Tube amplifier circuit for a ESL

[tjjohn]

I have built a ESL speaker size about 2.5 feet X 1.5 Feet . the bias voltage is about 1.5 KV and can be raised to 2.5 KV if required safely.

Can some one suggest suitable push pull vacuum tube amplifier circuit for driving this speaker directly without output transformers.

Thanks

tjjohn

 

[jazbo8]

Try searching for Sanders ESL or Acoustat OTL.

 

[Koonw]

I have built a ESL speaker size about 2.5 feet X 1.5 Feet . the bias voltage is about 1.5 KV and can be raised to 2.5 KV if required safely.

Can some one suggest suitable push pull vacuum tube amplifier circuit for driving this speaker directly without output transformers.

Thanks

tjjohn

I don't have the schematic yet, it would be similar to some of the commercial high voltage (about 5kv working voltage) OTL for an output of 1kv. I quote their specs for reference:

1) Acoustat Mono OTL direct drive amplifier for ESL loudspeakers
It's used by Steve's - Do It Yourself - Electrostatic Speakers - Project: ESL 36-6.1.

Max. signal level: 4600 Volt peak to peak
Input sensitivity: 0,2 Volt RMS at clipping point
Bias voltage: upon request 2kV-5 kV max.
Output tube: EL519 in Steve's amp

2) Q.E.D. - OTL Tube-amplifier for driving Quad ESL
Technical specifications
- The maximum output voltage at 1 kHz 4 kV
- harmonic distortion not more than 0.25%
- Nominal load capacitance of 200 pF
- The frequency range 10 - 20000 Hz
- Uneven frequency response of 1 dB
- Nominal output voltage of 1 kV
- Operation of lamps Class A
- Output lamps GMI-11, GP-3
- Sensitivity of 0.7 V
- Mains 220 V, 50-60 Hz
- Power consumption from the mains 500 W

 

[tjjohn]

Thanks for the pointers

Thanks Koonw for the pointers. Will have a look and report back results

tjjohn

 

[Koonw]

Thanks Koonw for the pointers. Will have a look and report back results

tjjohn

Here is another project, at the bottom of the page you find a schematic direct drive amp and power supply. It's also interesting to read the other articles here in Audiocircuit.

 

[hpeter]

how about 35T triode
2kv should do just fine

 

[Koonw]

Some info on EL519 high voltage amp:

If you find that the power out is insufficient to drive the ESL, you can increase the HT to the point that output tube can safely handle, also a clipping detector is useful:

Visit Elektrostatic Loudspeakers for schematic: http://home.kpn.nl/verwa255/esl/amp.zip

"High Voltage Amplifier
My colleague Marcel van de Gevel has designed and built a high voltage amplifier. The amplifier uses 2× PL509 or PL519 for the balanced output stage.The other stages are built with bipolar transistors.The amplifier sounded very clean and pure, but also too soft. It has a LED lamp that lights up during one second each time that the amplifier clips. When you adjust the volume such that it only lights up every now and then, the amplifier just sounds too soft.
This has to do with the supply voltage for the amplifier, which was only 2660V.
The main reason for such a low voltage was the high cost it would take to generate a higher voltage. Because the PL519 can handle peak voltages up to 8000V, the design can be modified (with another power supply) to produce a larger output voltage.

 

[Marco audio]

Hello, what about the 6s20s triode ?
http://klausmobile.narod.ru/td/data/_6s20s.GIF
https://frank.pocnet.net/sheets/113/6/6S20S.pdf
Regards

 

[MarcelvdG]

Wow, that's the first time I've seen a datasheet of a triode showing a mu of about 2000...

The mu and the voltage handling are fine, but the 1.5 mA maximum anode current is much too small, although that may depend on the electrostatic loudspeaker design and the desired power bandwidth. For the loudspeaker and amplifier linked to in post 7, the valves had to be biased at about 40 mA each, if I remember well. With a class-AB SRPP-like output stage, the quiescent current could have been made lower, but the peak currents would still have to be in the dozens of milliamps range.

By the way, Lampie519 has also built a high-voltage amplifier for electrostatic loudspeakers and he solved the power supply issue much better than I did. I stuck to standard off-the-shelf components and ended up building a cascade of which the output resistance got worse and worse as the number of sections increased, he simply had a transformer custom wound and just needed some rectification and smoothing. According to him, custom wound transformers are not that expensive.

In any case, the combination of voltages in the kilovolt range and currents high enough to cause cardiac fibrillation made the amplifier linked to in post 7 the scariest thing I've ever built.

The root of Frank Verwaal's ESL site has changed from ...esl_home.html into ...esl_root.html link

 

[Marco audio]

Thanks for reply.
Lampie 519 is a serious high level diyer.
I have just found that(In french but there is a schematic)

Document sans titre

 

[Lampie519]

I just have build a set of mono amps for a friend of mine plus rebuild my old amps as i had build these almost 15 years ago and over the years i added mod on mod so they became dangerous monsters. Now all has been rearranged and the psu has been beefed up. This created better definition in the micro detail of the music. These amps are used with the original Acoustat esl’s and have replaced the original Acoustat amps. Much more dynamic and spacious sound then the original amps. The original amps have been serviced by me and sold. I do still have spare parts for these amps if anyone would need to have one serviced.
Btw. No exceptional high voltage is needed to drive esl’s. Please check the maximum voltage the foil can take before sparking occurs first as this determines the limits of your esl.
Good luck and have fun building!

 

[Lampie519]

@tjjohn. As your esl’s are relatively low voltage you could use a standard tube pp power amp and connect your esl directly on the primary of the output transformer with coupling capacitors. You will need to terminate the transformers as well with 16 Ohm resistors.

 

[Marco audio]

Hello Lampie 519.
Great job !
Do you build them with the Beveridge patent ?
(I see 4 tubes for one panel:two tubes for one stator,isn't?).
Can you post an output stage schematic, please ?
Otherwise I must thank you for your help with my plasma speakers. They sound great and are perfect with my Sansui SP1000 speakers.

 

[Lampie519]

I used the original Beveridge circuit to start with but changed it to my liking. As hobbyists we are not limited. Companies can not use every circuit out there even if it is superior as some are protected intellectual property. As i am not commercially active i can use any interesting idea. The output stage is a mu-follower instead of the original srpp. Triode strapped lower part (not standard) as it needs to handle 3kv. Serious driver circuit using power tubes, dc coupled to act as dc servo to stabilize the amp.

 

[Marco audio]

I used the original Beveridge circuit to start with but changed it to my liking. As hobbyists we are not limited. Companies can not use every circuit out there even if it is superior as some are protected intellectual property. As i am not commercially active i can use any interesting idea. The output stage is a mu-follower instead of the original srpp. Triode strapped lower part (not standard) as it needs to handle 3kv. Serious driver circuit using power tubes, dc coupled to act as dc servo to stabilize the amp.

During this Covid periode i have studied the Mu follower stage(but no time for english).
The infinite load give a large voltage swing with low distorsion.
Great !
Thanks

 

[Lampie519]

This means that the top tube is actually doing all the work. I do not want to share the circuit at this time as maybe i will sell more amps in the future. Also i get a lot of questions why i stick to the PL519 (my avatar) instead of trying high voltage triodes. This because the triodes can not handle the high voltages and needed current at the same time. Plus pentodes are better followers then triodes. Sure there are different approaches possible.
Yes, i helped you with your plasma project but i am sure that without my help you would succeeded building a working set. Same with dd amps. People who really want them will build them one way or another. Only if you start from scratch you will understand your creation and if it fails you will be able to understand why and fix it. Not so when it is given. Even if it is explained in detail. Try finding someone who can explain the ZOTL concept even it is explained in detail in the patent. Still people tell you it us a digital amp or a hybrid etc. Only if you grasp the idea in all detail you will see the light and will proceed on your own way and succeed with or without help from others. Filtering out the relevant information available is also an art and needs fundamental knowledge of the topic discussed.
So if you are in progress of building i will again be of assistance but i will not give you prefab solutions.
Have fun building!

 

[Marco audio]

Grand merci et gardez bien vos secrets.