I guess I should stop calculating things. So I went to the basement and build a quick-n-dirty circlotron output stage using two 6C33C tubes. B+ was 90 V (didn't have anything higher), biased at 400 mA. The voltage gain I got out of this was closer to 0.2, certainly not what I estimated from my "cathode follower" brainfart.
What is the correct way to calculate the voltage gain of a circlotron?
The equation you use for a cathode follower gain is too simplified, (but it works well when load is much higher than rp). A correct equation is:
Gm x rk/1+rk(1/rp + Gm) with Gm 40mA/V, (which is a reasonable value for 6C33C at some current) and rp 80 ohm you get a gain of very close to 0.2 with 8 ohm load
Gm x rk/1+rk(1/rp + Gm) with Gm 40mA/V, (which is a reasonable value for 6C33C at some current) and rp 80 ohm you get a gain of very close to 0.2 with 8 ohm load
I think you have to write all the parantheses . In your first equation , if you don´t write them , how can you know , if the last parenthese is supposed to be (1/rp + Gm) or (1/(rp+Gm)) IMHO
Thanks. This is not clearer, it's just different (and seems to make more sense). Just take a look at this funky woman and her mammoth: YouTube
I can agree that I didn't write the formula clearly, it would be much better and more easily understandable if you would be able to write formulas in their fractional form as shown in text books.
The formula should then be written as this:
above dividing horizontal line Gm * rk
below dividing horizontal line 1+ rk (1/rp +Gm)
It would help many times if if it was possiblle to write as real formulas in this forum but I don't know how, anyone knows?
The formula should then be written as this:
above dividing horizontal line Gm * rk
below dividing horizontal line 1+ rk (1/rp +Gm)
It would help many times if if it was possiblle to write as real formulas in this forum but I don't know how, anyone knows?
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Whether or not you use the parentheses in this equation, the result is the same, perhaps you are influenced by the forced use that you have to make when you use the scientific calculator since you have to separate the sentences. However in this case the colleague had written it well given that with or without the result it is the same.
That , I think , is not so.
It could be interpenetrated this way:
(Gm x Rk/1)+ rk(1/rp + Gm) and that is clearly not the same. Surely it would be strange to write Rk/1 as this would be the same as Rk.
The solution to writing scientific equations could be to write them in a file and attach it. That would avoid any misunderstandings
Hi All,
Just wondering if anyone is still interested in this thread and if there are any amplifiers currently in build or still in use.
Am currently looking for my next project build having decided to retire my Transcendent Beasts. They are now around 12 - 15 years old and have become fairly noisy and unreliable.
The plan was to build a pair of Bruce's smaller OTL's while I rebuilt the Beasts, but having now read through this thread, I must admit to being intrigued by the design, and am therefore considering the M-60 instead. Conveniently, it would fit my Beast chassis very well, with 12 holes suitable for octal sockets, all the power and speaker sockets etc. already in place. I should even be able to use some of the transformers to keep costs under control. The other big plus is that I already have quite a few 6AS7's lying around and this then eliminates the need to buy 24 new JJ EL509's at £34.00 each. (Current price at Hotrox UK)
Cheers
Steve.
Just wondering if anyone is still interested in this thread and if there are any amplifiers currently in build or still in use.
Am currently looking for my next project build having decided to retire my Transcendent Beasts. They are now around 12 - 15 years old and have become fairly noisy and unreliable.
The plan was to build a pair of Bruce's smaller OTL's while I rebuilt the Beasts, but having now read through this thread, I must admit to being intrigued by the design, and am therefore considering the M-60 instead. Conveniently, it would fit my Beast chassis very well, with 12 holes suitable for octal sockets, all the power and speaker sockets etc. already in place. I should even be able to use some of the transformers to keep costs under control. The other big plus is that I already have quite a few 6AS7's lying around and this then eliminates the need to buy 24 new JJ EL509's at £34.00 each. (Current price at Hotrox UK)
Cheers
Steve.
Just been looking at otl for headphones.. it becomes “interesting” when you consider impedances etc.
Hi All,
Just wondering if anyone is still interested in this thread and if there are any amplifiers currently in build or still in use.
Am currently looking for my next project build having decided to retire my Transcendent Beasts. They are now around 12 - 15 years old and have become fairly noisy and unreliable.
The plan was to build a pair of Bruce's smaller OTL's while I rebuilt the Beasts, but having now read through this thread, I must admit to being intrigued by the design, and am therefore considering the M-60 instead. Conveniently, it would fit my Beast chassis very well, with 12 holes suitable for octal sockets, all the power and speaker sockets etc. already in place. I should even be able to use some of the transformers to keep costs under control. The other big plus is that I already have quite a few 6AS7's lying around and this then eliminates the need to buy 24 new JJ EL509's at £34.00 each. (Current price at Hotrox UK)
Cheers
Steve.
I use my M60 clones everyday.
Having started with the original Transcendent SE-OTL kit a good few years ago I'm now on my fourth OTL build with a fifth a possibility. That Transcendent SE-OTL is the only one I no longer own but I still own these two;
- Heavily modified scratch-built 300B SE-OTL based on the Transcendent design published in 'Tubes and Circuits'
- Scratch built amp using a single 13E1 per channel, driven by s6H30pi stage
Here's a link to the 13E1 thread;
My New SE-OTL Amplifier
I'm also just finishing a scratch build using a single 6C33C per channel, driven by a 6SN7 stage. This is a bit of an experiment because it will use regulated power supplies throughout (21st Century Maida regs).
Of course, the common theme is that they're all very low power, just a Watt or two of output but they work very well and sound great with my 15ohm Lowther EX4 units in back loaded horns. They're also all hopelessly inefficient!
The potential fifth OTL project could be the Tim Mellow design, for which I've collected many parts. Obviously it is quite a deviation from my previous road.
I've also been tempted by the S Bench 'Inverted OTL' concept - I have a friend who has built one and swears by it as the best amp he's heard - maybe one day.
Thanks guys for your replies. Will definitely have a go at building the amps, and will post a few pictures here as I go.
I do have one question which hopefully some-one can assist with -
Whilst I have plenty of experience of building valve gear, I am not an electronics engineer, and so do not have the design knowledge and experience to know what is essential and what could be tweaked to suit parts I already have. The power supply schematic shows a 5H / 300mA choke on the negative rail of the driver circuitry. How critical is the value of this choke?, and can we substitute other values, perhaps with a resistor in series to trim the dc voltage drop if required. It seems a little illogical to me to have a 300mA rated choke in a circuit that is only passing a few mA, but there again, perhaps this is my limited knowledge tripping me up.
All thoughts / help / comment appreciated.
Thanks
Steve
I do have one question which hopefully some-one can assist with -
Whilst I have plenty of experience of building valve gear, I am not an electronics engineer, and so do not have the design knowledge and experience to know what is essential and what could be tweaked to suit parts I already have. The power supply schematic shows a 5H / 300mA choke on the negative rail of the driver circuitry. How critical is the value of this choke?, and can we substitute other values, perhaps with a resistor in series to trim the dc voltage drop if required. It seems a little illogical to me to have a 300mA rated choke in a circuit that is only passing a few mA, but there again, perhaps this is my limited knowledge tripping me up.
All thoughts / help / comment appreciated.
Thanks
Steve
Why not Novacron clone with 6C33? Much more power and to my ears more dynamics and transparency.I am also using my M60 clones almost everyday
worst thing about these amp's are that they make me really really want to take it further and have a go at MA1's and an MP-3
Soon to experiment with autoformers and F4's to improve low impedance drive.