Not sure it this is the place for this, but here goes. Can't find the fault after a tube blowout. I have mono block tube amps that are feed directly from a DVD player. The amps feed dynaudio 1.3 mk2s. I had a el34 go out and took out the power supply fuse. I replaced the fuse and the el34. I checked the components for this tube, all was ok. Now for the very strange problem. The soundstage center is almost nonexistant. Just a blur(about a third of the normal width). Left and right is clear and position of components of the music are there. If you lean left or right from the listening position the center clears up(?). I have checked the amps with a distortion analyzer, OK, and ran a sweep of both channels while observing the output on a dual trace scope. Everything is in phase and looks normal. I checked the crossovers visually without removing it and it looks ok. The only way to get the center soundstage to position and sound ok is to offset the speakers by about one foot front to back. I changed the DVD player out with the same results. Am I missing something? The system sounded great before the loss of the tube....................
Try to listen again with a true Mono source or music.
Is the new tube in balance with the other output tubes, i.e. both plate current and transconductance
The surge current caused by the faulty tube may have hurt a power supply cap, something you won't see in a frequency sweep or distortion measurement ( at what frequency ? ) in an amp with feedback, but can be heard easy.
The surge current could also have a magnetize effect on the output transformer core, changing it's properties.
Should this thread be moved to the tube section ?
Is the new tube in balance with the other output tubes, i.e. both plate current and transconductance
The surge current caused by the faulty tube may have hurt a power supply cap, something you won't see in a frequency sweep or distortion measurement ( at what frequency ? ) in an amp with feedback, but can be heard easy.
The surge current could also have a magnetize effect on the output transformer core, changing it's properties.
Should this thread be moved to the tube section ?
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I have seen an EL34 fry the screen resistor. The resistor still measured OK, but would go way up in value as the volume was increased. I found it by cranking the volume and following the smoke! The amp sounded OK, but not quite normal at low volume, but one channel sounded weak and distorted when cranked. It was an SSE amp.
Still very Strange
First, I have been listening to this system(sans mods) for over 10 years, and this is the most difficult problem. I changed all the resistors for the failed tube with the same type and value, no change. The "new tube" is a mullard matched with Flying Cs, all biased within spec. I have tried listening at high volume setting and low. The soundstage with the offset is really quite nice, after reducing the volume slightly for the forward speaker. The bass is reduced as expected. The singer in the middle is rock solid(for this recording I know well) and he stays there no matter the listening position. Set the speakers in the normal symmetric position and sitting in my normal close field position, the singer become lost, like coming from the outer side walls. Lean left or right a few feet, and the singer becomes focused slightly off center(?). I have played a 20-20khz sweep through the system set up symmetric and the sound is centered throughout the freqs that these old ears can hear. Concerning the core of the output transformer having a magnetic bias, wouldn't playing a few hours of "AC" signal through it relieve this condition? Really lost on this one!!!
First, I have been listening to this system(sans mods) for over 10 years, and this is the most difficult problem. I changed all the resistors for the failed tube with the same type and value, no change. The "new tube" is a mullard matched with Flying Cs, all biased within spec. I have tried listening at high volume setting and low. The soundstage with the offset is really quite nice, after reducing the volume slightly for the forward speaker. The bass is reduced as expected. The singer in the middle is rock solid(for this recording I know well) and he stays there no matter the listening position. Set the speakers in the normal symmetric position and sitting in my normal close field position, the singer become lost, like coming from the outer side walls. Lean left or right a few feet, and the singer becomes focused slightly off center(?). I have played a 20-20khz sweep through the system set up symmetric and the sound is centered throughout the freqs that these old ears can hear. Concerning the core of the output transformer having a magnetic bias, wouldn't playing a few hours of "AC" signal through it relieve this condition? Really lost on this one!!!
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That's exactly what it sounds like. Or the tranny secondaries got swapped during the repair attempts. But I've gotten wire polarity swapped too many times because I like to use plain ol' #14 ribbed lamp cord and sometimes the smooth side on some of that stuff has a couple of molding ridges that I mistake for the fine ribs. I've gone for months with a system like that and then say to myslf why does this thing sound so bland, today? So I check it all out starting with the speaker connection and.....DOooooh!
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I never heard about OPTIMATION amplifiers but from the schematic you posted I can tell it's one of the most complex and elaborate tube amps I've ever seen. Was it made for some Industrial/Laboratory purpose or Hi-Fi ? Do you have more info's about this brand ? It would be nice if you could post a few pictures of the beast... Very impressive !
Even the overload indicator is very unusual: it's the very first time I've seen a (very rare) 7323 miniature gas triode (thyratron) used in an audio amp.
Back to your problem: it is obvious that you're listening to out of phase channels, which explains why your soundstage is blurry and you've lost the center (mono) image.
Either one of your connecting cables are reversed or the defective amp (or channel) introduces a 180° phase reversal where it shouldn't. First check your speaker cables and try reversing one channel just to confirm it's a phasing problem. (better to use a mono recording for your tests). If the amp is at fault, debugging may be difficult due to the complex circuit used but I would first check for a missing or broken ground return. With a missing ground return your speakers are connected in floating (or differential) mode and are reproducing only the L-R difference signal.
But without more accurate informations this is only an educated guess..
Even the overload indicator is very unusual: it's the very first time I've seen a (very rare) 7323 miniature gas triode (thyratron) used in an audio amp.
Back to your problem: it is obvious that you're listening to out of phase channels, which explains why your soundstage is blurry and you've lost the center (mono) image.
Either one of your connecting cables are reversed or the defective amp (or channel) introduces a 180° phase reversal where it shouldn't. First check your speaker cables and try reversing one channel just to confirm it's a phasing problem. (better to use a mono recording for your tests). If the amp is at fault, debugging may be difficult due to the complex circuit used but I would first check for a missing or broken ground return. With a missing ground return your speakers are connected in floating (or differential) mode and are reproducing only the L-R difference signal.
But without more accurate informations this is only an educated guess..
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Not sure how easy it is to hook your amp up to the net but I found the tests on this site a lot of fun. 
Online Stereo Polarity (Phase) Sound Test
Or download a phase test in mp3
empeg sound - Phase Test
Online Stereo Polarity (Phase) Sound Test
Or download a phase test in mp3
empeg sound - Phase Test
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http://www.diyaudio.com/forums/tubes-valves/213042-optimation-pa-250ac-lab-grade-audio-amplifier.html
unfortunately not, the current from the output tubes is to low compared to the surge, which magnetized the core.
This could create a weird sort of out of phase signal.
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information
The speakers and their cables have been solder for a year or more. The only disconnect point in the system is the RCA connectors between the amps and the DVD player. Yes, I did check the wiring connections anyway so I am satisfied that the connection are correct. I agree that the problem seem to be a phase issue, but where is the question. Out of phase speaker will null out the bass, not the case with the speakers symmetric in the room. However, it seem the mids are out of phase. The top hats on my reference recording I'm using are still in the same location in the sound stage and are clear. The 20-20khz sweep signal to the speakers are in phase. What about IM distortion? The sweep is a single varying signal. No leads of the output transformer are grounded. It has never been since I have been running the amps but there is a shorting bar that will allow one to connect one side to the frame. I did disconnect the distortion indicator and pulled the 7247 out years ago. Not a flashing light guy. The amps were used in a calibration bench in there younger days, built in 1963.
The speakers and their cables have been solder for a year or more. The only disconnect point in the system is the RCA connectors between the amps and the DVD player. Yes, I did check the wiring connections anyway so I am satisfied that the connection are correct. I agree that the problem seem to be a phase issue, but where is the question. Out of phase speaker will null out the bass, not the case with the speakers symmetric in the room. However, it seem the mids are out of phase. The top hats on my reference recording I'm using are still in the same location in the sound stage and are clear. The 20-20khz sweep signal to the speakers are in phase. What about IM distortion? The sweep is a single varying signal. No leads of the output transformer are grounded. It has never been since I have been running the amps but there is a shorting bar that will allow one to connect one side to the frame. I did disconnect the distortion indicator and pulled the 7247 out years ago. Not a flashing light guy. The amps were used in a calibration bench in there younger days, built in 1963.
The diagram shows that the speakers plug into jacks labeled, HI, LOW, or GND. Which jacks are you using now? I believe if you are using the LOW jack as your (-) or (common) you must use the shorting bar to ground it to the GND jack which should be tied to the chassis for grounding.
It looks like the amp requires some sort of jumpering plug for selecting different speaker impedances. If that is not there then you can only use the HI jack for the (+) side to the speaker. Is that correct?
It looks like the amp requires some sort of jumpering plug for selecting different speaker impedances. If that is not there then you can only use the HI jack for the (+) side to the speaker. Is that correct?
I long ago hard wired the speaker cable directly to the winding wires. The jack and it's many connection has been eliminated. This system has no contact point, just solder connection except the RCA jacks to the DVD player. I have never "grounded" the output wires of the output transformer. I don't understand the reason for having the secondary winding of the output transformer grounded.
djmiddelkoop: do you know how to check for a magnetized core? I am not sure how this could happen. Demagnetizing of this large unit would be a challenge. What would you use to do this? The transformer is rather large.
djmiddelkoop: do you know how to check for a magnetized core? I am not sure how this could happen. Demagnetizing of this large unit would be a challenge. What would you use to do this? The transformer is rather large.
Safety: If a short occurs between the primary and secondary anyone who comes in contact with any exposed output connections will know it.
Demagnetization process of remanent magnetization in the core :
• by applying minimum the same electrical force as the force caused the
magnetization effect.
recommendation:
• starting with similar force as the force which drove the core into saturation
than reducing step by step to demagnetize the core
The only way I see to demagnetize the core is to run an AC current through the primary winding belonging to the failed tube. This current should be slowly decreased to zero. The secondary winding (=output ) must be shorted.
The current could be supplied by a Variac connected to the mains. Measure the current through the winding to ensure you don't destroy it.
There has been some research on this subject, however it was on power transformers only : IEEE Xplore - Effect of Core Magnetization on Frequency Response Analysis (FRA) of Power Transformers
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