Does anyone have a line level common cathode stage using a 12BH7 that you have measured?
I'm doing some Spice sims and I'm getting some odd results. I suspect the models I'm using may not be accurate. So it would help if I can sim a circuit with known measured values. I would need the circuit values and %thd if available.
I'm doing some Spice sims and I'm getting some odd results. I suspect the models I'm using may not be accurate. So it would help if I can sim a circuit with known measured values. I would need the circuit values and %thd if available.
No numbers here, but the triode in 12BH7s and 6GU7s is quite similar to that found in 6SN7s and 6CG7s. FYI, RAM Labs sold 6GU7s as replacements for 6CG7s.
Most of the time, a 6GU7 is a drop in replacement for the 6CG7. Any proven circuit for the 6SN7 ... that tickles your fancy should be just fine.
Just in case you're interested, I'm providing a very linear, non-inverting, modest gain circuit that can drive some extremely difficult loads.
Most of the time, a 6GU7 is a drop in replacement for the 6CG7. Any proven circuit for the 6SN7 ... that tickles your fancy should be just fine.
Just in case you're interested, I'm providing a very linear, non-inverting, modest gain circuit that can drive some extremely difficult loads.
Attachments
So Eli Duttman, i have a question.
The circuit is more 'circuit design' than schematic of an actual circuit from the point of view that the 8 mA current source isn't really specified (tho' they abound, of course); likewise, the MRA–12 Mills resistors seem more like a “found-in-my-parts-bin, and they're really pretty solid, so why-not?” kind of specification. Certainly the precise value of 24.9 kΩ apiece isn't critical; certainly also, the only use of them, in 3 different positions, tickles my suspicions-meter.
Nevertheless, your circuit is sound. Line-level means what, exactly? Is the OP's question essentially “could all y'all help me design a preamp that amplifies modestly-to-unity below-LINE (1.77 VRMS) levels to LINE or higher?” or is his/her question one of taking a relatively high impedance set of sources that are already at line level and sturdy-ing them up?
I guess the answer to both questions is the same.
The preamplifier must not assume that the input is 'at the right level', but rather, needs amplification. And per your diagram, after amplification, the signal also needs significant impedance reduction (current amplification) in order to drive whatever-the-heck is downwind.
In which case, since — except for microphones — most of the idealized sources one commonly runs into range from 0.2 VRMS to over 1.5 VRMS, and because it might be nice to have a 'line stage' that outputs at the hot-end of professional line level signals (i.e. around 6.5 VRMS at peak amplitude), then it needs to have variable gain between maybe 20× down to 0.5x (well, 'zero' with a volume control).
Lastly will the preamplifier be in charge of switching alternate sources, such as tape decks, vinyl disk players, tuners, DVD and digital-to-analog converters, televisions, and the host of consumer equipment out there?
IF SO, then though more complicated, setting up a front end that has individual per-device attenuators is a really, really good idea. Normalizing them to where switching “sources” doesn't produce huge level changes, or ridiculous pops.
Well, I've written too much.
Its Sunday!
⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
⋅-=≡ GoatGuy ✓ ≡=-⋅
The circuit is more 'circuit design' than schematic of an actual circuit from the point of view that the 8 mA current source isn't really specified (tho' they abound, of course); likewise, the MRA–12 Mills resistors seem more like a “found-in-my-parts-bin, and they're really pretty solid, so why-not?” kind of specification. Certainly the precise value of 24.9 kΩ apiece isn't critical; certainly also, the only use of them, in 3 different positions, tickles my suspicions-meter.
Nevertheless, your circuit is sound. Line-level means what, exactly? Is the OP's question essentially “could all y'all help me design a preamp that amplifies modestly-to-unity below-LINE (1.77 VRMS) levels to LINE or higher?” or is his/her question one of taking a relatively high impedance set of sources that are already at line level and sturdy-ing them up?
I guess the answer to both questions is the same.
The preamplifier must not assume that the input is 'at the right level', but rather, needs amplification. And per your diagram, after amplification, the signal also needs significant impedance reduction (current amplification) in order to drive whatever-the-heck is downwind.
In which case, since — except for microphones — most of the idealized sources one commonly runs into range from 0.2 VRMS to over 1.5 VRMS, and because it might be nice to have a 'line stage' that outputs at the hot-end of professional line level signals (i.e. around 6.5 VRMS at peak amplitude), then it needs to have variable gain between maybe 20× down to 0.5x (well, 'zero' with a volume control).
Lastly will the preamplifier be in charge of switching alternate sources, such as tape decks, vinyl disk players, tuners, DVD and digital-to-analog converters, televisions, and the host of consumer equipment out there?
IF SO, then though more complicated, setting up a front end that has individual per-device attenuators is a really, really good idea. Normalizing them to where switching “sources” doesn't produce huge level changes, or ridiculous pops.
Well, I've written too much.
Its Sunday!
⋅-⋅-⋅ Just saying, ⋅-⋅-⋅
⋅-=≡ GoatGuy ✓ ≡=-⋅
Thanks Eli. I've had very good results with 6SN7, both in sims and real life. And 6CG7 sims identical to 6SN7, which is to be expected. But the 12BH7 models I have, the Ayumi and one other, don't seem to give the results I expect, so I thought I would see if I can vet them against some real world data.
Nope. Don't need help designing anything right now.
No again. The meaning of "line level" is irrelevant. It was just stated as being different than, say, operating the tube as a power (output) tube.
The question is as asked. I need data to vet a 12BH7 Spice model, preferably at somewhere around line level. Which can be anything, let's say 0.1Vp to 2Vp at the grid.
Hope you enjoyed your curiosity!
Following - I have two TAD 12BH7A-STR sat ready so it would be interesting to see if any other 12BH7A varies wildly from the model.
Your best bet is to cobble together your own circuit. That way you can do your own measurements in real time and try your changes.
The volts are needed to deal with drops across load resistors and operate the tail CCS.
The setup has no problem driving very low I/P impedance SS power amps. My hunch is that even a "ridiculous" 1 Kohm I/P impedance would be OK.
The signal is taken from the non-inverting triode of a differential gain block and is in phase with the I/P signal.
Gain will be somewhat > 1/4 μ, given the comparative low triode RP. It will take a good deal more than a 2 VRMS I/P to make the circuitry clip.
Which spice models are you using for 12BH7A?
I thought 6GU7 is to 12BH7A as 6EU7 is to 12AX7A, which is to say, pretty much the identical triode except with parallel vs series heaters (6.3V vs 12.6V).
In my journey, I've found 6GU7 (12BH7A) biases up almost exactly like a 6DJ8 at low plate voltages, not like a 6FQ7/6CG7 or 6SN7. I've found 6GU7 sufficiently different from 6FQ7 that I haven't found them to be drop-in replacements in all circuits. Close, though.
I thought 6GU7 is to 12BH7A as 6EU7 is to 12AX7A, which is to say, pretty much the identical triode except with parallel vs series heaters (6.3V vs 12.6V).
In my journey, I've found 6GU7 (12BH7A) biases up almost exactly like a 6DJ8 at low plate voltages, not like a 6FQ7/6CG7 or 6SN7. I've found 6GU7 sufficiently different from 6FQ7 that I haven't found them to be drop-in replacements in all circuits. Close, though.
Perhaps try this 6GU7 model by Wayne Clay?
That came from here:
Vacuum Tube SPICE Models
There's a slightly newer one here:
Vacuum Tube SPICE Models
--
Code:
* ==============================================================
* 6GU7_GE LTSpice model
* Modified Koren model (8 parameters): mean fit error 0.238599mA
* Traced by Wayne Clay on 10/25/2013 using Curve Captor v0.9.1
* from General Electric data sheet
* ==============================================================
.subckt 6GU7_GE P G K
Bp P K I=
+ (0.06701802393m)*uramp(V(P,K)*ln(1.0+(-0.0730722987)+exp((2.148817512)+
+ (2.148817512)*((22.75224837)+(-199.9767109m)*V(G,K))*V(G,K)/sqrt((48.25806774)**2+
+ (V(P,K)-(23.52521336))**2)))/(2.148817512))**(1.259517458)
Cgp G P 3.7p ; 0.7p added
Cgk G K 4.1p ; 0.7p added
Cpk P K 0.64p ; 0.2p added
Rpk P K 1G ; to avoid floating nodes
d3 G K dx1
.model dx1 d(is=1n rs=2k cjo=1pf N=1.5 tt=1n)
.ends 6GU7_GEThat came from here:
Vacuum Tube SPICE Models
There's a slightly newer one here:
Vacuum Tube SPICE Models
--
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