Hi I am pretty new to tube power amps, but since I really wanted to know how they can sound, I built one after some research. I like the idea of cheap and plentiful television tubes so I chose the pl36 as the power tube. The heaters are powered by a meanwell 48v smps, RF filtered with an additional choke and a cap.
Tom Schlangen has made the triode curves of the ef184 as well the ones from the el36 available and since the ef184 is cheap as well and seems a good tube for the task of driving the pl36, I use it. I need all the gain possible from the ef184 tube, so the "gyrator" from bartola valves as an anode load seemed a good idea. The 10M45 is the LTP current sink. I use two 1:1 10k pikatron input transformers, they are from some professional studio equipment and high quality, so I figured they won't hurt the signal but give me a balanced input and will help with a balanced signal flow all the way through the amp.
Output transformers are the toroidy 8K ones. They seem high quality, no LF saturation at full power (10W) and bandwidth at least up to 100k with a 3dB resonance up there (That is the limit I can measure) I could put a zobel in, but since there is no feedback involved and things are linear inside the audio band, I think I leave it as it is. Gain in Spice is 14, in reality it is more like 13dB, I guess transformer losses and not perfect tube models might cause that. Distortion on the other hand measures fairly close to what spice simulates. Around 0.1% k3 at one Watt, 1% k3 is approached at around 7 Watt and just before clipping at around 10 Watt I measure 2%. DF is around 6 Since I have pretty inefficient (87dB 1W) 4ohm speakers, I measured everything from the 4 ohm tab into a 4 ohm resistor.
The gain of the amp is just enough for very dynamic music like Arvo Pärt or Mahler with my source, a soekris 1021 da converter with 1,4v rms max voltage swing. I have to evaluate it a little more, but so far I like the sound a lot. Surprisingly a pretty tight bass, even compared to my solid state amp (a cubie3 from Juma, a pass F5 derivate) and beautiful mids and treble. What do you think? Is there an obvious mistake in the schematics? Is there something I could optimize? Would an UL connection of the output tubes be an idea to try? Maybe in combination with some plate to grid feedback on the pl36 for better output impedance? Should be easy to implement with the "gyrator" as the buffer to drive the grids I would have more gain, but better sound?
Tom Schlangen has made the triode curves of the ef184 as well the ones from the el36 available and since the ef184 is cheap as well and seems a good tube for the task of driving the pl36, I use it. I need all the gain possible from the ef184 tube, so the "gyrator" from bartola valves as an anode load seemed a good idea. The 10M45 is the LTP current sink. I use two 1:1 10k pikatron input transformers, they are from some professional studio equipment and high quality, so I figured they won't hurt the signal but give me a balanced input and will help with a balanced signal flow all the way through the amp.
Output transformers are the toroidy 8K ones. They seem high quality, no LF saturation at full power (10W) and bandwidth at least up to 100k with a 3dB resonance up there (That is the limit I can measure) I could put a zobel in, but since there is no feedback involved and things are linear inside the audio band, I think I leave it as it is. Gain in Spice is 14, in reality it is more like 13dB, I guess transformer losses and not perfect tube models might cause that. Distortion on the other hand measures fairly close to what spice simulates. Around 0.1% k3 at one Watt, 1% k3 is approached at around 7 Watt and just before clipping at around 10 Watt I measure 2%. DF is around 6 Since I have pretty inefficient (87dB 1W) 4ohm speakers, I measured everything from the 4 ohm tab into a 4 ohm resistor.
The gain of the amp is just enough for very dynamic music like Arvo Pärt or Mahler with my source, a soekris 1021 da converter with 1,4v rms max voltage swing. I have to evaluate it a little more, but so far I like the sound a lot. Surprisingly a pretty tight bass, even compared to my solid state amp (a cubie3 from Juma, a pass F5 derivate) and beautiful mids and treble. What do you think? Is there an obvious mistake in the schematics? Is there something I could optimize? Would an UL connection of the output tubes be an idea to try? Maybe in combination with some plate to grid feedback on the pl36 for better output impedance? Should be easy to implement with the "gyrator" as the buffer to drive the grids I would have more gain, but better sound?
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The Philips datasheet says 10W anode max and combined with g2 max 13W.
Conservative ratings (sweep duty) so 15W combined should be OK I think.
The ratings of the similar E235L depend a lot on which manufacturer you believe.
Only Telefunken has 20W/22W ratings there.
The way I use the EL36s in my amp is 'if the anodes don't glow, it's fine with me'.
If they wear out, I got some more. If I'm out, I'll rebuild with a different sweep type.
Conservative ratings (sweep duty) so 15W combined should be OK I think.
The ratings of the similar E235L depend a lot on which manufacturer you believe.
Only Telefunken has 20W/22W ratings there.
The way I use the EL36s in my amp is 'if the anodes don't glow, it's fine with me'.
If they wear out, I got some more. If I'm out, I'll rebuild with a different sweep type.
It is probably as simple as that, since NOS PL36s cost around 5€, indicating good supply and low demand, I can simply replace worn out tubes long into the future. Maybe I order a stash of them, since this amp sounds gorgeous with this tube.
By the way, are there differences in sound and/or durability between different makers of the tube?
Right now there are Valvo tubes made by La Radiotechnique in my amp.
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