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| Canon P + Canon 50mm f1.8 LTM Foma 100 in Rodinal |
Inspired by my plate choke-loaded 76 line stage preamp adventures, I was curious how a similar driver circuit configuration would sound in an SE2A3 amp. So I pulled out my Radiotron Designer's Handbook, 3rd Edition to gain a better understanding of choke-capacitance coupling (aka plate choke loading) vis-à-vis resistance coupling.
Below are highlights of relevant information I gathered.
!!!WARNING!!!
The voltages in this project are potentially lethal! Proceed at your own risk!
After testing and listening to various medium-mu/medium-gm triodes and their triode connected pentode equivalents with plate resistances between 7700 ohms to 10,000 ohms, I arrived at the above circuit. The 1K, 1W cathode + 6.8K, 2W dropping resistors are starting point values. These resistors can be adjusted to achieve a desired plate current. But don't exceed the 8 mA maximum rating of the Hammond 156C because it will look ugly on the scope and sound bad.
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| 100 Hz, 1 kHz and 10 kHz square wave output (bottom traces) from Hammond 156C plate choke loaded 2C22/7193 triode > 2A3 > Edcor GXSE15-3.5K |
If you appreciate the improved definition and extension at the frequency extremes but find the midrange less organic compared to classic resistance coupling, then follow me to the world of higher permeability plate chokes and output transformers.
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| JE Labs mono CCC SE2A3 amp - James JS 4120N nickel plate choke loaded 2C22/7193 triode + Hashimoto H203S output transformer |
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| 100 Hz, 1 kHz and 10 kHz square wave output (bottom traces) from a James JS 4120N nickel plate choke loaded 2C22/7193 triode > 2A3 > C-Core Hashimoto H203S |
Miles Davis & Co. improvising via the mono CCC (James JS4120N) SE2A3 amp + Altec mini 757.
I commissioned a pair of Intact Audio nickel plate chokes with similar specs to the JS4120N from Dave Slagle to use with triode connected 6C6 tubes, driving 2A3s coupled to Tamura F7002 permalloy output transformers.
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| 100 Hz, 1 kHz and 10 kHz square wave output (bottom traces) from an Intact Audio plate choke loaded triode wired 6C6 > 2A3 > Tamura F7002 |
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| JE Labs Stereo CCC SE2A3 - Intact Audio nickel plate choke loaded 6C6s (triode connected) + Tamura F7002 permalloy output transformers |
The unveiling!
If you've visited my YouTube channel, you've probably seen this video since it's gotten the most hits.😉 Yes, the CCC SE2A3 amp in the preceding picture is playing Donald Byrd!
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| Intact Audio nickel plate choke loaded 6A6s + 2A3s + Tamura F7002 permalloys! |
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| Radiotron SE2A3 amp + Finemet FM6WS OPTs |
Truth be told, in the past couple of years I've had a couple of visitors in the man cave who felt torn between the Choke-Capacitance Coupled and the Radiotron SE2A3. Ultimately, the Radiotron's vocal presentation was favored over the wider bandwidth CCC version. IMHO, that's a manifestation that there's no such thing as the best in this hobby. Now I can justify why I maintain and experiment with many different SE amps!😆
I wonder what J-Rob would think of a CCC driven 2A3 amp since this topology wasn't included in his Sound Practices Issue 15 article, "I've never met a 2A3 amp that I didn't like."? 😉
Man, you've been busy!! This looks interesting though, no matter Joe says! :-D
ReplyDeleteI started the plate choke adventure about six years ago when I unpacked the pair of James JS4120Ns I've been lugging around since the early 2000s. But I was still busy playing gigs so it was a slow process of integrating the topology in my hifi set up. :)
DeleteA cuestion about these AC heated projects: where I can find this humpots?
ReplyDeleteGoogle is your friend. Keywords: 25 ohm 2W potentiometer, actually, any value from 25-100 ohms at 2W or greater will work. Good luck!
DeleteWhat are your thoughts on testing amplifiers with square waves? I read discussions on the subject in forums, saying that square waves do not represent the operation of an amplifier, for example the sun audio 300be or some shindo have bad square wave samples, I have a 6v6pp triode amplifier and a 6v6SE (your design ) and the 6v6pp looks better, but I like the way the 6v6SE sounds better. I read articles and some do not pay attention to it and others, like Harman-Kardon, say that it is key. Thank you very much for your articles, I learn a lot!!
ReplyDeleteExcellent question and very timely! I'm just putting the finishing touches on my next blog post, which will address your questions in much greater detail.
DeleteIn a nutshell, my electronics mentor in the 80s, Tom Cadawas, who worked for Saul Marantz during the Model 7, 8B, 9 and 10B era, taught me how to use a signal generator + scope for troubleshooting and quick tests. He also showed me how to duplicate the 10 kHz square wave of a Marantz 8B on a Dyna ST70 by manipulating the feedback loop. However, he admitted that the 8B is still the better sounding amplifier.😊
Aside from having been a subscriber to TAS and Stereophile in the 80s, I also read articles by the late Bascom H. King in Audio. He also used square waves to analyze an amp's behavior. For an example of BHK's review, go to page 60 of the August 1985 issue of Audio - https://www.worldradiohistory.com/Archive-All-Audio/Archive-Audio/80s/Audio-1985-08.pdf
Since I'm a classically trained musician, I trust my ears more than the most sophisticated audio test equipment. My main motive in blogging about my audio adventures is to encourage music lovers to find the sound that gives them the most musical pleasure, so you're on the right track! 🍻😊