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Posted

Thanks guys.  This amp will take Stax and HE90.  I've put an additional 5M resistor for HE90 bias.  Should I make another 500V bias voltage for HE90 or will it be OK with 580V? 

 

Wachara C.

Posted

They really need to have the correct bias voltage, +500V and 10M.  It just so happens you have a nicely regulated +500V in there already.  :)  Just take a line from there with a small 10nf bypass cap and a 10M resistor to the Fischer socket. 

 

One thing to note, the HE90 should never see more than 1000Vp-p at any time which the HV will easily pass even with a 2V source. 

Posted

Oh yes!  I actually forgot about the +500V that is readily to use.  Thanks very much for pointing that out.

 

About the 1000Vp-p, I guess I'll just have to be very careful with that.

 

Wachara C.

Posted

Interested about the transformer too as I'm looking at other options.  The Asia suppliers usually fail to be cheap once I impose strict tolerances and specs such as low max heat rise.  They usually underspec the cores and use silly small wires to keep the cost down. 

 

I did contact Talema as they are so close to me in Ireland but haven't heard back. 

Posted

I have my transformers made locally. The maker learned it the hard way when I asked them to make the transformers for my DIY T2. In total, we burnt 5 transformers. So now when I ask them to build me transformers for electrostatic amps, they know that that have to over specs everything. :)

Wachara C.

Posted

Back when I was first thinking about building a KGSSHV, I remember reading you guys warning about taking the output bias too high, that the transformer/powersupply would run out of steam. Using the stock, non mini power supply, and a 135VA transformer at 500v rails, how high would you guys guess it would be safe to turn up the output stage biasing current without hurting anything? Would something like 15mAs be possible, or would i want to stay below 10mAs? I know that John only took it up a few to 8mAs?

 

Second question, would it be possible to make it so I could socket resistors to test different biases without having to solder all the resistors in each time?

Posted

on the subject of transformers I and several others have had good service from Toroidy Poland. I contacted him because he was recommended on a diy audio forum.

I've used three of his and they all work as intended, although only been in service for a few months so far.

They are also quiet in operation.

Contact

Tomasz Lachowski

[email protected]

Anyone else experience with them?

To answer SoupRKnowva's question; I defer to more experienced members, but I'd say the PS is not the problem as far as running out of steam. The max bias current I would use is around 10mA as the transistor is reaching its power limit.

.........

You could find something like an IC socket but I would just solder pins or short length of stiff wire in place and solder the resistors on temporary. Not much less than 100ohm though. There are comments ealier on about calculating the bias. and also the extra drift that comes with the higher bias.

Posted

I made a few changes to the inside of my HV recently. Put in the much larger encapsulated trafo and tidied up the wiring a bit. However I haven't figured out what to do with the ground hum at the pot's extreme left. Anything I should try first to see exactly where the issue is?
 
q0BO66vm.jpg

 

Also SoupRKnowva, I'm not sure about pushing it past 10mAx4 with IXYS parts. It would probably drift a considerable amount.

Posted

Is there no direct ground connection from the sockets to the pot?  Conduction in those boxes is shit unless you take special measures to get good contacts all over the place.  First thing I'd try... 

 

I've used one Toroidy transformer and it worked well enough but who in their right mind puts 10cm leads on transformers? 

Posted

Yes, it's a fault on their part, but they have no problem to do transformers with cable length you want if you tell them in the order the long of these leads, I ordered the last transformers with 40 cms long.

 

-- o --

Rodrigo

Posted (edited)

utsource has had 2SC3675s listed for $1/each for a while now on eBay.

 

as a test, i bought 10 pieces, they were all real, look exactly like my other 2SC3675s

 

so i bought their remaining 910 pieces, which....look different.

 

testing:

tested 10 pieces (of the 910pc lot), they all have breakdown voltages around 1025-1050V.  higher than the 900v spec but not as high as some other parts ive seen test in the 1150v range

 

HFe is around 50 which is good

 

This is what the 10 pieces look like from my sample purchase:

 

2sc_3675-1.jpg

 

This is what the next 910 pieces look like:

 

thumb2SC3675SANYO.jpg

Edited by justin
Posted

I've used one Toroidy transformer and it worked well enough but who in their right mind puts 10cm leads on transformers?

Yes I didn't give any spec details just a heads up on a supplier who seems OK. I specified 300mm leads.

Posted

Those odd 3675's could be real as I've encountered some odd markings.  One didn't look anything like the bulk stuff we bought but tests just the same...

 

Yes I didn't give any spec details just a heads up on a supplier who seems OK. I specified 300mm leads.

 

I didn't order this particular unit but it's something to consider. 

 

While we are discussing transformers, I'm talking to SumR now to see if we can get rid of the buzz issues I and some others have had. 

Posted

not familiar with the schematic on your board but try a 100 ohm resistor after the pot on each channel

 

Putting in 100 ohm resistors did the trick, thanks. It's dead silent from extreme left to extreme right now. :P

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