JoaMat

Thanks for clarifications George and Michael. The servo (opto servo) I'm talking about needs both OP27 and 4N25 installed and the jumper next to the 4N25 shortened (do not shorten the other jumper). The trimmer must be set high enough. The opto servo is only capable of lowering the offset set by the trimmer.

I use a similar opto servo as on Kevin's boards. Differences are KSC2690A for PZTA06, VOL618A for 4N25 and no resistor/trimmer cross KSC2690A. This servo works instantly on my DIY T2, Carbon, Grounded Grid and Grounded Grid with tube input. The amplifiers also have balance servos. With multimeter one decimal resolution I read 000.0 at the outputs. My impression is that the opto servo works well. I've no idea what the problem with your Grounded Grid is. The servo works on your Carbon then it should work on the Grounded Grid as well. I'm sure you will solve this, might take some time though but it will be worth it.

Happy Birthday!

After a second thought. Probably a bad idea put a test pin at pin2 OP27, might affect the servo. But the small variation at one output could very well be variation in the balance. +0.160V then you have -0.160V at the other output. I have four amplifiers with similar servos and they all have perfect offset behavior and the servos kick in instantly.

Turn trimmer up to max resistance. Measure voltage at pin2 op27 to ground with one decimal resolution and I bet you'll read 000.0 within a few seconds after applying the high voltages. That servo works.

Thank you pose, pixels appreciated. Give me the opportunity to steal good ideas. I like the led stax connector. Can that be bought somewhere? At the PSU, there seems to be something Arduino on the back panel - what's that?

You wanna circlotron? This is a circlotron... ... just where I live.

Nice. Big knob is volume control? But the small one is? Is there some light in the Stax outlet or is it just look like it is? Nice indeed. More pixles, please.

I love fish, salmon and lutefisk are fantastic. But surstromming, that’s awful. Eat surstromming for three months then you are light light weight.

好，謝謝。我是大如相撲選手。

Still another rainy day. Here with DHT. Shortest distance between tubes is 0.3 inch. This built was not intended for the huge triodes… ...but it is a good sounding thing.

Happy Birthday!

Look! Top plate, 1.6 mm copper clad single sided. I do think we have copper polish somewhere in the house…

Since you are one of the first builder if not the first builder of Carbon-Triode I guess we have to ask you about this new amplifier. Is the tube preheated when high voltage is switched on? For how long time does it latches to B+? Both + and - outputs are at B+? Pictures are always appreciated.

Interesting. The tail resistor, is that 120R on the silk screen?

piece of cake

OK, back on track. One burned resistor replaced. I guess the malfunction was due to the input tube, but I actually don't know for sure. So I took a new tube and the balance servo wasn't able balance it out. Tried two more still not able to get balance but eventually I found a tube that worked. I should have made room for a balance trimmer and jumper for the servo on the board. For the sound. I'm not very good at describing how something sounds, so you won't get any details from me, sorry. How does it compare to the T2? I'll pass on that one as well but I think Kevin somehow is hunting the T2….. We should let the blood hounds (Kerry, Birgir, et al.) join him.

No, 6.3 VAC. Just changed input tube on the last built board and powered on - no blow up but funny smell. Have to send it for repair. But I had an working stereo amp for a few hours and it did sound promising.

I can’t hear any noise - same as lsk389 input. Be aware my ears are old and I also suffer from some light tinnitus. Seems you have 500 ohms at current sink input stage while 300 at other of your amplifiers. Any particular reason?

The chassis belonged to a Grounded Grid, now transformed to something similar with tube input. Need to make a top plate else I think it’s finished. Ordered 50 pieces of ceramic discs. Got them in 50 plastic bags…..

Lowered the resistor value at OP27 output. Now both offset and balance are in the mV area. Very happy with the outcome.

Can you put that in a high altitude extended holding for a while? Need to save fuel. Almost finished the layout for the other channel. This is the first board layout I’ve done from schematic in the software. By doing it this way I hopefully can avoid mistakes in the process of copy, mirror from the right channel board to the left … Thanks Kevin, Kerry and others for new ideas that I can exploit.

Your wife is most certainly right, but to be five years you are really good.

Happy birthday!

Welcome MattN, great work. The offset servo is a new version and I'm not familiar with the board you are using. I guess the offset servo is working and reason the trimmer seems not affecting the offset might be because the resistor in series with the trimmer has a bit high value? One way to disable the servo might be to remove the ptza06 next to the 12V Zener diode.