JoaMat

The new Stax just arrived. Sorry for posting in CRNB thread.

Tomorrow before 6pm Swedish local time, according TNT.

Years ago I had problem with high temperature when stacking two transformer. It was so high so upper transformer started to “boil”. I bought some BERGQUIST GAP PAD VO Soft, 3mm thick, from Mouser. One piece between lower trafo and 3 mm aluminum bottom plate, one between trafos and finally one between top trafo and top aluminum plate bent and bolted to heat sink. This way the temperature was reduced considerable. Determine inner temperature of a transformer is not easily done. One way is the measure resistance of primary winding when cold and when hot. Put those figures in this formula, T(hot) - T(cold) = [[R(hot)/R(cold)]-1] x 235 and voila.. you have calculated the temperature raise of the transformer.

Early draft of a modified Megatron. Top EL34 is replaced by 3x2SC4686 and a 10N100D. Less transformers – reduced risk.

I'm sorry for your trouble. Transformers are not always nice things. When temperature rises - copper resistance goes up – power increase – transformer temperature goes up - copper resistance goes up more, as temp … und so weiter …

Nice progress Kevin. Did this test board today. I’ve an idea (have to many ideas) to replace top el34 with CCS. Save you lots of wires. Here a CCS of 10M90S/DN2540 and +/-400V applied. Current set to 22 mA gave 400V cross tube and cathode resistor.

So, another quarter has elapsed. Raised the current through output stage from 11 mA to 17 mA ...and, it all sounded shitty bitty. Fired up the desoldering gun. Removed FJPF2145 and replaced them with 2SC4686. Wow, what an upgrade and I’m happy again.

It’s a troublesome, difficult time – all shortages of components. KSC5026 might be replaced by STN0214 in a KGSSHV style PSU. Solder it in standing, bend outer “pins” slightly outwards if necessary.

Have you seen this, BCV61? To be used as current mirror. You get a hundred pieces for 22 USD, less than one 2SC3381.

Which ones do you have in mind?

Happy Birthday!

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From above picture it looks like there are 12ax7 anode current sources and 330K anode resistors. You shouldn’t have both, should you?

I use/have used those CCS. Good for +/-500V. I’ve replaced 2SA79/2SK216 with KSA1220/KSC2690. Looks like KSA1220 is ended, but TTA004/TTC004 should be fine.

Bohuslan Big Band plays Blue Note Available from Swedish public service company SVT, worldwide until 15. Dec. 2021. https://www.svtplay.se/video/31377250/jazzsommar-bohuslan-big-band-spelar-blue-note

Send me gerbers and I’ll take a look into it.

Happy Birthday!

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Yesterday I Had The Blues - The Music of Billie Holiday José James

I think you are right. I’ve used 2SK879 in one T2 battery since several years without any issues. From datasheet 2SK208 and 2SK879 look quite similar.

Happy Birthday!

Me too like schematics. I believe this goldenreference.pdf reflects goldenreference6.zip version.

Here are the connectors disassembled. Pins are from Neutrik NC3FD-L-B-1. Take a metal saw and make a cut so you can bend up the outer metal housing. Then pins can be removed from inner housing. I would have prefer Teflon over 3D printed. I haven’t figured out how to mill it out though, but I managed to 3D print something usable.

Thanks for dielectric values of PLA and PETG. Them in picture above are PETG but I’ve also used ABS which also works. I assume you can use PLA as well, but both PETG and ABS melting temperature are a bit higher than for PLA which might be an advantage when soldering wires to contacts.

As most other DIYers I use Teflon Stax connectors with a small PCB. But on below amplifier I use 3D printed connectors with female golden contacts from Neutrik 3 pole XLR. And they seem to work really well. On heat sinks are 4 groups of c4686/a1968/c4686.