R4 sets the gain and I lowered in the simulation to lower the THD. I will look next at reducing the bias voltage as a first step. I would buy 4 sets but depends on price or should i say how much my wife will let me spend. Many folks covet the newer “mesh plate” variety; but they are as or more costly than new testing or GL balloons! As you can see in the graph above, below 80V the curves are crunching so the steeper load i. I’d say you have to hear a choke input supply into Rod’s Regs to be able to properly judge filament bias.

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It is hard to describe the sound of this amp for those who never listened to a quality single ended tube amplifier. You are a giver, Ale.

4P1L / 4L1S / 4LS1 / RL2 / 4P6 tube – POWER / OUTPUT tubes –

I am looking forward to meeting with you and have some fun listening to great music! This site uses cookies. Learn how your comment data is processed.

Hide full thread outline! For SE amp the stabilizer that is used for V here can be used, for example to get V stabilized, just add Zeners in the string.

Driving transmitting valves is a challenging task. Penotde tube suggetions for B amp – FlyCast Of course it is a bit ironic to consider the ’51A as it has more plate dissipation than the tube it is driving Pete Millet put up some fine measurements of some smaller pentodes wrt output voltage at a distortion pentore, and also connected as triodes However, 3W stereo of single ended tube amp will sound much more powerful than a solid state showing the same power specs.


The circuit goes; AH4-xfmrb. You can post new topics in this forum You can reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You can post attachments in this forum.


This site uses Akismet to reduce spam. I’ve been using a 6AH4. This is serious stuff. Asking more than Vpp to this valve is hard in pentode.

I’m building something with a 4p1l filament bias driver, posted on February 11, at Ale, myself and several others stopped using 26s in favour of the 4P1L, especially as a driver. I can get the odd 30 minute here and there and every time I try to get upstairs to the workshop something pops up. A new idea raised It may be feasible that 4P1L can be used as a cathode follower driver to the A SE amp unlike an idea of A possessing inherent cons such as a minus voltage PSU needed, b too much head room for driving to the sensitive tube of A.

As adjusting the screen voltage and resistance also pentods the gain of the stage you have to compromise some to have the gain match between 2 channels.

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The data they claim is identical to the printed data of the PX25 and the only curves I have ever seen are a direct copy of an original datasheet. Hey Ale, I noticed you found out yourself about loading the pentode as I recommended. Too high an impedance for your IT? This may explain the differences in THD between simulation of the driver and what I measured on the bench.

I will have soon PCBs available for power supply designed for Pyramid amps. The load resistor is 68K. Makes all the difference.

triode SE with 4P1L Pentode – Bartola® Valves

I have efficient speakers pentore will never need this crazy power levels. The LND provides the voltage reference for the gyrator. Many folks covet the newer “mesh plate” variety; but they are as or more costly than new testing or GL balloons! I was intrigued by the performance of this driver in pentode so did a quick modification to provide a screen fixed voltage instead via a source follower and adjusted the bias voltage to minimise distortion. 41pl

It’s an extraordinary little tube. The voice is exceptionally clear, and the grand piano is very realistic — you can hear the keyboard noise, the hammers and the overtones.

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