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Getting ready to move the rest of our stuff that was not sent up to Vermont to our beach house rental where we will be living for the next 2+ months until Peter finishes high school (and the renovation finishes on our Vermont abode). Stay tuned for more later today.

Here is picture of the amplifier in work. Mono version. AMB sigma 22 PSU. It has four trimmers. Lower middle controls the offset. Middle upper controls the balance. The two outer controls respectively channels bias. Input stage current source/sink approximately 1.7 mA. Output bias 35 mA. Setup procedure I used: • Let heats sink get warmed up to working temperature • Trim offset to zero • Trim balance to zero • Set desired bias of both channels to desired bias Redo previous procedures if needed. I find the setup easily done.

I was on a Boat To San Francisco Where I benchmarked some Macs in the Apple Store In Union Square (Who knew they had their own IG account) Had some lunch with a Colleague, Then saw some Art at SFMOMA. There were signs of Normalcy, But I have to say, The City (or what we saw of it, downtown) felt depopulated, compared to the "Before Times". Even if there were 12K vaccinated nerds at the Moscone Center, for GDC.

The saga of messing with my 2nd Carbon build continues. Since the circuit is very close to the Grounded Grid, I'd like to give it a try. Being hesitant to spend big bucks on a nice quad EL34, I have been on the lookouts for a cheaper substitute. The curve of a pentode looks a lot like that of a SiC FET. I need a pentode with the following properties: The plate curve should have low kinks or no kinks at the low Va range. The lower the 'knee' the better. Low Ig2. Ig2 should be much smaller than Ia (20mA), ideally 1mA or less under the operational Va range such that Ig2 doesn't interfere with cathode drive/ cathode degeneration. The amount of negative bias needed to get 20mA at 400V should be reasonably easy to handle. High rated Va(max) and Pa(max) for using a higher supply voltage and/or idle current in the future. That means I may need to look into transmitting tubes. And the candidate is... (drum roll please) the FU-50/GU-50! The linearity looks pretty good at around Ia=20mA, from Va=100V all the way to 1kV! The bias voltage is between -20V and -25V, right around what Carbon has. The Ig2 is really low and changes very little from Va=100V to 1kV. More importantly, the FU-50/GU-50 are relatively inexpensive and plentiful. A lot of them were made in the USSR and China during the cold war era. I read somewhere that those were designed for the comm gear used in the tanks and had very little success in commercial applications. I paid less than $3 a pop from Ukraine about 15 year ago. The going price for a NOS tube should be close to a SiC FET today. Well, any tube not designed for audio can be cheap these days. However, that wouldn't stop people from chasing after the Telefunken LS50 and the east-Germany SRS-552s, I guess 😉 Adapting those to the Carbon is surprisingly easy. I removed the SiC FETs and the 20k bias resistor, replaced the two 175k resistors with a 100V and a 130V 3W zener diode for G2 supply. The Ig2 is really small and the two tubes can share one set of the zener diodes. They drop 230V from GND and set Vg2 right at 150V, with about 22V left for the PZTA42 and the offset pot. The heaters are powered by a 12.6V filament trans with one side tied to B-. I could have tied the CT but there was very little hum to worry about. Guess what, the GU-50s work right out of the box. I didn't even need to adjust the balance and offset! The measured performance is pretty decent: Although the distortion is low, the FFT does show some higher order 'pentode nastiness'. I guess the reasons being The pentode is not super linear to begin with. The transconductance of the GU50 is about 1/10th of the SiC FET. The PZT42 has to work much harder and the global NFB is less effective. Something else worth looking into I'm not yet able to seriously listen to the sound, because I couldn't find another pair of tube sockets in my stash for the second channel 😂. If you want to know how it sounds, try it! The GU50 with 400V PSU comfortably beats the KGST (below) on the frequency response and the output swing: Next to try is to use the pentodes on the KGST, or should I call it KGSP then?

So, I am good with my four OPA445. Thanks, Kevin for confirming.

opa551 is a cheaper opamp that is good to 60 volts opa445 is good to 90v. at least that is what the pricing used to be

Reminds of the scene in Naked Gun:

Doug has kitty visitors, we have coyote visitors. At noon no less.

I can't quite see the calendar from where I'm sitting.

Interesting ideas, wish list, for future Dynahi, Bespav. Here is a new amp board. Initial tests have been successful. The bias control seems to work. Heat sink is Modushop 80mm x 200mm.

Actually, I like his version better.

Second day of packing our U-pack-it truck. They dropped it off yesterday at about 2:00 pm EDT and as of 5:00 pm EDT today we have approximately 75% of the house packed up and 99% of the heavy, bulky shit. Now sitting down for an adult beverage.

@ktm - i feel your pain, almost literally. Yesterday, for the second time in six months I had the dryer almost fully apart. Midway thru: The last time I "fixed" it the problem was just that the belt had jumped the idler pulley. I did notice while I was in there that the belt had a good sized crack but the need to continue to do laundry trumped the need to fix everything. It's only about an hour to get to that level of disassembly. So when it started making a weird screeching noise last weekend I ordered a maintenance kit (belt, idler assembly, and some other misc. bits) for a whopping $40. Andrew and I started disassembling it yesterday around 8:30 and two hours later had a fully functioning, much better sounding, 12+ year old dryer.

Swag day at work...

You have tantalum ones at 35v. I bought some of these to use in this amp and also in the Grlv.

Cranked the bias current to 180mA. Broke out my LCD2 as I had a feeling that this amp will be a good match for it. People with LCD2 really ought to listen to it driven by this amp at least once just for the experience. I am still in awe of the speed, clarity, resolution and control of this amp. I can understand now why Kevin said in his post that this should be the end-all of dynamic amps. This is my favorite of all my dynamic amps and I don't think it's entirely a new toy syndrome at play.

Another CFP lives. Started with a single-ended, two-board pilot, proceeded to testing a four-board, balanced setup. Have been listening to it for the past hour or so. Have to settle with 22VDC rails from a Sigma 22 owing to the limit of the transformer I have. Bias set to 150mA. Heatsinks barely get warm. Next is to build yet another GRLV for it with possibly 30VDC rails and higher bias current. Even in its somewhat compromised state, the speed, transparency and resolution of this thing is just incredible!

https://news.obozrevatel.com/ukr/show/people/vse-zaminovano-na-vulitsyah-bagato-til-komarov-pokazav-pershi-kadri-zi-zvilnenoi-buchi.htm

That permanently attached power cord gives me flashbacks to 1990s components. I remember in the late aughts when I donated two LCD panels to my friends DVD rental business (which I motored up to in my model T) because his were failing. Remember the bad capacitor curse of the first half of the 00s? My frind's business got hit pretty hard by bad caps. I helped him replace two monitors and a HT receiver, but I digres... Both of the LCDs that I gave away had permanently attached VGA cables. One of them also had a permanent power cord as well. Apple's choice makes even less sense given that they engineered a very nice magnetic power cord for newer iMacs. I expect better both from Tim Apple and for a fricken $1600-$1900 display. For that money, even from Apple, there are some basics that need covering. A power cord contemporary with the century in which we are living is one of them. There's also the issue of the "Studio Display" being a really poor match for the fricken Mac Studio, with which it shares a name and presumably a market segment. I have talked to a number friends who produce music, video and photos. I have a gentleman's bet with them that more or less all of them will be buying a Studio in the next few years. The amount of desk space and power consumption it saves vs a cheesegrater Mac Pro is something that looks appealing to basically everyone. The only holdout I can name in my personal friend group is the one guy who has make use of a couple PCI-E cards. ...also, anyone else find it highly amusing that El Cabeza de Sputnik needs an app called "Magnet"?