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This post is a bit long, but if you're interested in alternative filament supply ideas for DHTs, feel free to read on. I know @kevin gilmorehas already mentioned and implemented a solid filament supply solution for 300B tubes using five modular switch-mode power supplies from Traco. One 12V unit is used for controlling soft start, and the others supply 5V for the 300B filaments. It’s a good and proven design. However, I believe it may take up more space than I can afford in my chassis, so I’ve been working on an alternative. Summary of My Design Concept: 1. Inspired by @JoaMat approach using rectification + DC-DC regulation, aiming for a similar or smaller footprint. 2. Native soft-start behavior with no need for external resistors to set ramp-up current or output voltage. 3.Up to 5V @ 3A output per module. 4. Molded inductors for reduced EMI 5. Adjustable switching frequency (to avoid audio band). 6. Dual-random spectrum modulation for further EMI suppression. 7. No heatsink required. I’m currently working on the PCB layout based on my schematic (slow progress – I’m not a professional). Any suggestions, corrections, or feedback would be greatly appreciated! 1.Design Rationale (skip if you’re only interested in the result): There are many DC-DC converter chips available, but my criteria were: Very small footprint Adjustable switching frequency (to avoid 20Hz–20kHz band) Integrated soft-start, over-voltage, and over-current protection (to safeguard DHT filaments) Output current ≥2A @ 5V Low noise and ripple Adjustable output voltage (to support both 2.5V for 2A3 and 5V for 300B) After some research, I settled on the TI LMQ664x0 series, which offers 1A/2A/3A variants. To leave some headroom, I chose the LMQ66430, rated for up to 3A output and 36V input. Datasheet:https://www.ti.com/lit/ds/symlink/lmq66430.pdf This chip is extremely compact – only 2.6mm x 2.6mm – though I’m still unsure if I can hand-solder something that small.☹️ 2. Circuit Topology (text version for now): Although I’ve drawn a test schematic, the files are on another computer. I’ll post them later if needed. In general, the topology is quite typical: Use a transformer with a secondary in the 9–16V AC range, Rectify the output, Feed it to the LMQ66430 module. Key connection notes (based on the datasheet): PIN 1 and PIN 3: Rectified DC input PIN 6: GND PIN 7: Output through an inductor (preferably molded) PIN 8: NC PIN 10: 1μF to GND PIN 11: Feedback resistor network for setting Vout (see page 29) PIN 13: Set switching frequency (tie to GND for 2.2MHz; see page 14) PIN 14: NC PIN 15: GND For layout reference, check Page 39. Also, combinations and example circuits are shown in Page 9.2 Disclaimer: I haven’t verified every detail yet. In this way, there may be changes before I finalize the layout and perform live testing. I have some concerns if two modules can work in parallel. In Megatron XL, the two 300Bs per channel share the same filament supply. If I use two separate LMQ66430s in parallel, I’m unsure whether uneven current draw might become a problem, since these chips don’t have a master/slave current-sharing mechanism. I have another separate question, please bear with me for bringing this up here: If I substitute 300B with EML 20B-V4, I understand that I no longer need the pair of 3300Ω balance resistors and should instead use a cathode resistor connected to the center tap (CT) of the filament. But I’m unsure about how to treat the G-stage resistor R4 (680kΩ). Should it connect from the grid to the cathode, or from the grid to -450V? My guess is that the G-stage connects to -450V through the 680k, and the cathode bias is set independently via the CT, not the filament ends. I admit I’m not very confident when working with DHTs – I often get confused by how CT-based cathode bias works when combined with DC filament supplies. Any insight would be really appreciated!😊

RIP Jim Marshall, 87, the first of the Minnesota Vikings four defensive linemen known as the "Purple People Eaters" to pass away. Always thought it was a crime that he was never elected into the NFL Hall of Fame. Grew up as an avid Vikings fan in the 70s. By all accounts, he was a good man otherwise as well. Time sure flies.

Man is singing my very middle-aged song for what it's worth.

50yo Wind On The Water by Crosby & Nash (1975) https://album.link/5vnkkwtcmj2vj Example: There were a couple albums of just the duo. Nice set of tunes.

Damn, even condoms were cooler in the past. https://www.rijksmuseum.nl/en/press/press-releases/rijksmuseum-exhibits-200-year-old-condom-featuring-erotic-print

you are aware that you need a heatsink touching all the sot transistor. still with heatsink it typically can take about 5 minutes to reach high temps.

The tube 6E5P in triode connection has Ka c.a 50 - I know because I tried it. So probably yes, it is not enough for 300B, when you consider even low NFB. And this tube has a really huge microphonic problems, every single one - not useable in audio first stage amplification, in my opinion ofc.

Hi all new to Estats...looking for the best value estat amplifier,the Blue Hawaii is a name I hear.Can somebody explain why this particular amp is so good for estats unlike Stax,Topping etc. I ask because already theres a low opinion on the new Feliks amplifier...so looking for something really good.Thanks

i am aware of the overheating issues. i have an assembled board coming to me to look into this. something clearly has changed from the original parts i used and there is some positive thermal runaway that did not happen with the prototype. there is a later version board now, 4 layers, still does not fix the problem. putting 12v zeners in series with the 1.1meg resistors may introduce enough negative thermal compensation. otherwise the bias needs to be trimmed a lot. hate the parts situation i do.

Has anyone tried building this? Not sure if it's just me - after power on, the board overheats within a minute and then comes the magic smoke. PSU voltages are correct but output balance (i.e. L+ vs L-) goes from -2 to -60v quite quickly then suddenly normalises to around 4v). Pretty sure there are no shorts or issues with soldering on my board...

You won’t find them boards at Kevin’s library. Custom made.

Thank you. My friend is very grateful. He says he cannot see the center board to be found? He also says that the boards attached to heatsink is also not found?

Those are always uplifting, and I could use that today. Thanks for that.

Another take on recent events

I knew it was bad, but I didn't know it was fucking-with-someone's-dog bad. That's horrible.

I can only hope the murderer is put in prison and made someone's - or better yet SEVERAL someones' - ass bitch! Scum deserves it deeply.... A dog, too.....

That is heartbreaking! WTH is wrong with some people... Sam

This shit is crazy. King of the Hill actor Jonathan Joss fatally shot in Texas after argument with neighbor. EDIT: The second page didn't paste for some reason:

Check this link - lots of good stuff. There you find gg.zip .

In case you were wondering (I was, initially) ELI5: TLDR: https://www.twz.com/air/russia-covering-its-aircraft-in-tires-is-about-befuddling-image-matching-seekers-u-s-military-confirms

Have heard good things about it and it was on my list; guess I'll bump it up.

Funny, I just came here to post what I listened to yesterday. The sound quality is pristine. I've always been a fan of HDCD, especiallly in Reference Recording's hands. YMMV, but I very much enjoy the performance as well. I've had this disc for years.

Copland: Our Town Suite, The Red Pony Suite & El Salón México by Aaron Copland (1988) https://album.link/kjqzqbb7js4mt Example: Finally getting back to finish off the trio of CBS Masterworks: Copland v Copland... Like the others, just lovely, maybe not the most audiophile of the recordings out there, but super lush and the performance is unquestionably good. I may poke around a little bit more for other recordings, I have a few others in my queue (Bernstein, MTT, Marriner), but I feel that in the future, I will probably just come back to these.

ew... {begin rant} Well you were right. I didn't have the stomach to watch past a few minutes. As soon as I heard 'Physics Establishment' I knew that it was Crackpot time and I was done. I am sorry I gave it that much time, they probably got credit for a view. I at least was able to give it a thumbs down. There are several vids by Angela Collier about Crackpots - and they are scary people that are mad.... I like Sean Carroll - I read his pop physics books back in the day: From Eternity to Here: The Quest for the Ultimate Theory of Time The Particle at the End of the Universe: How the Hunt for the Higgs Boson Leads Us to the Edge of a New World Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime I would rather read papers than books aimed for public consumption now. But Sean is a well respected in the industry with over a hundred published research papers. He falls in the camp of Brian Greene for me as a science educator. In some ways I hate that he did this. It raises the status of 'people that yell' that their theory is worthy of debate. {end rant} Back to working on my theory of everything that they cannot handle....