Dear all,
inspired by this forum post from ASR, I decided to prepare for my next project in advance.. and build something distorting next year.
No, not a guitar amp, I mean I'd like to stay at HiFi quality but rather aiming for insanely low THD, I'd be happy to build a more triode-close amplifier, preferably with 0 feedback (or at least adjustable between 0 and full) and don't care of measurements. If it sounds sweet and great to my ears, my goal is achieved.
Efficiency is no aim either.
I have right now
I can have power and output transformers wound in exceptional quality, not begun yet. Trying to estimate load (with KT-150 in mind).
Are there any good, reliable KT88 designs out there you are aware of which could be sized/extended with very minor modifications (maybe 1-2 switches, etc) to accomodate KT120s and KT150s too ?
I'm also a fan of microcontrollers so mechanical (or even solid state) relays are not an issue to use (if they don't degrade signal in the intended application and I can double them if needed for safety).
But if circuit design allows with very minimal modification I could live with that hard-wired option too. A switch (or bypass or any kind of quickly adjustable thing) on the amp's outside itself would be more convenient of course.
I'd really like to build 2 very simple Class-A monoblocks, tubes in triode mode with aforementioned tubes first, designed so that these amps could later also be happy with the heaviest KT-150 guys.
Just out of pure fun and learning - and wasting not only heat but time too.
Any tips, ideas ?
inspired by this forum post from ASR, I decided to prepare for my next project in advance.. and build something distorting next year.
No, not a guitar amp, I mean I'd like to stay at HiFi quality but rather aiming for insanely low THD, I'd be happy to build a more triode-close amplifier, preferably with 0 feedback (or at least adjustable between 0 and full) and don't care of measurements. If it sounds sweet and great to my ears, my goal is achieved.
Efficiency is no aim either.
I have right now
- 2x NOS JJ KT88
- 2x NOS JJ E88CC
- 2x NOS JJ ECC99
I can have power and output transformers wound in exceptional quality, not begun yet. Trying to estimate load (with KT-150 in mind).
Are there any good, reliable KT88 designs out there you are aware of which could be sized/extended with very minor modifications (maybe 1-2 switches, etc) to accomodate KT120s and KT150s too ?
I'm also a fan of microcontrollers so mechanical (or even solid state) relays are not an issue to use (if they don't degrade signal in the intended application and I can double them if needed for safety).
But if circuit design allows with very minimal modification I could live with that hard-wired option too. A switch (or bypass or any kind of quickly adjustable thing) on the amp's outside itself would be more convenient of course.
I'd really like to build 2 very simple Class-A monoblocks, tubes in triode mode with aforementioned tubes first, designed so that these amps could later also be happy with the heaviest KT-150 guys.
Just out of pure fun and learning - and wasting not only heat but time too.
Any tips, ideas ?
What comes into my mind now just quickly are:
- KT150s need more juice of course, hence:
- more heater power capability -> PSU oversizing compared to pure KT88 calculations
- more anode dissipation -> same here, so overall PSU and OTs need to be somewhat bigger
- probably more current from driver section (parallel & matched ECC99s maybe ?)
- other minor (if possible) circuit modifications to match good biasing when switching to KT150s after using KT88
My 2 cents?
SS amp vendors in the '80's stateside were engaged in a race to zero point zero distortion as marketing tool...
A reflex occurred soon after in which listening panels concluded that the lowest #'s didn't coincide with the best human auditory experience.
So then, IMO- high end amp designers shifted to a hybrid approach of SS and tube combination... and struck gold to the present, adding a bit of 'human element' to the experience. Sales have since responded favorably. This trend is found in current Hi End audio Mag's review of $10k+ products...
Jim
SS amp vendors in the '80's stateside were engaged in a race to zero point zero distortion as marketing tool...
A reflex occurred soon after in which listening panels concluded that the lowest #'s didn't coincide with the best human auditory experience.
So then, IMO- high end amp designers shifted to a hybrid approach of SS and tube combination... and struck gold to the present, adding a bit of 'human element' to the experience. Sales have since responded favorably. This trend is found in current Hi End audio Mag's review of $10k+ products...
Jim
Yepp and then came another "bad boy", today's best Class D designs.. Hypex is good and nice (and even has a "warm" tone regarding mids, with precise highs and amazingly well controlled bass), I like the sound of it but then when I switch on my OTL headphone amp, a little different world.. the latter has some "magic" which might be added harmonic distortions in the highs or dunno but the statement of combining these being the best world is valid, at least I fully agree with what you say. (Vincent also uses tube gear on the input stage while being SS on the output).
Anyway, I'm planning/designing my 3-way system and the tweeters will be driven by my 25W8R capable OTL tube amp (I'll most probably go for 95-98dB AMT-s).
With this KT88-KT150 build I'm just experimenting with a real SE, will be part of my smaller home office room, driving 2-way smaller speakers.
What I'll choose for midrange and bass for the 'big' 3-way is still a story of the future. (Hypex NC400 probably).
Anyway, I'm planning/designing my 3-way system and the tweeters will be driven by my 25W8R capable OTL tube amp (I'll most probably go for 95-98dB AMT-s).
With this KT88-KT150 build I'm just experimenting with a real SE, will be part of my smaller home office room, driving 2-way smaller speakers.
What I'll choose for midrange and bass for the 'big' 3-way is still a story of the future. (Hypex NC400 probably).
Assume power requirements and transformer ratio would vary
enough to make a all in one unit difficult to support the whole tube family.
For lower distortion and drive stages needed for 120 and 150 types.
Typical KT-88 and even 6550 likely more favorable.
Far as legacy products and support for the tubes in general.
More likely 88 and 6550 will be around and 120 , 150
will disappear.
Probably just build with what you got and use the 88's
Plenty of pre wound transformers which support it
enough to make a all in one unit difficult to support the whole tube family.
For lower distortion and drive stages needed for 120 and 150 types.
Typical KT-88 and even 6550 likely more favorable.
Far as legacy products and support for the tubes in general.
More likely 88 and 6550 will be around and 120 , 150
will disappear.
Probably just build with what you got and use the 88's
Plenty of pre wound transformers which support it
Plenty of reasons to just stick with 88’s. They will be supported by someone if New Sensor fails. They sound good. If you need more power, parallel two or more. When you go to buy a transformer for THAT, the required primary Z will be lower. This is actually what you WANT when scaling up power. All other things about the construction of it equal, the lower Z trafo at X watts will go higher in frequency before taking a dive because it requires less turns at the same turns per volt to hit your target flux density. The required B+ doesnt rise (increasing the cost of everything else, disproportionately).
Exactly, good point was going to mention
Parallel devices.
Something a good old 6550 BEAM TETRODE will do
Unless you wanna just re live the trendy stuff
people did with large radio transmitter tubes.
Around 1998 / 2000
High power with 10 to 45 dollar tubes.
Not renamed " KT " 500 dollar modern tubes
Parallel devices.
Something a good old 6550 BEAM TETRODE will do
Unless you wanna just re live the trendy stuff
people did with large radio transmitter tubes.
Around 1998 / 2000
High power with 10 to 45 dollar tubes.
Not renamed " KT " 500 dollar modern tubes
H
HAYK
I advise you the luxman MQ68C in open loop. The Amp uses specially designed and manufactured for Luxman the 50C10 triode. This triode is derived from an old US one but purposely more nonlinear to provoke odd order harmonics of opposite phase.
It has a constant THD from 0.1W to 25W of 0.3% in open loop.
This tube is no more available, Luxman launched a similar amp using kt88 in triode PP mounted for 20W, I forgot the reference, it was in Stereophile magazine 3 or 4 years ago.
It has a constant THD from 0.1W to 25W of 0.3% in open loop.
This tube is no more available, Luxman launched a similar amp using kt88 in triode PP mounted for 20W, I forgot the reference, it was in Stereophile magazine 3 or 4 years ago.
Here is my simple KT120 SEUL amp, which is a minor adaptation of a design Kegger published, and is a variant of that Blueglow/Kegger KT88 build. I built them as monoblocks with Themionic Labs OT and they sound amazing. I built them with fixed bias rather than cathode bias to allow them to be adjusted to use KT88 tubes as well.
I'm not sure how good it would sound as UL with no feedback, but I think if you triode strap the output tubes, you could eliminate it. Here are the schematics and I did a whole video series on building them. There is a video in series showing power vs THD testing, 18W at 2% and I believe around 10-12 at 1%. That was with the bias maxed out of what I would feel comfortable with.
One problem you may run into is finding a pair of KT120/KT150 tubes you can bias up to run single ended, higher than a KT88. Most of the newer samples don't like being biased hotter than about 80ma @ 500V without starting to red plate. Some don't even get that far. In my testing they need at least 80ma @ 500V % bias point to sound good. I found an earlier pair that are fine at up to 110ma, so they do exist. I believe it's due to the getter placement on some of them. Just be aware of that if you plan to run KT120/KT150 single ended. I cover that issue also at the end of the video series. Here is the playlist https://www.youtube.com/playlist?list=PLtEhh3UpOsiDh6orcLPoJjPWSy--6g675
I'm not sure how good it would sound as UL with no feedback, but I think if you triode strap the output tubes, you could eliminate it. Here are the schematics and I did a whole video series on building them. There is a video in series showing power vs THD testing, 18W at 2% and I believe around 10-12 at 1%. That was with the bias maxed out of what I would feel comfortable with.
One problem you may run into is finding a pair of KT120/KT150 tubes you can bias up to run single ended, higher than a KT88. Most of the newer samples don't like being biased hotter than about 80ma @ 500V without starting to red plate. Some don't even get that far. In my testing they need at least 80ma @ 500V % bias point to sound good. I found an earlier pair that are fine at up to 110ma, so they do exist. I believe it's due to the getter placement on some of them. Just be aware of that if you plan to run KT120/KT150 single ended. I cover that issue also at the end of the video series. Here is the playlist https://www.youtube.com/playlist?list=PLtEhh3UpOsiDh6orcLPoJjPWSy--6g675