Man… you sure could dispense with a lot of that 6080-as-active-series-regulator business with a couple of dirt-cheap, rock-solid, 600 V MOSFET enhancement-mode devices. I know, less bottles to glow in the dark, but if you want the glow, keep the 0B3 regulator gas references. As voltage references go, if not operated TOO far into their post-strike conduction current range, they last for a good long time. And, were you to be particularly 'âhnal' about it, you also could sneak in a pair of 100 volt, and another pair of 120 volt Zeners … in parallel, should one of the gas regs stop conducting.
Likewise, the way the amplifier is set up, the 2nd 6SN7 in the chain is acting as a cathode follower for the phase-in-and-inverted signal. Thus… instead of just driving 2 of the 6550s, you could also drive 4 or 6 of them, per channel. Easily hitting 100 to 150 watts per channel.
Again, the MOSFETs in the power supply would be your friend. They easily scale to hundreds of milliamps of pass current. Do a great job with ripple rejection as well. Just got to give them a proper heat sink. Insulated from chassis. If underside (preferred), then with plenty of ventilation holes in the chassis, above.
The front-end is nice-and-sweet. Good amplification followed immediately by symmetric phase inversion. And per Mr. KodaBMX, followed again by phase-specific amplification. Making more symmetric the 6SN7 triode affective transconductance onto the signal chain.
Apart from the historically quirky use of NO-k-Ω values, but only integers and MΩ, it is likely that the circuit dates to either the earliest 1960s or possibly late 1950s.
Anyway,
⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
⋅-=≡ GoatGuy ✓ ≡=-⋅
Likewise, the way the amplifier is set up, the 2nd 6SN7 in the chain is acting as a cathode follower for the phase-in-and-inverted signal. Thus… instead of just driving 2 of the 6550s, you could also drive 4 or 6 of them, per channel. Easily hitting 100 to 150 watts per channel.
Again, the MOSFETs in the power supply would be your friend. They easily scale to hundreds of milliamps of pass current. Do a great job with ripple rejection as well. Just got to give them a proper heat sink. Insulated from chassis. If underside (preferred), then with plenty of ventilation holes in the chassis, above.
The front-end is nice-and-sweet. Good amplification followed immediately by symmetric phase inversion. And per Mr. KodaBMX, followed again by phase-specific amplification. Making more symmetric the 6SN7 triode affective transconductance onto the signal chain.
Apart from the historically quirky use of NO-k-Ω values, but only integers and MΩ, it is likely that the circuit dates to either the earliest 1960s or possibly late 1950s.
Anyway,
⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
⋅-=≡ GoatGuy ✓ ≡=-⋅
Believe it or not.... in the "old days" when selenium rectifiers were used, that diagram is correctly marked.
Really? I always had thought that the “rectifier symbol” was to memorialize that electrons would “follow the arrow”, and “hit a blockage” in that pointed-to direction. Electrons, being negative, being unable to make it past the blockage would 'go the other way'. Thus the pointed-to end of the symbol would become 'positive' relative to the AC on the other side.
Well, that's at least how an ancient-but-highly-amusing old TV tech told me when I was getting into it, in the mid 1960s.
⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
⋅-=≡ GoatGuy ✓ ≡=-⋅
A quite Google search shows that you are absolutely correct WiseOldTech. Who knew? By the 1960s, most-everyone building stuff had made the transition to silicon rectifiers, cuz they were so cheap, and so remarkably reliable over time.
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Earlier in June 1955 there was the original article, starts on page 15-
https://www.americanradiohistory.com/Archive-Audio/50s/Audio-1955-Jun.pdf
Zeners are FAR LESS stable and far less reliable than gas regulators.
Ask me how I know.
Because the Si junction breakdown voltage and temperature are fundamentally unstable.
As temperature rises the junction voltage rises.
Which means as the zener heats up (it's cold to begin with) your bias voltage can rise, effectively slowly turning your amplifier output stage off back into cross over distortion or overloading another section of the circuit.
It led to an interesting exchange with D C from Tronola, who had tried the same thing, with similar results.
I did manage to make one of my systems work, by using outsize (8W) zeners with say small values 5-8V in a long cascade of up to half a dozen in series so the temp became far more stable, but still had a strange time constant "rocking" from one extreme to another.
The zener chain derived what was supposed to be a rock steady -ve bias line for directly coupled AB2 class output valves.
In reality when the amp was cranked the zeners got really hot, (because the entire return current of the amp passed thru them into the GND return), - the amplifier started to become seriously unstable varying from too low a quiescent current (where the zeners cooled) to way too HIGH a quiescent current (where the zeners would heat up again).
Nothing rivalled the sheer stability of the old fashioned gas stabilisers, which would scarcely move by more than a few mV over 300V, (2 x 150V in series), gave a totally hum free 25m/a shunt regulated supply and scarcely got warm...
As temperature rises the junction voltage rises.
Which means as the zener heats up (it's cold to begin with) your bias voltage can rise, effectively slowly turning your amplifier output stage off back into cross over distortion or overloading another section of the circuit.
It led to an interesting exchange with D C from Tronola, who had tried the same thing, with similar results.
I did manage to make one of my systems work, by using outsize (8W) zeners with say small values 5-8V in a long cascade of up to half a dozen in series so the temp became far more stable, but still had a strange time constant "rocking" from one extreme to another.
The zener chain derived what was supposed to be a rock steady -ve bias line for directly coupled AB2 class output valves.
In reality when the amp was cranked the zeners got really hot, (because the entire return current of the amp passed thru them into the GND return), - the amplifier started to become seriously unstable varying from too low a quiescent current (where the zeners cooled) to way too HIGH a quiescent current (where the zeners would heat up again).
Nothing rivalled the sheer stability of the old fashioned gas stabilisers, which would scarcely move by more than a few mV over 300V, (2 x 150V in series), gave a totally hum free 25m/a shunt regulated supply and scarcely got warm...
I was wondering how long it would be until selenium rectifiers were mentioned.
I'd never seen one until I had to repair a remote closing coil supply, which used a large 3 phase rectified stack.
I wonder how many years these things were used, ot seems that they were only a short term stop gap between what came before and rectifiers that we know today.
So… 6VHeater, not to detract from your awful experience, but did you even look at the schematic presented at the outset, while reading my comment? Perhaps you missed the bottom half of the schematic. You know, the power supply part. With its 6080 bottles and gas voltage references and so on.
I have not, nor would I except in the least-power-demanding situations advocate using Zeners for anything other than their remarkable ability to serve as low-current voltage references, not as power regulators.
Sheesh.
However, I also acknowledge that as with most things, when you attempt to use a device near or above its “sweet spot” (working power), well … then all kinds of shît happens that we mostly wouldn't want … except possibly for high-distortion electric guitar amps.
Best wishes, old onion.
⋅-=≡ GoatGuy ✓ ≡=-⋅
I have not, nor would I except in the least-power-demanding situations advocate using Zeners for anything other than their remarkable ability to serve as low-current voltage references, not as power regulators.
Sheesh.
However, I also acknowledge that as with most things, when you attempt to use a device near or above its “sweet spot” (working power), well … then all kinds of shît happens that we mostly wouldn't want … except possibly for high-distortion electric guitar amps.
Best wishes, old onion.
⋅-=≡ GoatGuy ✓ ≡=-⋅
Using zeners in a situation that doesn't allow them to perform in a predictable way isn't the best anyways. I use them as the reference on a mosfet gate to feed the screens on a pentode amplifier. The zeners are isolated from the changing current, and only change a couple volts from cold to warmup. In a situation like this where they are used as a reference voltage they work fantastic. If you wanted to use them as a direct shunt a string of lower voltage ones like in Morgan Jones's Statistical regulator would be a better choice than higher voltage ones, as the temperature coefficient is a bit better for changing current.
Like goatguy says, reference voltage is the way to go in high current situations. They would drop right in for gas regs in most classic designs that use them as a reference rather than a shunt.
Like goatguy says, reference voltage is the way to go in high current situations. They would drop right in for gas regs in most classic designs that use them as a reference rather than a shunt.
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Vacuum tube equipment has and always will have it's own peculiarities, and its limits.
Tube equipment is flexible and forgiving of variables, to a point, and has for decades been designed with these things in mind.
Sensible inclusion of anything solid state into tube circuitry has its own added benefits, also up to a point.
You have to consider the technology and its fundamental limitations
But once something is "overdone" with obsessive, overboard designing by individuals concerned with absolute perfection of some sort in mind, issues can arise.
Like squeezing a lemon to get that absolutely last bit of juice from it, you'll likely wind up with seeds in your sauce.
Tube equipment is flexible and forgiving of variables, to a point, and has for decades been designed with these things in mind.
Sensible inclusion of anything solid state into tube circuitry has its own added benefits, also up to a point.
You have to consider the technology and its fundamental limitations
But once something is "overdone" with obsessive, overboard designing by individuals concerned with absolute perfection of some sort in mind, issues can arise.
Like squeezing a lemon to get that absolutely last bit of juice from it, you'll likely wind up with seeds in your sauce.
ahum.
The zeners in question have to cope with peanuts.
The total idle current of the amp, is 100m/a with only the larger currents at full loads, (up to 1/4 amp peak is dead easy for an 5V 8W power zener, it's what they are made for!).
100-120m/a on an 8W 5V zener at idle is perfect, but sharing notes with D C, he had found the same problems, leading to his EFB™ Bias Circuit.
The problem is, a proper bias supply requires accuracy to within say 50-100mV or the quiescent current wanders around all over the show with anode volts exceeding 500V and the screen on the book limit for that valve.
As I stated, a 45m/a shunt gas stabiliser in my experience performed far better than any zener.
I totally disagree, but there you are.
I am expecting mV of ripple with DC coupled cathode followers, which is why that amp is triple regulated, and NO..you are wrong, it's not a guitar amp with loads of distortion as you gleefully like to hint...
It's a particularly nice implementation of a hifi amp which suffers ZERO blocking distortion thanks to the ability to supply loads of control grid current at the right time.
and yes
It wasn't an "awful experience" at all.
Fact is with a total bias supply of -43V and a cathode follower supplying up to 10m/a of drive to drive the g1 up to 20v +ve the loads up on the original HT supplies were so large as to make everything sag all over the place despite it being a nice choke input filter supply. (it has 2 seperate ones, 1 for screen, the other for anode).
TBH I think a near trebling of linear output power simply by stabilising the SCREEN voltage, the bias voltage, the main HT and the AF amp section to within a few mV was a really good implementation of what STC originally intended.
Having said that, my new amp which uses an absolutely similar series zener PSU implementation of about -32V total, but AB1 PPP AC coupled instead of just a pair of AB2 DC coupled output valves doesn't suffer from this instability,
AND
has a screen stabiliser using a proper series stabiliser triode, essential in that case.
Funny things happen when you have lower dissipation aligned grids in beam tetrodes compared with the monster screen grid currents in pentodes.
I did a similar screen grid regulator for another non aligned screen beam power valve,which could easily drag 60m/a out of a 320V supply (!) and it altered the THD figs out of all recognition.
(yes 19W disappearing down the screen grids at 100W output in 1 case and as much from the PPP design at 50W!)
The zeners in question have to cope with peanuts.
The total idle current of the amp, is 100m/a with only the larger currents at full loads, (up to 1/4 amp peak is dead easy for an 5V 8W power zener, it's what they are made for!).
100-120m/a on an 8W 5V zener at idle is perfect, but sharing notes with D C, he had found the same problems, leading to his EFB™ Bias Circuit.
The problem is, a proper bias supply requires accuracy to within say 50-100mV or the quiescent current wanders around all over the show with anode volts exceeding 500V and the screen on the book limit for that valve.
As I stated, a 45m/a shunt gas stabiliser in my experience performed far better than any zener.
I totally disagree, but there you are.
I am expecting mV of ripple with DC coupled cathode followers, which is why that amp is triple regulated, and NO..you are wrong, it's not a guitar amp with loads of distortion as you gleefully like to hint...
It's a particularly nice implementation of a hifi amp which suffers ZERO blocking distortion thanks to the ability to supply loads of control grid current at the right time.
and yes
is simply not good enough in a DC coupled amp.
It wasn't an "awful experience" at all.
Fact is with a total bias supply of -43V and a cathode follower supplying up to 10m/a of drive to drive the g1 up to 20v +ve the loads up on the original HT supplies were so large as to make everything sag all over the place despite it being a nice choke input filter supply. (it has 2 seperate ones, 1 for screen, the other for anode).
TBH I think a near trebling of linear output power simply by stabilising the SCREEN voltage, the bias voltage, the main HT and the AF amp section to within a few mV was a really good implementation of what STC originally intended.
Having said that, my new amp which uses an absolutely similar series zener PSU implementation of about -32V total, but AB1 PPP AC coupled instead of just a pair of AB2 DC coupled output valves doesn't suffer from this instability,
AND
has a screen stabiliser using a proper series stabiliser triode, essential in that case.
Funny things happen when you have lower dissipation aligned grids in beam tetrodes compared with the monster screen grid currents in pentodes.
I did a similar screen grid regulator for another non aligned screen beam power valve,which could easily drag 60m/a out of a 320V supply (!) and it altered the THD figs out of all recognition.
(yes 19W disappearing down the screen grids at 100W output in 1 case and as much from the PPP design at 50W!)
The arrows in diode and BJT symbols point the direction of current flow, not electron flow.
The symbol is an accident of history I believe, the original diode symbol represented point-contact diodes which happened to use n-type semiconductor so that the point was effectively the p-type end. The original experimental PNP transistors were point-contact too, hence the PNP symbol.
The point became re-interpreted as a conventional-current arrow later.
Where did I hint at a guitar amp or mention distortion? Why are your responses so combative to everything? Or is it just your writing style?
Also, mV of ripple is absolutely obtainable with zeners. running them in certain applications, like as a reference voltage for a mosfet gate or pass tube error amplifier is totally fine. On my particular application I have an RC filter running off of them for a slow warm up anyway, so the slight change in voltage drop once warm is a non issue for a simple screen regulator voltage reference. For a more advanced regulator I would do something different, yes.
I do like gas regs, and do use them. I really like the 0D3 and really like the stability, but don't always wish to throw that much current through a reference, and they don't carry enough to work in all instances, such as a screen voltage shunt regulator for a big sweep tube output stage.
So you don't know about Russian regulators eg. SG5b?
Tiny little things 150v 5-10m/a no equivalent in the west, same size as a zener.
Costs next to nothing.
Then there's the big loctal gas beasts nobody wants....quite OK for 45m/a...even the wire ended thingy I liked a lot.
Dead stable 2 x = 300V, doesn't move, threw out a valve rect, replaced with silicon and stuck in this instead.....