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PP PL36 Amp
PP PL36 Amp
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Old 20th July 2019, 08:10 PM   #1
hop.sing is offline hop.sing  Europe
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Default PP PL36 Amp

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?
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Old 21st July 2019, 01:05 AM   #2
PRR is offline PRR  United States
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What is the idle current in the EL36es?

At 300V and -50V, it would seem to be *very* low.
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Old 21st July 2019, 05:36 AM   #3
Tubes4e4 is offline Tubes4e4  Germany
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Hi PRR

Quote:
Originally Posted by PRR View Post
What is the idle current in the EL36es?
At 300V and -50V, it would seem to be *very* low.
Should be between 45 to 50 mA. µ about 5, gm about 6,7 mA/V, rp about 750 Ohm. Close to max Pd.

Regards, Tom
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Old 21st July 2019, 07:25 AM   #4
hop.sing is offline hop.sing  Europe
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Quote:
Originally Posted by PRR View Post
What is the idle current in the EL36es?

At 300V and -50V, it would seem to be *very* low.
The amp is biased at 50 mA per tube.
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Old 21st July 2019, 11:11 AM   #5
Ketje is offline Ketje  Belgium
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Some (long?) time ago forum member YverM proposed this circuit.
Looks nice, but i don't understand the reason for the curious feedback construction.
Mona
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Old 22nd July 2019, 04:55 AM   #6
v4lve lover is offline v4lve lover  Netherlands
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PP PL36 Amp
Max PD on the E/PL36 series is very conservative. The E235L is electrically and mechanically identical minus the top cap and is 20W, 22W for anode+G2

If for any reason you need triode curves, the E235L datasheet has them.
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Old 22nd July 2019, 11:42 AM   #7
hop.sing is offline hop.sing  Europe
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The Amp sounds notably better, the hotter I bias it. I started with 10W, just to be safe, right now I am at 15W Pd per tube, the maximum from the data sheet. What is the absolute maximum, I could try to approach? Can I really safely bias up to 20W dissipation at 300V B+?
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Old 22nd July 2019, 04:29 PM   #8
Parafeed813 is offline Parafeed813  Netherlands
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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.
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Old 22nd July 2019, 05:15 PM   #9
hop.sing is offline hop.sing  Europe
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Quote:
Originally Posted by Parafeed813 View Post
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.
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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Old 22nd July 2019, 06:16 PM   #10
Parafeed813 is offline Parafeed813  Netherlands
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I only have Phillips so can't compare brands.
Besides, I run them pentode. Close to 440V anode, 150V screen and cathode feedback. Ca 50W output.
Different ballgame
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