I wish no one had invented the notion to use B+ as shorthand for the high voltage supply connected to the output transformer. Why? Why not write down the designed/intended VDC? Why not state the current requirements?
It leads to sloppy schematics, unusable to anyone other than the original designer, and has caused a lot of headaches to people trying to understand and learn from good designs. You know what I’m talking about. You have seen it!
Ely Duttman’s highly valued design “El Cheapo”, as example (Sorry, Ely, thank you for a great design, sharing it, and being a good example). Why did you not show VDC on the “official schematic” instead of posting a bunch of transformers by name without ratings? I understand you wanted builders to benefit from your insight into the market as it was at the time of writing, and that would be very beneficial for contemporary builders, but what about 20-50 years from now? (Many tube amp designs have been around for 50+ years). Why not give the timeless information first and where possible any current commercial offerings?
Now we have schematics showing B++, B2+, B+++, B3+, etc, etc. Again WHY not the state VDC and current requirement?. Not even to mention missing current rating, etc.
While I’m on the soap box, why do folks post schematics of tube amplifiers without EXPLICITLY indicating the input/output impedance of output transformers? How many times have I seen an interesting design that thought I wanted to build, except to see that the output transformer is completely unreferenced, or given as some XYZ brand, model so-and-so, that went out of production 55 years ago?
PLEASE people, my plea is to take the few seconds to it takes to state the obviously needed information for power and output transformers. Input/output impedance, current rating, at least, inductance and more if available. But please don’t draw an output transformer symbol without the needed information on your schematic.
It leads to sloppy schematics, unusable to anyone other than the original designer, and has caused a lot of headaches to people trying to understand and learn from good designs. You know what I’m talking about. You have seen it!
Ely Duttman’s highly valued design “El Cheapo”, as example (Sorry, Ely, thank you for a great design, sharing it, and being a good example). Why did you not show VDC on the “official schematic” instead of posting a bunch of transformers by name without ratings? I understand you wanted builders to benefit from your insight into the market as it was at the time of writing, and that would be very beneficial for contemporary builders, but what about 20-50 years from now? (Many tube amp designs have been around for 50+ years). Why not give the timeless information first and where possible any current commercial offerings?
Now we have schematics showing B++, B2+, B+++, B3+, etc, etc. Again WHY not the state VDC and current requirement?. Not even to mention missing current rating, etc.
While I’m on the soap box, why do folks post schematics of tube amplifiers without EXPLICITLY indicating the input/output impedance of output transformers? How many times have I seen an interesting design that thought I wanted to build, except to see that the output transformer is completely unreferenced, or given as some XYZ brand, model so-and-so, that went out of production 55 years ago?
PLEASE people, my plea is to take the few seconds to it takes to state the obviously needed information for power and output transformers. Input/output impedance, current rating, at least, inductance and more if available. But please don’t draw an output transformer symbol without the needed information on your schematic.
In fact at the beginning **everything** Tube based was Battery powered and for *clarity* there were *THREE* groups of batteries, VERY different and incompatible so to minimize confusion they were referred to by different letters:
A battery: low voltage very high current for filaments.
Typically a lead acid car type battery, so 6.3V (what, among others, a Ford A or T used), or a single lead acid element, so 2.1V , current measured in Amperes (feeding many tubes)
Now you understand why so many tubes use 6.3V filaments and some early ones were available with 2V filaments.
Portable equipment often used 1.5V filaments when lead acid was too heavy and inconvenient.
Much later, when car bartteries standardized on 12.6V , not surprisingly tubes began to use that voltage too.
Some like 12A*7 cleverly could use both.
B batteries were higher voltage and current measured in milliamperes, specifically for tube plates.
Minimum voltage for portable radios was 22.5V , using special tubes, but most common was 90V
And tes, they were labelles "B" batteries righr on the envelope, this one is 45V:
So if you have a complaint, complain to them
C batteries were very long life (measured in years) , very stable voltage (around 1.35V) and ZERO current, in practice picoamperes.
Some fancy designers wanted different bias voltages in their designs,so used a multitapped bias battery:
The cherry on the cake: this very advanced RCA Battery Eliminator" was a *Power Supply* offering then popular;: 22.5V , 45V , 90V (all +B) and 1.35V (C bias).
A battery: low voltage very high current for filaments.
Typically a lead acid car type battery, so 6.3V (what, among others, a Ford A or T used), or a single lead acid element, so 2.1V , current measured in Amperes (feeding many tubes)
Now you understand why so many tubes use 6.3V filaments and some early ones were available with 2V filaments.
Portable equipment often used 1.5V filaments when lead acid was too heavy and inconvenient.
Much later, when car bartteries standardized on 12.6V , not surprisingly tubes began to use that voltage too.
Some like 12A*7 cleverly could use both.
B batteries were higher voltage and current measured in milliamperes, specifically for tube plates.
Minimum voltage for portable radios was 22.5V , using special tubes, but most common was 90V
And tes, they were labelles "B" batteries righr on the envelope, this one is 45V:
An externally hosted image should be here but it was not working when we last tested it.
So if you have a complaint, complain to them
C batteries were very long life (measured in years) , very stable voltage (around 1.35V) and ZERO current, in practice picoamperes.
Some fancy designers wanted different bias voltages in their designs,so used a multitapped bias battery:
The cherry on the cake: this very advanced RCA Battery Eliminator" was a *Power Supply* offering then popular;: 22.5V , 45V , 90V (all +B) and 1.35V (C bias).
An externally hosted image should be here but it was not working when we last tested it.
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I don’t object to B+ per se, but to the use of it to be lazy and to omit the really important characteristics of a power supply.
It doesn’t need changing, except that folks use it as an excuse not to be explicit in their power supply requirements. Besides, when was the last time you heard a power amplifier powered by batteries? (Oh my, now i will hear about 4 or 5 of those).
It doesn’t need changing, except that folks use it as an excuse not to be explicit in their power supply requirements. Besides, when was the last time you heard a power amplifier powered by batteries? (Oh my, now i will hear about 4 or 5 of those).
Tube amps, like ones that you mentioned, work on wide reasonable range of voltages. It is not a solid state amp that would go out of bias on lower voltages, and damage transistors on a bit higher voltage. Also, when we discuss circuit ideas, it does not matter much what values are, except when it matters, it is stated. I think that if you are going to learn, you should start learning, instead of bringing own charter to an university. If you have some questions, ask the author. Just ask; "knock and it openeth".
Of course I’m only concerned with parameters “when it matters” in a “final design schematic” but NOT stated. I did not “mention tube amps”, except the “El CHEAPO” as an example of a final design without the necessary parameters. Don’t assume that I’m “starting to learn” - I’ve rebuilt my first tube amplifier 48 years ago, and many after that. I may be a slow learner, but not that slow��
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We call it HT this side of the pond, that aside I think you have a point, IE that schematics should show as much info as possible. A lot of old (and new) schematics don't show voltages where they'd be useful for fault finding and very few show current, making some schematic's little better than a 2D map.
One last thing, very few also show what V was measured with.
Andy.
One last thing, very few also show what V was measured with.
Andy.
There could be some reticence from a maker to put voltage values on a schematic, due to the tolerance of allowable bias setup and stage loading - eg. some amp schematics show a power supply connection to a tuner, or preamp, and some amps are ok to operate with a range of output stage valves (each with their own bias settings).
Sometimes a schematic comes with other references, such as a webpage of setup information, or a vintage instruction manual (such as for Heathkit amps), and over time just the schematic has been cut and pasted. That can then be to the makers advantage to remove values from the schematic, as the schematic may stand the test of time, but the parts list and operating levels gets documented elsewhere as revisions and tweaks accumulate.
I use VS1, VS2 etc nomenclature as that then allows cut/paste use for other projects, and in a wide variety of text locations in a document (not such an issue with word find/replace tools nowadays, but a royal pain if you only had a typewriter).
It is a generic issue for any manufacturer or electronic system - with examples such as Vdd, Vcc, .... 5V, 3.3V, ....
Sometimes a schematic comes with other references, such as a webpage of setup information, or a vintage instruction manual (such as for Heathkit amps), and over time just the schematic has been cut and pasted. That can then be to the makers advantage to remove values from the schematic, as the schematic may stand the test of time, but the parts list and operating levels gets documented elsewhere as revisions and tweaks accumulate.
I use VS1, VS2 etc nomenclature as that then allows cut/paste use for other projects, and in a wide variety of text locations in a document (not such an issue with word find/replace tools nowadays, but a royal pain if you only had a typewriter).
It is a generic issue for any manufacturer or electronic system - with examples such as Vdd, Vcc, .... 5V, 3.3V, ....
So a push pull amplifier uses 350V on the output stage. What current do you want to have listed, the quiescent current . . . Or the current when the amplifier is at maximum rated output . . . And at max power at 1 kHz . . . or at 20 Hz. Schematics should show some details. Perhaps a second page with more details is needed. I have seen some schematics so full of numbers that you could not follow the circuit paths.
I too would like to see the B+ voltage value, but some (lots) schematics don't have it.
The first tube amp I built was the Svetlana 6bm8 (#2) Eric Barbour
https://web.archive.org/web/20000611150750/http://www.svetlana.com/graphics/TB/No10fig2.gif
It shows 150 to 450 volts. I asked why was the B+ listed with such a wide range. No one could give an answer other than the 6bm8 could handle it. I think I had a B+ 300 volts. It worked.
Technical Bulletin 10
The first tube amp I built was the Svetlana 6bm8 (#2) Eric Barbour
https://web.archive.org/web/20000611150750/http://www.svetlana.com/graphics/TB/No10fig2.gif
It shows 150 to 450 volts. I asked why was the B+ listed with such a wide range. No one could give an answer other than the 6bm8 could handle it. I think I had a B+ 300 volts. It worked.
Technical Bulletin 10
Yes, "Ground" that come from 1-wire car electricity is the most confusing. Because of that people do not consider resistances of wires, and assume that if they connect rectifier to the chassis, it would be the same as connecting one side of a filtered voltage to the chassis. As the result, when 2 of such components interconnected using unbalanced cable, well, even when 1 of them is "ground-wired" such a way, the voltage drop that charges filter capacitors from rectifiers are being applied to inputs of their amplifiers through ground loops.
They result in more weird work-arounds like tube rectifiers, chokes before capacitors, thick ground buses, ground lifts, and the whole industry of power conditioners and power cables.
...and all is because of the "GND" sign!
HT should be reserved for the AC unrectified high voltage on the secondary. B+ is for the filtered DC.
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