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Old 14th April 2009, 04:15 AM   #11
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Default Re: has anyone built the modern high-end valve amplifiers?

Quote:
Originally posted by xenu

Any updates?
original article



All very well, from that Plitron-Ekland amp but the article quotes "vintage snobs have no facts to base/ claim objections". Well my response to this is, lets take the gloves off and see the proof of their pudding. For the price of that Plitron core I'd love to see some confessions of their amp, some claimed power squarewave and thd quality stuff but unfortunately it won't happen as this forum isn't about sales promotion so this is left to the individual to figure out. The use of an impedance tapped secondary on a toroid is questionable for claimed ultimate performance and has to be very carefully wound at considerable expense.
(sim art; Morgan Jones p.238 valve amps 3rd edit.)

Some vendors of E&I cores can claim -3db down at 50KHz is excellent with 4 sep secondary windings and can accept considerable flux misbalancing. What more ?
The B+ of 525V seems punishing for todays o/p tubes when half the time is just spent running around listening levels. Admittedly the single set of o/p tubes does make amp design simpler, but remember most 4 stage amps one will just hear the hiss from 92dB/watt loudspeakers. i.e amp noise typ -65-70dB down.
This is hifi borderline and a preamp has to be mighty quiet not to make this figure worse.

The crystal palace amp does seem complex regarding power supplies and worst is the 13E1, even with discounting these tubes aren't cheap.
As for Silicon sand in the amps, In the past I was a sceptic, but having tried it, go-for-it. The CCS semi does an excellent job with linearity and this is the way forward.
richy
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Old 14th April 2009, 06:03 AM   #12
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Default Re: Re: has anyone built the modern high-end valve amplifiers?

Quote:
Originally posted by richwalters



A. For the price of that Plitron core I'd love to see some confessions of their amp, some claimed power squarewave and thd quality stuff but unfortunately it won't happen as this forum isn't about sales promotion so this is left to the individual to figure out.
richy

Thanks, I had my doubts too, this why I asked for individual experience.
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Old 14th April 2009, 06:03 AM   #13
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Default Re: Re: Modern tube amplifier designs?

Quote:
Originally posted by leadbelly


Well, if you have been following this forum for a long time, you certainly have not been paying much attention. No modern techniques? No solid state? LED bias, MOSFET source follower, numerous SS/hybrid CCS designs, nothing ring a bell? Maybe you should turn off the TV while you are "following this forum"?

Actually, I do not have TV...
I mentioned that I've seen some solid state (also seen auto bias on other sites) but not as mainstream. I will follow more closely on the hybrid designs.
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Old 14th April 2009, 06:03 AM   #14
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Quote:
Originally posted by atmasphere
What qualifies as a new tube design? Something that was not around in the 50s, 60s, or 70s?

Well, I have several solid state amplifiers and speaker from the 60s and seventies. While I love their retro look, they sound poor as compared to modern solid state amps and speakers. The amps have noticeable poor sound floor, are much less dynamic,have muddy bass and and closed sound stage. The speakers have the same characteristics plus uneven frequency response.

If speakers and solid state amps had been changed to accommodate modern standards and taste, I suppose tube amps should have done so too.
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Old 14th April 2009, 07:11 AM   #15
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Quote:
Originally posted by xenu



Well, I have several solid state amplifiers and speaker from the 60s and seventies. While I love their retro look, they sound poor as compared to modern solid state amps and speakers. The amps have noticeable poor sound floor, are much less dynamic,have muddy bass and and closed sound stage. The speakers have the same characteristics plus uneven frequency response.

If speakers and solid state amps had been changed to accommodate modern standards and taste, I suppose tube amps should have done so too.
Actually, modern standards and taste means stereo (actually, 5 channels) above 200 Hz only, a single channel for frequencies below 200 Hz with a resonant peak around 40 Hz, and a digital equalizer. It is what I heard today in a factory outlet of one modern flagman of an audio industry, they had a show for potential buyers... Quite impressive show, but an artificial water running on the screen sounded very artificially.

Good audio systems were good always, I mean systems that can fool perceptions creating imaginations of live sources of sounds, but today some modern parts may be used to make them more affordable for the general public, but anyway good systems are still expensive.
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Old 14th April 2009, 11:05 AM   #16
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Good audio systems were good always>>

They had the technology way back but didn't necessarily implement it. I've just built a 300b SET amp, and I think most of it could have been built about 1930, the rest in the 50s/60s.

Circuit is RC coupled 01A into 71A into 300b. That's 30s. Power supply is 6BY5 into choke into polypropylene caps into a pair of 0D3 giving me 300v for the input stage. That and the Russian teflon caps must be 50s/60s.

It's just that nobody put together good sounding combinations like that until the 80s and 90s. The componants were all out there, but doing other things.

300b is AC filaments - only sand is LM1086 regs for the current source of the 01A and 71A filaments, plus the schottky diodes.

andy
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Old 14th April 2009, 12:08 PM   #17
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Default Re: Modern tube amplifier designs?

Quote:
Originally posted by xenu
While I've seen few high voltage regulation circuits, I have not seen an amplifier design that takes advantage of solid state capabilities such as auto-bias control (vs. fixed or manual). Not to mention heresies like (negative) feedback.

Am I'm missing the modern designs that exist out there?
To follow up on what Leadbelly said, it seems to me that most of the most popular designs here incorporate solid state devices and negative feedback! Look at Tubelab's SimpleSE: CCS chip and feedback! I'm building Eli Duttman's El Cheapo with Mosfet CCS's and global negative feedback. Sy's bank of LED's? I don't think that was around in the 50's. How about triodes with no NFB? Certainly not 50's, 60's and 70's. I don't see too many folks here building basic Williamsons.

Also keep in mind that while there are a few folks designing and building high end modern stuff, many of the projects around here tend towards the simple and cheap. DSP is fun and all, but not something amateurs like myself can implement with skill and budget restrictions. A couple of mosfets, a chip here and there, those are things we newbies and weekend warriors can handle.

pj
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Old 14th April 2009, 12:46 PM   #18
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Default Re: Re: Modern tube amplifier designs?

Quote:
Originally posted by pjanda1


I don't see too many folks here building basic Williamsons.

Also keep in mind that while there are a few folks designing and building high end modern stuff,

pj

The Williamson concept, concertina front end and diff drivers is my set-in-stone design for both low & high power. It is flexible and can be used with parallel p-p as I do with lower B+. With CCS ingenuity replacing hi power resistors it has never faulted and gives repeatable performance.
The output transformer is always a headache component, and I can't see how a Plitron toroid o/p would give improved performance over a well designed-standard E&I. After 70 yrs the E&I design has a proven track record.
As the accepted global nfb standard for hi-fi tube p-p amps is between 10-20dB, an optimised designed Williamson config can accept around 35dB global nfb before both low and high freq instability sets in. To me this headroom is quite acceptable.
It is well known that p-p tube amps which have high ratio feedback circuits (Mullard 20W design) sound tight even though thd is low. Using a design with exotic toroid may claim even lower thd, but perhaps at the increase of transient overhang at the lower end.
Morgan Jones avoids o/p toroidal deep water, the fact the "Crystal palace" design is a claimed ultimate performing amp using an E&I core. So what more do we need from an expert ?

richy
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Old 14th April 2009, 01:01 PM   #19
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Hi SpreadSpectrum

Quote:
It's true, many here are stuck in decades past and will gladly pay big money for a 10 pound choke to do a job much better and much cheaper done by a bit of sand.
It has been a while that I have been looking into circuits to eliminate ripple of PS based on 'sand'. I have seen reference to gyrators, capacitance multipliers, series and shunt regulators, etc. I have always been somewhat hesitant as the mosfet tab is at high voltage, requiring the electrical insulation of the chip itself and/or the heatsink to which it is mounted...until yesterday, when I bought a large lot of insulated mosfets and IGBT's for respectively 600V and 1200V.

So my question is, can you tell somewhat more about the techniques used by you in the 'sand' based PS?

Erik
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Old 14th April 2009, 01:55 PM   #20
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Quote:
Tubelab's SimpleSE: CCS chip and feedback!
CCS chip yes, feedback is optional. I use it when I want to get loud in UL mode, and turn it off in triode mode. The Simple SE was intended to be just that, simple. It uses the minimal amount of circuitry to get good performance. The CCS was added because it reduces the nonlinearity of the 12AT7. A few amps have been built without the CCS.

Quote:
How about triodes with no NFB?
Tubelab SE, DHT output stage zero feedback. SAND, CCS loads for 5842, mosfet follower to drive the DHT, IC regulator for DC filaments and SS rectifiers for filament and bias supplies. 5AR4 rectifier for B+. Sand is carefully applied where it offers a performance improvement over a tube and nowhere else. The Tubelab SE is a well regarded amp by those who have built it.

Quote:
DSP is fun and all, but not something amateurs like myself can implement with skill and budget restrictions.
The DSP thing was something I developed to enter into a design contest sponsored by Microchip (the dsPIC maker) and Circuit Cellar (an embedded systems magazine). It won a major prize and a design article was submitted to the magazine. My goal was to see a picture of a vacuum tube amp in the magazine. We will see if it ever happens.

Quote:
A couple of mosfets, a chip here and there, those are things we newbies and weekend warriors can handle.
I plan to do much more along these lines as time permits. I have done some preliminary experiments that use hybrid designs for screen drive and cathode follower output stages, and "darlington" connected output stages using a tube and a mosfet. There will be more coming this year.

Quote:
All very well, from that Plitron-Ekland amp but the article quotes "vintage snobs have no facts to base/ claim objections". Well my response to this is, lets take the gloves off and see the proof of their pudding. For the price of that Plitron core I'd love to see some confessions of their amp, some claimed power squarewave and thd quality stuff but unfortunately it won't happen as this forum isn't about sales promotion so this is left to the individual to figure out.
Plitron had some "400 watt at 20 Hz" toroid OPT's on sale for just over $100 a while back. I took the bait and bought a pair. I have not built the "ultimate monster power amp" with these yet mostly for lack of time. I have tested them in several different breadboard designs. They are very good OPT's with the upper 3db point at 75 KHz (no feedback). A 20 KHz square wave looks like a square wave at 50 watts! (2 x 6lw6). There are issues however. These things are huge(about 8 inches in diameter) but they are VERY sensitive to DC imbalance and even output tube Gm mismatch. Saturation can be seen at 50 watts and 20 Hz if things aren't perfectly matched. More sand (opamp DC servo bias control) will be needed to take full advantage of these transformers.
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