I read on the Russian forum that the 6P14P-K (6П14П-К) tubes has the best parameters among Russian tubes.
When I read read the forums and various people call the best tube Mullard EL84.
Nice!
I see some neat tricks in there...
The positive feedback from the split load phase inverter to the input 6EU7 is unusual. Did you increase the amount of NFB to offset the increase in gain?
The adjustable cathode bias network is nice, even though a 360k 2W resistor might be a little expensive/hard to source. Not too bad, though. I like it. I might steal that from you.
I've been meaning to try some kind of switchable NFB. Your switching network looks very good. Can you switch that with the amp on and the volume up to normal listening level? If you do that, do you hear a 'pop'? Or is it pretty much silent?
Why a 68k grid stopper on the input 6EU7? That seems like a high value. 6EU7 will have fairly high input capacitance, maybe 150pF. 68k in series might introduce a HF rolloff. Or is that to compensate the NFB loop (HF stability)? If so, very clever!
I see some neat tricks in there...
The positive feedback from the split load phase inverter to the input 6EU7 is unusual. Did you increase the amount of NFB to offset the increase in gain?
The adjustable cathode bias network is nice, even though a 360k 2W resistor might be a little expensive/hard to source. Not too bad, though. I like it. I might steal that from you.
I've been meaning to try some kind of switchable NFB. Your switching network looks very good. Can you switch that with the amp on and the volume up to normal listening level? If you do that, do you hear a 'pop'? Or is it pretty much silent?
Why a 68k grid stopper on the input 6EU7? That seems like a high value. 6EU7 will have fairly high input capacitance, maybe 150pF. 68k in series might introduce a HF rolloff. Or is that to compensate the NFB loop (HF stability)? If so, very clever!
That is negative feedback from cathodyne to the first stage .
I don't want to say it is bad , but in this way the gain is of the 6EU7 / 12AX7 would be very low ... Plus global negative feedback and negative feedback for being ultralinear .
I don't want to say it is bad , but in this way the gain is of the 6EU7 / 12AX7 would be very low ... Plus global negative feedback and negative feedback for being ultralinear .
Last edited:
Edited -- I get it. Screen grid inverts, cathode output of cathodyne is non-inverting. NFB, yes.
Gain of 6EU7 can be very low because grid bias of EL84 output stage is only about -12V or so. If gain of input 6EU7 is only 25X, probably still enough to drive EL84s plus NFB. Should be... I think.
Gain of 6EU7 can be very low because grid bias of EL84 output stage is only about -12V or so. If gain of input 6EU7 is only 25X, probably still enough to drive EL84s plus NFB. Should be... I think.
Last edited:
The 6EU7, being basically the same as a 12AX7, doesn't exhibit any hearable HF rolloff, but having the "taming effect" of the grid stopper does reduce any chances of overloading.
It's a nice silent front end IMO, and the 6EU7's lower filament voltage helps, as does the hum balance pot. - dead silent.
Switching the feedback during use only mildly effects apparent volume levels, no pop, as long as the rotary switch is a make-before-break type.
I wanted to be able to "tune" the feedback/control to my liking with any type of speakers.
With my floor-standing 4 ohm air-suspension Advent Maestros, I wanted more control, so I'm using the max feedback setting.
In the one photo of the chassis, it shows an extra 6EU7 tube far left, now removed, I didn't need the extra gain, that was before I went to Gillespie's unique biasing system.
While the PS is robust enough, they all have some "sag" due to heavy draws in music, and the "EFB" system tracks this, and instantly compensates the output biasing, thus keeping the control grids from varying, going "positive" with possible distortion caused by transients.
And being basically a "fixed bias" type of arrangement, you naturally get more watts, even in my UL configuration.
Those Dyanaco clone Z565's are terrific, and worth the one-time cost.
I was getting two schematics mixed up -- ay yi yi
Forget what I wrote about positive vs. negative feedback.
How is floating the 'bottom' of the cathodyne cathode load resistor on the input triode's cathode causing negative feedback?
Forget what I wrote about positive vs. negative feedback.
How is floating the 'bottom' of the cathodyne cathode load resistor on the input triode's cathode causing negative feedback?
How ... the phase in the cathode of the cathodyne is inverted vs the cathode of the first triode . This is negative feedback .
The Tina Turner CD selection of "I can't stand the rain", when played at room-filling volume through my tube amp into the Advent Maestros is utterly amazing.
Crisp, clear, and the bass knocks me over.
It was like she was standing in my living room.
When I heard that performance, I knew I was finished tweaking/designing my amp.
Listen to this track.... imagine.
★ Tina Turner ★ I Can't Stand The Rain ★ [1984] ★ "Private Dancer" ★ - YouTube
Crisp, clear, and the bass knocks me over.
It was like she was standing in my living room.
When I heard that performance, I knew I was finished tweaking/designing my amp.
Listen to this track.... imagine.
★ Tina Turner ★ I Can't Stand The Rain ★ [1984] ★ "Private Dancer" ★ - YouTube
Last edited:
No, it's positive feedback.
Supose the grid of the first triode goes up, down goes it's anode and so does the cathode of the phase inverter.That down is partely passed to the first cathode.Grid up cathode down is more drive, is positive feedback.
Mona
😀 Belive me , I made that circuit and is negative feedback . I was at first surprised because not only you claim positive feedback .
The grid and cathode are in phase , more drive on the grid means cathode goes up also , not down ... more current flow in the cathode resistor so the voltage is higher . If is receiving "down" from cathodyne will conduct less
Last edited:
Think again 🙂
First triode,anode is in phase with the cathode.Second triode, cathode is in phase with the grid.
So no phase inversion in the loop cathode1-anode1-grid2-cathode2-cathode1.
Mona
On pages 23 to 28 from the book "Hi-Fi Amplifier Circuits" (E. Rodenhuis, second edition, Philips, 1965) it says that this is positive feedback.
Since the second stage of the amplifier of wiseoldtech is a cathodyne, so with a 'gain' of a little under 1, the risk of instability is probably low (addition: and ofcourse there's also GNFB going on).
Since the second stage of the amplifier of wiseoldtech is a cathodyne, so with a 'gain' of a little under 1, the risk of instability is probably low (addition: and ofcourse there's also GNFB going on).
Attachments
Last edited:
You also must take in account how many capacitors are in signal path ... guess what , they shift phase too 😀 This is the key .
For Ketje "First triode,anode is in phase with the cathode.Second triode, cathode is in phase with the grid"
Please don't insult the basic lows of phisics ... anode(plate) is allways in opposite phase with the cathode , as collector with emitter
For Ketje "First triode,anode is in phase with the cathode.Second triode, cathode is in phase with the grid"
Please don't insult the basic lows of phisics ... anode(plate) is allways in opposite phase with the cathode , as collector with emitter
Last edited:
If you look at John Broskie's Tetra Sans phono preamp, you'll see that he includes the option to lift the cathode follower's cathode load resistor on top of the input triode's cathode. That is positive feedback there.
Now, of course a cathodyne phase splitter is a phase splitter, so that does make things confusing. Perhaps lifting it all on top of the 1st stage cathode makes it negative FB from the plate and positive FB from the cathode?
That does beg the question 'Why bother?'....
Now, of course a cathodyne phase splitter is a phase splitter, so that does make things confusing. Perhaps lifting it all on top of the 1st stage cathode makes it negative FB from the plate and positive FB from the cathode?
That does beg the question 'Why bother?'....
Or perhaps is the obvious ... negative feedback , no need for inventing anything 😀 I must remind you , I build it and measured it ( by chance ) .
Last edited:
Perhaps it is not so obvious and you are missing half the phase reversals that are happening in the phase splitter.
Writing on internet is cheap ... by now if you really wanted to prove something you could have build it 😛
As far as I can see, Mona explained it well in post #30. I just rewrite it in my own words here.
The output voltage of the first triode depends on voltage difference between its grid and its cathode. On a positive going input signal the voltage between grid and cathode becomes larger. The negative feedback over the non-decoupled cathode resistor reduces this a bit because the rising current highers the cathode voltage a bit. This feedback is negative because a bit higher cathode voltage means a bit lower voltage difference between grid and cathode. But still the voltage between grid and cathode becomes larger on a positive going input signal, else there would be no amplification at all.
The voltage on the anode of the first triode goes down, so also the voltage and current over and through the cathode resistor of the second triode goes down. This diminishing current of the second triode flows through the cathode resistor of the first stage. This lowers the voltage drop over the cathode resistor of the first triode. So it lowers the cathode voltage of the first triode. This in turn means that the voltage difference between the grid and the cathode of the first triode goes up. This rising difference has the same direction as the positive going input signal. So they add up.
Note that this is positive feedback (ofcourse) works in the opposite direction of that of the negative feedback caused by the first triode in its cathode resistor. But even if the amount of positive feedback is low, like even lower than the amount of negative feedback, still it is positive feedback.
The output voltage of the first triode depends on voltage difference between its grid and its cathode. On a positive going input signal the voltage between grid and cathode becomes larger. The negative feedback over the non-decoupled cathode resistor reduces this a bit because the rising current highers the cathode voltage a bit. This feedback is negative because a bit higher cathode voltage means a bit lower voltage difference between grid and cathode. But still the voltage between grid and cathode becomes larger on a positive going input signal, else there would be no amplification at all.
The voltage on the anode of the first triode goes down, so also the voltage and current over and through the cathode resistor of the second triode goes down. This diminishing current of the second triode flows through the cathode resistor of the first stage. This lowers the voltage drop over the cathode resistor of the first triode. So it lowers the cathode voltage of the first triode. This in turn means that the voltage difference between the grid and the cathode of the first triode goes up. This rising difference has the same direction as the positive going input signal. So they add up.
Note that this is positive feedback (ofcourse) works in the opposite direction of that of the negative feedback caused by the first triode in its cathode resistor. But even if the amount of positive feedback is low, like even lower than the amount of negative feedback, still it is positive feedback.
Last edited: