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Decided to find some motivation this morning.

Internet doesn’t play.

its possible that Q1 is only just providing enough current for the replay contacts to just about close resulting in poor switch contact - that might lead to noise. Also does the relay have a built in diode for transient protection when the relay switches state? If not the transients could be damaging Q1 and or the opamps.

LED: The numbers are all over the place: Your IV curve shows the LTL4213 should have Vf between 1.725V and 1.750V with 0.5mA of current. You've got three different voltage ranges for the LED. Which one is correct? You need to find out where the dependencies come from. Your previous LED chain voltage measurement shows 12.1-10.7=1.4V of voltage variations with not much If change. Is the 1.4V evenly distributed across 7 LEDs? If you suspect Vf change due to the temperature coefficient, that's easy to verify. Just keep monitoring the LED voltage with the amp powered on from cold. 2SK246: Your test indicates that the 'backup ones from ebay' are probably good. Unless the ones on the board are from the same seller and same batch, the test result probably doesn't help much more than that. Rather than replacing parts shotgun style. I'd take voltage measurements shotgun style, then sit down and analyze the data. Replacing parts without knowing why and what would be a very inefficient way of troubleshooting. For example, when looking into the active battery, measure voltage on all nodes. Beware of the burden by the DMM input impedance (usually 10M Ohms but YMMV), so plan carefully when you measure across high-value resistors. When looking into the final stage, collect enough voltage data within the CCS so you can calculate the current supplied by the CCS. Measure the voltage at Output+/Output-, then determine if the tubes are in the right operating point. If you know very well how the circuit works, you can strategically take only a few measurement at key spots; otherwise just do more leg work and collect all data. Don't worry if some could be redundant. They often end up helping you where least expected.

Oof. Matt Perry dies at age 54, apparent drowning.

^ so good.

Based on the recent @mikeymad Casual Jazz/Gleason post in the music thread.

I really enjoy your simple overhead god's view Wes Anderson style food shots Steve...

Yes the 2SK246 looks suspicious. Its |Yfs| should be around 1mS around Id=300uA, so changes in Vgs of 1.51V-1.43V=80mV should generate 80uA of change in Id. Apparently that's not the case here. You could use a 2SK373 or even a 2SK117 as a substitute. The 2SK208 is also a close sub, albeit in SOT-23 package. Also, Q16 Ib should not be that high. The current thru R39 is about 100uA, split between Q16 and Q17. If Q16 has an hFE >100, it's Ib should not be over 1uA even in the extreme case.

It looks like most of the voltage adjustment comes from the wandering reference, no wonder you said RV1 doesn't have much effect. Assuming your Q16 path works okay, comparing the two diagrams, V(R42) dropped (6.22-6.56)/6.56=-5.18%, almost the same as the LED string voltage drop (11.4-12)/12=-5%, which means the 2SK246 ccs didn't have much effect at all. To give you a data point, my mocked-up 2SK246 ccs changes V(22k) from 6.5496V to 6.5446V (less than -0.1%) when the supply changes from 12V to 11.4V. Your LED string seems not great, either. When the current drops from 703uA to 663uA (-5.7%, ignoring the Q16 base current), the LED string voltage drops -5% as well. Not much of regulation, isn't it? I grabbed a random red LED from my stash and in similar situations its forward voltage changes from 1.7914V to 1.7881V, only -0.18%. Your LED probably has 700uA right around the knee on its IV curve. It may not be a bad part, just not suitable for this location. The above assumes the Q16 and the rest of the battery circuit works okay. Oh well, let's fix one problem at a time.

The difficulty setting the V(R42) to 6.55V could be due to something else. I assume that you observed different pin out when substituting 2SA1486 with 2SA1413. As long as the LED strings are lit stably and not flickering, the RV2 should adjust smoothly for 6.55V across R42. The idea is to set the 2SK246 ccs to about 297uA with the majority of that going through R42 and only a tiny bit from the base of Q16. If you have some spare 2SK246 from the same batch, resistors and pot, breadboard a circuit and test with a bench DC power supply. See if the pot hits the bottom or something wrong with your 2SK246. It’s a good idea to measure around the active battery circuit, using the top node as the reference point, mark voltages and currents on the schematic. The active battery does not take rocket science to troubleshoot. You just need to know 1) Ohm’s law, 2) Transistors have hfe, and 3) A forward-biased silicon junction has a voltage drop about 0.6V. There is no need to be paranoid about the battery not being spot-on at 740V. Since it is transparent to the audio signal, they can even be purposely set slightly differently from each other to compensate unbalances elsewhere in the circuit. But if your amp don’t like them being near 740V at all, that means some other parts of the amp is quite different from what the designer has envisioned. There are quite a few feedback loops in the works that maintain a near-zero offset. Let go of the active battery voltage temporarily in exchange for zero offset can set those loops at their normal operating point and help you find out who’s not behaving correctly. Mark any voltage reading with a ‘*’ if you hear oscillation when you get the reading, as it may not be reliable.

Peter Gabriel last night in SF. I’m glad I got to see him while he is still doing his thing. With the same warhorse band he has been with for damn near 50 years at this point, no less. He can still hit the high notes, but his voice is more fragile now that gives the songs a different feel, appropriate for a guy who is now 73. The new songs are pretty good!

Richard Moll, who found fame as a bailiff on the original sitcom ‘Night Court,’ dies at 80. RIP Bull.