They are indeed step-up transformers, so you need less valves for a given amount of gain than with RC coupling. The fewer the valves, the longer it takes until you have to replace the plate battery or have to get the heater battery recharged.
The UV-201 vacuum triode had a tungsten filament - later models went to thoriated tungsten, then oxide. It came out in 1920, so it's a possibility this year. It will make a reasonable driver or possibly headphone amp. If you wait for next year, you can use a 211 for power output - it appeared in 1921.
A few weeks ago I found a copy of Rice and Kellog's paper on the first cone speaker from 1925 or so. RCA offered it in a cabinet with a 1-stage booster amp using the recently-developed type 10 to get an astounding 1000 milliwatts of power (!) It used an electromagnet, so it needed a DC power supply, which powered the 10 as well. The electromagnet doubled as the power supply filter choke.
A few weeks ago I found a copy of Rice and Kellog's paper on the first cone speaker from 1925 or so. RCA offered it in a cabinet with a 1-stage booster amp using the recently-developed type 10 to get an astounding 1000 milliwatts of power (!) It used an electromagnet, so it needed a DC power supply, which powered the 10 as well. The electromagnet doubled as the power supply filter choke.
It would be a fine sounding circuit with better transformers. For pre-WW2 amplifiers, transformer coupling was the main topology. Because triodes of the day had low gain, step-up transformers were broadly used as additional gain devices. I dissected a lot of 1920s-30s ITs, and most were very crude, just two windings with no interleaving. 1:3 step-up was considered a minimum; 1:5 and 1:10 were common. It is not difficult to imagine what kind of sound these transformers produced, with their horrendous leakage inductance and winding capacitance. No high frequencies beyond 2-3 kHz.
However, engineers of the time were aware of audio transformer problems, and knew how to solve them. Some manufacturers offered high quality transformers that would satisfy higher standards of today. For example, in 1924 Ferranti came up with the legendary AF-3 interstage that had flat frequency response from 50 to 10,000 Hz when driven by a 01A tube type.
Maybe using the loudspeaker field coil as the power supply choke was a fairly common practice. I've seen it in two Gibson guitar amps from the late 1930s - the EH150 (a pair of 6N6s as outputs, with an inter-stage transformer) and the EH185 (a pair of 6L6s, R-C coupled) - and there are probably others out there? It would be interesting to know.
The practice might have evolved in the transition from battery powered to mains powered receivers and amplifiers. Early on, designers sometimes avoided adding yet another battery just for the field coil and gave double-duty to one of the existing batteries. With the advent of rectifiers (the earliest I know of is the Amrad S cold-cathode half-wave rectifier of 1922 and there likely to be European rectifiers too, perhaps earlier) it would have been a logical step to adapt battery designs, with the bonus of the field coil as a power supply choke. Any takers for a hi-fi amp?😀
PS: I have seen a c1927 design that kept batteries for the amplifier and applied AC mains to the field coil ... is there nothing new under the sun?
It is odd that Field Coil speakers are not used in high end audio these days. Are there any even made new? Many say they sound better than magnet speakers, I suppose that is debatable, the issue I have is that I have only heard cheap field coil speakers, the high end ones cost many thousands. Add to that the coil provides a better noise reduction than a resistor and less voltage loss. One would think the very top end SE amp would use Field coil speaker and inter-stage transformers. Not a single cap in the entire circuit. Metal film resistors. Also notice they are using batteries DC, for the filaments with DHTs. The old way appears better than what we have today from a purists perspective.
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Speaker's field coil is not really effective as smoothing choke. FC works close to magnetic satiration, so iron doesn't contribute much to its inductance. FC acts more like resistor than like inductor in a ripple filter.
Power supply for 100 year old amp
Setting the field-coil-as-filter-choke to one side (just for a moment), the hundred year old power supply is an interesting issue. We have the choice of battery power, rectified AC, or possibly a combination of the two?
John Atwood's site (thank you John) includes the 1928 Raytheon Bulletin for its BA and BH cold cathode rectifiers (here: http://www.one-electron.com/Archives/Tube/Raytheon/Raytheon 1928 Type BA Bulletin TS5.pdf). The Bulletin includes schematics for rectified AC supplies to bias, plates and filaments, replacing ("eliminating") the C, B and A batteries respectively.
Raytheon patented its design in 1925 - maybe there were earlier rectifiers that could support a 100 year old amp design?
Setting the field-coil-as-filter-choke to one side (just for a moment), the hundred year old power supply is an interesting issue. We have the choice of battery power, rectified AC, or possibly a combination of the two?
John Atwood's site (thank you John) includes the 1928 Raytheon Bulletin for its BA and BH cold cathode rectifiers (here: http://www.one-electron.com/Archives/Tube/Raytheon/Raytheon 1928 Type BA Bulletin TS5.pdf). The Bulletin includes schematics for rectified AC supplies to bias, plates and filaments, replacing ("eliminating") the C, B and A batteries respectively.
Raytheon patented its design in 1925 - maybe there were earlier rectifiers that could support a 100 year old amp design?
Just a few comments----
Field coils I am used to repaired very many late ,20,s into ,30,s valve/tube radios with them installed worked off the HT+/plate/anode supply .
Yes they cost to produce but I still have 2 examples in my workroom.
When magnets improved they diminished in radios.
In radios they worked quite well unless somebody tried to cut corners financially then very thin copper was used etc resulting in dead loudspeakers .
As far as -quote-"not used these days " have a read of a blog simply put by an advocate of field coils in modern use-
Field Coils Are The Future!!! - Tweek Geek
Remember its his personal opinion as this type of hi-fi loudspeaker system is not something I am familiar with.
The U5 was the first full-wave rectifier -Marconi-Osram -1926 only 60ma current capacity meant for normal 4/5 valve/tube radios with low audio output in those days.
U5 @ The Valve Museum
Even earlier was a USA invention of the mercury arc rectifier -1902-Peter Cooper Hewitt
Field coils I am used to repaired very many late ,20,s into ,30,s valve/tube radios with them installed worked off the HT+/plate/anode supply .
Yes they cost to produce but I still have 2 examples in my workroom.
When magnets improved they diminished in radios.
In radios they worked quite well unless somebody tried to cut corners financially then very thin copper was used etc resulting in dead loudspeakers .
As far as -quote-"not used these days " have a read of a blog simply put by an advocate of field coils in modern use-
Field Coils Are The Future!!! - Tweek Geek
Remember its his personal opinion as this type of hi-fi loudspeaker system is not something I am familiar with.
The U5 was the first full-wave rectifier -Marconi-Osram -1926 only 60ma current capacity meant for normal 4/5 valve/tube radios with low audio output in those days.
U5 @ The Valve Museum
Even earlier was a USA invention of the mercury arc rectifier -1902-Peter Cooper Hewitt
Take some very old technology and wire it up in a new and unique manner and get a patent....never mind that it is so "obvious to someone skilled in the art" that I had built one in in high school electronics class in the 1960's.
It used a 15 inch field coil speaker from an old Hammond organ reverb cabinet, a bridge rectifier (4 top hat diodes), an electrolytic cap, and a small Variac. It was a means to turn my already low powered guitar amp down to "parent friendly" volume levels while making that cranked to 11 tone that I liked.
It actually made enough sound to annoy my father with the field coil turned completely off. Those old field coil speakers had weak suspensions, either by design, or due to old age. it was relatively easy to get the voice coil to bottom out if you whacked the guitar strings hard, especially with a bass guitar.
How it Works - FluxTone Speakers | Guitar Amp Attenuator
It used a 15 inch field coil speaker from an old Hammond organ reverb cabinet, a bridge rectifier (4 top hat diodes), an electrolytic cap, and a small Variac. It was a means to turn my already low powered guitar amp down to "parent friendly" volume levels while making that cranked to 11 tone that I liked.
It actually made enough sound to annoy my father with the field coil turned completely off. Those old field coil speakers had weak suspensions, either by design, or due to old age. it was relatively easy to get the voice coil to bottom out if you whacked the guitar strings hard, especially with a bass guitar.
How it Works - FluxTone Speakers | Guitar Amp Attenuator
I remember those diodes ,those old field coil speakers were never meant to stand up to a big low frequency blast on a guitar just nice "swing " music or Bing Crosby/Frank Sinatra ballads .
Not learning to play the guitar still irks me even in old age .
Not learning to play the guitar still irks me even in old age .
The speakers I had came from an old Hammond reverb or "tone" cabinet. They were intended for deep bass organ notes, but not capable of large sub bass transients that resulted from big string movement, and a DIY guitar amp with a power transformer miswired as an OPT.
We found several and a couple Leslies in the trash behind a large piano and organ store in Miami in the late 1960's. All had been stripped of their electronics and motors, but the giant oil filled reverb tanks, speakers, spinning horns and baffles remained.
My amp made 10 - 15 watts on a good day, so it could not "blow" one of those speakers, but the repeated pops created by smacking the end of the voice coil into the steel frame eventually made it sound bad. By the time I had destroyed two of those speakers, I had moved on to a much bigger amp made with 4 X 6L6's and 8 X 12 inch Utah guitar speakers. No way to tone that thing down, it had two levels loud, and unbearably loud.
We found several and a couple Leslies in the trash behind a large piano and organ store in Miami in the late 1960's. All had been stripped of their electronics and motors, but the giant oil filled reverb tanks, spinning horns and baffles remained.
On the topic of "mis-wired" OTs I was looking at a 6V6 output curve and while 5k is what it is wired for the OT in the amp (A Champ 5C1 clone) has 8k and 5k available. The big difference was a 5% increase in 3rd harmonics. If I switched to the 8k tap. Any idea what that would mean for the sound and performance of the amp? Might sound good for metal?
Various old manufacturers quote both 5K+8.5K ,Mullard quotes -
Anode=250V
Screen=250V
at -12.5V Grid
with a distortion figure of 8% which is below two others at 12% for -
Anode=315V
Screen=225V
Grid=-13V
I am sure Tubelab will know the answer to your sound question.
Of course it also depends on what class you run them in big drop in distortion in class AB1.
Anode=250V
Screen=250V
at -12.5V Grid
with a distortion figure of 8% which is below two others at 12% for -
Anode=315V
Screen=225V
Grid=-13V
I am sure Tubelab will know the answer to your sound question.
Of course it also depends on what class you run them in big drop in distortion in class AB1.
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They are being used and there are some new manufacturers on the market. But those are not mainstream speakers, this is high level audio and as you may know, the very best speakers and components are often not used in the very most expensive systems because of their price tag. Even in those high priced premium called speakers you will find low quality ferrite designs.
So here are some new manufacturers:
EMS, WVL, Fertin, GIP, Line Magnetic. Search for them in combination with the term field coil and you will find some extraordinary good speaker chassis that are huge, high efficiency and very expensive and almost not being used with the ordinary high- end speakers. It's still a sidestep from the mainstream. Same as a Leica, this brand will never become mainstream because its upper class, superior design and way too much expensive for most customers.
Had some experiences with great field coil designs like Lansing, Saba, Körting, Mende. Those speakers can make for much better sound than permanent magnet but they can be easily more worse sounding because thats Audio in its purest form when the term Audio wasn't invented at all. Often they are limited bandwith highs and lows. But that makes it a purist speaker. Not many like those very old speaker designs but if you happen to treat them right they can be audio heaven.
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Leica either makes, or licenses their name to the lenses used on most of the Panasonic "Lumix" Branded cameras from low end to expensive. My 10 year old DMC-ZS15 carries both the Panasonic and Lumix brands ant the lens is Leica branded. The later two carry only the Lumix and Leica brands Panasonic is only mentioned in the owners manual.
The sane is true with Zeiss and Sony. I have a Sony DSC-F828 that has a Zeiss lens and a relatively new DSC-HX80 that has the Zeiss brand on the lens.
I made about 10 amps that I called "Turbo Champs" back around 1999. Each was slightly different since I was using what parts I could find, especially speakers, but several had a Hammond 125CSE OPT.
These have 4 different taps for different impedances. I put a 4 way selector on them so each tap could be used. The results were different on each amp, and most of this was due to the differences between the speakers. Each speaker will have a different resonant frequency, and impedance VS frequency curve. This will make a big difference in how the amp sounds with different load impedances. If you already have the amp built with the extra tap, the only way to really know how it sounds it to try it.
Wow, that is interesting, so what you're saying is the speaker can have more influence on the sound than the amp? You see less influence with the OT's effect? I am saying this from a guy that has a LOT of experience in speaker building and a limited experience with tube amp design. Obviously this is a relative statement, but I think you know where I am going with this. These harmonics are coming from the amp not the speaker.
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If you believe those mobile phone lenses or licensed name lenses from Zeiss or Leica are comparable to their TOTL lenses for real photographers cameras than you might trapped into this marketing trap.
In fact, making pictures with a real Leica camera has nothing to do with snapshots done with a mobile phone or a cheap Lumix/ Panasonic automated camera. Todays compact cameras are in fact out of fashion as they offer the same performance than a mobile phone camera and they are fully automated as a mobile phone. Thats the reason why you will see nine out of ten amateur snapshot takers today throwing away their compact cameras and only snapshotting with their phones. The rest uses big asian SLR and one out of thousand uses an original Leica camera.
It is like I said, the original Leica cameras/Zeiss lenses are the same sidestep away as the field coils from the main market. Thats a fact and can easily be proofen by their sales figures.
Leica/Zeiss phone lenses are just a marketing gag.
Btw, when talking of "turbo champs" or Fender Champs, were talking guitar tube amps. A totally different world and a different goal in designing guitar and audio amps. Different circuits are used and the goal is always a special sound.
The combination of amp and speaker makes or breaks the sound of both.
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I'm not sure whether tubelab is talking strictly guitar amps.
But of course, the speaker has always more influence in an audio system than the amp. The speaker makes or breaks the sound. An amp just can worsen the sound, but never to that degree a speaker can easily worsen it.
When were talking field coil its always high efficiency speakers.
And those are able to destroy the three houseblocks that you normally think they are between the speakers and the listener.
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I fully understand the marketing game. I worked for Motorola for 41 years, and watched it happen from the inside.....Do you think that the Motorola phone that I have has anything at all to do with the Motorola company that I worked for? No, it does not. Lenovo, the Chinese computer company owns the Motorola brand for use with cell phones. Care must be used when a company does this or brand dilution happens, and all Leica (or whoever) products become associated with Panasonic, Sony and the like.
I just mentioned the fact that the Leica brand has become relatively mainstream if only as a marketing gimmick for Panasonic. I got into photography 40+ years ago, had my own darkroom, shot large format and 35mm.... All with relatively modest equipment, often used cameras from my buddies when they upgraded. My interest waned as film died, and "they took my Kodachrome away" and Cibachrome went with it. I never had the justification for spending the big $$$ for Leica, Zeiss, or even TOTL Nikon stuff. My first SLR was a used Pentax that I paid $20 for.
When it cost you money every time you push the shutter button (even if for just film, chemicals, and enough paper for contact sheets) you take the time to set up each shot. Now it has become too easy to put the camera in auto, and hold the button down, take a zillion pictures, and maybe get one good one. When it matters, I do that with one camera on a tripod, and another in manual mode in my hand.
I do own a budget Canon DSLR, two Sony's and three Panasonics. Each has their purpose, but unlike my phones, I can dial in whatever manual settings I need for the particular moment.
I have built amps, speakers, and combos (including all the Turbo Champs) for over 50 years. Yes, those harmonics DO come from the amp, but the amp reacts to the load that it sees. It does not work alone. There is a complex interaction between the output tubes, the OPT, and the speaker, and ALL THREE together affect the way the output tubes distort the signal.
If you have the Master Volume dialed way back so that all the distortion happens in the preamp, then the choice of speaker doesn't matter too much, as far as how the output tubes distort.....because they are not distorting.
Crank that MV up full and the tubes try to pass more signal than they can. Depending on the tubes, the power supply voltage, and the load presented to the tubes, they will be clean, run out of voltage headroom (sharp clipping) or be unable to pass the current needed to push the speaker cone (softer rounding of the signal). In a cranked amp all three of these are often happening at the same time, but at different frequencies.
A seasoned speaker builder should know that an "8 ohm" speaker is NOT always 8 ohms. It can be 32 ohms or more at it's resonant frequency, usually somewhere low on the 6th string. It can also be 4 ohms way up on the first string. A different speaker will have different characteristics. These numbers are usually (but not always) available on the speaker maker's web site.
The OPT is a ratio device. That 5K OPT will present the tube with a 5K load ONLY when there is an 8 ohm load attached to it. At resonance that 32 ohm speaker will present a 20K ohm load on the output tube, where it WILL run into voltage related clipping. At the other extreme, it can be 2.5K ohms in the high frequency region, resulting in a softer saturated sound.
Running a speaker like that on a 8K tap could make the bloated, clipped bass worse, but possibly clean up the highs for more "chime."
When I made the Turbo Champs, often the amp would do the cranked Strat thing best on the 5K setting with one speaker, but sound better on the 2.5K setting with another. Pop out the KT88 and stuff in an EL34, and the settings change since the tubes react differently to the changing load. It is not possible to accurately predict what will happen in your situation with a change from 5K to 8K....The individual speaker characteristics in your amp, will have a large influence on the outcome. Changing from 5K to 8K is not that big of a change.....my guess is that there will be a noticeable difference, but not a major change, unless you play right on the edge of clipping.
All 6V6 tubes are not created equal either. Some of what is called a 6V6 today bear little resemblance to what Leo put in the 5C1. Some of the fat Russian 6V6's made today can pass far more current than the old RCA's of yesteryear. They will handle a lower overall load impedance far better than an old RCA, but the old tubes don't have the sharp clipping that some Russian tubes do.
What I said here applies to all amps, but this post is aimed directly at the post referring to a 1950's Fender Champ 5C1 guitar amp, and how it deals with different load impedances presented to it by the speaker....any speaker.
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