Home » Audio » Thermionic Emissions » New Production Tung Sol 6550, Penta KT88s (Concerning Audio Quality)
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Re: Demagnetizing Tung Sol 6550, Penta KT88s [message #97789 is a reply to message #97463] |
Fri, 21 June 2024 17:29 ![Go to previous message Go to previous message](/forum/theme/AudioRoundTable/images/up.png) ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
positron
Messages: 110 Registered: May 2020
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positron wrote on Mon, 26 February 2024 21:44positron wrote on Tue, 21 February 2023 22:45After more testing/auditioning, I prefer the Pentas over the
Tung Sols. I find the new Tung Sols are still zingy in the highs.
The Pentas are just slightly fuller compared to the Tung Sols.
That is it for now.
Cheers
pos
I am eating some crow now. I just checked and the new Tung Sols (gift years ago) I have been using needed to be demagnetized again. The JJs not so. There is also a difference in the midrange I think I like better with the JJ KT88s.
cheers
pos
Minute changes in speaker crossover can make a sonic difference. The Penta (Chinese KT88-sc) is outclassed by both new JJ and Russian Tung Sol.
Tung Sol and JJ have their plus and minus. The JJ has less but tighter
bass, maybe too tight.
Tung Sol has fuller and maybe more realistic bass (I have never heard a double bass indoors that was super tight like outdoors and JJs) but the depth is, I think, accurate.
But then the JJs have more hours than the Tung Sols which have moderate usage.
Harmonic distortion wise, The Chinese Penta and JJ have nearly twice the
HD as the Tung Sols.
Plate dissipation wise, The Chinese is 50 watt, the JJ is 42 watt, and the
Tung Sol is 35 watt. I ran all three at approximately 29 watt idle plate
dissipation.
All and all, over the months of testing, changes in minor xover design, electronic conditions, a music lover would probably choose between the JJ and
new Russian Tung Sol 6550 over the other Russian brands. (I received the Tung Sol many years before the war.)
I have never tried the western continental, expensive European brands.
Cheers
pos
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Re: Demagnetizing Tung Sol 6550, Penta KT88s [message #97806 is a reply to message #97790] |
Fri, 28 June 2024 11:28 ![Go to previous message Go to previous message](/forum/theme/AudioRoundTable/images/up.png) ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
positron
Messages: 110 Registered: May 2020
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gofar99 wrote on Fri, 21 June 2024 20:50Hi, Personally I prefer the JJs. In class A amps (like all my designs) they have a solid and clean bass with good mids and nice extension on the top end. They are also really consistent and stay "biased" over a long time. I use them at about 35-36 watts dissipation (each tube A+S). For a seemingly "crisper" sound the JJ EL34s are great at about 25 watts (A+S) dissipation. But my go to now in the amps are TS KT120s running at 25 watts dissipation (A+S) into 8K load. Magical IMO. Obviously class A U/L P-P is not efficient. A good source of heat in the winter though.
Hi Go,
Don't get me wrong Go. The JJ KT88 is right at the top of tubes
I prefer. The only issue I have is the bass, although very tight,
just seems a little light in my system. Playing Moody Blues
at Royal Albert Hall, the music sounds 30 feet behind the
front wall, a little more than I like. The russian Tung Sols sound
15 feet or so. Could be old/used JJ tubes that I am using though.
I did some checking and found out that JJ uses
lead free solder in their pin connections (EU law)
so I added some quad solder with lead. Not many can perform
such adjustments though.
Bass increased some as well as the harmonic structure.
The JJ KT88s are still highly favored.
The JJ E88CC (similar to 6DJ8) is the only tube I use in my
monoblocks, preamps, and phono stage. The HD is the lowest
I have ever measured in any small signal tube, ~1/9th,
some 18db less.
I just started performing some cathode testing by
lowering the filament voltage to see if I can lengthen
tube life.
For newbies, cathode life is mainly determined by:
1. residual gas which forms positive ions which strikes/destroys
the oxides
2. high filament voltage evaporates oxides. Some transfers to the
grid etc.
3. low filament voltage tends to deplete the space cloud protecting
the oxides
4. cathode sleeve impurities poison the oxides
5. Even the temperature of the Plate structure affects the oxide
temperature (reference for given filament voltage).
Pt 3 is important. If we operate at reduced maximum/peak cathode
current, we may also reduce the cathode temperature and still
retain a descent space cloud, and lessen the oxide evaporation.
Since each tube manufacturer is different (including NOS tubes)
I hope the experiment allows me to determine if cathode temperature
is the main culprit in new JJ tube life span or another point listed
above is more important.
cheers
pos
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Re: Demagnetizing Tung Sol 6550, Penta KT88s [message #97818 is a reply to message #97810] |
Tue, 02 July 2024 00:14 ![Go to previous message Go to previous message](/forum/theme/AudioRoundTable/images/up.png) ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
positron
Messages: 110 Registered: May 2020
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gofar99 wrote on Fri, 28 June 2024 20:46Hi, I get asked all the time on the Oddblock amps as to how often the tubes should be replaced. I used the original tubes (blue glass JJ KT88s) for 12 years in class A U/L at 36 watts dissipation (A+S) and they still were sounding fine and tested good. My estimate was nearly 8000 hours. Well beyond the 2K or so they spec for. Since I switched to the KT120s in the amps I figure they will last to the next century at about 25 watts dissipation. That BTW is a sweet spot in the sound, not done to be be frugal. The preamp and drivers either NOS Phillips JAN 5751 or NOS JAN Sylvania 12SL7s will likely never need replacing. In the past 15 years I have had one fail due to an internal short but none ever tested or sounded bad. BTW I suspect the Blue JJs were probably not no lead but I could be wrong. Sometimes the socket is the issue and not the tube. I normally use Belton ones. They can be testy as they grab the tube really hard though and can make it difficult to get out. I now always use SMPS for heater power that are well filtered, isolated and closely regulated.
Hi Go,
I thought the russians were having trouble with the KT120/150s? But then
at 25 watt plate dissipation, that is quite easy operation.
Personally, due to rising NOS prices decades ago, I set out to design
the perfect preamplifier and amplifier using new tubes. (Proper ics
are extremely important along with proper component jacks, part of
the accuracy equation.)
I used the JJs E88CCs due to the extremely low distortion, and
very wide frequency response without global feedback. The JJ KT88s
are not known for low distortion, about twice that of the russian
tubes. Chinese tubes are also known for high distortion, although
I have not measured all the output tubes available.
The ultra, ultra low distortion of the JJ E88CCs basically eliminates
the higher orders created by combining the driver and output tube
harmonics.
Another reason I designed around new tubes because I saw that the
prices were rising and limited quantity. Although not as long lasting,
the JJs do allow me to produce a perfectly accurate preamplifier and
near perfect amplifier. This after sophisticated listening testing.
I have heard good things concerning the Beltons.
I have to be really really careful as a near all poly cap
power supply audio system is extremely, extremely sensitive.
For instance, it is extremely important to have the speaker
wires connected wrench tight at the amplifier's jacks for
consistent bass tightness. Finger tight is insufficient.
Next few months, will keep track of the filament hours and
oxide quality of the E88CCs. Thanks for the tip on the KT88s.
I am running approximately 6.0 volts on the filaments.
cheers
pos
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Re: New Production Tung Sol 6550, Penta KT88s [message #97820 is a reply to message #96284] |
Tue, 02 July 2024 13:50 ![Go to previous message Go to previous message](/forum/theme/AudioRoundTable/images/up.png) ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
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Wayne Parham
Messages: 18752 Registered: January 2001
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Illuminati (33rd Degree) |
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I've been meaning to reply to this thread for a long time, but keep forgetting. When a post is made here, I read it, make a mental note to respond when I get time, then eventually forget 'til the next post.
I have an Audio Note Kit 2, which uses a 6550 tube wired as a triode and run Class A. I love it, but it did show some oddities over the years, some of which may have been due to things other than the basic circuit.
One of which was a predisposition to draw excessive output circuit current after a tube had been run for a few years. I use this amplifier often, so a few years means several thousand hours. At that time, it would usually start overheating the cathode resistor. This, of course, raised the voltage across it and its bypass capacitor. After a few years, I installed a 1/4A fuse in series with the cathode resistor, and that was magic. When a fuse pops now, I swap both fuses and both tubes. That makes everything very predictable.
I have noticed, though, that after moving from Tulsa to Bella Vista, the excessive current problem seems to happen less often. Seems like we've gone from maybe every four years to every six or maybe even longer. It just seems rarer now.
But none of that is scientific at all. I haven't measured the voltage in either place, haven't looked at the waveform, nothing. I mean, I've seen both voltage and waveform in both places. From time to time, I've needed to troubleshoot something and on those occasions, I look at power sometimes. But just for a few seconds, just enough to get a reading, and no real deep dive into what's happening. Just noting that I've got 170V peak, sine looks smooth, nothing deeper than that. In fact, I'm surprised that Bella Vista power is "better" than Tulsa 'cause no other utility services are.
Anyway, all that was just a qualifier to show what "m working with when I talk about 6550 and KT88 tubes in my particular setup.
For me - I have tended to really like Tung-Sol and Electro-Harmonix for new production tubes. They both sound great and they both behave. They last a long time.
I also have RCA and Tung-Sol 6550 tubes that were manufactured decades ago. They're strong, almost could be called NOS but they have been used. Just lightly. They're too precious for me to run full-time, all the time.
I like Svetlana tubes too, but for whatever reason, I don't like 'em as much as the Tung-Sol and Electro-Harmonix tubes. It may just be psychological, because without the Cyrillic letter on them, they're "pretenders" to me. And these days, I'm not sure I'd want the "real thing" if it existed anyway. So that bias may have nothing at all to do with quality.
The one that really stands out as a "bad part" for my amplifier is the JJ 6550. It's a "snap-crackle-pop" tube for me. Many of them actually make strange noises in my Audio Note circuit and they always fail very rapidly, like in months. Not sure what's up with that, but it has happened more than once.
This seems to track with many of the KT88 tubes as well. I have a handful of different brands, and I'm sure some are better than others in my application. But all of the KT88 tubes seem to fail sooner than 6550 tubes. I'm not sure what the actual structural differences are, but KT88s don't seem to fare as well as 6550s in my Audio Note Kit 2.
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Re: New Production Tung Sol 6550, Penta KT88s [message #97824 is a reply to message #97820] |
Tue, 02 July 2024 23:41 ![Go to previous message Go to previous message](/forum/theme/AudioRoundTable/images/up.png) ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
positron
Messages: 110 Registered: May 2020
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Viscount |
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Wayne Parham wrote on Tue, 02 July 2024 13:50
I've been meaning to reply to this thread for a long time, but keep forgetting. When a post is
made here, I read it, make a mental note to respond when I get time, then eventually forget 'til
the next post.
I have an Audio Note Kit 2, which uses a 6550 tube wired as a triode and run Class A. I love it,
but it did show some oddities over the years, some of which may have been due to things other
than the basic circuit.
One of which was a predisposition to draw excessive output circuit current after a tube had been
run for a few years. I use this amplifier often, so a few years means several thousand hours.
At that time, it would usually start overheating the cathode resistor. This, of course, raised
the voltage across it and its bypass capacitor. After a few years, I installed a 1/4A fuse in
series with the cathode resistor, and that was magic. When a fuse pops now, I swap both fuses
and both tubes. That makes everything very predictable.
I have noticed, though, that after moving from Tulsa to Bella Vista, the excessive current
problem seems to happen less often. Seems like we've gone from maybe every four years to
every six or maybe even longer. It just seems rarer now.
But none of that is scientific at all. I haven't measured the voltage in either place,
haven't looked at the waveform, nothing. I mean, I've seen both voltage and waveform in
both places. From time to time, I've needed to troubleshoot something and on those occasions,
I look at power sometimes. But just for a few seconds, just enough to get a reading, and no
real deep dive into what's happening. Just noting that I've got 170V peak, sine looks smooth,
nothing deeper than that. In fact, I'm surprised that Bella Vista power is "better" than Tulsa
'cause no other utility services are.
Anyway, all that was just a qualifier to show what "m working with when I talk about 6550 and
KT88 tubes in my particular setup.
For me - I have tended to really like Tung-Sol and Electro-Harmonix for new production tubes. T
hey both sound great and they both behave. They last a long time.
I also have RCA and Tung-Sol 6550 tubes that were manufactured decades ago. They're strong,
almost could be called NOS but they have been used. Just lightly. They're too precious for
me to run full-time, all the time.
I like Svetlana tubes too, but for whatever reason, I don't like 'em as much as the Tung-Sol and
Electro-Harmonix tubes. It may just be psychological, because without the Cyrillic letter on them,
they're "pretenders" to me. And these days, I'm not sure I'd want the "real thing" if it existed
anyway. So that bias may have nothing at all to do with quality.
The one that really stands out as a "bad part" for my amplifier is the JJ 6550. It's a
"snap-crackle-pop" tube for me. Many of them actually make strange noises in my Audio Note circuit
and they always fail very rapidly, like in months. Not sure what's up with that, but it has happened
more than once.
This seems to track with many of the KT88 tubes as well. I have a handful of different brands, and
I'm sure some are better than others in my application. But all of the KT88 tubes seem to fail
sooner than 6550 tubes. I'm not sure what the actual structural differences are, but KT88s don't
seem to fare as well as 6550s in my Audio Note Kit 2.
Hi Wayne,
Increasing cathode current over the years could be caused by
excessive Gas causing grid leakage, thus bias changes. This can
occur even though the top getters show no gas absorption.
Speaking of gas absorption, top getters are not the best placement
for gas absorption. It just does not get as hot as along the sides
of the tubes. I noticed that my Tung Sol side getters collecting
gas after a few hundred hours. However, the tube's side getters
have been getting hotter and connecting more gas than I care to
see. By the way, I run my output tubes at ~29 watts plate
dissipation, though rated at 35 watt plate dissipation.
Another situation could be caused by fluctuating AC line voltage;
higher would cause faster cathode oxide evaporation, some of
which settles on the control grid 1. Just a thought.
I have a little plug in AC line voltage meter. Here is a link
showing a typical one. My line voltage varies just a volt,
maybe 2 volts extreme. YMMV.
Eversame AC Voltage Meter
I compared the Svetlana KT88s vs the Winged C KT88s, they are
sonically different in my experience. I have an octet of both
WC KT88s and WC 6550, and they sound different as well.
Fortunately, I have not tried the JJ 6550s. Thanks for the
heads up Wayne.
I am wondering what the idle plate dissipation is with the
Audio Note kit 2?
Cheers
pos
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