I have no experience with tube. I want to use ECC88 for LTP (in hybrid amplifier). I use +-77VDC power supply (PSU). I read that ECC88 can operate at low voltage. With that PSU can I use 5,7mA anode/plate current? How much maximum anode/plate current using that PSU?
In simulation I can not achieve high slew rate (only around 58V/uS), but THD is very low.
In simulation I can not achieve high slew rate (only around 58V/uS), but THD is very low.
ECC88 can run at relatively low plate-to-cathode voltage compared to most other tubes, but +77V isn't enough to work with from B+ to cathode.
Forgive me if you already know this, but your plate load should typically be at minimum 3X in resistance (or impedance) than the internal impedance of the triode. At low plate currents like 3mA for an ECC88, the rp will be about 4k or 5k ohms. That means you want at least a 15k ohm plate load resistor for each ECC88 triode.
15k ohms * 3mA = 45V, which only leaves +22V plate-cathode across the tube. That won't work.
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Forgive me if you already know this, but your plate load should typically be at minimum 3X in resistance (or impedance) than the internal impedance of the triode. At low plate currents like 3mA for an ECC88, the rp will be about 4k or 5k ohms. That means you want at least a 15k ohm plate load resistor for each ECC88 triode.
15k ohms * 3mA = 45V, which only leaves +22V plate-cathode across the tube. That won't work.
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Your simulation/circuit would be useful to see.
What signal level is needed and what is the load impedance ?
What signal level is needed and what is the load impedance ?
Indeed! How much swing (Vrms) do you need from this stage? Active loads (ccs or gyrator) come to mind.
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.MODEL BC550_Cordell npn IS=45f BF=689 VAF=162 IKF=0.09 ISE=4600f NE=2 NF=0.9965 RB=167 RC=1 RE=0.04 CJE=18.7p MJE=0.35 VJE=0.75 CJC=6.2p MJC=0.25 VJC=0.4 FC=0.5 TF=595p XTF=10 VTF=10 ITF=1 TR=10n BR=12.2 IKR=0.34 EG=1.2 XTB=1.65 XTI=3 NC=0.996 NR=1.0 VAR=120 IRB=7e-5 RBM=1.1 XCJC=0.6 ISC=5f mfg=CA030111
.MODEL 2SA1381_Cordell pnp IS=50f BF=160 VAF=328 IKF=0.5 ISE=10f NE=1.5 NF=1 RB=17 RC=4.1 RE=0.05 CJE=71p MJE=0.35 VJE=0.75 CJC=8p MJC=0.35 VJC=0.55 FC=0.5 TF=900p XTF=10000 VTF=35 ITF=20 TR=1n BR=1.6 IKR=0.09 EG=0.6 XTB=0.9 XTI=3 NC=2 ISC=3.2e-10 VAR=100 mfg=CA031111
.MODEL 2SC3503_Cordell npn IS=40f BF=170 VAF=769 IKF=0.08 ISE=200f NE=1.5 NF=1.0 RB=75 RC=1.5 RE=0.1 CJE=95p MJE=0.35 VJE=0.75 CJC=7p MJC=0.35 VJC=0.75 FC=0.5 TF=585p XTF=10000 VTF=35 ITF=20 TR=10n BR=0.6 IKR=0.05 EG=0.75 XTB=1.5 XTI=3 NC=1.5 ISC=7f NR=1.0 VAR=100 IRB=3e-6 RBM=0.035 .0 mfg=CA031111
.MODEL MJE340C npn IS=800e-15 BF=180 VAF=100 IKF=0.35 ISE=25e-12 NE=1.5 RB=21 RC=2 RE=0.01 CJE=170e-12 CJC=140e-12 TF=7600e-12 XTF=10 VTF=10 ITF=1 TR=10000e-12 BR=0.004 IKR=0.05 EG=0.64 NC=2 ISC=1.5e-10 VAR=100 mfg=CA030711
.MODEL MJE350C pnp IS=110e-15 BF=118 VAF=100 IKF=0.06 ISE=1.7e-12 NE=1.5 RB=9 RC=1 RE=0.01 CJE=200e-12 MJE=0.35 VJE=0.75 CJC=120e-12 MJC=0.35 VJC=0.55 FC=0.5 TF=4500e-12 BR=0.04 IKR=0.0075 EG=0.75 XTB=1.1 XTI=3 NC=2.0 ISC=5e-12 VAR=100 mfg=CA030711
.MODEL 2N5401_Cordell pnp IS=25f BF=220 VAF=196 IKF=0.2 ISE=2f NE=1.4 NF=1 RB=60 RC=2 RE=0.1 CJE=35p MJE=0.40 VJE=0.75 CJC=15p MJC=0.55 VJC=0.75 FC=0.5 TF=800p XTF=60 VTF=0 ITF=4 TR=1.5n BR=4 IKR=0 EG=1.1 XTB=1.5 XTI=3 NC=2 ISC=0 mfg=CA031011
.MODEL 2N5551_Cordell npn IS=9f BF=125 VAF=667 IKF=0.09 ISE=1f NE=1.3 NF=1 RB=92 RC=1 RE=0.1 CJE=45p MJE=0.35 VJE=0.75 CJC=4.9p MJC=0.30 VJC=0.75 FC=0.5 TF=565p XTF=300 VTF=5 ITF=2.0 TR=1.2n BR=3 IKR=0 EG=1.1 XTB=1.5 XTI=3 NC=2 ISC=0 mfg=CA031011
.MODEL KSA992 pnp ( IS=5.7544E-14 BF=348.1 NF=1 BR=3.62 NR=0.95 ISE=5.7544f NE=1.5 ISC=1.8378E-14 NC=1 VAF=144 VAR=16.68 IKF=0.298 IKR=0.0525 RB=140 RBM=16.084 IRB=1.4125m RE=0.38 RC=0.47 CJE=2.3093E-11 VJE=0.855 MJE=0.4104 FC=0.5 CJC=8.9251p VJC=0.5 MJC=0.3497 XTB=1.2849 EG=1.1603 XTI=3 XCJC=0.3062 )
.MODEL 2SC5200_k npn IS=300f BF=100 NF=1 BR=8.025 NR=1 ISE=200p IKF=18 NE=2.0 ISC=2.01764E-10 NC=1.5 VAF=400 VAR=100 IKR=1.39087 RB=1.1 RBM=0.00011 IRB=1.51189E-6 RE=0.0032 RC=0.0183 CJE=6.1n VJE=0.711 MJE=0.304 FC=0.5 CJC=380p VJC=0.84 MJC=0.25 TF=5n TR=3.342E-7 XTB=1.72 EG=0.78 XTI=3
.MODEL 2SA1943_k pnp IS=650f BF=100 NF=1 BR=8.805 NR=1 ISE=10p IKF=15 NE=2.0 ISC=2.01764E-10 NC=1.5 VAF=600 VAR=100 IKR=1.39087 RB=1.1 RBM=0.00011 IRB=1.51189n RE=0.0061 RC=0.0103 CJE=5.26n VJE=0.711 MJE=0.304 FC=0.5 CJC=750p VJC=0.84 MJC=0.25 TF=5n TR=3.342E-7 XTB=2.28 EG=0.81 XTI=3
.MODEL BD139_Cordell npn IS=150f BF=260 VAF=99 IKF=1.2 ISE=70f NE=1.2 NF=1.0 RB=5 RC=0.01 RE=0.08 CJE=293p MJE=0.33 VJE=0.67 CJC=49p MJC=0.39 VJC=0.52 FC=0.5 TF=585p XTF=10000 VTF=35 ITF=20 TR=10n BR=78 IKR=0.14 EG=1.21 XTB=1.14 XTI=3 NC=1.45 ISC=19p NR=1.0 VAR=7.5 IRB=0.03 RBM=0.001 XCJC=0.53 mfg=CA041311
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With present 5,7 mA anode current the Ug-k = 1,56 V, which is fully OK.
You could go a bit lower, say to 1,2 V, which represent 8...9 mA anode current, but there is no reason to go to that high current.
There is huge GNFB used in your design, so I can't analyze if the tube is in optimum operating condition, but the present anode current / grid voltage are in right values.
The frequency response (-1 dB) of your amplifier is about 200 kHz.
I can't say anything about the sufficiency of the slew rate, but the frequency response is OK for audio purposes.
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Yes, typical Blameless with TMC compensation have high open loop gain. I have design 2 amplifier with this topology using BJT. It sound good. A friend compare my amp with Symasym. Low frequency symasym better, but mid and high my amp better. I like to design amplifier with high slew rate and I push it as high as possible until I can not hear the difference, of course it should stable (enough phase margin and gain margin).
Now, I want to try use tube. I want to now how it sound.
imho, transconductance is a precious commodity with tubes, and unlike transistors you just don't give them away easy...
so why parallel the sections and then degrade transconductance?
so why parallel the sections and then degrade transconductance?
ECC88 LTP can be made so low THD, that there is absolutely no reason to have it inside NFB loop.
Just to show an example, I tinkered with Spice a bit. This is the LTP topology I like to use.
Schem1 is using +-77V supplies and CCS tail from original schematic. Plate loads are different.
Output is 12 VPP, taken from sources of the plate loads. Looking at the FFT, the distortion is not horrible even at that low plate voltage.
Schem2 has a B+ more suited to tubes, B- can be -15 V or more. In schematic it's -25 V. I also used the tail I like to use.
With the same output, distortion is much lower as can be seen from the FFT. For comparisons sake I used the same scale; there are harmonics but they are just below the view using the same scale. In practise, the harmonics are so low they cannot be heard in my opinion.
Schem1 is using +-77V supplies and CCS tail from original schematic. Plate loads are different.
Output is 12 VPP, taken from sources of the plate loads. Looking at the FFT, the distortion is not horrible even at that low plate voltage.
Schem2 has a B+ more suited to tubes, B- can be -15 V or more. In schematic it's -25 V. I also used the tail I like to use.
With the same output, distortion is much lower as can be seen from the FFT. For comparisons sake I used the same scale; there are harmonics but they are just below the view using the same scale. In practise, the harmonics are so low they cannot be heard in my opinion.
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