Whoah, how did I miss that! that's a great read. Very interesting piece of nearly forgotten history. That simulation showing the count of tubes makes me smile-
Thanks for that link. Gives me some altogether unreasonable ideas 🙂
(like a similar build using a bunch of russian 6S19P instead of 12B4)
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I'm always Happy 🙂 to convey "unreasonable" ideas! Gets the brain cells firing up. You won't even need an OT.
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Going back to the 300 Watt design, one economical approach to the OT would be to use two 440/480 VCT to 120V power toroids in a N. Crowhurst Twin Coupled type design. That effectively gives one a near 8 to 1 turns ratio OT for around 430 Ohm (to 512 Ohm) P to P. Some parallel Sweeps (or even 40 6197s !! ) could drive that readily. 120V at 60 Hz maps to 300 Watts out at 24.5 Hz.
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Going back to the 300 Watt design, one economical approach to the OT would be to use two 440/480 VCT to 120V power toroids in a N. Crowhurst Twin Coupled type design. That effectively gives one a near 8 to 1 turns ratio OT for around 430 Ohm (to 512 Ohm) P to P. Some parallel Sweeps (or even 40 6197s !! ) could drive that readily. 120V at 60 Hz maps to 300 Watts out at 24.5 Hz.
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I reject your "KT150" because it is single-source, small market, is likely to vanish when you need replacements. I'm tired of throwing-out funny-tube amps when supplies dried-up.
The KT150 is a big KT88 which is a Euro 6550. Let's look at daddy's spec-sheet.
A pair in Triode is said to give 28 Watts. That's far short of 300-400W. Gonna need a lot of bottles. And an extra-custom OT.
And 282 Watts of Heater power!!
And note that Max G1 resistance is 50k per tube. 14 grids per side, you should use a 3.5k(!!) grid resistor to avoid grid current runaway. (Actually you use a cathode follower.)
Yes, using the "150" you might expect 40W/pr and 20 bottles. But "reliable" implies long life, perhaps longer than the production of KT-150.
I don't know that there is anything wrong with a well designed Pentode amp for bass. Bogen 300, Ampeg SVT, Fender 300 would shake the room or park pleasurably, with 6 or 8 bottles. And with less-insane OT impedance.
Dream all you want. But it is a heap easier to find an off-the-rack OT than to go custom. Aside from replacements for the above amps, Hammond makes a 280W part suitable for a pack of pentodes.
If you will go custom OTs: the next step up from flocks of little bottles is transmitting tubes. The HK-257 (it has new names today, 4E27 or 5-125B) pentode is a go-to for 300+W audio. Like any commercial tube it favors high voltage at low current (and high load Z) for best cathode economy. The 14k-20k loading is distressing for a bass amp, though the large size of this OT makes it not as bad as a 14W design.
The KT150 is a big KT88 which is a Euro 6550. Let's look at daddy's spec-sheet.
A pair in Triode is said to give 28 Watts. That's far short of 300-400W. Gonna need a lot of bottles. And an extra-custom OT.
And 282 Watts of Heater power!!
And note that Max G1 resistance is 50k per tube. 14 grids per side, you should use a 3.5k(!!) grid resistor to avoid grid current runaway. (Actually you use a cathode follower.)
Yes, using the "150" you might expect 40W/pr and 20 bottles. But "reliable" implies long life, perhaps longer than the production of KT-150.
I don't know that there is anything wrong with a well designed Pentode amp for bass. Bogen 300, Ampeg SVT, Fender 300 would shake the room or park pleasurably, with 6 or 8 bottles. And with less-insane OT impedance.
Dream all you want. But it is a heap easier to find an off-the-rack OT than to go custom. Aside from replacements for the above amps, Hammond makes a 280W part suitable for a pack of pentodes.
If you will go custom OTs: the next step up from flocks of little bottles is transmitting tubes. The HK-257 (it has new names today, 4E27 or 5-125B) pentode is a go-to for 300+W audio. Like any commercial tube it favors high voltage at low current (and high load Z) for best cathode economy. The 14k-20k loading is distressing for a bass amp, though the large size of this OT makes it not as bad as a 14W design.
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Here is a simulation using 8 6P45S per channel. This is triode connection, of course!
The 250R transformer would be two pair of VPT36-6940 in series/parallel (4 OPT's per channel).
It will make 420W, and 600W to idle, and you need two for stereo, but there's a 63W class A limit! You'd either need to run it from a 20A branch circuit, or each amp gets it's own circuit. You'll probably need air conditioning, too.
EDIT: You could also use 3 pair per channel, and lower the idle from 100mA to 40mA... Then they only use 234W but you only get 5W class A... Trade off?
The 250R transformer would be two pair of VPT36-6940 in series/parallel (4 OPT's per channel).
It will make 420W, and 600W to idle, and you need two for stereo, but there's a 63W class A limit! You'd either need to run it from a 20A branch circuit, or each amp gets it's own circuit. You'll probably need air conditioning, too.
EDIT: You could also use 3 pair per channel, and lower the idle from 100mA to 40mA... Then they only use 234W but you only get 5W class A... Trade off?
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Hmm okay, got it. I've never thought 300 W is such a heavyweight class even with KT150s.
If we stick to braincell-inspiring insanities, let me show you one of my favourite Youtube videos: Eimac 250th SE.
And there are more 100th-250th SE bulids, all look amazing (and probably sound amazing).
So sad I'm not there yet by myself.. but learning.. learning..
Regarding my 300W intentions I might stick to Mosfets in the output stage and maybe use tubes on the input and maybe driver stage, if that works.
PS Audio has done some similar with the BHKs, tubes on the input.
(Okay, I could 'colour' the sound with a 1:1 tube circuit in front of a well made Class D amp module too, like Hypex.. but this topic is not about plain simple sound coloration or adding distortion to a superior-measuring amp device)..
If we stick to braincell-inspiring insanities, let me show you one of my favourite Youtube videos: Eimac 250th SE.
And there are more 100th-250th SE bulids, all look amazing (and probably sound amazing).
So sad I'm not there yet by myself.. but learning.. learning..
Regarding my 300W intentions I might stick to Mosfets in the output stage and maybe use tubes on the input and maybe driver stage, if that works.
PS Audio has done some similar with the BHKs, tubes on the input.
(Okay, I could 'colour' the sound with a 1:1 tube circuit in front of a well made Class D amp module too, like Hypex.. but this topic is not about plain simple sound coloration or adding distortion to a superior-measuring amp device)..
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there is a big reason for the invention of the pentode, that is to get more power than a triode can...
Yes, but the topic of even and odd harmonics .. triode wins. For bass I wouldn't care but for midrange ? Otherwise I'd go for pentode mode, for sure.
This sounds like another shed load of idle speculation.
If you have never heard a really good PP Pentode amp, don't try to come up with theories about stuff and powers that are just ridiculous and unattainable.... FYI, you get a lot more working on speaker efficiencies than you will ever get messing with those speculatory powers, THD & "harmonic content"
As for this..
since when have the Russians actually given up making valves in Reflektor Saratov?
I don't see it happening any time soon!
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you must be reading a lot of other forums....i suggest that you get a copy of Morgan Jones book and learn from it...or go to the valvewizard.com, lots of tube learning can be had there....
Patrick Turner has a 300 watt pp design in his website, 300w-monobloc-about
i made a kt88 triode wired pp amp many years back, 16 kt88 for about 150 watts of power....
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no, the owner have it, that amp became part of a 4 way system, driving subwoofers...
Although I have never been to the Moon, based on observation of many others (especially professionals like John Lindsey Hood and others I read nowadays) I can still choose to skip it completely and travel to Mars. My choice, right ? (Right). Of course I heard PP pentode amp, my father used to build some 2 decades ago. If it was good, I would say yes, amazing, relative to my ears. In absolute terms (whatever this means) they might have been just average, who knows. But then the 2A3 triode amp of my friend sounded like still being in the womb before birth, a totally different, soul-soothing experience. Okay, material, speakers, everything was absolutely different.
Speakers are at around 95-96dB together, no problem with sensitivities. A single 300B SE could drive these to loud levels.
But regardless of a pentode being superior or inferior to a triode in sound character (depending on circuit of course) my intention for now is to force the triode way 'cause I want it all red like Mars.
Amazing piece. Can he live with that heat in a hot summer, or maybe using it in the chilly basement ? (Just like I will mine).
i really do not know, the amp migrated to happy valley in california, and recently moved back to manila....
that amp was inspired by the carver silver 7, but i found out after the build that no global feedback was needed, although i made provisions for it, i never connected it....sound was already too good....
his JBL horn speakers....
that amp was inspired by the carver silver 7, but i found out after the build that no global feedback was needed, although i made provisions for it, i never connected it....sound was already too good....
his JBL horn speakers....
An externally hosted image should be here but it was not working when we last tested it.
yes, it did....4 way, system, jbl sub boxes, low mid horns, high mid horns, super tweets...
electronic crossover, multi amp, system, composed of several KT88 triode mode single ended amps...
electronic crossover, multi amp, system, composed of several KT88 triode mode single ended amps...
Great. Designed something smaller but also active 3-way. Building is pending (new house, winter), these 2 monoblocks would drive the midranges and as long as the whole set isn't ready, they would serve as an all round amp for my little monitors.