GM70 and Other LTSpice Tube Models

[revintage]

Hey Kevin,
I use Stephie´s GM70 model and it seems to work OK. Have you compared the two by simulating the U/I-curves in LTSpice?

[revintage]

R1 is Kevin, R6 is Bench. I haven´t checked against datasheets. Ug 0 to -100V in 10V interval.

[kevinkr]

Hi Lars,
I haven't compared the two, and in fact did not know of SB's GM70 model's existence until you mentioned it.

Interesting that the curves appear so different, and I have no clue as to which is more accurate, but given Stephie's level of experience possibly her's is the more accurate model. I used paint_kit.jar to create my model and got a very good curve match the second attempt. Wondering if this is a reflection of the complexity of the model, a goof on my part or both..

I have noticed a number of differing curves for the GM70 on the web that do not seem to match well. I no longer remember where I got mine, but the predictions from those curves match actual measured performance well. (I can probably locate those curves at some point though)

I have not gotten very far in correlating the actual measured electrical performance of the GM70 in my amp with the spice model predictions, but there didn't seem to be anything that immediately caused concern. The predicted OP seems to match up reasonably well with what I have measured.

[kevinkr]

Hi Lars,
As a reality check Ug across six different GM70 samples at 980V and 120mA ranged from about -75V to -85V, at least 4 of these devices were almost exactly -80V.

Next time I am working on the amplifiers I will take some more careful measurements just to verify/refute/refine these values.

[revintage]

Remove .txt and try the two models. Check curves by clicking R1 resp. R6. Seems like none of them neither the datasheets are like your IRL tests.

Why not make curves from your reality test data and a Spicemodel according to that? Seems like the tubes measure quite consistent.