work of a quad of 6L6GC if you flog everything hard enough.
100W is possible from a pair of EL34.
6550, KT88 had Pda rating of 42W, KT90 raised that to about 50W, then
KT120 raises it to 60W, but the KT120 tube curves look very close to
KT88/KT90 etc. Seems like its no more linear than its smaller older
brothers.

I'm getting a few KT120 soon to try out, and then I will really know
if they are worth the extra dough.

Patrick Turner.

Hi Pat!
Most of the EL34 made today are impossible run over 650V. Not sure
about the GL reissue KT77. I know the Russian Mullard reissue can take
600-625V, not sure what is going to happen if runs the tube higher
than that.

[Fai C]

On Jan 8, 7:28*am, "Phil Allison" wrote:
"Fai C"

They claimed capable over 700V, even 800V operating voltage. Is that
really true?

** The plate supply can be that high, but the screen cannot - same goes for
EL34s, 6L6GCs and 6550s.

The safe limit for the screen supply is about 500V.

For a pair in push pull, it should be capable high power such as 100W
in UL!!

** To get 150W, the screen and plate supplies must differ by 250V or so.

.... *Phil

So what do you think the current production EL34 the max voltage can
run?

[Phil Allison[_3_]]

"Fai C"

Most of the EL34 made today are impossible run over 650V.


** That is 100% BULL**** !!

The plate supply can be up to 750 volts on any EL34 worthy of the number.

The screen supply must be not exceed 400 volts at the same time.

Tens of thousands of guitar amps use them this way - eg MusicMan and
Dynacord.

Peak plate voltages can reach +/- 5kV without failures, long as the base and
socket hold.

Smart designers include reverse diode strings on each plate to chassis to
limit peak values.

Pat will give you the details ....



.... Phil

[Phil Allison[_3_]]

"Fai C"

So what do you think the current production EL34 the max voltage can
run?


** See my other recent post.

Go look up the data sheet for the EL34 too.



.... Phil

[Fai C]

On Jan 8, 2:52*pm, "Phil Allison" wrote:
"Fai C"

So what do you think the current production EL34 the max voltage can
run?

** See my other recent post.

*Go look up the data sheet for the EL34 too.

... *Phil

I read this thread about the reliability of EL34 current production
running high voltage.

http://vintageamps.com/plexiboard/vi...+kt77&start=15

[Phil Allison[_3_]]

"Fai C"
"Phil Allison"
"Fai C"

So what do you think the current production EL34 the max voltage can
run?

** See my other recent post.

Go look up the data sheet for the EL34 too.


I read this thread about the reliability of EL34 current production
running high voltage.

http://vintageamps.com/plexiboard/vi...+kt77&start=15


** Never believe anything a guitar player says about tubes or tube amps.



..... Phil

[Patrick Turner]

On Jan 8, 10:28*am, "Phil Allison" wrote:
"Fai C"

They claimed capable over 700V, even 800V operating voltage. Is that
really true?

** The plate supply can be that high, but the screen cannot - same goes for
EL34s, 6L6GCs and 6550s.

The safe limit for the screen supply is about 500V.

For a pair in push pull, it should be capable high power such as 100W
in UL!!

** To get 150W, the screen and plate supplies must differ by 250V or so.

.... *Phil

In pure beam tetrode mode, the Eg2 probably cannot exceed +500V, while
Ea may be up to +800V.
The higher the Eg2, the greater must be the Eg1 bias, but the greater
Eg1 then the more class AB1 you can have which means less reliance in
class AB2 to get the high power.
UL does allow Eg2 to operate a little higher than the rated beam
tetrode Eg2 value because the Vac on the screens reduces the Pg2.
In the old days, 807 were deemed to be safe to operate in 43% UL ( or
triode ) with Ea = Eg2 = +450V max, even though Eg2 rating was +300V,
like plain old 6L6.

For hi-fi considerations with KT88/6550, the maximum possible Class
AB1 or AB2 power of a given pair of output tubes is not ever sought,
and usually a maximum possible AB1 PO of 60Watts at 3 ohms with Ea =
500Vdc when the RLa-a is lowest for maximum PO is all enough. So with
loads of 4 ohms the first 15W is class A and there is a total of 54W
class AB1. With 8 ohms, class A has risen to 30W, with total of 40W
AB1 perhaps.
With KT120 in the same circuit as one have used to produce the above
PO with KT88/6550 as mentioned, one may increase idle Ia to raise Pda
- IF the PSU can provide the extra plate power. This way the class A
power percentage of total AB power rises so fidelity may increase.
Total AB1 power might increase marginally.
One could expect perhaps 70W with 3 ohms before PO becomes limited by
grid current and transformer winding losses etc.
For most ppl, the extra power and available class class A may not be
worth paying extra for especially if they find a pair of EL34 are
already enough.

But for musos who like to have more poweful amps to drown out the next
guy along, the KT120 helps just a little bit.

Patrick Turner.

[Patrick Turner]

On Jan 8, 5:24*pm, Fai C wrote:
On Jan 8, 4:03*am, Patrick Turner wrote:





On Jan 8, 1:08*am, Fai C wrote:

On Jan 7, 9:08*pm, NX211 wrote:

On Jan 7, 6:28*am, Fai C wrote:

I see a local tube builder work on a tube KT120 and it belongs to the
KT88/6550 family based on what the web says. But it kicks out more
power than the 6550/KT90.

Some even says this tube capable more than 150W in push pull.

Is that really true??

Bought a pair of them about six months back and they work great. *I
run out of plate current before they run out of the ability to produce
power.

They claimed capable over 700V, even 800V operating voltage. Is that
really true?

For a pair in push pull, it should be capable high power such as 100W
in UL!!

My ancient 1960s copy of the british amateur radio handbook has a
schematic for class AB2 operation of one pair of TT21 which could make
140 Watts.
The TT21 was a KT88 with a top cap, which meant 800V could be used on
the anode. Screen voltage was flexible, but up to 600V for Eg2 was
allowed.
KT120 has octal base and no top cap, so if 800V is used for Ea, beware
arcing at the socket. *But maybe high Ia ability without grid current
allows for a steeper load line to be used, ie, use of Ea = 600V with
lower load than used for KT88 etc may be better tolerated, without
cooking tubes.

But for more class A and hi-fi performance one could get more class A
because Pda could be higher with the lower Ea for class A1.

The KT120 should indeed be able to produce 150W from a pair, thus
doing the work of a quad of 6L6GC if you flog everything hard enough.
100W is possible from a pair of EL34.
6550, KT88 had Pda rating of 42W, KT90 raised that to about 50W, then
KT120 raises it to 60W, but the KT120 tube curves look very close to
KT88/KT90 etc. Seems like its no more linear than its smaller older
brothers.

I'm getting a few KT120 soon to try out, and then I will really know
if they are worth the extra dough.

Patrick Turner.

Hi Pat!
Most of the EL34 made today are impossible run over 650V. Not sure
about the GL reissue KT77. I know the Russian Mullard reissue can take
600-625V, not sure what is going to happen if runs the tube higher
than that.- Hide quoted text -

- Show quoted text -

Mullard seemed to think their EL34 could run with Ea = 850V and Eg2 =
425V, and I have seen amps with +900V abd +450V. These amps were
marvelous smoke producing devices. For a pair, RLa-a needed to be
about 12k ohms for a rated 96W of output power, and I've seen amps
giving 125W.
The smoke all too easily occurs when Mr Idiot connects a 4 ohm speaker
instead the rated 8 ohms. Mr Idiot knows less ohms are easier to
drive, but he don't know it means the anode load halves, so that tubes
immediately have to operate with Pda exceeding the 25W Pda rating, so
the tube cook. Many output tubes cook because Mr Idiot has set the
bias current too high without knowing what he's doing, but this dc
state condition may be tolerated if the ac state condition does not go
too high, as may be the case if Ea = 500V or less, but with extreme
high Ea = 900V, the product of Ea x average Ia with a low load value
can cause the smoke.
In amps with EL34 Ea = 900V, Ia might be 15mA, giving Pda = 13.5W, and
that might seem safe, but one doesn't need a huge change in grid bias
to give a lot more Ia, and you have a tube idling at the Pda rating,
and likely to cook if AC Pda goes high. Many amps with multiple EL34
in parallel have the ONE bias voltage applied to all tubes, so as tube
age, the Ia changes, some tubes Ia reduces, some tubes Ia increases,
and smoke&**** happens.

Probably russian EL34 could take Ea at 900V if Eg2 were kept low, say
less than 400V, but the idea of trying to use such high Ea is all
bull****, a stupid idea, and if one wants 100W from EL34, then its
safer to use a quad of EL34 at least, or quad of 6550.

Many ppl have forgotten how to build tube amps which will last much
time without smoke. Many makers arrange the OPT ratio so that RLa-a is
too low, thus giving high PO to impress dumbass buyers who will never
understand that there is much more to performance than having a high
PO rating.

The worst EL34 I ever used were some el-cheapos made by Siemens which
looked like the internals had been downsized by 15%. They'd run red
hot with Pda = 25W, and a few failed of the batch fairly easily. Maybe
they'd be OK with low Ea = 350V and Ia at 40mA max, for a low 20W of
PO per pair.

Patrick Turner.

[Phil Allison[_3_]]

"Patrick Turner"


But for musos who like to have more poweful amps to drown out the next
guy along, the KT120 helps just a little bit.


** As a marketing idea - the KT120 is sheer brilliance.

Supplying a heavily beefed up KT88 / 6550 for similar money to ordinary ones
has the potential to take a big share of the replacement valve market off
the suppliers of those types.

Amps that run 6 valves in one stage may only need four KT120s to do the same
job - a major cost saving.

I predict they are gonna sell heaps of them.



.... Phil

[Patrick Turner]

On Jan 10, 4:49*pm, "Phil Allison" wrote:
"Patrick Turner"

But for musos who like to have more poweful amps to drown out the next
guy along, the KT120 helps just a little bit.

** As a marketing idea - *the KT120 is sheer brilliance.

Supplying a heavily beefed up KT88 / 6550 for similar money to ordinary ones
has the potential to take a big share of the replacement valve market off
the suppliers of those types.

Amps that run 6 valves in one stage may only need four KT120s to do the same
job *- *a major cost saving.

I predict they are gonna sell heaps of them.

... *Phil

I have aquired 8 x KT120 which a colleague has forwarded to me at the
right price for designing all his OPTs. He's more prolific at making
amps, but he can't calculate anything even if his life depended on it.
Anyway, he has a client asking for a 200W amp for hi-fi and I
suggested a six pack of KT88/6550 so that max PO is 66W per pair of
tubes, and then you can have each one with 15Watts of idle Pda for
long tube life, so total PDA = 90W, thus allowing 40W of pure class A
if desired, and if the RLa-a is about 4 times th value used to get
200W.

In other words, if max PO is developed when the nominated RL = the
labelled output, the one wood be wise to have 2, 4 and 8 ohm outlets,
and if an 8 ohm load is ised at the 2 ohm terminal, you get 40W pure
class A, and that's for mature ppl who would never ever need a pair of
200W amps.

In 1957, a pair of standard KT88 with 43% UL OPT and with Ea
maintained at +560Vdc at full load, you could get 100W, with RLa-a =
4k5, and the amp was AB1. So only 4 were needed for 200W, and In the
guitar amp world Ampeg made an amp with 6 x 6550 for 300W, with tubes
in tetrode mode, fixed Eg2, Ea about 600V, and Eg2 about +450V.

I worked on such an amp to replace its PT which was taken out before
it was shipped to an Oz buyer from the US. OK, so you can set up the
new tranny for +600V at idle, but if the B+ sags down to say +520V at
full stick continuus, maybe you get only 220W instead of 300W.
Instantaneous PO is 300W though. It matters not because when there's
severe overdive and a square wave signal, PO is somewhat higher from
what is effectively class C, because coupling caps retain a -V charge
so tubes are biased into class C.

I cannot see that using KT120 plugged straight into an Ampeg would
give much more PO using the same loads.

I begain testing the KT120 this week using an very good quality PP OPT
with 20% CFB windings. But first I began with tests on 6550, to get
the test circuit running right. I found the "diode" Ra line for Eg1=0V
below Ea = 120V does not give the more vertical diode lines shown in
data for original KT88, or 6550. Those older tubes could swing more Ea
lower than more modern tubes. Unfortunatly, my bench top power supply
I made in 1993 using an olf TV tranny and other parts I could
scrounge, and including a series regulator with 2 x 6AS7G pass
elements does not hold regulation over 200mA at highB+. So, I have
begun to rebuild the whole power supply, to allow a well regulated
600Vdc at 300mA at least.
Everyone will just have to be patient while waiting to observe results
I might obtain, but so far, it seems the increase in PO is marginal,
ie, one cannot just set them up with Ea at 600V, then halve the RLa-a
from say 5ka-a down to 2k5, and expect 200W from a pair.

It'll take days to finish the PSU re-build, and a day to see how well
the CFB OPT works ***compared with existing modern 6550 or KT88***.
This means ensuring both Eg2 and Ea remain well regulated, then
plotting graphs for maximum clipping PO for RLa-a from say 1k5 to 15k0
ie, loads between horrid low loads to give high PO in nearly all class
B and up toloads for low PO and pure class A.

The data I have seen so far on KT120 is, IMHO, quite inadequate. There
are curves and they cab be seen at
http://www.newsensor.com/releases/KT...Sol-Curves.pdf

The curves look quite horrible, and such badly drawn curves just don't
look right at all. Maybe a Russian dude who prepared the figures and
the curves had been drinking far too much vodka before spending an how
drawing curves.

If one compares the kind of data presentation in 1957 of the KT88,
EL34, 6550 and others, it was good, but now, we get ****. So there's
only one way to ascertain if these newly devoped tubes are worth their
price - do all the tests properly myself, comparing with others well
known under identical situations.

1957 data and curves were not necessarily very correct. The tube
testing gear and curve plotters was all driven by tube circuits, and
subject to considerable distortions. When I tested 6550 in SE triode
with a very high value choke as a load, ie, load was close to a CCS, I
measured considerably less THD than what the old 1950s curves
indicated, and its not a surprise that tubes will measure better than
they have been drawn up in curve sheets.

I'me expecting good things from KT120. They sure look nice, being like
a KT88 which has been sent to the gym and told to work out for months
while eating a good diet, so they look like they can do more. They are
maube 10% larger dimensions which translates to a volume increase of
much more, and anode is bigger, hence can run up to 60W anode
dissipation.

In practice, theis means that Pda in class A amp could be 40W, just
like where one might use 20W for EL34, or 30W for 6550 / KT88.
So someone with just ONE KT120 with Ea = 400V, and Ia at 100mA could
expect 18 W of pure class A using tetrode mode, with load of 3k6.
Using a pair with RLa-a = 7k2 would give a genuine 36W of pure class
A, and a lot more in class AB if the RLa-a load was reduced to 3k6.
Triode operation probably would yield 13 watts in SET, and a PP pair
would give 26W pure class AB1.

I have used KT90 in amps such as Quad-II. One might think this is
butchery, but where heater power is available in any given amp, and
space allows, there is no reason why KT120 may not be used providing
the bias Ia does not exceed that of the original tubes used in the
amp. Of course, people won't give a **** about the finer points of
substituting tubes, and no doubt a few ppl will cause smoke to pour
from their amps because they have tried to draw far too much power
from a given PSU, and the extra heat generated by KT120 with high Ia
bias affects surrounding parts.

The KT120 represents a welcome development and at this time I see
little reason why the product should not be successful for the makers.

The emphasis on being able to make 150W from a pair of KT120 is to me
a real bull**** idea, because once you set up any pair of OP tubes to
produce 1.25 times the maximum Pda for the pair, then the power is
nearly all class B, with very little class A, and correspondingly low
natural fidelity, ie, high THD/IMD at all levels. With EL84, Pda for a
pair = 24W max, and if you try to extract 30W, then don't expect the
best sound. Musical Reference did achieve 35Watts from a pair of EL84,
using Ea = 700V and Eg2 = 350V, and I repaired one, and lemme tellya,
a pair of 6550 making the same 35W just sounded better.

140W was possible from class AB2 TT21 which were the RF version of
KT88 with anode top caps. Eg2 could be safely low, while Ea up to
800V, and WOW. Hams used them for modulators for ther ham gear, and
who knows what KT120 would be capable of in class AB2. I have no idea
whether the grids would cope with the heat produced by driving grids
positive.
With speach signals and no clipping, the duty cycle of heat production
is fairly low, but with a sine wave signal, watch out!.

When I made my first 8585 stereo amp in 1995 using a quad of 6550 per
channel, it was originally set up with 12.5% CFB, Ea = +400Vdc. There
was also some UL screen FB, so Eg2 = Ea, and Ia was 60mA per tube. It
made 50W in pure class A and without any global NFB the THD = 0.7%,
better than any pure class A triode output stage without GNFB.

I want to know if KT120 will give similar excellent results, and also
know exactly what operating conditions are needed to satisfy the head
banger brigade who seem to only think of maximum Watts when
considering amps, rather than focus on the possible fidelity of the
essential high quality needed for the first ten Watts from the amp.

Patrick Turner.