Great news! Looking forward to your blog's new entries. I spent a good part of the afternoon trying to get a simple log potentiometer to work in SIMetrix, but no luck, hopefully you will show us how it is done.
Jaz
FFT?
Hello All,
Did anyone run a Fast Fourier Transform in the simulation to show the simulated harmonic output of the 6CB6 in the circuit?
DT
Hello All,
Did anyone run a Fast Fourier Transform in the simulation to show the simulated harmonic output of the 6CB6 in the circuit?
DT
Hello All,
Another question. The 6AU6 is a similar triode and is often mentioned in the same breath as the 6CB6. The 6AU6 data sheets show data for triode connection with both the screen and suppressor connected to the plate. How does this 6CB6 tube model have the 6CB6 triode connected?
DT
Another question. The 6AU6 is a similar triode and is often mentioned in the same breath as the 6CB6. The 6AU6 data sheets show data for triode connection with both the screen and suppressor connected to the plate. How does this 6CB6 tube model have the 6CB6 triode connected?
DT
I alway run a Fourier analysis on my circuits to measure the total harmonic distortion on a 1000 cycles period at any frequency for a good evaluation and I start the analysis after one second simulation to give the circuit time to stabilise itself.
Of course, the analysis don't measure the intermodulation distortion that can be twice higher. The results also depend on the operation point of the tube (or transistor) and the associated parts arround.
To do it, you have to chose the "Transient Analysis" in the "Simulator" menu bar, at 1Khz for example, "Start data output" at 1 second and the "Stop time" at 2 seconds because 1 cycle last 1mS. For 20Hz, set "Stop time" at 51 seconds because 1 cycle last 50mS and for 20Khz at 1,05 seconds because 1 cycle last 50uS. But at 20Khz, the simulation take a much longer time to be completed than at lower frequency ...
After you choose the analysis, you run the simulator. In the curves graphic window, you can select many usefull measurements in the "Measure" menu bar, like the RMS voltage, the minimum and maximum swing, the mean voltage, frequency, etc. But if you click on the "A More Functions ..." item, many other appear, like "peak to peak", "total noise" and also the distortion ...
The 6CB6 triode connected is not the best triode but is not bad, it is like many average linearity triode. The 6CB6 is a very cheap tube you can get for 1$ each on eBay when you buy a lot, perfect for inexpensive small projects, and many DIYers got many of them in their junkbox because they was widely used in TV and radio set.
The 6CB6 is connected the same way as the 6AU6 to emulate a triode, when the suppressor grid is not connected to the cathode internally, it is the usually done like that for the "sharp-cutoff pentodes". For the power pentode, it is another story.
I will probably update my Simetrix Simulator blog soon, but my DIY projects keep me very busy, I actually study a "Futterman amplifier circuit" because it is one of the best way to get a good bass response with a small low cost output transformer ... I will try to use a 6$ "speaker matching transformer" to get a 500 ohms load.
Cheers 😉
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Is this schematic the current "state of the art"? I am trying to follow your lead in making a 6CB6 preamp.
Thanks in advance.
Thanks in advance.
status?
Well, a couple of years have gone by . . . and I've re-discovered and want to build the preamp. Is there any way that I can coax Mr. Poitras to update the discussion?
Thanks in advance.
Well, a couple of years have gone by . . . and I've re-discovered and want to build the preamp. Is there any way that I can coax Mr. Poitras to update the discussion?
Thanks in advance.
Hi briansdad,
I was looking for a 6CB6 spice model just to make some one stage preamplifier section spice simulations with this tube triode connected, not to build a complete preamp ... I try to find as much sharp-cutoff triode connected pentodes for my SiMetrix tubes library because they are very rares, most triode connected pentode models I have are for power pentode or beam power tube, not suitable for preamp.
Also, when I show a simulation schematic on this forum, it is only theoretical and not tested in real life, so if somebody use it to build an amplifier, it is at is own risk ... So it is important to make experimental prototypes on "bread board" of the circuits found on Internet before spending money to build a final version.
Most triode connected pentode models I have in my library have their grid #3 tie to the cathode but in most sharp-cutoff pentodes datasheet, the grid #2, grid #3 and internal shield, are connected to the plate when triode connected. This probably make a difference between models and real tubes.
To build a complete preamp, it depend on your particular needs : A tone control ? A balance control ? A source selector ? A magnetic phono input with RIAA equalization ? What is the minimum gain you need (Vout/Vin) ? What must be the input impedance ? What is the maximum input signal for the desired output level ? What is the input impedance of the power amplifier ? ... If the input impedance of the power amplifier is low, then you need a cathode follower stage at the end of your preamplifier or you will have a lot of distortion and maybe no bass (if the output coupling capacitor is too small) ...
Design and build a complete preamplifier can be difficult to do, also notice some small pentodes like 6AU6 are "microphonics" and this can give unwanted results. There is also the question of the heaters supply, DC is better than AC but more complicated. the power supply have to be very well filtered and the circuit properly wired for preamp or the hum will be amplified ... Tube rectifiers are better than silicon diodes but if you use "high speed" diodes, the results will be good.
A triode connected pentode like a 6CB6 or 6AU6 will not have a very high gain like a high-mu 12AX7 or a 12AT7 for example but more like a medium-mu triode like a 12AU7, a 12AY7 or a 6DJ8 so they are not really suitable for a magnetic phono preamp with a very small input signal ...
I will not actually build any preamplifier or amplifier because I don't have time for that, that's also why I don't visit this forum very often, I am very busy doing other things than DIY. But I often make small circuits spice simulation just for fun because it don't take long and it cost nothing. 😉
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