a C3g driver…

Sunday morning and my brain already started with a lot of activity early today. Should be the other way round. I spent all week working and weekends should be about relaxation, but can’t help it 🙂 Before going up to the workshop and continue with the 4-65a SE amplifier build, I put into work some of these ideas that are flying around.

The 46 filament bias driver with its hefty supply will be “the driver” for the 4-65a, yes, no doubt. I may want to try some other combinations such as 4P1L pentode in filament bias, or why not some other drivers as 6e5p, C3g and D3a. All these are brilliant candidates. But final judge should be my ears. We all know that what looks really good in paper not necessarily translates into a great sounding driver, but at least is the best start.

C3g driver with gyratorC3g (as well as D3a) a really linear and revered valves in triode mode. Huge gain, current capability and transconductance. Perfectly engineered valves. C3g can easily provide a great performance as a driver with a gyrator load. I found playing around that with a simple LED bias, a bias of -2V, 190V and 30mA provides an outstanding 0.15% @ 200Vpp at least on the simulations..

I may try this in my 4P1L/6C4C project as well…. (so much to do)




Hi Ale,
A few observations.
190V with 31mA provide dissipation of 5.9 W !! It is excessive.
Use Telefunken data. Pa max is 3,5W.
Also, look data : “G2 and G3 connected to A

Just as a long-time user C3g as driver :-)


You’re right, interesting oversight which reflects that I shouldn’t be doing this early on a Sunday morning! Looking at the datasheet, we could get out 4.9W maximum if using Pa=3.5W + Pg2=0.7W + Pg3=0.7W. Well, a bit too much, perhaps safer running it below 4.5W.

So let’s see how it performs if we dial down the anode current. I ended up changing the LED to minimise distortion:
C3g driver gyrator load

The THD is 0.26%@ 200Vpp which is similar to my two stage 4P1L-46. I wonder how much distortion the 4P1L will give at 200Vpp?



16 Replies to “a C3g driver…”

  1. Hi Ale,
    A few observations.
    190V with 31mA provide dissipation of 5.9 W !! It is excessive.
    Use Telefunken data. Pa max is 3,5W.
    Also, look data : “G2 and G3 connected to A “.

    Just as a long-time user C3g as driver 🙂


    1. Ops completely overlooked the Pa of this one. Got dragged into improving the THD response.
      Will correct and simulate again. Thanks for spotting it out!

        1. Absolute maximum allowed.
          I was never so forcefully pushed my C3g. Maximum of 3 watts total in pentode mode now.

          In triode mode, if I remember good, practical test was 180V/13 mA with 2xDN2540 CCS on anode and RC in cathode. But that was years ago.

  2. I,ve done the same thing with triode strapped pentodes, many of them seem to perform best over their diss limits. have you tried the russian 6j9p, not the 6j9p-e. i’ve had some breath taking figures from those, at and especially well above their limits, actually very similar biases to your C3g. these triode strapped pentodes i think are best biased insitue as i find they need very precise biasing unlike the triodes i’ve tested. 6e5p is still my best driver valve tested, everytyhing considered.

  3. Enzo, Have you tried 4P1L? Best one ever so far. 6e5P is my second favourite. Haven’t done any extensive testing on the 6J9p but also was keen to try the 6z52p (close D3a)

  4. Hi Ale,
    C3’s are indeed excellent engineered valves. I don’t have the equipment to test tubes yet, but I tried a C3m sound. I used it to drive 2xKT77 on UBT_1 One Electron. In triode mode the sound is amazing. It is a bit pricey an I wish to find a russian valve equivalent…

    1. C3’s are expensive indeed. I like some of the Russian such as 6J9P, 6e5P, 6Z52P, etc…
      They all measure really well and cost nothing compared to the German ones. Still need to further do some listening tests…

  5. Dear Ale,
    I love the way you present all these tests on your wonderfull blog. I have been through the same route of THD testing “sleeper” valves some years ago and definitely D3a and C3 are superb performers but a bit expensive nowdays (thank god I bought some dozens in the 90s)! However, some Russian sleepers are great too as you noticed, I personally love 6E6p-d but the most amzing of all is 6J11p which is kind of similar to D3a but in my opinion even better sounding, my second best is 6J9p or 6j49p. Check these out as they are still very cheap and worthy!

    Congratulations on your blog!
    I really envy your diy valve tester!!!

    1. Hey Panos,
      Thanks for the message! I tried 6e6p-d as well. Really nice. I have some 6j9 and 6j49p, but no 6j11p. need to buy some I guess…

      The tester has been a pain in the neck, I invested a lot of time last year (probably 6 months) on it to get it working….


  6. Hi Ale!
    I’m building a amp using C3g/triode with gyrator load to drive a 845! (Ok I know the potential troubles, but it sims very well…)
    16mA/200V will be the starting operating polnt (approx 3,2V grid bias through lithium battery)
    I have a couple of questions:
    -Regarding the “Rmul” resistor, it obviusly biases the DN2540 ,about 7V (=31,6*0,220) in your top schematic… What value would you recommend for my amp as a starting point (16mA)? I used 1k once in a 12b4a preamp, it worked but I have no idea what a different value might do..
    -The 1uF capacitor “C3”, have you tried different types, any sonic impacts, what type would you recommend?
    Thanks for a great site and many hours of nice reading!

    1. Hi Niklas,
      Rmu should be around 1/gm approximately. It will change the bias point but ultimately the FET (and anode) operating point is given by the voltage set at the gate provided by the CCS and the resistor to ground.

      Try the value in the diagram as simulated quite well!

      C1 should be the best quality cap you want (can afford) as it’s somehow in the signal path. Try film, russian PIO, etc. I got very good results but couldn’t notice a big difference as the capacitor is shunting the signal, not coupling it.

      Keep us posted on your progress

      1. Hi again Ale!
        I got the amp playing some music yesterday, sounded great until I blew the gyrator mosfets…
        Some background: I’m trying to help a friend with getting some music rather than noise out of his “Music Angel 845 mk III” This is an amp “designed” so much wrong that I dont really know where to begin explain it… I did away with the entire input/driver section, figuring I would replace it with C3g/gyrator load/3.2V lithium battery grid bias. As the psu (dual mono) is made with a voltage doubler to about 850V they took the driver voltage by means of a large R R/C coupling, with severely undersized resistors. I did the same by 4x 27k 10w resistors per ch, series-parallelled to get 27k/40W but with an addition of a 4x100V zener string in parallell with the 120uF/450V driver psu caps.
        But as tubes vary the actual gyrator drain voltage was about 390-430V. Somehow this got the better of the DN2540’s although the drain/source voltage should have been in the ~200V region assuming the C3g’s were “online”. Probably they were not, all the time…
        Now I’ll try making a makeshift shunt regulator (again with DN2540’s and 100V zeners as thats about all SS I’ve got in the junkbox) to be able to set the “driver b+” in the 360V region.
        2 octal places but no available psu windings left for a tube regulator
        Wish me some luck, I’ll be running low on DN2540’s if it blows again. 😉

          1. Well, I could not get this to work with the DN2540’s so I decided to order some 01n100d’s. I soldered in a ordinary rc loading (20.2k load res.-0.44uF pio coupling cap) for the C3g so my friend can use the amp while we wait for high voltage mosfets. While i did no thd or power measurements, this dirt simple C3g-RC-845 amp plays really nice, Loud too…;-) much better than I ever would have thought possible considering the amps origin, comparable to some of my best 2a3 amps actually. Not much low bass though, the opt’s are probably not top notch…
            I’ll post an update when we get the gyrator working. Perhaps with measurements. 😉

Comments are closed.