Fisher KX-200 driving a pair of ESL from the plates - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 24th April 2015, 06:55 PM   #1
mazur is offline mazur  United States
diyAudio Member
 
Join Date: Dec 2005
Location: Rockville, MD
Default Fisher KX-200 driving a pair of ESL from the plates

Hi.

I have a Fisher KX-200 that I connected an electrostatic panel stators directly to the 7591 plates. The ESL speaker is covering the band >200Hz with an active crossover. It works fine and sounds pretty good, but I had two questions:

- What happens if I take the OPT out completely and connect B+ directly to the plate? If it's doable, are there any advantages to doing it?

- How about the feedback from the OPT common...can I lower or even disconnect?

You can see the service manual on Fisher KX-200 Manual - Stereophonic Master Control Amplifier - HiFi Engine

Here is the output section of the schematic:

kx200.JPG

Thanks for the help
Elias
  Reply With Quote
Old 24th April 2015, 07:22 PM   #2
diyAudio Member
 
Join Date: Feb 2010
Location: Helsinki
Quote:
Originally Posted by mazur View Post
I have a Fisher KX-200 that I connected an electrostatic panel stators directly to the 7591 plates.
Ah, direct drive ESL! The King of High End Fidelity! =)

Quote:
- What happens if I take the OPT out completely and connect B+ directly to the plate? If it's doable, are there any advantages to doing it?
If you take the OT out of the circuit, the output tubes' anodes stop producing any voltage swing.

You could replace the OT with two chokes possibly.

Quote:
- How about the feedback from the OPT common...can I lower or even disconnect?
Your amp is not very linear without that NFB.

You're on to an excellent thing (direct drive ESL), but I'd start fresh. I've done some experiments with (all DIY) ESL headphones and some some small panels, and direct drive really is the way to go.

It's a big project though. I'd use about 1000V B+, and a transmitter triode with a MOSFET plate load. All balanced, CCS tails of course.
  Reply With Quote
Old 24th April 2015, 07:39 PM   #3
mazur is offline mazur  United States
diyAudio Member
 
Join Date: Dec 2005
Location: Rockville, MD
Thanks MrCurwen. In reality, because I'm only using the amp from ~200Hz and above, the load on the OPT is not too bad. I had it at full power driving the ESL panels for a while and the dummy load barely got warm.

Agreed that a DIY amp like you suggest is the way to go and I'm planning to eventually build one. I have a copy of the Audio Amateur issue with the article from David Hermeyer describing his amp, which is very much like what you suggest. I have a few 1625 tubes around and though about using them, though they do not go that high in terms of voltage.
  Reply With Quote
Old 24th April 2015, 07:56 PM   #4
diyAudio Member
 
Join Date: Feb 2010
Location: Helsinki
What kind of voltage swing do your panels need?
  Reply With Quote
Old 24th April 2015, 08:13 PM   #5
mazur is offline mazur  United States
diyAudio Member
 
Join Date: Dec 2005
Location: Rockville, MD
Not sure. These panels were built by a friend's dad long time ago, probably by the time David Hermeyer's article came out :-) I got them a few years' back and now finally decided to bring them to life. They are segmented, each panel about 38"x6", I have 4 in each speaker. The KX-200 has about 430V B+ and it plays loud enough for my listening room. Not too loud though. I can vary my bias supply, at ~2500V it starts to crackle a bit, so that's probably as much as it likes. I think around 1000V voltage swing would be just about right.

Here are the panels after I rebuilt the frame:

WP_20150421_001.jpg
  Reply With Quote
Old 24th April 2015, 08:42 PM   #6
diyAudio Member
 
Join Date: Feb 2010
Location: Helsinki
That's a thing of beauty!

Well, cheap and easy to obtain 2C22 would do about 800 V differential swing. Then there's 2C26A, which could do a whole lot more. It's also cheap.

I would use real triodes, and low current types. Dissipation becomes a real issue with high B+.

I've built (for a electrostatic deflection TV no less) a balanced amp that did 700 V differential swing with 650V B+, using 2C22. Great linearity. For my ESL experiments I used the same kind of amp. My panels were really bad though (one caugh on fire rather dramatically), so I couldn't comment on volume.

I'll draw up a schematic of the 2C22 amp on Spice.
  Reply With Quote
Old 24th April 2015, 08:49 PM   #7
mazur is offline mazur  United States
diyAudio Member
 
Join Date: Dec 2005
Location: Rockville, MD
A schematic would be great!! Thanks.

I'm really hoping my panels don't follow yours and go up on flames. According to my friend, his dad use to play them often, so I'm hoping that won't happen. He probably built an amp too but I could not find it :-(
  Reply With Quote
Old 24th April 2015, 09:15 PM   #8
diyAudio Member
 
Join Date: Feb 2010
Location: Helsinki
I don't have a Spice model for 2C22, but this approximates it close enough.

Swings 900 volts before clipping. FETs should be 1000V types. Output to stators is at the sources of the plate loads.

Hard to say how loud it would be on a particular panel. Good thing is, this kind of amp is not that expensive to build, and most parts can be reused if it turns out insufficient.
Attached Images
File Type: png big swing amp.png (9.0 KB, 68 views)
  Reply With Quote
Old 27th April 2015, 03:19 PM   #9
mazur is offline mazur  United States
diyAudio Member
 
Join Date: Dec 2005
Location: Rockville, MD
Quote:
Originally Posted by MrCurwen View Post
I don't have a Spice model for 2C22, but this approximates it close enough.

Swings 900 volts before clipping. FETs should be 1000V types. Output to stators is at the sources of the plate loads.

Hard to say how loud it would be on a particular panel. Good thing is, this kind of amp is not that expensive to build, and most parts can be reused if it turns out insufficient.
Thanks for the schematic. I connected the Fisher KX-200 yesterday and it sounded really nice. They have about 440V on the plates. Pretty loud and the sound is amazingly clear.

I'll start looking into building the amp.

Thanks again.
Elias
  Reply With Quote
Old 4th May 2015, 08:17 PM   #10
mazur is offline mazur  United States
diyAudio Member
 
Join Date: Dec 2005
Location: Rockville, MD
Quote:
Originally Posted by MrCurwen View Post
I don't have a Spice model for 2C22, but this approximates it close enough.

Swings 900 volts before clipping. FETs should be 1000V types. Output to stators is at the sources of the plate loads.

Hard to say how loud it would be on a particular panel. Good thing is, this kind of amp is not that expensive to build, and most parts can be reused if it turns out insufficient.
Hi MrCurwen. I have a 500V variable PS that I was thinking about using to power these. If I put 500V instead of 800V, what adjustments I need to do? What's the wattage of the load resistors?

Thanks
Elias
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Driving ESL from tube plates mazur Planars & Exotics 48 6th May 2015 10:17 PM
WTT dynaco st-35 for Fisher kx-200 Sk8Ter Swap Meet 1 11th March 2015 10:25 PM
Fisher KX-100 transformers deicide67 Swap Meet 1 7th September 2013 12:32 PM
Fisher kx-100 Recitfire problem Audimax Tubes / Valves 6 23rd November 2009 08:56 AM
FS: Fisher KX-100 speaker Swap Meet 1 12th May 2007 10:14 PM


New To Site? Need Help?

All times are GMT. The time now is 07:55 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2015 DragonByte Technologies Ltd.
Copyright 1999-2015 diyAudio

Content Relevant URLs by vBSEO 3.3.2