i rebuilt his annastasia... http://kathodyne.coconia.net
(didn't update lately but quite some pictures)
But about the schematic, they don't appear to be in triode.....then g2 should be connected to b+(anode) (and if necessary a 100ohm resistor between it to prevent oscillation)
Did you look at the bias for the gu50?? or are they directly replaceable?
you can measure if the bandwidth is correct by placing 8 or 4 ohm resistor at the speaker outputs (big resistors)
then let it give about 3v at the outputs....connect a scope at the output and a tone generator at the input and sweep through the frequency to see when it starts falling on both sides of the spectrum
you can also calculate the bandwidth of the coupling capacitors (but i don't remember the formula now
)
something with 1/(2xpixrxc)
you can also look at distortion then by cranking up volume...at clipping both ends of the sinuses have to be flattened equally (which i doubt this splitter-thing will do)
(didn't update lately but quite some pictures)
But about the schematic, they don't appear to be in triode.....then g2 should be connected to b+(anode) (and if necessary a 100ohm resistor between it to prevent oscillation)
Did you look at the bias for the gu50?? or are they directly replaceable?
you can measure if the bandwidth is correct by placing 8 or 4 ohm resistor at the speaker outputs (big resistors)
then let it give about 3v at the outputs....connect a scope at the output and a tone generator at the input and sweep through the frequency to see when it starts falling on both sides of the spectrum
you can also calculate the bandwidth of the coupling capacitors (but i don't remember the formula now
)something with 1/(2xpixrxc)
you can also look at distortion then by cranking up volume...at clipping both ends of the sinuses have to be flattened equally (which i doubt this splitter-thing will do)
You are right, they are in pentode, not triode, my mistake.
"this splitter thing" is a well balanced long tailed pair. Not an uncommon splitter.
The bias is adjustable with NRS and st to 62 mA or so
The size of the coupling cap depends on the output impendance of the splitter and the input impendance of the output tubes, but i can't find the correct formula's anymore, nor can i calculate the impendances.
"this splitter thing" is a well balanced long tailed pair. Not an uncommon splitter.
The bias is adjustable with NRS and st to 62 mA or so
The size of the coupling cap depends on the output impendance of the splitter and the input impendance of the output tubes, but i can't find the correct formula's anymore, nor can i calculate the impendances.
> "this splitter thing" is a well balanced long tailed pair.
"Balanced"? Seems unlikely. One plate resistor is 15K+15K=30K, the other is 68K||82K=37K, a 24% unbalance.
This type splitter does need a little more gain to the far side of the pair, but often 5%-10%, not 24%. I'd suspect 24% gives a significant unbalance.
Since it does work as pure Pentode with no negative feedback, ouptu impedance is high, speaker damping is low. That will make it sound different on every speaker (and on most speakers, "not as the designer intended").
"Balanced"? Seems unlikely. One plate resistor is 15K+15K=30K, the other is 68K||82K=37K, a 24% unbalance.
This type splitter does need a little more gain to the far side of the pair, but often 5%-10%, not 24%. I'd suspect 24% gives a significant unbalance.
Since it does work as pure Pentode with no negative feedback, ouptu impedance is high, speaker damping is low. That will make it sound different on every speaker (and on most speakers, "not as the designer intended").
The designer is a very respected designer in the Netherlands, his amplifiers are being built in vast numbers by diy enthousiasts. The critics about his amps are usually VERY good.
He himself claims that the phase splitter is very symmetrical, and i know he has a very good set of measuring devices...
Is there a better way to connect the output tubes? Triode? Or even..UL? I have taps, but there is no data available...
He himself claims that the phase splitter is very symmetrical, and i know he has a very good set of measuring devices...
Is there a better way to connect the output tubes? Triode? Or even..UL? I have taps, but there is no data available...
Sorry all, I was absent for a while compliments of server troubles.
Firstly, I will try to post the promised KT88 performance when moving G2 from B+ to anode. I have difficulty in scanning the original graph by GEC in 1957, am also careful of copyright infringement, so I have rather tabulated values for 10% steps of G2 "movement". A graph drawn from this would be illustrative.
KT88 TAPPED SCREEN OPERATION
[P.p. operation: RL(a-a) = 6Kohm]
%G2 tap - Pout(W) - Zout(ohm) - D(%)
Pentode ---47-----------20K------3.0
10---------48.3---------12K------2.3
20---------49.7----------8K------1.8
30----------50----------5.5K-----1.8
40----------50----------4.2K-----1.8
50----------47----------4.0K-----1.8
60----------39----------3.8K-----1.8
70----------35----------3.5K-----1.8
80----------30.5--------3.3K-----1.8
90----------26.8--------3.0K-----1.6
Triode-------25----------2.5K-----1.2
From this it should be clear that at 43 - 50% taps the best of both worlds are available. Also note that the distortion (1.8%) does not stay constant; these are the figures at maximum output for each tap, so that at say 25W, the equivalent distortion decreases continually as the max. output rises. The distortion is t.h.d. and the composition is of course important (not given in this example), but I recall from other analyses that for 43% taps it is already largely 2nd harmonic. I am also told that other power tubes behave more or less similar, so that one can take this as a general indication.
From this I cannot bring myself to using either pentode or triode instead. The Zout rises too sharply for pentodes, while the Pout drops too much for triodes. But I would repeat a previous request that I would like to find other data. (Also, as a further illustration, there are curves shown on other sites - pardon my laziness to quote them here for easy access; rather the middle of the night now - which will show that UL characteristics resemble those for triodes rather more than for pentodes.)
About the Schmitt phase inverter (long-tailed pair): Yes, the anode load resistors do differ quite a lot for balance in low mu triodes. There is a practical formula for calculating these if one wants to be academic, which I will not dare try to quote here. It is far easier to sort matters out by experiment. Classically an ECC82 (6SN7) with a mu of about 18 will need the following values for balance: Cathode (common) resistor = 15K; anode resistors = 56K and 68K (21% difference) with next stage grid resistors of 470K. I used this phase inverter preceeded by a directly connected pentode input stage many times in my younger days (sigh . . . ) I usually included a small pot between the RL's for fine balance adjustment. For rather constant working point definition despite valve spreads one could feed the 1st stage G2 from the common cathode (d.c. feedback), but this requires a rather large G2 decoupling capacitor.
Firstly, I will try to post the promised KT88 performance when moving G2 from B+ to anode. I have difficulty in scanning the original graph by GEC in 1957, am also careful of copyright infringement, so I have rather tabulated values for 10% steps of G2 "movement". A graph drawn from this would be illustrative.
KT88 TAPPED SCREEN OPERATION
[P.p. operation: RL(a-a) = 6Kohm]
%G2 tap - Pout(W) - Zout(ohm) - D(%)
Pentode ---47-----------20K------3.0
10---------48.3---------12K------2.3
20---------49.7----------8K------1.8
30----------50----------5.5K-----1.8
40----------50----------4.2K-----1.8
50----------47----------4.0K-----1.8
60----------39----------3.8K-----1.8
70----------35----------3.5K-----1.8
80----------30.5--------3.3K-----1.8
90----------26.8--------3.0K-----1.6
Triode-------25----------2.5K-----1.2
From this it should be clear that at 43 - 50% taps the best of both worlds are available. Also note that the distortion (1.8%) does not stay constant; these are the figures at maximum output for each tap, so that at say 25W, the equivalent distortion decreases continually as the max. output rises. The distortion is t.h.d. and the composition is of course important (not given in this example), but I recall from other analyses that for 43% taps it is already largely 2nd harmonic. I am also told that other power tubes behave more or less similar, so that one can take this as a general indication.
From this I cannot bring myself to using either pentode or triode instead. The Zout rises too sharply for pentodes, while the Pout drops too much for triodes. But I would repeat a previous request that I would like to find other data. (Also, as a further illustration, there are curves shown on other sites - pardon my laziness to quote them here for easy access; rather the middle of the night now - which will show that UL characteristics resemble those for triodes rather more than for pentodes.)
About the Schmitt phase inverter (long-tailed pair): Yes, the anode load resistors do differ quite a lot for balance in low mu triodes. There is a practical formula for calculating these if one wants to be academic, which I will not dare try to quote here. It is far easier to sort matters out by experiment. Classically an ECC82 (6SN7) with a mu of about 18 will need the following values for balance: Cathode (common) resistor = 15K; anode resistors = 56K and 68K (21% difference) with next stage grid resistors of 470K. I used this phase inverter preceeded by a directly connected pentode input stage many times in my younger days (sigh . . . ) I usually included a small pot between the RL's for fine balance adjustment. For rather constant working point definition despite valve spreads one could feed the 1st stage G2 from the common cathode (d.c. feedback), but this requires a rather large G2 decoupling capacitor.
PRR - your post #39 (the @#$%*&*& cut-and-past will not work now):
No, sure man, you were not in my face.
This business of what is audible is also - well. . . . a business! It might go a little off-thread, and nerves are easily trodden upon in this field, that is why I stay out. As for how I design, mercifully I never had to vow the public with foofies to make things buyable. I have had enough success keeping the basics right, and staying with "a wire with amplification". But more about that later. Thanks for your contribution.
No, sure man, you were not in my face.
This business of what is audible is also - well. . . . a business! It might go a little off-thread, and nerves are easily trodden upon in this field, that is why I stay out. As for how I design, mercifully I never had to vow the public with foofies to make things buyable. I have had enough success keeping the basics right, and staying with "a wire with amplification". But more about that later. Thanks for your contribution.
Yes, sorry man - as said I had a problem here and there to get all nicely even.
Under "%G2 tap" the screen goes from 0, i.e. at B+, i.e. pentode which term I used instead of 0%, in 10% steps to 100%, which is at the anode side, where I just said triode instead of 100%.
Thus, e.g. at a G2 tap at 20% from the B+ side, the output under these conditions of current and supply voltage is 49.7W, the Zout (which is actually the internal resistance referred to the primary) is 8K.ohm, at a t.h.d. figure of 1.8% at the quoted 49.7W. At 60% tap (from B+) the maximum output (same supply voltage) will be 39W, the internal resistance 3.8K and the distortion at 39W is 1.8%.
The original graph has as horizontal axis (screen tapping points) 0 - 100%, which is pentode left and triode right, and then vertical axes for the various scales: Distortion up to 5%, output power from 10 - 60 W (suppressed zero) and Zout 0 - 20%, in a convenient way so that curves do not cross each other. They furthermore give 3 output curves for loads of 5K, 6k and 7K. I chose the normal 6K curve; the others follow the same contours. Maximum output into 5K is 57W at 40% tap, and for 7K = 43W.
Hope this is now clear.
Under "%G2 tap" the screen goes from 0, i.e. at B+, i.e. pentode which term I used instead of 0%, in 10% steps to 100%, which is at the anode side, where I just said triode instead of 100%.
Thus, e.g. at a G2 tap at 20% from the B+ side, the output under these conditions of current and supply voltage is 49.7W, the Zout (which is actually the internal resistance referred to the primary) is 8K.ohm, at a t.h.d. figure of 1.8% at the quoted 49.7W. At 60% tap (from B+) the maximum output (same supply voltage) will be 39W, the internal resistance 3.8K and the distortion at 39W is 1.8%.
The original graph has as horizontal axis (screen tapping points) 0 - 100%, which is pentode left and triode right, and then vertical axes for the various scales: Distortion up to 5%, output power from 10 - 60 W (suppressed zero) and Zout 0 - 20%, in a convenient way so that curves do not cross each other. They furthermore give 3 output curves for loads of 5K, 6k and 7K. I chose the normal 6K curve; the others follow the same contours. Maximum output into 5K is 57W at 40% tap, and for 7K = 43W.
Hope this is now clear.
Johan Potgieter said:
99.5% clear. Zout refers to the tube's internal output impedance looking into the primary and GEC used a specially wound output transformer tapped for all these screen drives. The only thing I wish they'ld done is break the THD figure into individual harmonics. There's that big stretch from 20% to 80% tap where the other parameters change dramatically and THD is locked at 1.8%.
Thx for the clarification.
...i went up from a kathodyne splitter using ecc99 to a long-tail with ccs (was done by a lm317) using 5965
now i have a ccs built with 2xbc547b biased by 2 led's(red)
so the tubes get 5ma each at 150v (similar anode resistors 39k5)
it was so beautiful to see the differences on my scope(kathodyne vs. ccs); even at hard clipping the waveformes stay exactly the same now
it is said bandwidth would now be much better because the lm317 has poor hf specs.
Can one really always draw a straight horizontal line in tube graphs (at the desired ma current) when using a ccs??
if so..
what difference would another type of ccs have (bandwidth?) they all would be almost infinite resistance.
then...why use another type of splitter?? they all have some sort of disadvantage....impedance,voltage swing
is this because of the transistor?? (effectively it should not be in the signal...is it?)
If anyone knows a nice little schematic for tube-ccs (pref. with psu) i'd really like to try!
greets
now i have a ccs built with 2xbc547b biased by 2 led's(red)
so the tubes get 5ma each at 150v (similar anode resistors 39k5)
it was so beautiful to see the differences on my scope(kathodyne vs. ccs); even at hard clipping the waveformes stay exactly the same now
it is said bandwidth would now be much better because the lm317 has poor hf specs.
Can one really always draw a straight horizontal line in tube graphs (at the desired ma current) when using a ccs??
if so..
what difference would another type of ccs have (bandwidth?) they all would be almost infinite resistance.
then...why use another type of splitter?? they all have some sort of disadvantage....impedance,voltage swing
is this because of the transistor?? (effectively it should not be in the signal...is it?)
If anyone knows a nice little schematic for tube-ccs (pref. with psu) i'd really like to try!
greets
Re Rp/RL, previous posts (#35);
This is still on my conscience; I got it from decades back at varsity. It was from a very basic experiment - cannot trace it now. But PRR's advice is sound, so could we just push the Hide button on that one; apology, not intentionally trying to mislead.
CCS in Schmitt phase inverter:
The CCS is in the signal path, and the balance still not strictly perfect impedance wise. The input stage is common cathode with a degenerative cathode impedance in series, the inverter is common grid, cathode driven - higher plate impedance (these are the common objections). But we must get practical; we are dealing with the very limited field of audio. All of this is pretty much academic, with any ill effects way up almost in the RF field. (The same goes for the humble equal Ra-Rc phase splitter.) Tube differences (unfortunately even 2 triodes in the same envelope are not always equal!) are subdued by the degenerative nature of the circuit. The only real disadvantage might be the limited anode swing in cases where maximum is required. A CCS is of course capacity sensitive, but then again it feeds a low impedance cathode drive which swamps that. Oh and of course: one must must keep the cathode-heater voltage in mind (folks would know that it is better to have the heater at a few volts positive wrt an active cathode in case of internal leakage). As said I have never found this phase inverter a problem, even with a cathode resistor instead of the CCS. But in these days of transistors, why not.
I personally would not go for the complexity of a valve CCS, although yes, it SEEMS nicer (a bit of a travesty to put sand devices in a tube circuit. But again let us get with it; this is 2005, and I do not think many still use tube rectifiers.)
Part of being practical must also be consideration of the WHOLE picture. Most of the distortion comes from the power stage; imbalance in an output transformer (and power tubes) probably contributing a whole lot more than a few degrees of phase difference generated by a phase inverter.
. . . . on to the UL data of the KT88. Yes, a break-up of distortion figures would be more informative. But looking at what is available, one would not be far out by taking a (say) 50% tap operation as performing pretty close to triode mode also regarding distortion products. These things do not suddenly jump up and down over the spectrum. At this point the load impedance would have more effect on the final result. Yet again, how I would have liked to have one of those PII audio analysers, but with our exchange rate . . . . I am limited to SPICE, which with the present tube data is not too useful.
This is still on my conscience; I got it from decades back at varsity. It was from a very basic experiment - cannot trace it now. But PRR's advice is sound, so could we just push the Hide button on that one; apology, not intentionally trying to mislead.
CCS in Schmitt phase inverter:
The CCS is in the signal path, and the balance still not strictly perfect impedance wise. The input stage is common cathode with a degenerative cathode impedance in series, the inverter is common grid, cathode driven - higher plate impedance (these are the common objections). But we must get practical; we are dealing with the very limited field of audio. All of this is pretty much academic, with any ill effects way up almost in the RF field. (The same goes for the humble equal Ra-Rc phase splitter.) Tube differences (unfortunately even 2 triodes in the same envelope are not always equal!) are subdued by the degenerative nature of the circuit. The only real disadvantage might be the limited anode swing in cases where maximum is required. A CCS is of course capacity sensitive, but then again it feeds a low impedance cathode drive which swamps that. Oh and of course: one must must keep the cathode-heater voltage in mind (folks would know that it is better to have the heater at a few volts positive wrt an active cathode in case of internal leakage). As said I have never found this phase inverter a problem, even with a cathode resistor instead of the CCS. But in these days of transistors, why not.
I personally would not go for the complexity of a valve CCS, although yes, it SEEMS nicer (a bit of a travesty to put sand devices in a tube circuit. But again let us get with it; this is 2005, and I do not think many still use tube rectifiers.)
Part of being practical must also be consideration of the WHOLE picture. Most of the distortion comes from the power stage; imbalance in an output transformer (and power tubes) probably contributing a whole lot more than a few degrees of phase difference generated by a phase inverter.
. . . . on to the UL data of the KT88. Yes, a break-up of distortion figures would be more informative. But looking at what is available, one would not be far out by taking a (say) 50% tap operation as performing pretty close to triode mode also regarding distortion products. These things do not suddenly jump up and down over the spectrum. At this point the load impedance would have more effect on the final result. Yet again, how I would have liked to have one of those PII audio analysers, but with our exchange rate . . . . I am limited to SPICE, which with the present tube data is not too useful.
OK SY:
In trying to point out that a lot of criticism from purists in audio is not practically relevant, I was perhaps over-academic in saying "though balance was not perfect . . " - as said then, I referred to the above brigade.
Let as have clarity by an example: For a typical ECC88 circuit with 100K-ohm load resistors, the balance amplitude and output impedance-wise would be within 2% for a common cathode resistance of over 170K-ohm; indeed a very achievable value for a current source, especially semi-conductor.
In trying to point out that a lot of criticism from purists in audio is not practically relevant, I was perhaps over-academic in saying "though balance was not perfect . . " - as said then, I referred to the above brigade.
Let as have clarity by an example: For a typical ECC88 circuit with 100K-ohm load resistors, the balance amplitude and output impedance-wise would be within 2% for a common cathode resistance of over 170K-ohm; indeed a very achievable value for a current source, especially semi-conductor.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.