“Shiny Eyes” PSE with my cherished 4P1L DHP in triode mode

“Shiny Eyes” PSE with my cherished 4P1L  DHP in triode mode


I was working for quite a while (on and off) on my second amp from the series “Shiny Eyes”.

It is a 2 stage single ended amp, using Lundahl ITs and OTs. All tubes are 4P1L and filament biased. Driver biased at 155V/35mA/-8.5V loaded on a LL 1692A Alt”T” (2:3.5) step up. Final stage is a PSE 2x4P1L biased at 245V/35mA/-21V loaded on a LL1664/70mA. All filament biased using Coleman regulators and driver stage using a SSHV (K&K audio clone with Kevin Carter’s approval). Amp gain is about 14dB (1Vrms input leads to 5Vrms on 8ohm output).

It was little challenging to solve the problem of driver’s microphonic behavior. A careful selection of the driver tube, starving filament at 550mA and rubber suspension took care of the above issue.

Sound is amazing and can’t wait to finish my Alpair12P cabinets soon.

Right now the amp cabinet is finished and the amp is assembled. I am working on the power supply that will be enclosed in a separate cabinet. Hope to see it finished by the end of January.

PSU Coming soon…


4 thoughts on ““Shiny Eyes” PSE with my cherished 4P1L DHP in triode mode

  1. Hi Radu,
    It looks really nice! I’m sure it will sound terrific. I found 4P1L into 4P1L a tad too bright in comparison to other drivers, but overall is a fantastic amplifier.
    I think that 560mA of filament bias current was the lowest I used to minimise microphonic noise without impacting the valve performance. You better want to check whether the 4P1L swings full volts without distortion at 550mA. I think it should be ok.

    Keep us posted with your progress on this great project.

  2. Hi Ale,
    Thanks for your comments. I will check the starved filament current. It is starved only for the driver where the swing needed is low no more than 25 Vp-p. But indeed I have to take more measurement. I m trying to figure out how to use Dr.Jordan’s design software now. and I am not done yet with the power supply. Main transformer is mailed to me right now. I’ll post my progress soon. From all the drivers that I had and tried I liked 4P1L the most. And also I wanted an all DHT amp… must be influenced by Andy Evans enthusiastic approach…
    This will be the second amp in the “Shiny Eyes” series. I am also starting to design a third in this series: a headphone amp. And, probably I will be done with 4P1L…..:)

    • Hi,
      Thank you for the kind words.
      I will publish soon a newer version of this amp.. Not many changes, but slightly improve sound, more refined and detail.
      Best regards,

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