56 Tube Spice Model

[hacknet]

Hi Guys,
'm back after nearly two decades of hibernation, I've been planning a 56 driver stage for my 811a and struggled to find any tube models online, so I bit the bullet and made some effort to retrace the steps of Ale and paint_kit.jar.

Here's my model in case anyone is interested, it is based off the Cunningham 56 datasheet's curves. Please share any comments, or how I can make the curve more accurate.

Cheers

.SUBCKT 56 1 2 3 ; Plate Grid Cathode

• PARAMS: CCG=3.2P CGP=3.2P CCP=2.2P RGI=2000
• MU=14.49 KG1=2250 KP=180 KVB=129 VCT=0.0225 EX=1.344

*----------------------------------------------------------------------------------
E1 7 0 VALUE={V(1,3)/KP*LOG(1+EXP(KP*(1/MU+(VCT+V(2,3))/SQRT(KVB+V(1,3)*V(1,3)))))}
RE1 7 0 1G ; TO AVOID FLOATING NODES
G1 1 3 VALUE={(PWR(V(7),EX)+PWRS(V(7),EX))/KG1}
RCP 1 3 1G ; TO AVOID FLOATING NODES
C1 2 3 {CCG} ; CATHODE-GRID
C2 2 1 {CGP} ; GRID=PLATE
C3 1 3 {CCP} ; CATHODE-PLATE
D3 5 3 DX ; POSITIVE GRID CURRENT
R1 2 5 {RGI} ; POSITIVE GRID CURRENT
.MODEL DX D(IS=1N RS=1 CJO=10PF TT=1N)
.ENDS
*$

*Edited to a slightly more accurate model

 

[Bill_P]

Type 76 is electrically the same as a 56 except for heater ratings.

*

• Generic triode model: 76
• Copyright 2003--2008 by Ayumi Nakabayashi, All rights reserved.
• Version 3.10, Generated on Sat Mar 8 22:41:47 2008
• Plate
• | Grid
• | | Cathode
• | | |

.SUBCKT 76 A G K
BGG GG 0 V=V(G,K)+0.99999999
BM1 M1 0 V=(0.021188923*(URAMP(V(A,K))+1e-10))**-0.55369678
BM2 M2 0 V=(0.7303902*(URAMP(V(GG)+URAMP(V(A,K))/12.724092)+1e-10))**2.0536968
BP P 0 V=0.00075511262*(URAMP(V(GG)+URAMP(V(A,K))/17.420951)+1e-10)**1.5
BIK IK 0 V=U(V(GG))*V(P)+(1-U(V(GG)))*0.00043487165*V(M1)*V(M2)
BIG IG 0 V=0.00037755631*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)-(0.00044349824*URAMP(V(A,K))**1.5)))+1e-10*V(A,K)
BIGK G K I=V(IG)
* CAPS
CGA G A 2.8p
CGK G K 3.5p
CAK A K 2.5p
.ENDS

 

[andyjevans]

I have a driver stage where I can use 27, 37, 56 and 76. They are all good, but the 56 has a little special magic. Good choice.

 

[gary s]

I have a driver stage where I can use 27, 37, 56 and 76. They are all good, but the 56 has a little special magic. Good choice.

I would be very interested in your driver stage schematic if you can post it here, thanks.

 

[kb2wyl]

I have a driver stage where I can use 27, 37, 56 and 76. They are all good, but the 56 has a little special magic. Good choice.

2nd, I'd like to see that. It just so happens I have a few of those sitting around (especially the 76s). I was thinking the same, as a driver, for GM70, 845, etc.

Hacknet and Bill, thank you for sharing the models 🙏

 

[andyjevans]

Here you are. I like resistor loads, no sand. Same for the cathode. Bypass is Kemet DC Link, coupling cap is teflon FT-3. I use at least 4x the Rp of the tube for the load resistor. The higher the B+ the better.

 

[gary s]

Thanks for that Andy, can I ask that the circuit is the same for all 4 tube types you mention in post #3 and that the voltages and currents are the same for all tubes - therefore I assume the only difference is the different filament supply voltages? Thanks.

I built your 6AH4 linestage, which is a very similar circuit and I am very impressed with the quality of sound it provides, so I look forward to trying some of these older tubes.

 

[andyjevans]

Yes, same for all 4 of these 5 pin tubes. The 6AH4 is another very good tube, and those who I've built for love it. More versatile for preamps due to its lower Rp. These tubes are only available in the USA in any large numbers, and even then they're getting moe uncommon. Snap them up! The 27 mesh is interesting too. I don't like the RCA much but the Philco is brilliant. Wish I had more of them, I just have one if anyone can help.

 

[hacknet]

This is what i have on the drawing board at the moment, the IRF530 should be a 830, but I don't have the spice model handy.

I've have a variant of this running right now, its a bit different without the neg rails, 6e6p into a Fet source follower driving the 811A.

 

[hacknet]

This is what i have running at the moment.

 

[gary s]

Andy, for these 4 off tubes - do you use DCV or ACV on the filaments ( either 2.5V or 6.3V depending on tube type), thanks?

 

[kevinkr]

It would be great if you posted the models to the spice models thread here. 😀

https://www.diyaudio.com/community/threads/vacuum-tube-spice-models.243950/

 

[andyjevans]

Andy, for these 4 off tubes - do you use DCV or ACV on the filaments ( either 2.5V or 6.3V depending on tube type), thanks?

I use AC. A Hammond 266M5 transformer for the 2.5V.

 

[kevinkr]

You want to look into what George (TubeLab) has to say about IMD with DHT AC heating. I recommend Rod Coleman's (Lyrima) DHT filament regulators from direct experience.

 

[andyjevans]

Completely agree about DHT heating with Coleman regs. But the 56 isn't a DHT, neither are 27, 37 and 76.

 

[kevinkr]

Right, DUH. 🤣 Apparently I have been spending far too much time in solid state land designing discrete amplifiers. LOL

 

[hacknet]

has anyone tried putting more than 1 watt on the plate?

 

[Sorento]

Here's my model in case anyone is interested, it is based off the Cunningham 56 datasheet's curves. Please share any comments, or how I can make the curve more accurate.

@hacknet:
I believe your spice model is way off.
e.g. for 200V / -8V your model gives 12mA plate current, while the data sheet curves indicate 9mA.
Attached is my improved model, also derived from the same data sheet and using Dimitjy's paint_kit.
I am also posting it to the Spice Model Thread where it actually belongs.
https://www.diyaudio.com/community/threads/vacuum-tube-spice-models.243950/post-7788267

 

[hacknet]

I just double checked this specific operating point on my model, with 200v @ -8 Vg, i got 9.6ma. Maybe there's a error somewhere?

 

[hacknet]

I've updated the model slighly to make it more accurate.