Need to handle 4kV+. Someone recommended 4CX250, but I read on a website that they have high IMD and the focused cathode 3CX800A7 should be used. However, the measurements were in RF applications. My question is whether the 3CX800A7 would also perform better in the audio band, and whether there is a HV tube as good or better for the application but lower power (the 3CX800A7 is over 700 Watts and costs half a grand; two channels with a pair for output and pair for current source ends up at four grand just for the tubes).
That's rather a lot of voltage! Most ESLs expect about 1kVRMS of audio to be applied to each stator, and 5kV of bias on the diaphragm. One valve that you might like to consider is 6HS5 or 6HV5A. It's dead cheap, but Va(max) = 5.5kV and Pa(max) = 30W. Even if you used forty of them for a stereo amplifier, it wouldn't be expensive!
I've been looking at these 8' full range beasts:
http://www.ele.tut.fi/~artoko/audio/speakers/fullrange_esl.html
They are using a 1:60 transformer that can take 100V on the primary...
http://www.ele.tut.fi/~artoko/audio/speakers/fullrange_esl.html
They are using a 1:60 transformer that can take 100V on the primary...
The 6HV5 is a good suggestion. Avoid the 6HB5; it's quite squirrely.
I haven't tried the 572B (American spec, not Svetlana) in audio service, but in RF, I've run them at 3kV with no problem. I'd wager they'll handle 4kV OK. They're about $35, and have a plate dissipation of 125-160W, depending on the manufacturer.
I haven't tried the 572B (American spec, not Svetlana) in audio service, but in RF, I've run them at 3kV with no problem. I'd wager they'll handle 4kV OK. They're about $35, and have a plate dissipation of 125-160W, depending on the manufacturer.
Over at head-fi.org there's a discussion about electrostatic headphone amplifier such as this one by Kevin Gilmore:
http://www.cs.ubc.ca/~trifonov/blueHawaii.png
I asked about direct driving speakers, and Kevin said that the above can be used by raising the positive rail to 4kV and substituting 4CX250 for the output tubes and current source. When researching those tubes, I came across the recommendation for 3CX800A7 instead.
That would need one hell of a power supply
http://www.cs.ubc.ca/~trifonov/blueHawaii.png
I asked about direct driving speakers, and Kevin said that the above can be used by raising the positive rail to 4kV and substituting 4CX250 for the output tubes and current source. When researching those tubes, I came across the recommendation for 3CX800A7 instead.
That would need one hell of a power supply
For sanity's sake, I think you need to use an output choke (like a standard push-pull output transformer, but without a secondary). This allows each anode to swing to 2HT in theory, but a little less in practice. Rule of thumb is that you can swing (VRMS) about 0.9 x Vht between the anodes. Thus, if you needed 2kV between the anodes, a 2.2kV HT would be fine. Just very dangerous.
SY: What do you mean by "squirrely"? Does it run very fast up trees and hide nuts?
SY: What do you mean by "squirrely"? Does it run very fast up trees and hide nuts?
Indeed, Kevin is right.
The Acoustat direct drive amp runs at 4.8kV !
At this moment I'm repairing one, and no it's not the audiotubes that have gone bad, but some electrolytics have dried out.
The tube used in this design is the 6HB5, and like Sy said it can be flaky but that's depending on the manufacturer used.
At this moment I have reliable results with the National brand.
Another tube that has been used with good succes at these B+ voltages is the PL519. (Like the 6HB5 this is also a TV sweep tube)
This tube is very rugged and can be punished without dying.
In both cases the output amp is an SRPP, so it uses 2 tubes for driving one stator.
Depending on the ESL used, most of them need more then 1kVrms to drive them to loud levels.
Dick.
The Acoustat direct drive amp runs at 4.8kV !
At this moment I'm repairing one, and no it's not the audiotubes that have gone bad, but some electrolytics have dried out.
The tube used in this design is the 6HB5, and like Sy said it can be flaky but that's depending on the manufacturer used.
At this moment I have reliable results with the National brand.
Another tube that has been used with good succes at these B+ voltages is the PL519. (Like the 6HB5 this is also a TV sweep tube)
This tube is very rugged and can be punished without dying.
In both cases the output amp is an SRPP, so it uses 2 tubes for driving one stator.
Depending on the ESL used, most of them need more then 1kVrms to drive them to loud levels.
Dick.
EC8010 said:
In a manner of speaking, yes. They tend toward random oscillations and runaways.
I'd agree with you on the former points. The prototype I've been itching to scale up (currently, it's at about a kV, but really needs to be closer to 4-5kV in my application) uses just the secondary of an ESL stepup transformer as a centertapped choke- this allows the tubes to run close to class B. And the now-disconnected primary can be shunted with various things to provide damping or compensation. It's also a convenient feedback take-off point, since the voltage swings there are more easily managed.
Acoustat X
Hi,
Im planning to build a direct drive amp for ESL Speakers based on the circuit diagramm of the acoustat X amp.
Is there anybody who has some experience with this amp?
Would like to know how much current is flowing in each branch
of the output at zero load. Also would like to know how big the output transformer is. (Dimensions of the iron part of the transformer)
Greetings form Germany
Zelter
Hi,
Im planning to build a direct drive amp for ESL Speakers based on the circuit diagramm of the acoustat X amp.
Is there anybody who has some experience with this amp?
Would like to know how much current is flowing in each branch
of the output at zero load. Also would like to know how big the output transformer is. (Dimensions of the iron part of the transformer)
Greetings form Germany
Zelter
Zelter,
I have experience with this amp.
Each branch has 5mA current flowing.
Which output transformer ?
It's an OTL.
Don't use the original opamp, use a TL084.
Even better, design a tube stage instead.
Despite it's original design is from the 70ies the sound is good, better with the TL084. It really sings when totally tubed.
Dick.
I have experience with this amp.
Each branch has 5mA current flowing.
Which output transformer ?
It's an OTL.
Don't use the original opamp, use a TL084.
Even better, design a tube stage instead.
Despite it's original design is from the 70ies the sound is good, better with the TL084. It really sings when totally tubed.
Dick.
Hi,
He, he...Well most of the time the amps run the speaker panels full-range and are integrated in the speakers themselves.
So, there aren't really any speaker cables to speak of. Put in a better way, there aren't any speaker terminals exposed to the outside world.
While the voltage is very high, current is usually very low.
Not that you can discard all safety rules of course but I suppose you get the idea.
Cheers,
P.S. I noticed someone mentioning the Acoustat OTL amp...I could be wrong but wasn't there a problem with that particular design?
He, he...Well most of the time the amps run the speaker panels full-range and are integrated in the speakers themselves.
So, there aren't really any speaker cables to speak of. Put in a better way, there aren't any speaker terminals exposed to the outside world.
While the voltage is very high, current is usually very low.
Not that you can discard all safety rules of course but I suppose you get the idea.
Cheers,
P.S. I noticed someone mentioning the Acoustat OTL amp...I could be wrong but wasn't there a problem with that particular design?
Elkaid said:
Well, the amp itself will be highly dangerous. Whether or not there's a shock hazard at the speaker depends on the specific implementation; for example, my design puts several thousand volts DC on the stators, but the stators are insulated-wire types, so there's no real issue there. IIRC, the Acoustat design capacitively couple to the stators (also insulated!), so they ran with zero DC on them.
DD ESL amps should only be attempted by someone with lots of experience with high-voltage circuits, their care and feeding, and safety precautions. The voltages are deadly, and death is quite permanent.
SY said:
It's not just the DC that could permanently kill you, 1kV of audio is quite capable of the job. The audio for electrostatics has to come from a source capable of maintaining a high voltage at a high frequency across a capacitance, and that means that the amplifier can easily supply the 20mA needed to kill you.
I still remember the shock I received as a schoolboy whilst wiring the 100V line PA system in the sports field. I had left everything connected because it never occurred to me that some fool teacher would switch it on, plug in a microphone, and puff into it to see if it worked...
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