JoaMat

You might try the diode test method described by Kerry in this post. If lucky you get a hint which component that is the faulty one.

Nice Kerry and Kevin! How about Grounded Grid with tube input, c4686 CCS....?? Lots of opportunities – hoping for a rainy summer.

No, I haven’t. I guess it’s some sort of EMI. One question is how to stop it and another is how it effects the quality of the amplifier. Now I’m most interested in if the DC/DC converter can be used at all. One T2 is modified with DC/DC converters and it seems to work alright. The idea with DC/DC converter is IMO absolutely worth being tested.

I want the output current source to be c4686 with DC/DC converter.

The ultimate DIY? Absolutely magnificent! Nascent Audio. Sounds promising.

Just had to try the DC/DC converter. Converter in red circle. According to the datasheet the converter is rated at 1400VAC 60 Hz for one minute. So one of four current sources has the converter. Seems to work. Regarding spikes mentioned earlier I’ve done some "googling" and I believe the issue can be solved.

It’s spikes from the DC/DC converter. The way I built this the spikes are passing through the LT3045 more or less unaffected. I lack understanding of and knowledge how to filter the spikes and also how to design the board so it will work properly. Any help is appreciated. I find the idea with isolated DC/DC converter interesting.

Seems Birgir is right about noise. I tested it with a scope. As expected the output from the converter is ugly. It’s better after the LT3045 but there is too much noise passing through.

The output from DC/DC converter is pretty ugly. How much of this that will be stopped by LT3045 is to be seen. LT3045 datasheet looks rather nice though. P.S. Should have ordered LT3042 instead.

Which part is the noisy one?

DC/DC converter followed by LT3045 regulator. If this works I've well-regulated 9 V well isolated and hopefully it could be used with NPN current sources. If not I've two dozen of L3045 for sale.

I think I like the c4686 with two LEDs and a 9 volts battery current source.

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I’ve been using the cascaded CCS in T2 since December 2014. It’s my favorite CCS, also used in Blue Hawaii and other amplifiers. Kevin’s idea using DC/DC converter with the T2 CCS is appealing. So I removed unnecessary components and put in 9 volts cells. It works (why shouldn’t it?). Personally I prefer cascaded CCS but if there is a nice way to introduce DC/DC converters I might reconsider. Battery cells is not very convenient.

What kind of gear do you use to get the thermal pictures?

Nothing to fear. With some practice everyone can do SMD soldering and it's fun.

Congratulations Kevin! So now I don’t have to feed ducks anymore, great.

squirrels on Iceland? didn't know that...

The squirrels sits on them.

Lots of converters at Mouser – just have to find a suitable one in stock. Alternatively 9 volts cells....

this one, 12V to 12V and 1/4W

Can a DC/DC converter be used as it is or is some filtering needed?

Very nice indeed.

I like the way Skooby attachs the heat sinks. It’s a Fischer SK 81 - 100 x 37.5 x 15 mm. Found it at a local dealer. Cut it in two halves and it fitted quite nicely. I also use an aluminum net for top cover. Heat sink or nor the heat has get out of the cabinet. At 74 degree Celsius the PTZA06 is good for some 450 mW.

Take a look at this 3M product. 3m8810[1].pdf I use it and I'm confident it will hold the heat sinks safely in place.