Hi folks,
I am looking for a "pentode connected" 6CB6 Spice Model, did somebody have one for me ???
I was thinking about using a 6AU6 but this tube is less linear than the 6CB6 and is plate to cathode capacitance is too high, then if the load resistance is high, there is a big treble loss ...
Thanks in advance.
Alain. 😉
I am looking for a "pentode connected" 6CB6 Spice Model, did somebody have one for me ???
I was thinking about using a 6AU6 but this tube is less linear than the 6CB6 and is plate to cathode capacitance is too high, then if the load resistance is high, there is a big treble loss ...
Thanks in advance.
Alain. 😉
Found these lurking on my hard drive: 😉
Code:
*
* Generic pentode model: 6CB6
* Copyright 2003--2006 by Ayumi Nakabayashi, All rights reserved.
* Version 3.01, Generated on Wed Mar 22 17:20:00 2006
.SUBCKT 6CB6 A G2 G1 K
BGG GG 0 V=V(G1,K)+0.7350712
BEP EP 0 V=URAMP(V(A,K))+1e-10
BEG EG 0 V=URAMP(V(G1,K))+1e-10
BEG2 EG2 0 V=URAMP(V(G2,K))+1e-10
BM1 M1 0 V=(0.031445788*(URAMP(V(EG2)-1e-10)+1e-10))^-2.20504
BM2 M2 0 V=(0.40485393*(URAMP(V(GG)+V(EG2)/18.926098)+1e-10))^3.70504
BP P 0 V=0.0046867337*(URAMP(V(GG)+V(EG2)/46.747967)+1e-10)^1.5
BIK IK 0 V=U(V(GG))*V(P)+(1-U(V(GG)))*0.010960467*V(M1)*V(M2)
BIG IG 0 V=0.0023433669*V(EG)^1.5*(V(EG)/(V(EP)+V(EG))*1.2+0.4)
BIK2 IK2 0 V=V(IK,IG)*(1-0.4*(EXP(-V(EP)/V(EG2)*15)-EXP(-15)))
BIG2T IG2T 0 V=V(IK2)*(0.78046782*(1-V(EP)/(V(EP)+10))^1.5+0.21953218)
BIK3 IK3 0 V=V(IK2)*(V(EP)+21225)/(V(EG2)+21225)
BIK4 IK4 0 V=V(IK3)-URAMP(V(IK3)-(0.0024945513*(V(EP)+URAMP(V(EG2,EP)))^1.5))
BIP IP 0 V=URAMP(V(IK4,IG2T)-URAMP(V(IK4,IG2T)-(0.0024945513*V(EP)^1.5)))
BIAK A K I=V(IP)+1e-10*V(A,K)
BIG2 G2 K I=URAMP(V(IK4,IP))
BIGK G1 K I=V(IG)
* CAPS
CGA G1 A 0.02p
CGK G1 K 3.9p
C12 G1 G2 2.6p
CAK A K 1.9p
.ENDS
Code:
*
* Generic triode model: 6CB6T
* Copyright 2003--2006 by Ayumi Nakabayashi, All rights reserved.
* Version 3.01, Generated on Wed Mar 22 17:20:00 2006
.SUBCKT 6CB6T A G K
BGG GG 0 V=V(G,K)+0.7350712
BEP EP 0 V=URAMP(V(A,K))+1e-10
BEG EG 0 V=URAMP(V(G,K))+1e-10
BM1 M1 0 V=(0.031445788*(URAMP(V(EP)-1e-10)+1e-10))^-2.20504
BM2 M2 0 V=(0.40485393*(URAMP(V(GG)+V(EP)/18.926098)+1e-10))^3.70504
BP P 0 V=0.0046867337*(URAMP(V(GG)+V(EP)/46.747967)+1e-10)^1.5
BIK IK 0 V=U(V(GG))*V(P)+(1-U(V(GG)))*0.010960467*V(M1)*V(M2)
BIG IG 0 V=0.0023433669*V(EG)^1.5*(V(EG)/(V(EP)+V(EG))*1.2+0.4)
BIAK A K I=URAMP(V(IK,IG)-URAMP(V(IK,IG)-(0.0024945513*V(EP)^1.5)))+1e-10*V(A,K)
BIGK G K I=V(IG)
* CAPS
CGA G A 2.6p
CGK G K 3.9p
CAK A K 1.9p
.ENDSIf anyone has a 6CB6 PSPICE model I would love to have one. I've tried converting the ones above to use in MicroCap but have been unsuccessful so far...made my head hurt. 
Thanks in advance!
Thanks in advance!
And another one:
Code:
*
* Generic pentode model: 6CB6
* Copyright 2003--2006 by Ayumi Nakabayashi, All rights reserved.
* Thanks to Tooru Kuroda.
* Version 3.01, Generated on Wed Mar 22 17:20:00 2006
.SUBCKT 6CB6 A G2 G1 K
.param GG {(V(G1,K)+0.7350712)}
.param EP {URAMP(V(A,K))}
.param EG {URAMP(V(G1,K))}
.param EG2 {URAMP(V(G2,K))}
.param M1 {((0.031445788*EG2)^-2.20504)}
.param M2 {((0.40485393*URAMP(GG+EG2/18.926098))^3.70504)}
.param P {(0.0046867337*URAMP(GG+EG2/46.747967)^1.5)}
.param IK {(U(GG)*P+(1-U(GG))*0.010960467*M1*M2)}
.param IG {(0.0023433669*EG^1.5*(EG/(EP+EG)*1.2+0.4))}
.param IK2 {((IK-IG)*(1-0.4*(EXP(-EP/(EG2+1e-10)*15)-EXP(-15))))}
.param IG2T {(IK2*(0.78046782*(1-EP/(EP+10))^1.5+0.21953218))}
.param IK3 {(IK2*(EP+21225)/(EG2+21225))}
.param IK4 {(IK3-URAMP(IK3-(0.0024945513*(EP+URAMP(EG2-EP))^1.5)))}
.param IP {URAMP(IK4-IG2T-URAMP(IK4-IG2T-(0.0024945513*EP^1.5)))}
BIAK A K I=IP+1e-10*V(A,K)
BIG2 G2 K I=URAMP(IK4-IP)
BIGK G1 K I=IG
* CAPS
CGA G1 A 0.02p
CGK G1 K 3.9p
C12 G1 G2 2.6p
CAK A K 1.9p
.ENDSThank you very much cogsncogs,If anyone has a 6CB6 PSPICE model I would love to have one. I've tried converting the ones above to use in MicroCap but have been unsuccessful so far...made my head hurt.
Thanks in advance!
I will try them with my SIMetrix simulator right now to see if they work as they are and give some new's about that later. Precises pentode models are hard to find, it is more complicated than a triode because there is also the action of the screen grid.
But I also have problems with some triodes models, they work well in most circuits but not in others, like the cathode follower using the simulator "current source" instead of a resistor, both made with the CurveCaptor program and 8 Koren parameters ... I have to find out why the cathode voltage raise to severals negative kV ...
Alain. 🙂
Try putting a diode eg. 1N4007 from (anode) grid to (cathode) cathode. Not elegant, but it should run then.
I just try the triode connected 6CB6 model and it seem to work very well.
I made those curves with my SIMetrix simulator :
Unfortunatly, I look in many 6CB6 datasheet and I don't find any triode connected curves or data, so I have no way to compare them except measuring a real physical average 6CB6 ...
I quickly made this small preamplifier circuit to test the 6CB6 triode model, of course not the best that can be done. It will be much better with no bypass capacitor and a current limiter or a big inductor instead of the 36K anode circuit resistor.
I will next try the first "pentode connected" model with a similar code and come back with the results. 😉
I made those curves with my SIMetrix simulator :
An externally hosted image should be here but it was not working when we last tested it.
Unfortunatly, I look in many 6CB6 datasheet and I don't find any triode connected curves or data, so I have no way to compare them except measuring a real physical average 6CB6 ...
An externally hosted image should be here but it was not working when we last tested it.
I quickly made this small preamplifier circuit to test the 6CB6 triode model, of course not the best that can be done. It will be much better with no bypass capacitor and a current limiter or a big inductor instead of the 36K anode circuit resistor.
I will next try the first "pentode connected" model with a similar code and come back with the results. 😉
Looks great, just a little glitch in the zero bias curve showing some current with no plate voltage. Some comparison can be made at certain points to the published pentode curves, like along the axis where plate voltages match a screen voltage that curves were provided for. One also has to add the values from both the screen and plate current curves for triode. To get an idea what actually makes a real-world improvement, some non-ideal things added can be helpful, like a source resistance for the generator (a tube preamp might be as high as 100K), input cable capacitance, maybe 100 pf, and some sort of input capacitance for the next stage. The miller effect can make the input capacitance large in triode stages. With those added you'll see the side effect of more high frequency rolloff as you go higher with the plate load impedance. RCA published many circuits with the 6CB6. The 6EW6 is a bit newer and has about 50% higher transconductance. Older lower gm types included the 6AG5 and 6BC5. If you want to try a type to see what large gm changes do to distortion, the 6BA6 is what's called remote-cutoff (as opposed to sharp). Basically the the pitch of the grid wires is non-uniform so that as bias goes negative, a smaller area of the grid allows flow, reducing current and gm. That's used for gain control (by bias) in receivers and works fine for small signals, but introduces considerably more distortion in large signals. I'm a little surprised to see the attention these tubes are getting as triodes with 12AX7s working so well. These really shine as pentodes. The gain of triodes is lower since the plate acts like an input (falling voltage lowers attraction and thus current), but that negative feedback can be reduced by some positive feedback (see input stage of Dynaco ST-35 amp) or by getting rid of the voltage variation (transistor or tube added in series between tube and load - cascode mode. I like to call it the tetrode/pentode mode for triodes, as that makes people think about the tube behavior more). As pentodes the 6CB6 was widely used as a gain stage at about 45 MHz (after a tv tuner down-converts the desired channel to a fixed intermediate frequency a.k.a. I.F. band for filtering and gain) In pentode mode, distortion can be lowered by feedback - unbypassing the cathode is common. However that linearizes cathode current which isn't quite the same as plate current. You can see from the curves that the plate current falls off, sometimes even gets kinks, at lower plate voltages. A closer look shows that much of that error is due to cathode current being robbed by the screen. Feedback in the cathode circuit doesn't normally remove screen grid related nonlinearity. A floating screen supply with the negative return to the cathode instead of ground is one akward way to avoid the screen error. Another is to feed the screen with a current source (set low enough to limit screen power/current to a safe value), and then use a zener or other shunt regulator from the screen back to the cathode NOT GROUND to regulate voltage to the desired value. Then the total of the shunt and screen current in the cathode resistor is just the clean DC from the current source, so it won't affect AC feedback or distortion. Note also, that the current sum is still a constant even if the screen current rises to where voltage regulation is lost and screen voltage decreases. That's sometimes needed in output pentodes for protection (and is neglected in many designs). As can be seen from the datasheet curves, pentode screen current goes way up at very low plate voltages. That happens when an amp is clipping, and notably is a problem with light loads, like when a speaker is at the bass resonance frequency.
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Yes the models curves made with SIMetrix look nice and are very usefull when drawing load lines because the simulated circuit voltages and currents are exactly the same.
When I make a "final" circuit and like to know the exact frequency roll-off with a particular source impedance, I make a special circuit at the input. But for a fast simulation like that, I just put a 50K volume control at the input and verify the frequency at 100% and 50%, the worst position, it is not perfect but give a good idea of what is going on ...
Here is an example involving source impedance and Miller effect :
A member of this forum design this pre-amplifier and use a 10pF at the input ... Of course, everybody tell him it was wrong ... But I simulate is circuit to see "for myself" what was the "exact" effect of this capacitor on high-frequency roll-off with a 50K source output impedance.
An externally hosted image should be here but it was not working when we last tested it.
As you can see, to simulate a 100mV RMS input from a 50K source impedance, I use a 4,34228uA "peak" current source in parallel with a 50K resistor and a DC blocking 100000 farads capacitor ... This give a steady input voltage all over the frequency range, it is impossible to do that with a simple series resistor at the input because it make a voltage divider with the input "capacitive impedance" of the preamplifier ...
The input impedance of the amplifier is "about" 100K, the output impedance of the source is 50K, both in parallel = 33,333K ... To get 100mV RMS at the input at any frequency, since the current source is peak current, 0,1 x 1,4142 / 33333 ohms = 0,000004242 A or 4,4242uA ...
To get exactly 100mV, I have to ajust the current at 4,34228uA because the four parallel triodes also have a input impedance ... This method is very cumbersome, that's why I don't do that very often, it is much simpler and faster to make the simulation with a volume control at 100% and 50% assuming the output source impedance is 0 ohm. 😉
Your trick work very well but as you can see, it is better to put the diode directly across the "ideal current source of the simulator" because this is where the real problem is, not really in the tube ... When I make a current source with a MOSFET, a JFET or a pentode, there is no problems and no diode is needed ...
An externally hosted image should be here but it was not working when we last tested it.
Thanks again, another simulator mystery solved. 😛
Dear cogsncogs,
I am happy to tell you both of your 6CB6 pentode connected models work very well in my SIMetrix simulator, I will keep only the one of your first message because they are same anyway.
Like for the triode connected model, I made a control grid and a screen grid curves graph with the simulator to compare to the datasheet ones, I also made a little preamplifier test circuit for it.
This is the GE datasheet control grid curves graph with screen grid at 125V
The control grid curves graph I made with my simulator and your 6CB6 model. Notice I add the - 3,5V curve, GE "forget" it in their graph, I think it is only a marketing trick to make the pentode look more linear ... The current of your model is about 2 ma over at 0V bias but just a little bit higher at - 4V, I can live with a so little error.
This is the GE datasheet screen grid curves graph
The screen grid curves I made with my simulator, very usefull to design a "screen grid drive" circuit. All those curves are "shifted up" 2ma, it don't make a big difference at 150V but a bigger one at 50V and under a Vak of 100V, the curves slopes are different ( like in the control grid graph ). The important is to know those differences exist and consider them in the circuit design, pentode models are rarely "perfect".
This is the test preamplifier circuit I made for this model, compared to the triode connected one, the "gain" is over 5 times higher but the distorsion is higher too. But the high frequency "roll-off" occur at a much higher frequency. Of course, this is with a very low value resistor in the plate circuit (36K), higher this value is and lower is the frequency where the roll-off occur.
I am very happy to have this 6CB6 in my library because "sharp-cutoff pentode" models are rares, I only have the 6AU6 one before that. Those tubes are very common and cheap on the "used" market, they where used in so many TV and radio receivers. I got plenty of them in my "junk box", testing around 100% with my Jackson 648 tubes tester, so I like to incorporate them on my circuits as much as possible.
Thanks again for your help. 🙂
I am happy to tell you both of your 6CB6 pentode connected models work very well in my SIMetrix simulator, I will keep only the one of your first message because they are same anyway.
Like for the triode connected model, I made a control grid and a screen grid curves graph with the simulator to compare to the datasheet ones, I also made a little preamplifier test circuit for it.
An externally hosted image should be here but it was not working when we last tested it.
This is the GE datasheet control grid curves graph with screen grid at 125V
An externally hosted image should be here but it was not working when we last tested it.
The control grid curves graph I made with my simulator and your 6CB6 model. Notice I add the - 3,5V curve, GE "forget" it in their graph, I think it is only a marketing trick to make the pentode look more linear ... The current of your model is about 2 ma over at 0V bias but just a little bit higher at - 4V, I can live with a so little error.
An externally hosted image should be here but it was not working when we last tested it.
This is the GE datasheet screen grid curves graph
An externally hosted image should be here but it was not working when we last tested it.
The screen grid curves I made with my simulator, very usefull to design a "screen grid drive" circuit. All those curves are "shifted up" 2ma, it don't make a big difference at 150V but a bigger one at 50V and under a Vak of 100V, the curves slopes are different ( like in the control grid graph ). The important is to know those differences exist and consider them in the circuit design, pentode models are rarely "perfect".
An externally hosted image should be here but it was not working when we last tested it.
This is the test preamplifier circuit I made for this model, compared to the triode connected one, the "gain" is over 5 times higher but the distorsion is higher too. But the high frequency "roll-off" occur at a much higher frequency. Of course, this is with a very low value resistor in the plate circuit (36K), higher this value is and lower is the frequency where the roll-off occur.
I am very happy to have this 6CB6 in my library because "sharp-cutoff pentode" models are rares, I only have the 6AU6 one before that. Those tubes are very common and cheap on the "used" market, they where used in so many TV and radio receivers. I got plenty of them in my "junk box", testing around 100% with my Jackson 648 tubes tester, so I like to incorporate them on my circuits as much as possible.
Thanks again for your help. 🙂
Here's the zip of Ayumi Nakabayashi's tube models...
tubemodel_3.01_win
Also do a search for pctube_1.04_win. There are lot of nice models to be found in those zip files! They will run in ltspice, just by changing all the ^ to **. Still working on getting them to run in Micro Cap 6, my simulator of choice. I ran a bunch of his models in ltspice last night and the curves look pretty much dead on, as far as my blind eyes could see. The reason those small signal pentodes models are hard to find is because most (unlearned) 'know' them to be TV tubes, which as we all know are not-good-for-audio, HA! They should try reading the data sheets of their darling audio tubes without skipping over the description at the top of the page. 😛
tubemodel_3.01_win
Also do a search for pctube_1.04_win. There are lot of nice models to be found in those zip files! They will run in ltspice, just by changing all the ^ to **. Still working on getting them to run in Micro Cap 6, my simulator of choice. I ran a bunch of his models in ltspice last night and the curves look pretty much dead on, as far as my blind eyes could see. The reason those small signal pentodes models are hard to find is because most (unlearned) 'know' them to be TV tubes, which as we all know are not-good-for-audio, HA! They should try reading the data sheets of their darling audio tubes without skipping over the description at the top of the page. 😛
I'm thinking about throwing together a UL-PP 6V6 or similar type, using some of those useless TV sharp cutoff pentodes in the front end as I have oodles of them and they are dirt cheap. 🙂
Thank you for the link.
I just download both of them, but I don't have to search for the pctube_1.04_win.zip file very long, the link is on the same page just under the "Other Downloads" green title ... There is a list of the zipped tubes models on the page, this file really contain a lot of them, here is the direct link :
pctube_1.04_win.zip
So you have blind eyes ... Me too, I will have to spend about 400$ for new glasses this month, my chevy '90 don't worth as much but I need the glasses to drive it ... I am ball headed too, nobody is perfect, specially at my age of 56 ...
About my car ... The motor was running very bad at idle since I put a new battery on 3 months ago, it often stall when I put it into gears and this was getting worst every time I use it ... I when to see a old GM mechanic in my village today and he tell me the "throttle body" probably have to be clean ... He remove the air duct from the air filter and clean the inside of those parts with a special "air intake cleaner", also the "idle air flow sensor/solenoïd", both was full of thick dark s..t ... It took him about 30 minutes to do this cleaning job and a motor oil change and charge me only 20$ + the oil and filter cost, now the big 3,1L motor is purring like a brand new one. 😀
Cheers,
Alain. 🙂
I am actually trying to design some good circuits with the "also useless and dirt cheap" 6AS7/6080 and 6S19P regulator power triodes but they need a very high driver output voltage swing with low distortion and this is a real puzzle ... PP and SE cathode follower give very good results with those tubes and a low output impedance.
I am thinking about some kind of "solid-state" servo-bias circuit to reduce the "amplitude distortion" of the "high output swing" tube driver or maybe using a 1000V depletion power MOSFET as driver. 😉
I just notice Ayumi Nakabayashi give many good Tamura output transformers Spice models in is pctube_1.04_win.zip file, almost all the F, F2000, F2020 and F2010 series. This is very interesting because he give all their specifications in the models data, including the "coupling factor" and it is the first time I see this very important specification for commercial transformers ...
See : Tamura Tube Lamp Type Output Transformers
See also : Tamura Audio Transformers
And : Tamura output transformers with Euro price list ...
Many brands : Audio Note, Tango, Hashimoto and Tamura 😉
See : Tamura Tube Lamp Type Output Transformers
See also : Tamura Audio Transformers
And : Tamura output transformers with Euro price list ...
Many brands : Audio Note, Tango, Hashimoto and Tamura 😉
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There was a little mistake in my 6CB6 curves graphic, I wrote on it was for 6AU6 ... Since I can't edit the message, I delete the graphic at ImageShack and upload the corrected one.
The fact is when somebody make an image search with the "6CB6" and "amplifier" keywords, it is one of the first images that show up, so I feel it is important to make this correction. 😉
Noob Questions on SIMetrix
Alain,
Thanks for the links. I am just getting started with SIMetrix, just gone through the user manual quickly, it seems many aspects are similar to LTSpice, but I am not clear on how you get the tube models into the schematic yet, can you do ".inc"? And can you implement drop-down tube selector like in LTSpice? If so, what is the proper procedure to accomplish it? Sorry for the noob questions😱, if they have already been covered before...
Thanks,
Jaz
Alain,
Thanks for the links. I am just getting started with SIMetrix, just gone through the user manual quickly, it seems many aspects are similar to LTSpice, but I am not clear on how you get the tube models into the schematic yet, can you do ".inc"? And can you implement drop-down tube selector like in LTSpice? If so, what is the proper procedure to accomplish it? Sorry for the noob questions😱, if they have already been covered before...
Thanks,
Jaz
Hi Jaz,
I start to write a blog on DiyAudio to help the new SIMetrix users, just to put them on tracks. I will give the tricks I already learn over a one year of steady use, I always discover new things about this simulator, this blog will be time saving for everybody including myself ...
I am very busy, so I can't work on this blog every days, but I expect to be able to explain the most importants things before one or two months.
Alain. 😉
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