6CB6 Spice Model wanted

[Alain Poitras]

Originally Posted by cogsncogs

Try putting a diode eg. 1N4007 from (anode) grid to (cathode) cathode. Not elegant, but it should run then.

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 ...



Thanks again, another simulator mystery solved.

[Alain Poitras]

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.

[cogsncogs]

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.

[cogsncogs]

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.

[Alain Poitras]

Originally Posted by cogsncogs

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.

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.

[Alain Poitras]

Originally Posted by cogsncogs

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.

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.

[Alain Poitras]

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

[Alain Poitras]

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.

Originally Posted by Alain Poitras

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.

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.

[jazbo8]

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 Poitras]

Originally Posted by jazbo8

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.