Analogue revived !

Greenvalve Luddite 2 10 Amp

Have you ever been sitting at home, listening to your stereo and thought “I wonder if this is as good as it gets?” Well, I have. I guess it doesn’t matter much since the idea of what is best is different to every ear. But that hasn’t stopped me from trying! I will say that this is one of the best sounding amps in existence.

Shown below is the schematic of my finest design. Although choke loaded VT-25 driving VT-25 finals is fantastic, it sounds best using the stunning RCA 210 driving another RCA 210. For those who know, they know this is special. This is my gift to you, the DIY guy with great ears.

I have changed the amp to use filament current bias on the input tube, while allowing a choice of driver tubes. The VT-51 (841) tube is a detail monster. If you are into vinyl the 841 driving the 10 is something you’ve just gotta hear!  An added bonus of using the 841 is slightly higher gain, but because of less current draw the B+ ripple is lower. However, my favorite is the schematic shown… a 10 interstage coupled to another 10.

How can I say that this is the best sounding amp in existence? Well, I can not. I haven’t heard them all yet. But compared to every amp I have heard so far… things look pretty good!

This amp would make a nice front-end for GM70 finals wouldn’t it? 😉

I wish you could hear this amp for yourself. The best I could do is make a few videos of it. They do give a sense of how well the amp images. For your entertainment… Link to Videos of the Luddite 2 10

The photos below show the amp at various stages of its development. It no longer uses the Mundorf SGO caps for coupling, instead using Hammond 126C 10K:10K interstage transformers.

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10 responses

  1. manu (nicoch46 on diyaudio)

    HI great amp with the vt25 as drivers , I see a lot nice stuff in the circuit …

    I’m cooking 10y>10Y>300b es I need some watt…now I have 6em7 as driver.

    best manu

    August 4, 2010 at 1:59 pm

    • Thank you Manu,

      I am using a 25W resistor and filament current to bias the input tube now. It sounds very good likely because it does not require a bypass capacitor.

      August 4, 2010 at 11:12 pm

  2. manu

    HI I use a simple ldr ,fix 27k and ldr to ground ,can I ask the 500k you use between the ldr ?

    is to see a source a smart load ?

    you remouve the cl60 from b+ …is not good for a sort of softstar?

    best manu

    PS I haved send a pm from diyaudio….

    October 26, 2010 at 5:32 am

    • Hi Manu,

      Yes, the shunt LDR will work, but sonics are better with no resistor in series with signal. My 500k shunt resistor is to prevent the input tube from going into grid-leak bias, since the optocouplers will go over 1M resistance when turned off.

      For current limiting… I found that the current limiters (CL60 etc) are not adequate for mercury vapor rectifiers. There is still too big of a current surge at turn on. Right now I am using 10K 5W resistor that allows B+ to slowly rise during a 3-5 minute warmup. There is no flash or arc.

      Best wishes! I will look at your DIYA PM.

      October 26, 2010 at 5:50 am

  3. manu

    HI buzz I see new rev ….do you like better the IT vs parafeed ?

    you change the driver op 225v/20ma vs 180/10ma plus the od3 for the driver…

    December 14, 2010 at 4:41 am

    • Hi Manu, I have played with operation points and the Hammond 126C interstage transformer seems to like 10-12ma the best. I like it better than cap coupled because it has even better soundstage plus more power now that I can let it slide into A2 on peaks. I think the new inexpensive Hammond IT easily beat even the best capacitors.

      December 14, 2010 at 5:03 am

  4. A mercury rectifier! Nice.

    January 5, 2011 at 4:03 am

  5. bigbeluga

    First of all, compliments on the very high quality of the build. Looks fantastic!

    Question – what limits the output of this amp to 1 watt? Keeping it in class A1? It appears that dropping in an 801A would allow a little over 3 watts (@ +30 grid volts), though it would require a preamp capable of swinging 15 volts peak to peak.


    January 31, 2011 at 12:19 am

    • Hi Ryan,

      The original build was a resistance loaded / cap coupled driver that did not allow any grid current. The schematic I am using now will indeed allow A2, and has almost 3W of power. The 801A / 801 would be great! The 801 would let us increase B+ to 600V giving more power and better dynamics. The reason I have not tried it is because the 801A has become very rare and expensive. I purchased my RCA 210 tubes before they were “discovered” and cannot bring myself to buy an ST tube at 4 times the price that the great sounding globe 210 tubes cost.

      Thanks for the note!

      January 31, 2011 at 7:11 am

      • bigbeluga

        Very interesting – makes me think about designing a power supply with an adjustable B+ built around glow tubes. OB3 + 2 x 0A3 + 0D3= 390v, swap out for 4 x 0D3 to get 600v. Keep the Hg rectifier of course. Luddite 210, glow bug edition?

        January 31, 2011 at 11:11 am

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