kevin gilmore

so due to a comment i made over there, someone wanted to know if i had the eddie current dht filament schematic. here it is. eddiecurrentfilament.PDF

no the zero feedback version does not have high loop gain. no feedback anywhere. not at the input stage and not at the output stage. first stage is a transimpedance amplifier with a output resistor that fixes the gain. output buffer is just that, voltage gain of 1 with no feedback. the feedback version bumps the gain of the input stage and adds about 5db of feedback. or whatever you set it to.

no, you really need that much current gain when you are doing zero feedback. especially if you like those really low distortion numbers. but sure, go ahead and modify.

you definitely need another cap to ground on pin 3 of the opamp.

sure, why not. nelson pass does the same thing with an opto isolator. i've seen various other versions of the same thing over the years, not sure why its not more popular.

because that is the way the original did it. certainly possible to use one pair of led's.

The vbe multiplier really needs to be on the heatsink otherwise thermal runaway may happen.

put a 1.5v battery on the input, and cycle thru the steps and watch the output voltage.

dc filament power supplies normally cause way more trouble than they fix. and you definitely want that supply floating and leave in the 47 ohm resistors.

unless the kitty chewed the pins enough to break the vacuum i don't see how they would get damaged this way.

the perfect amount of sear.

red actually. was looking at the green egg but the kamodo has an infinitely better heavy duty spring loaded hinge that holds the top in any position. total weight of this beast is close to 400 lbs. not easy to move. but unlike the weber which topped out at about 450F, this easily gets to 900F. tonight, tomahawk steak.

opened up the weber a few weeks ago and the rusted bottom dropped out and the thing collapsed. So... steak florentine

norton ghost or whatever its called these days.

sure. and i have 4 original esl63 transformers in stock. (2 transformers make a center tapped pair)

actually for 4cx250, maximum power supply would be +/-1000 volts and forced air cooling for the tubes 3-500z much better. maximum power supply would be +/-2000 volts no forced air cooling after that it gets really large really fast. all tube golden reference power supply is not that hard. custom transformers will have to use very high voltage wire. will look like flyback transformers from old crt color tv.

start with a megatron and change the 8 output tubes to 4cx250 then use +/- 3000v power supplies far more fun. and just a slight bit more dangerous.

all electrostatic headphones are balanced loads. much better and lower distortion to have a balanced input. otherwise you need a phase splitter which is not guaranteed to maintain a gain of -1 as the mu of the tube changes with time. much better to use a differential input amplifier. and once you do that you already have the balanced input. its certainly cheaper to do an unbalanced input amp. if for no other reason a 2 gang vs 4 gang pot. unless you are eddie current and use a 2 gang pot for balanced input. (similar to bryston)

the paltauf is not exactly poorly made. certainly not in the same junk class as eddie current and singlepower. both of which are now out of business. But the chassis is a standard hifi2000 with wood panels bolted to it. the wires attached to the metal panels for circuit board support are not really what i would consider acceptable. an unbalanced amplifier where one more tube would have made it balanced input would seem much more practical. and since we are comparing companies to companies, the woo audio es8 is basically the same thing at 1/3 the price. And built better.

aeras is a fully dc coupled design similar to blue hawaii with no caps in the signal path and no output iron. for those people that want a smaller single box design. beautifully built with custom chassis and quality parts. does anyone really want an inductor based design? take a megatron, remove 4 of the output tubes and add lundahl center tapped inductors and output capacitors. or if you want something physically smaller, pick your favorite 5 watt pentode and do the same thing point to point. i can certainly whip up a circuit board, people just have to decide which is their favorite tubes. maybe $800 in parts total of which $200 is the inductors.

if you want an all tube amplifier with no output capacitors or inductors then get someone reputable to build you a megatron. large voltage swings, and thd < .02%. absolutely flat 20 to 20khz. Bonus points for the all tube power supply. large and heavy to be sure. when you talk to people ask for frequency response and thd #.

the lta unit is something different entirely. and has 1% distortion and switching noise due to the square wave oscillator, diodes and high frequency transformer. The eddie current electra is a center tapped inductor with capacitors on the output. No distortion specs ever published. The original woo audio wes is a pair of inductors with capacitors on the output. No distortion specs ever published. The malvalve has an output transformer and in electrostatic mode the headphones are run off the transformer primary. The new es8 finally has a center tapped inductor and output capacitors. Low power output tubes. The palatauf is highly similar to the es8 with lundahl center tapped inductors ($100 each) and output capacitors. None of these amps have enough voltage gain to have enough feedback to reduce the distortion to reasonable levels. None of these amplifiers have inductors or transformers specifically designed to drive electrostatic headphones which result in various phase and frequency response issues. if i knew of a company that would be willing to correctly wind me some transformers i might be willing to make an amp like this. Even if i wanted to wind my own transformers, availability of the cores i want and the rest of the parts are impossible to find. And there would be 1 more tube gain stage. re: birgir's baked goods. seriously you people have no idea.

front end fets are definitely available. measure the resistance of the plate resistors first. put it on the bench and measure the dc output levels after 30 minutes.

they are the big resistors and they are labeled. 4 or 8 of them depending on model all in a row.

replace all the plate resistors. this is the most likely failure.