Guys, cool 
I still recommend to wait for me to test the IPS before you start building, but you can go ahead with OPS - this one is already tested and minor corrections are implemented in both schematic and PCB (see post #61).
Regarding the heat, coming from the tubes - much less than coming from the output section. Just don't put anything right above the tube. Overall dissipation is rather low and mostly goes up.
Cheers,
Valery
I still recommend to wait for me to test the IPS before you start building, but you can go ahead with OPS - this one is already tested and minor corrections are implemented in both schematic and PCB (see post #61).Regarding the heat, coming from the tubes - much less than coming from the output section. Just don't put anything right above the tube. Overall dissipation is rather low and mostly goes up.
Cheers,
Valery
Ah, I see. Well, I believe it's possible. You can put the elements closer to the tubes, no problem - this will save some space.
Starting from this one, I try to keep at least 3" width, for better compatibility with the other designs around.
Let us know if you succeed
Cheers,
Valery
I ordered some OPS boards today. Should have them in about three weeks. I will have some extras so if someone is interested they can give me a PM and we'll work something out. I'm waiting for Valery to proof the IPS before I order those. This looks like a nice project and the fact that Valery has designed it to work with the other Slewmaster projects makes it a slam dunk. Getting excited.
Valery,
I'm a little late responding to your post #35 but I design a lot with tubes and I've found the triode models from Ayumi Nakabayashi to be very accurate. He has created an extensive library but I've included the 12AU7 model here. It has been formatted for LTSpice but should be adaptable to other simulators as well.
Code:
* Generic triode model: 12AU7
* Copyright 2003--2008 by Ayumi Nakabayashi, All rights reserved.
* Version 3.10, Generated on Sat Mar 8 22:41:08 2008
* Plate
* | Grid
* | | Cathode
* | | |
.SUBCKT 12AU7 A G K
BGG GG 0 V=V(G,K)+0.89005722
BM1 M1 0 V=(0.028826571*(URAMP(V(A,K))+1e-10))**-0.90897681
BM2 M2 0 V=(0.622671*(URAMP(V(GG)+URAMP(V(A,K))/13.089625)+1e-10))**2.4089768
BP P 0 V=0.00087237591*(URAMP(V(GG)+URAMP(V(A,K))/21.021735)+1e-10)**1.5
BIK IK 0 V=U(V(GG))*V(P)+(1-U(V(GG)))*0.00055330711*V(M1)*V(M2)
BIG IG 0 V=0.00043618795*URAMP(V(G,K))**1.5*(URAMP(V(G,K))/(URAMP(V(A,K))+URAMP(V(G,K)))*1.2+0.4)
BIAK A K I=URAMP(V(IK,IG)-URAMP(V(IK,IG)-(0.00049917061*URAMP(V(A,K))**1.5)))+1e-10*V(A,K)
BIGK G K I=V(IG)
* CAPS
CGA G A 1.5p
CGK G K 1.6p
CAK A K 0.4p
.ENDS
Code:
* 12AU7 LTspice model from GE 12AU7A datasheet
* Generated by Joel Tunnah using Curve Captor v0.9.1
.subckt 12AU7 P G K
Bp P K I=(0.01701593477m)*uramp(V(P,K)*ln(1.0+(-0.1251806139)+exp((1.234948774)+(1.234948774)*((34.50197863)+(-26.60747394m)*V(G,K))*V(G,K)/sqrt((22.53603268)**2+(V(P,K)-(-4.400778147))**2)))/(1.234948774))**(1.369425091)
Cgp G P 1.5pF
Cgk G K 1.6pF
Cpk P K 0.4pF
.ends 12AU7I hope these are helpful.
I do not sim the tube version. May be next time.
I already dowload tube library from somewhere.
This is library.
Thanks. I'll see if I can make time to sim the tube version and if I can do so successfully I'll post the LTspice file here.
Ah, I see what you mean
12AU7 (ECC82) is one of the tubes, working well at rather low voltages...
The 6DJ8 / ECC88 / 6922 is also a good performing tube at low anode voltages, since it was originally designed for cascode operation. Here is a link to the Sylvania datasheet.
http://www.hifitubes.nl/weblog/wp-content/sylvania-6dj8.pdf
For those that would like to experiment with it, here is a good LTspice model.
Code:
* Generic triode model: ECC88
* Copyright 2003--2008 by Ayumi Nakabayashi, All rights reserved.
* Version 3.10, Generated on Sat Mar 8 22:42:43 2008
* Plate
* | Grid
* | | Cathode
* | | |
.SUBCKT ECC88 A G K
BGG GG 0 V=V(G,K)+0.34001426
BM1 M1 0 V=(0.009343174*(URAMP(V(A,K))+1e-10))**-0.49661195
BM2 M2 0 V=(0.75127268*(URAMP(V(GG)+URAMP(V(A,K))/26.621288)+1e-10))**1.9966119
BP P 0 V=0.007130155*(URAMP(V(GG)+URAMP(V(A,K))/35.434921)+1e-10)**1.5
BIK IK 0 V=U(V(GG))*V(P)+(1-U(V(GG)))*0.0041180199*V(M1)*V(M2)
BIG IG 0 V=0.0035650775*URAMP(V(G,K))**1.5*(URAMP(V(G,K))/(URAMP(V(A,K))+URAMP(V(G,K)))*1.2+0.4)
BIAK A K I=URAMP(V(IK,IG)-URAMP(V(IK,IG)-(0.0038690245*URAMP(V(A,K))**1.5)))+1e-10*V(A,K)
BIGK G K I=V(IG)
* CAPS
CGA G A 1.4p
CGK G K 3.3p
CAK A K 1.8p
.ENDSHi Ray,
Thank you for the models and for raising the point of using different tubes.
In fact, in both >Low TIM Hybrid< and >TubSuMo<, 12AX7 will also work smoothly, without any adjustments. It would be interesting to compare sonic performance between those two (12AU7 vs 12AX7). The second one has got slightly higher gain, however, in these designs with rather high loop gain, the difference will not be really noticeable. Pin-outs are fully compatible.
6DJ8 is a slightly different creature. You are right, it is designed for cascodes (SRPP), so its sections are not the same. They are optimized for common-cathode (pins 6,7,8) and common-grid (pins 1,2,3) cascades, having different inter-electrode capacitances between the sections. It will work in both amps, mentioned above, but for TubSuMo lead compensation cap will need to be decreased ~50% (3.3pF instead of 6.8pF).
However, 6DJ8 will really shine in >"Hybrid Madness"<, particularly having two SRPP cascodes. Those, who'd like to try - don't forget it's got different heater pin-out, and additional "shield" - pin 9, that has to be grounded for better performance.
Cheers,
Valery
Thank you for the models and for raising the point of using different tubes.
In fact, in both >Low TIM Hybrid< and >TubSuMo<, 12AX7 will also work smoothly, without any adjustments. It would be interesting to compare sonic performance between those two (12AU7 vs 12AX7). The second one has got slightly higher gain, however, in these designs with rather high loop gain, the difference will not be really noticeable. Pin-outs are fully compatible.
6DJ8 is a slightly different creature. You are right, it is designed for cascodes (SRPP), so its sections are not the same. They are optimized for common-cathode (pins 6,7,8) and common-grid (pins 1,2,3) cascades, having different inter-electrode capacitances between the sections. It will work in both amps, mentioned above, but for TubSuMo lead compensation cap will need to be decreased ~50% (3.3pF instead of 6.8pF).
However, 6DJ8 will really shine in >"Hybrid Madness"<, particularly having two SRPP cascodes. Those, who'd like to try - don't forget it's got different heater pin-out, and additional "shield" - pin 9, that has to be grounded for better performance.
Cheers,
Valery
In general, the 12AX7 is not interchangeable with the 12AU7 in a Class A circuit without changing resistor values, as the electrical characteristics for the two tubes are very different. I suspect that is also the case here but I haven't really looked at that possibility. I'll model the input stage when I get a minute and let you know what I find.
EDIT: Can anyone tell me what the typical DC supply voltage is on the emitter side of Q2 in the TubSuMo schematic? I'll need this to model the tube input stage.
Last edited:
Hi Ray,
Voltage on emitter of Q2 is roughly 61V DC.
You are right, because of higher gain of 12AX7, I would recommend to increase degeneration resistors' values roughly 5 times, so that R32, R54 will be 220R, R31 pot - 50R.
Terry, for Low TIM Hybrid, you can try it as is - it is more heavily compensated, so excessive gain is going to slightly reduce distortion even further, still maintaining enough stability.
Cheers,
Valery
Yes, comparing almost no-feedback conditions, 12AX7 will give roughly 6db more gain than 12AU7 does (twice as much in terms of RMS voltage). Higher degeneration makes the difference less significant, but still 12AX7's gain will be higher in the same circuit.
Cheers,
Valery