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The DIY Electrostatic amp thread


spritzer

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Kind of a random place to ask this, but I want to build the Jecklin 'stat amp at some point. I have a whole bunch of mixed 12AU7/A tubes but no idea how to tell what is what. Eventually I'll have to invest in a tube tester for matching but does anyone have a link to some reference that lists the defining features of various 12AU7s?

Might have to buy another mixed lot of 12AU7s to actually find some that are same internally and match...

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Thanks, that's a start. The thing is I have 20 or so tubes and iirc ~15 of them have different labels so I'm trying to find the ones that are the same internally or if they are all different. I'll go through the list and sort the tubes when I get home. Here's a crappy ebay pic of a production unit:

jecklinamp.jpg

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Very cool bringing back them pics sptizer, kodus señor :)

So i own a DIY KGSS (not by myself) and was suggested the 17N80C3 for replacing the N-channel Mosfets at the PS section after previous repeated failings of one the IRF830 that was there...though i'm not techwise i think it's the one who handles the +350V, beacuse it's dropped almost flat. Is it a better fit? I see it's very pricey compared to IRF830, Is there some other decent alternative on a budget?

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Depends on which version of the power supply board you have, but

24 volt zeners across the gate to source prevents the pass

transistor from blowing up. The fairchild part used in the T2

is way better anyway.FQPF8N80C or FQP8N80C and they are cheap.

Probably still out of stock at mouser, so get them at

futureelectronics.

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I can only speak regarding the KGSSHV board that I have built.

I'm assuming that others would be similar depending on if they have

bleeder resistors across the supplies filter capacitors.

Also bleeddown time is governed by the cap's size (in mfd's) and the size of the bleeder resistor.

I'm sure there is a mathematical formula that describes this, but I dont know it.

The best way (for me) to be sure is to use a voltmeter to read the remaining voltage charge

across the filter capactiors on the psu when switched off. For a given power supply, I use a stopwatch

and check the caps multiple times until they bleed down to a "safe" voltage, say a couple of volts DC.

Make sure that the thing is unplugged before starting and remember that the voltages encountered here are deadly!

If you become part of the circuit, it can stop your heart, that is cause fibrillation that may result in death.

My KGSSHV supply bleeds down to a safe level in about a minute.

The specified bleeder resistors for this psu are 300K ohms to 400K ohm units.

The intial voltage on each rail is 450 volts DC, so it has a total potential of double that, or 900 volts DC.

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I was definitely going to check with a dmm before handling, but I didn't want to set up the psu here at the lab and have to stick around for an hour before things were safe to handle.

400V is the most I've worked with here at the lab so far, and it was more than enough to kill me at the currents I was working at. I'll definitely be keeping track of anything I touch. My plan is to use two DMMs, one on the positive rail and one on the negative rail, and attach probes before turning the psu on so I don't have to worry about exposing myself to the HV supplies.

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Depends on which version of the power supply board you have, but

24 volt zeners across the gate to source prevents the pass

transistor from blowing up. The fairchild part used in the T2

is way better anyway.FQPF8N80C or FQP8N80C and they are cheap.

Probably still out of stock at mouser, so get them at

futureelectronics.

I don't have the amp to check the board version currently but that's exactly what happend the second time, the IRF830 actually blew apart to pieces, and the fuze got whacked too. I'll check those T2 parts, thanks. Couldn't be any worse i guess ... heh.

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@DQ, Some may think this is excessive, when I work with high voltages like this

I have a ground strap attached to each arm and the device under test

and perform the work while using a nonconductive rubber mat underfoot & on the workbench.

I make a lot of mistakes, like slipping with the test probes, some of which are chronicled here on HC.

I dont want a multi-hundred volt charge crossing through my heart, if you get my drift.

On the job as a maintenance electrician, I have been shocked many times.

Using safety procedures like these has probably saved my bacon numerous times.

Edited by livewire
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I was definitely going to check with a dmm before handling, but I didn't want to set up the psu here at the lab and have to stick around for an hour before things were safe to handle.

400V is the most I've worked with here at the lab so far, and it was more than enough to kill me at the currents I was working at. I'll definitely be keeping track of anything I touch. My plan is to use two DMMs, one on the positive rail and one on the negative rail, and attach probes before turning the psu on so I don't have to worry about exposing myself to the HV supplies.

That is a good idea, keep in mind that if the psu does not utilize bleeder resistors,

your DMM will act as one due to it's internal (high) impedance.

The bleed-off time if noted, will only be valid for bleed down with that meter attached.

At least you will know when it has become discharged and be safe to handle.

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inu sent me these which are variations on the srx circuit.

http://earsp.web.fc2.com/log/stax-r/stax-r-3.pdf

warning, the 1150 volt version is only for those that

really know what they are doing. And obviously the

output caps need to be rated for 1200 or more volts.

With respect to high voltage electrolytics, and also

mylar caps, a resistor across the cap is pretty much

required at all times. Even if you discharge the

cap, and then remove the resistor, the capacitor

will self charge, usually to very dangerous voltages.

The higher the rating on the cap, the worse it gets.

Edited by kevin gilmore
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inu sent me these which are variations on the srx circuit.

http://earsp.web.fc2.com/log/stax-r/stax-r-3.pdf

warning, the 1150 volt version is only for those that

really know what they are doing. And obviously the

output caps need to be rated for 1200 or more volts.

With respect to high voltage electrolytics, and also

mylar caps, a resistor across the cap is pretty much

required at all times. Even if you discharge the

cap, and then remove the resistor, the capacitor

will self charge, usually to very dangerous voltages.

The higher the rating on the cap, the worse it gets.

Words of wisdom! (regarding the caps)

Can anybody here translate the japanese?

I'm sure just viewing the schemos is all KG needs to see. :D

Rest assured, I wont be messing with any of that HV tube stuff.

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i'm sure inu could translate it. but i know a couple of people

at work that can do it too. maybe in the next few days.

really, these things are just the srx circuit with an extra

tube stage for more gain so that you can have more feedback.

50ca10's are probably impossible to get, as are the sockets,

6ra9's might be easier. Still nothing wrong with 6ca7's.

But the resistor plate loads are guaranteed to do the same

thing that has happened to a bunch of the es1/es2's when

the output tube lets go. So much better idea to replace

with current source. Then make sure you have adjustable

bias on the output tube. Pretty soon you end up with the

modified singlepower schematic.

There are errors in the schematics, in the 3rd one, "B"

is actually -440 volts.

With the 50c10's you can do adjustable self bias without

an additional negative power supply.

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