Your speakers are 95 db? How big is the room? You do not need 100mA OPT's to get a big sound with these kind of speakers. Ok, its not a biggie. You can still use them with less than 100mA. It won't be quite optimal since the gap is set for 100mA, but honestly if I had them I would just use them first and see how they sound.
You could power 95db speakers with 1 Watt and be pretty happy, unless it is a BIG room. I Like to use DHT's like the 45 tube or the 2a3. I built with 300b before but the amp was more powerful than I needed. I sold it to a friend who loves it. His speakers are only 89db efficiency.
Difference between 2a3 and 300b is that the 2a3 (usually) has a flatter frequency response, is (usually) less expensive than the 300b which (usually) can deliver more power. Also the heater voltages are different. And the electrical characteristics (plate curves) are of course also not the same. They are different tubes/valves!
Single ended amps (usually) have more distortion than push-pull, so you need to look for a design that keeps that in check. This was noted already.
If you must use 6SN7 then a cascode is not a bad idea. Lots of people like driving 45, 2a3, 300b with a pentode, and a cascode is a LOT like a pentode. You could also use a pentode....
You can also use a Pentode that is Triode strapped, like D3a, etc. You can use a Gyrator to load it too, but maybe this will be more complex.... However you can buy a nice board for a gyrator circuit if you want.
I would avoid high Mu triodes since they often have high internal (plate) resistance. You will not really drive 300b well with 12ax7 or 6k5 unless you use some kind of follower circuit to reduce the output impedance. High output impedance with 6k7 will not work well with the high input (miller) capacitance of 300b. You lose high frequency response...
Good luck with it. I think the 6sN7 cascode is a nice idea. 😉
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I’d like to understand, what’s the influence of the certain transformer to the certain schematic behind it. For example, we have a schematic with hammond onboard. What if i change it to my lundahl? As i see there is a difference in internal resistance and inductance. But how do these parameters affect on sound?
Example:
Take two different manufacturer's transformers that are both rated for 5k to 8 Ohm.
For each transformer:
What is the primary DCR; What is the secondary DCR?
What is the primary to secondary leakage inductance (leakage reactance)?
What is the distributed capacitances of the primary, secondary, primary to secondary, primary to laminations and end bells, secondary to laminations and end bells (hopefully the laminations and end bells are grounded, Safety First!)?
What is the total dimensions and mass of the laminations; and what kind of material is used, steel, amorphous, etc.?
If the transformer is for a Single Ended stage, what is the Air Gap dimensions?
Some items that are known to be affected by the above factors:
Low Frequency bandwidth, high frequency bandwidth
Damping Factor
Insertion loss (for example 12 Watts from output tube = 11 Watts out at the secondary).
Saturation at what DC current, and at what signal current, and what signal frequency.
Distortion: Harmonic and Intermodulation
Then there are other factors:
Cost, weight, size, open connections, end bells, potted, "Pretty Looks Factor", etc.
I probably forgot some important items, but at least this is a start.
I have used Lundahl and Electra-Print (interstage); and output transformers from Hammond, Electra-Print, One Electron, and salvaged Fisher 500C 800C receivers.
All have good features, and all have tradeoffs.
To keep the comparison fair, the transformers should be rated for the same primary and secondary impedance; and rated the same type: single ended or push pull.
You should not compare a 5k:8 Ohm, to a 3k:8 Ohm, because you are now also comparing how the output tube responds to a different load line.
I am "preaching to the choir", most of you know lots about this, but hopefully some newbies will find this helpful.
Take two different manufacturer's transformers that are both rated for 5k to 8 Ohm.
For each transformer:
What is the primary DCR; What is the secondary DCR?
What is the primary to secondary leakage inductance (leakage reactance)?
What is the distributed capacitances of the primary, secondary, primary to secondary, primary to laminations and end bells, secondary to laminations and end bells (hopefully the laminations and end bells are grounded, Safety First!)?
What is the total dimensions and mass of the laminations; and what kind of material is used, steel, amorphous, etc.?
If the transformer is for a Single Ended stage, what is the Air Gap dimensions?
Some items that are known to be affected by the above factors:
Low Frequency bandwidth, high frequency bandwidth
Damping Factor
Insertion loss (for example 12 Watts from output tube = 11 Watts out at the secondary).
Saturation at what DC current, and at what signal current, and what signal frequency.
Distortion: Harmonic and Intermodulation
Then there are other factors:
Cost, weight, size, open connections, end bells, potted, "Pretty Looks Factor", etc.
I probably forgot some important items, but at least this is a start.
I have used Lundahl and Electra-Print (interstage); and output transformers from Hammond, Electra-Print, One Electron, and salvaged Fisher 500C 800C receivers.
All have good features, and all have tradeoffs.
To keep the comparison fair, the transformers should be rated for the same primary and secondary impedance; and rated the same type: single ended or push pull.
You should not compare a 5k:8 Ohm, to a 3k:8 Ohm, because you are now also comparing how the output tube responds to a different load line.
I am "preaching to the choir", most of you know lots about this, but hopefully some newbies will find this helpful.
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The turns ratio gives a ratio of step-down from the plate signal to the speaker circuit, and the square of that turns ratio with the speaker impedance put in the formula at the output end (secondary) gives the figure for plate load impedance at the primary.
But, while 10:1 and 100:10 is the same ratio, the greater the number of turns the more inductance is possible. That then is supported or not by the geometry of the windings (eg. interleaving) themselves and then the core structure (core material, type, size) .
These variables bring into play varying amounts of leakage inductance and capacitance which in their own ways work against the theoretical ideal.
The possibilities for variation are close to infinite , and everything is a compromise , hopefully chosen with understanding , though luck seems to play a role for many of us.
In general, the level of inductance is associated with the ability to support low frequency output. In general, the presence of leakage/or strays is associated with the erosion of high frequency quality. In both cases however there are things (like feedback, for example) that can be done elsewhere in the circuit to take care of transformer "deficiencies" to some degree or other.
The right balance of build considerations in an output transformer, matched with a circuit, can lead to mush or magic. It's not always easy to know what you'll get before you try it. Which is why I'm such a vocal advocate of breadboarding before doing a finished build.
But, while 10:1 and 100:10 is the same ratio, the greater the number of turns the more inductance is possible. That then is supported or not by the geometry of the windings (eg. interleaving) themselves and then the core structure (core material, type, size) .
These variables bring into play varying amounts of leakage inductance and capacitance which in their own ways work against the theoretical ideal.
The possibilities for variation are close to infinite , and everything is a compromise , hopefully chosen with understanding , though luck seems to play a role for many of us.
In general, the level of inductance is associated with the ability to support low frequency output. In general, the presence of leakage/or strays is associated with the erosion of high frequency quality. In both cases however there are things (like feedback, for example) that can be done elsewhere in the circuit to take care of transformer "deficiencies" to some degree or other.
The right balance of build considerations in an output transformer, matched with a circuit, can lead to mush or magic. It's not always easy to know what you'll get before you try it. Which is why I'm such a vocal advocate of breadboarding before doing a finished build.
sorry if i missed something but where in the world did this amp design become associated with jc morrison? if it was from the "fi primer", that was a collection of circuits made by various people, mainly japanese, that were popular in the 80's and 90s. this was explained clearly in the notes. i saw a schematic from "skunkie" that was a reprint of a shishido amp that was part of the "fi primer"... not a jc morrison design. not a "skunkie design". just wondering...
The schematic I posted using the cascode wasn't a reprint of anything. No idea what you are even talking about. As far as that other design being associated with JC Morrison:
300B Single-Ended (SE) Tube Amplifier Schematic (6SN7 input)
DIY 300B (SET) Tube Amplifier - Hellbach blog
Antique Radio Forums • View topic - A new 300B amp project
Pin on HIFI
Google "JC morrison 300B", I got 135,000 hits. He said this about the circuit:
"This amp is the quintessential triode amp.It just does its job, period. It is honest and accurate and sweet and will drive
a surprising number of commercial speakers to acceptable levels. If you use the best available parts and materials in
constructing it (as well as stash away a few tubes for a rainy day), it will pass down to your children and continue
to wow 'em in the next millenium. - J.C. Morrison (1993)"
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Ok, could someone please show good hi-fi single-end schematic example to consider. Maybe with other tubes
i've found some nice designs from Audio note. Has anybody tried to build on of those amps?
Audio Note [Аудио-википедия]
Audio Note [Аудио-википедия]
I have already asked this question and got the same unhelpful blizzard of links as a response.
I can't help but notice that in every instance where the original Sun Audio schematic is posted, the "Sun Audio SV-300BSE" nomenclature that is clearly printed in the body of the original schematic is erased. Why not give credit to the originator of the schematic? I believe that the probable answer is that the schematic is proprietary to Sun Audio as a current product, so assigning it to Mr. Morrison is a convenient way of avoiding copyright infringements.
Attachments
Asking why this is is attributed to him, after the cow left the barn 2 decades ago, is kinda pointless tilting at windmills. People attribute it to him because of these facts: a) he published this in a packet of schematics decades ago. b) There is a quote of him saying this is an "heirloom amplifier". c) There are 10's of thousands of web references to this being "The JC Morrison 300B".
Google "300b amplifier schematic" and the number one hit attributes this to him, and you wonder why people attribute this to him?
The better question is: Why do people keep bringing this up? If someone says "The JC Morrison 300B amp" are you confused as to what they are talking about? Once something has a commonly used name, trying to change it is like trying to get people to call the color blue, something else.
Yeah, I would use 2a3 single ended. Even the humble 45 can power these speakers and provide beautiful full sound in this room, assuming the driver stage is done well.
Thank you. I’ve been studying some schematics, but they are based on old-school transformers like Murata and so on. Which are hard to get
If you can judge a good circuit by looking at a schematic I'm not sure why you are asking for anybody's advice. Can you say more about what is it that you are looking for that you are not finding? or , put another way, when you say "I've found some nice designs . . . .
" What is it about them that you are seeing as nice?
Thanks
" What is it about them that you are seeing as nice?
Thanks
I’m judging on schematic based on measurements: frequency response, thd, harmonic response etc. Some designs have them although I understand that it says nothing about the sound. I’m looking for schematic based on the following criteria:
1. Approved design
2. Components should be in production (many circuits use old stock tubes, transformers which are very hard to get)
3. Measurements or feedback about the sound.
1. Approved design
2. Components should be in production (many circuits use old stock tubes, transformers which are very hard to get)
3. Measurements or feedback about the sound.