spritzer

Those look like the real deal but the 2SA1968 has such a distinctive casing that fakes are easy to spot. That's why I caught the ones I had as they looked very different so I never fire tested any of them...

The 300B is very voltage limited and can't handle anything like the 211/845 or even a triode strapped EL34. What we want here is voltage swing which is for instance why the 6S4A is such a perfect tube for the job, far better than most of the DHT's. No use anywhere else though which is good for us. If you want to use the 300B/2A3 then you have to use an output transformer for some voltage "gain". B+ of 300V will not get you a whole lot so at least double that but that means the 2a3 won't work. Something like the EML20B with a 600V B+ and anode resistors would work but it's not cheap.

I'm also a bit worried about the "maxing out my meter" comment as the cheap crap doesn't work at these voltages. They give the wrong data and the error range is huge.

Well first off, what are you seeing out of the transformer unregulated? The regulator needs a certain headroom to function correctly.

The BOM is for the 450V version so the voltage divider in the PSU has to be altered for 500V. There is detail of this elsewhere in the thread but nobody ever bothers to update the BOM. Most of the time we don't even bother with BOM's so there is that....

Glad you and Kent got them working again. Winding electrostatic transformers is a bit of a black art and there are plenty of things to consider. Now you just need to find somebody to build a direct drive amp for both the both speakers...

It was never impossible to cram 507 drivers in the Sigma just not a very good idea. Just look at how the drivers were glued... It's also nice to see that indeed all the WES amps are fubar. What a waste of nice caps...

True dat which brings up the 4-pin XLR issue once again. Even Sennheiser have adopted it now...

Would it really matter if they were wired like that? No need for ground with balanced and I doubt any manufacturer will have accomodated for shield at pin 1.

It should be noted that we are well aware of the Electra only having one cap in the signal path but this setup yields better distortion numbers. Personally I'll take an extra cap and lower distortion.

Might also be mixing up % and proof. 30% is easy to reach but 60% is harder.

I sure hope so...

I do have two 450V transformers in stock so that would be workable. Perhaps we should take the T2 psu board and adapt it to the HV for offboard sinks? I'm also going to cut the onboard pcb files down in size when I have time.

They did but I had to pay extra since they were more expensive to source now. Didn't have much of a choice but I'll never buy anything from them again. They were quick to shut up about me having to test the parts on arrival once I told them with a reputable seller such as Mouser or Bdent there was no need for testing.

That's what I keep telling myself when I buy these large lots. WRT upping the HV bias keep in mind just how far the transistors can be pushed. 20mA at 500V is a lot of power and the PSU needs to be oversized as well. My plan is to lower the rails to 400-450V and increase the current that much more.

If these are the same Dalbani then I sent them 600 or so fake 1968's earlier this year. They were an utter pain to deal with and tried to make it all my fault for not testing the parts when I got them.

Those look horrible and sound even worse.

HD800 and a roll of tape?

To change the current in the fourth stage you have to increase the voltage reference, i.e. the led.

Yeah, inrush current is a concern but even the simple tricks used in the Firstwatt amps will make it much easier to deal with. The problem we are talking about is the insufficient current draw from that huge core so the output voltage will rise. The PSU has only a single prereg cap so 500V is the max operating voltage and the transformer could easily reach 340-345VAC which is right on the limit. This also makes it harder for the PSU to regulate to the correct voltage and excess voltage will just lead to more heat.

Nylon will do just fine and if you are going to use the Antek 400VA transformers then look out for excessive rise in output voltage as the amp doesn't draw that much.

The only problem I see is heat with something like this. The BH runs hot, very hot and I've seen enough of them burnt up to know there is no such thing as enough ventilation. That means over spec everything, transformers, heatsinks and ventilation slots. Those PCB's also have some known issues so take care with the standoffs you use and where you use them as some high voltage lines are a bit too close for comfort. The mosfet heatsinks have to be grounded and use the thick pads on them. The amp gets rather hot there so you might want to look into some larger sinks there as well.

Thanks Todd!!

Australian, Canadian, Swedish and British, all brilliant in their own way.

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