D3A IT coupled to a 2A3

All the parts have to be put together at some point. Have fun!
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dave slagle
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D3A IT coupled to a 2A3

Post by dave slagle »

This area is a bit sparse and rather than host some images for posting elsewhere, I'll add some comments. The general topic was that "a driver pentode "cannot" be IT loaded to feed an output".

The pics tell the rest of the story and I spent maybe 10 minutes to come up with these results. I'm sure they could be easily be bettered by playing with the d3a operating points or by using a different tube. I should also not that I would never personally build this circuit (due to my distaste for the sound of pentode drivers) and this was more of a simple proof of concept. I will of course encourage anybody out there to play and report back.

dave
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The actual distortion numbers tell the rest of the story.  so maybe the topic of the post should be how to get 5W out of a 5K loaded 2A3 @ 5% THD :-)
The actual distortion numbers tell the rest of the story. so maybe the topic of the post should be how to get 5W out of a 5K loaded 2A3 @ 5% THD :-)
Screen shot 2009-09-10 at 9.04.52 AM.png (47.59 KiB) Viewed 3064 times
The FFT shows what is going on (not that i'm a fan of it mind you)
The FFT shows what is going on (not that i'm a fan of it mind you)
Screen shot 2009-09-10 at 9.06.43 AM.png (30.81 KiB) Viewed 3064 times
output sine.  that translates to 4.85W (remember this is 5K!)
output sine. that translates to 4.85W (remember this is 5K!)
Screen shot 2009-09-10 at 9.08.02 AM.png (29.91 KiB) Viewed 3064 times
This is the circuit.  Note the load on the 2A3 is 5K.
This is the circuit. Note the load on the 2A3 is 5K.
Screen shot 2009-09-10 at 9.11.48 AM.png (39.22 KiB) Viewed 3064 times
First lets look at the frequency response.  I chose reasonable numbers and -1dB @ 20hz for an entire amp doesn't bother me.  The high end is ideal except for the miller of the 2A3.  Call it -1dB at 40K for a good IT-OT combo
First lets look at the frequency response. I chose reasonable numbers and -1dB @ 20hz for an entire amp doesn't bother me. The high end is ideal except for the miller of the 2A3. Call it -1dB at 40K for a good IT-OT combo
Screen shot 2009-09-10 at 9.15.48 AM.png (24.44 KiB) Viewed 3064 times
D3a-2A3.asc
as usual.... i use the bench drop down menu's so you must delete and replace the tubes if you don't have that installed.
(3.43 KiB) Downloaded 175 times
reVintage
Posts: 365
Joined: Fri Sep 07, 2007 9:54 am
Location: Sweden

Post by reVintage »

Hey Dave,
What about parallelling the load with the primary winding? This as I have seen you recommend unloaded secondaries. It works in spice where I tried 150V/150V/20mA/5k.

Must admit I have never tried pentode drivers in hifi. Whats wrong with them in your opinion?. They play great in guitar amps where it ads some kind of magic sparkle to the tone......
Brgds
Lars
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