Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Lennart on July 23, 2013, 02:25:32 pm
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Hi!
A friend of mine has a Music Man 410 HD that makes him very unhappy. It has blown a bunch of speakers.
After replacing the blown original speakers the same shit happened. He describes it as when he had played for a while the amp suddenly got silent for three seconds or something and then sounded again, but with distortion at low frequences. And the speakers were hot! Two of the new ones blown. Iīve heard it could be short circuit from primary to secondary. When I measure there is no DC at the output jack. Could it be an intermittent problem caused by vibrations? And is there any other possible cause to the problem?
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I believe that there should be no DC on the output jacks.
Normally, no.
What kind of instrument was being played?
Guitar
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OT is probably shunting DC voltage to the speakers , turn amp on check output jack for DC voltage.
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OT is probably shunting DC voltage to the speakers , turn amp on check output jack for DC voltage.
As I said before there is no DC on the output jack...
1. I suspect something intermittant as a result from vibration. Could I be right here?
2. If not 1, is there any other possible cause?
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That amp as with other MM amps has pretty high output tube plate voltages and has SS (current?) drivers on the cathodes of the output tubes. when they first came out Clapton and J. Winter were playing them on the road along with others. Well until they started catching on fire on stage anyway.
Has any work been done on the amp before, like new filter caps? It's old enough to need new ones at this point.
I wonder if something is wrong with the SS cathode drivers?
I did a search for Musicman 410 HD and it came up with that it's probable a HD 130. Which amp is it exactly, there is no MM 410 HD listed in Doug's schemo library.
If it has a 12AX7 for the PI it's an older model that was favored by many.
Brad :think1:
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Has any work been done on the amp before, like new filter caps? It's old enough to need new ones at this point.
I donīt think so. But would new filter caps protect from the speakers to burn?
I did a search for Musicman 410 HD and it came up with that it's probable a HD 130. Which amp is it exactly, there is no MM 410 HD listed in Doug's schemo library.
Yes,the amp is an HD 130. 410 means 4X10" speakers...
If it has a 12AX7 for the PI it's an older model that was favored by many.
This one has IC in the preamp.
But nobody here seems to have any answers to my questions. So far.
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The output stage is more complex on those amps than standard tube only output PA's that are the norm that most guys here have experience with.
I used to own a RD50 with 1x12" speaker but never worked on it. It had a pretty good sound to it.
Setting the bias on those amps is also a little different than what most guys are used to as far as -voltage value readings.
Why is the amp burning up speakers? :dontknow: PRR, HBP or Sluckey (maybe some others) will be able to help you.
But as in any amp if the filter caps are old and are starting to leak they will not be able to support the dc voltages that the amp needs and as they leak more and more they will get hotter which will speed up the aging process. Then at some point 1 or more of them will blow up/short out to ground. That's when things can go from simple fix to big money fix many times.
Anyway if a filter cap went out that could have messed with output stage including the SS driver. That would then mess with the PA's bias which would mess with the OT? All of this is speculation on my part, but filter caps are the kind of thing that is the 1st domino to fall that leads to catastrophic PA failure. But why this would kill speakers? :dontknow:
Brad :icon_biggrin:
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But as in any amp if the filter caps are old and are starting to leak they will not be able to support the dc voltages that the amp needs and as they leak more and more they will get hotter which will speed up the aging process.
Yeah, there are a lot of parts in an amp... :wink:
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This one has IC in the preamp.
But nobody here seems to have any answers to my questions. So far.
It would be of great help to know exactly which amp it is. It's not just a simple run of the mill Fender Champ or even a 5E3 deluxe.
The MM amps in Doug's schemo library are not listed as HD 130.
Brad :think1:
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This one has IC in the preamp.
But nobody here seems to have any answers to my questions. So far.
It would be of great help to know exactly which amp it is. It's not just a simple run of the mill Fender Champ or even a 5E3 deluxe.
The MM amps in Doug's schemo library are not listed as HD 130.
Brad :think1:
http://www.el34world.com/charts/Schematics/files/musicman/musicman_2475-130_&_2275-130.pdf (http://www.el34world.com/charts/Schematics/files/musicman/musicman_2475-130_&_2275-130.pdf)
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Ok, that amp does have the SS cathode drivers.
Schemo says 700vdc for OT plate PS but the cathodes are lifted by about ~60dcv. So you end up with ~640dcv on the output tube plates. Maybe a little more because the wall voltages now area little higher then back in the 70's when the amp was made?
That amp has a high dcv PS with enough current to drive 4x6CL4 (EL34) to ~130w. Who ever works on it should have a good amount of experience because of this. That amp can kill you.
Brad :think1:
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> short circuit from primary to secondary
That should not be fatal to speakers.
Short from B+ to one side of speaker winding.
One end of speaker winding is grounded, and speaker winding has very low DC resistance (<1 ohm). So about 7/8 of any DC current from B+ goes through winding, not speaker.
What is the most current that B+ can supply? 130 Watt output, say 240 Watts of DC from B+ normally, so 0.34 Amps steady-state. A transformer can maybe supply 10X rated current into a short. 3 amps.
7/8 of that 3A in OT speaker winding, 1/8 in speaker. 3/8 or 0.375 Amps in speaker. 0.375A^2*8r is 1.13 Watts of power in the speaker. A "130 Watt" speaker array can stand 1.2W forever.
Assume a *second* defect. OT speaker winding has gone open. All the 3 Amps possible from B+ flow in speaker. 3A^2*8 is 72 Watts of heat in the speaker. A "130 Watt" stage-speaker array "should" survive 72W for many seconds, though if DC the huge excursion will stretch the surround and just-maybe jump the voice coil out of the gap. It is also a race between speaker damage and melt-down of the Power Transformer supplying 10X its rated output.
So it could happen; but I'm real doubtful on the chance of two different faults (short P-S and open S) and in an amp which often works fine.
> amp suddenly got silent for three seconds or something and then sounded again, but with distortion at low frequences. And the speakers were hot!
Something is going on, but I don't have a glimmer.
The 3-second silence, then part-life, ought to be a clue, but I'm blank.
I assume the speakers are good hi-power jobs. (I've seen 100W amps with $30 30W speakers installed thoughtlessly then blown.)
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Something is going on, but I don't have a glimmer.
A picture of my friend: :sad2:
What about a parallell universe influence? :icon_biggrin:
I assume the speakers are good hi-power jobs. (I've seen 100W amps with $30 30W speakers installed thoughtlessly then blown.)
Hmmmm.... When the original speakers burned he installed Jensen JCH 10/35, $45... made in Italy. Mistake? They are really light weight = tiny magnets.
But we are not talking heavy metal.
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Hmmmm.... When the original speakers burned he installed Jensen JCH 10/35, $45... made in Italy. Mistake? They are really light weight = tiny magnets.
Doesn't matter, you still have an amp that's putting out 130w.
Brad :w2:
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Hmmmm.... When the original speakers burned he installed Jensen JCH 10/35, $45... made in Italy. Mistake? They are really light weight = tiny magnets.
Doesn't matter, you still have an amp that's putting out 130w.
Brad :w2:
Not with the volume knobs halfway. And there are four of them. But what speakers would you suggest?
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Better speakers are a good idea, but if youhaven't found the problems upsteam of them
they may not last any longer.
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.........seems like there is only one solution here...a new amp... :w2:
But is it really 100% sure the OT canīt be the cause? The speakers are connected only to the OT. The current that burns the speakers has to come from somewhere, and certainly not from somewhere over the rainbow. Or can it?
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The speakers were too hot!
May be the amplifiers is oscillating at a high frequency at full power. Speakers do not like this.
Take an oscilloscope an look!
Regards,
M.
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The speakers were too hot!
May be the amplifiers is oscillating at a high frequency at full power. Speakers do not like this.
Take an oscilloscope an look!
Regards,
M.
Someone told me that an amplifier of this kind could oscillate with the bias set too hot. Now itīs not too hot but was at first. With the bias at a correct level, what would make the amps oscillate?
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Not with the volume knobs halfway.
When they would list an amps output it was supposed to be full output measured clean. Now they could cheat that number but an map with every thing turned up full could put out 2x that output because the output sine wave is now square. So a 130w amp could put out 260w.
Brad :icon_biggrin:
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Not with the volume knobs halfway.
When they would list an amps output it was supposed to be full output measured clean. Now they could cheat that number but an map with every thing turned up full could put out 2x that output because the output sine wave is now square. So a 130w amp could put out 260w.
Brad :icon_biggrin:
But now we have a situation where the original speakers suddenly burned, and the new replacement speakers burned too. Would it not be very stupid just to buy a set of new ones and hope for the best?
I want to hear more about the oscillation issue.
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I'm just saying don't think that an amp with the knobs set at half only puts out half the wattage rating. It's probably closer to around it's full wattage rating.
Brad :icon_biggrin:
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I did not read all the answer .
The only thing I see is the negative feedback send DC voltage to speaker jack . But Lennart said there is no DC voltage; intermittent , please check in the amp , any mods ?
loose wire ...touching output speaker jacks ????
Amps with Output transformer can't sed DC by the transformer itself
Pictures inside the amp please
Or you friend always put to low powered speakers ?
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Testing testing, one two,
(http://www.flickr.com/photos/99357732@N02/9358876855/[img])http://www.flickr.com/photos/99357732@N02/9361660898/ (http://www.flickr.com/photos/99357732@N02/9361660898/)(http://)http://www.flickr.com/photos/99357732@N02/9358928095/ (http://www.flickr.com/photos/99357732@N02/9358928095/)
(http://www.flickr.com/photos/99357732@N02/9361726928/[img])http://www.flickr.com/photos/99357732@N02/9358953703/ (http://www.flickr.com/photos/99357732@N02/9358953703/)
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Look original , not mods , everything is clean .
Can you tell us what is the speaker your firiend put in and blow .
This not explain why original speaker blow , maybe too old ?
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I succeeded in adding three of five. :dontknow:
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Look original , not mods , everything is clean .
Can you tell us what is the speaker your firiend put in and blow .
This not explain why original speaker blow , maybe too old ?
They are already mentioned in the thread. Jensen JCH 10/35
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I should read all the post , Thank's
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I did a search for Musicman 410 HD and it came up with that it's probable a HD 130. Which amp is it exactly, there is no MM 410 HD listed in Doug's schemo library.
Brad :think1:
Yes Music Man 410 exist .
I have Music man amp book, it is a 75 watts RMS amp, I'll read it but no shematic . I'll comme back later
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I did a search for Musicman 410 HD and it came up with that it's probable a HD 130. Which amp is it exactly, there is no MM 410 HD listed in Doug's schemo library.
Brad :think1:
Yes Music Man 410 exist .
I have Music man amp book, it is a 75 watts RMS amp, I'll read it but no shematic . I'll comme back later
The schematics for the amp is linked earlier in the thread...
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I did a search for Musicman 410 HD and it came up with that it's probable a HD 130. Which amp is it exactly, there is no MM 410 HD listed in Doug's schemo library.
Brad :think1:
Yes Music Man 410 exist .
I have Music man amp book, it is a 75 watts RMS amp, I'll read it but no shematic . I'll comme back later
The schematics for the amp is linked earlier in the thread...
The schematic link I see is for the 130 series ; the HD 130 , 212 HD130 and the 210 HD130
Not same amp as 410 sixty five or 410 seventy five listed in my book
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I did a search for Musicman 410 HD and it came up with that it's probable a HD 130. Which amp is it exactly, there is no MM 410 HD listed in Doug's schemo library.
Brad :think1:
Yes Music Man 410 exist .
I have Music man amp book, it is a 75 watts RMS amp, I'll read it but no shematic . I'll comme back later
The schematics for the amp is linked earlier in the thread...
The schematic link I see is for the 130 series ; the HD 130 , 212 HD130 and the 210 HD130
Not same amp as 410 sixty five or 410 seventy five listed in my book
This is a 130 W amp with 4X10" speakers.
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In my Music ma book I found 410 HD at 150 watts. Yes the 130 shematic could be the good one.
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What the output nominal ohm rating for the 130 HD?
Schematic show 8 ohms !!!
If you use 4 X 8 ohms speaker ; two in parallele IN series with 2 in parallele = 8 ohms
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Music Man amp link
www.pacair.com/mmamps/Misc__Info/Model_Chart/model_chart.html (http://www.pacair.com/mmamps/Misc__Info/Model_Chart/model_chart.html)
Service bulletin ;
pacair.com/mmamps/Documents/MM%20Service%20Bulletins%20All.pdf
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Itīs wired series/parallell 8 ohm.
Is this discussion really necessary?
Can you tell me the reasons an amp would oscillate?
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The speakers are 8 Ohm and wired in series/parallell.
And all knobs go from 1 to 10. :wink:
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I would put a new good quality phase inverter tube ; 12AX7
As I read here ;
www.mk-guitar.com/2009/02/15/music-man-guitar-amps/ (http://www.mk-guitar.com/2009/02/15/music-man-guitar-amps/)
Originally there was one pre-amp tube a 12AX7 used for the phase inverter stage of the amp. This is the stage between pre-amp and power amp. This way a certain amount of tube distortion was added. In about 1977 this tube was replaced with a solid-state version. The reason was that a certain malfunction of this tube could cause severe damage to the complete output section, including a damage to the power tubes and the expensive output transformer. The amps with the new solid-state phase inverter still sound very similar to the earlier models, but are nevertheless by some considered as sounding not as warm as before.
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The speakers are 8 Ohm and wired in series/parallell.
You are sure of that ? Most people don't what it is serie parallel.
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I would put a new good quality phase inverter tube ; 12AX7
Read post#6
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The speakers are 8 Ohm and wired in series/parallell.
You are sure of that ? Most people don't what it is serie parallel.
I do.
:help:
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I would put a new good quality phase inverter tube ; 12AX7
Read post#6
Sorry I did not understand this mean the need to replace the 12AX7
"...If it has a 12AX7 for the PI it's an older model that was favored by many. ......"
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> Not with the volume knobs halfway.
Volume control just means you have to play harder; you can always max-out an amp. (I've had systems clip with knobs at "2".)
> And there are four of them.
Four 35W speakers is 140 Watts. Amp is 130W? If they are good speakers, marketed for serious guitar-amp use, that should be OK. I'm not over-impressed with that series of Jensen. OTOH, I know full-well that a re-speakering of a quad box is BIG money.
I'm still disturbed by the 3-second silence and recovery.
I'd try a 200 Watt dummy load resistor, so the amp can be worked HARD in the shop without attracting cops from the next county. Across that some good speaker with a 100 ohm 10W resistor in series so it plays at part-Watt level.... you can hear OK, but won't hurt the speaker or disturb the peace.
Also clip-lead a DC voltmeter to the amp's B+. Watch it when idle, when working hard, and especially if you manage to get to to crap-out. Both in the silence and the subsequent fuzz. If you have more meters, monitor the amp's bias (if you can figure it out on a MusicMan; on those plans, the 3.9 or 10 ohm resistors are useful points), and the 350V to the screen grids.
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I'm still disturbed by the 3-second silence and recovery.
Iīd like to follow the oscillation track for a while. Letīs say the amp starts oscillating at a certain moment, the speakers get hot, short circuit in two of the speakers, all current run through them and no sound is heard until the coil wire is melted in the two, and the current can run through the other two. :think1:
So my question still is: what creates the oscillation?
To check for oscillation a oscilloscop is needed.
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So my question still is: what creates the oscillation?
To check for oscillation a oscilloscop is needed.
You can read/ see oscillation with Voltmeter on AC mode
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You can read/ see oscillation with Voltmeter on AC mode
OK. And what would cause this oscillation?
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You can read/ see oscillation with Voltmeter on AC mode
OK. And what would cause this oscillation?
I did not have a chance to read you before about that oscillation. Now I must go for the day .
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Oscillation can come from a problem in the feedback circuit. Semiconductor(s) problem. Bad capacitor(s). Problem in powersupply (stabilisation component if used). etc. etc.
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On the board, what seems to be the tremolo section, there are two transistors. One of them are shorted base-collector, both directions. I canīt find it on the diagram. 2nd page to left (Page is turned 90 degress clock wise) is 2N 3391. That one is OK. Could the tremolo unit oscillate uncontrolled some way, even if not used?
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Yes that is possible, and its also possible that then the oscillation is brought to the powersupply.
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Yes that is possible, and its also possible that then the oscillation is brought to the powersupply.
Nice if that is the problem...
Could somebody help me to find that transistor in the diagram?
Here a picture with the two transistors. The broken one is to the right, above the blue trim pot. The three cables with white isolation goes to tremolo foot switch. Edit: Black to tremolo, white to reverb.
http://www.flickr.com/photos/99357732@N02/9361660898/ (http://www.flickr.com/photos/99357732@N02/9361660898/)
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Maybe the reason the transister is not found in the diagram is that the diagram is for a later updated model. In the diagram is written: "On 2275 chassis, bright switch & 0.15 cap. are eliminated." There is a bright switch on this amp. And the chassis number is correct.
I tested the tremolo function. Both transistors is for tremolo. I took out them one at a time and the tremolo stopped. Would the tremolo work with a defct transistor? I mean, maybe the transistor I think is broken, is not. Zero ohm from base to collector schould indicate that the transistor is defect?
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Thank you. Iīm aware of all this.
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Picture of OT upside down. Edit: what am I doing? This is the PT.
http://www.flickr.com/photos/99357732@N02/9368500676/ (http://www.flickr.com/photos/99357732@N02/9368500676/)
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When you say blown, torn speaker cones come to mind. fried, suggests the coils went isup in smoke.
Fried or burned is the case.
If you have a fried transistor, then some thing went wrong and fried it.
Don't know if itīs fried. Broken doesnīt necissarily mean fried?
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You can read/ see oscillation with Voltmeter on AC mode
OK. And what would cause this oscillation?
Try with a new Phase Inverter tube first
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There is none. Itīs solid state.
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There is none. Itīs solid state.
Oups !! So it is the first schematic the good one :BangHead:
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I get the impression that you do not, but just to be clear:
Do you have an oscilloscope and a suitable dummy load?
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An oscilloscop I can borrow, but donīt have a dummy load. How to make one? Order big resistors from somewhere?
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As load I use sometimes an old iron.
And when it gets too hot I put the old iron in a bucket of water. (not too much water).
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I have an iron wich measures 33 ohms. And a 200 W light bulb 19.5 ohms. And five 4 ohms car speakers.
What can I do with this collection? :smiley:
One alternative Iīm thinking of is to swap all electrolytes, 8 pcs, and then test the amp through a 2X12 cabinet witch i do not use. If the speakers are fried, I swap the OT. (is "swap" a correct word here? Iīm Swedish..) Would that be something?
With a oscilloscop, what would the procedure be?
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Use the iron and the lightbulb in parallel.
It is not the max power, but if it oscillates, you can see it, and measure it.
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Lennart,
If you are going to replace parts at random, you might be there for a while. Although replacing the electrolytic filter caps is probably OK, they are starting to age.
First off. The schematics you referenced is actually for 2 amps. One with tube PI and one with SS driver. I take it we are looking at the first schematic on that page that you listed.
Two of those 200 watt light bulbs wired in parallel should, but may not, do the job of dummy load, set the output impedance of amp to 8 ohms.. Solder some leads to them.
You will need an oscilloscope to properly test for oscillation. Most multimeters can't reliably measure anything above 500Hz.
Check the whole circuit board for signs of bad solder joints first. You can see bad ones with a magnifying glass: crystalline, powdery, discoloured, appearance of wire not actually glued to blob of solder, microscopic cracks between solder blob and circuit board, etc.
Really, you need test gear, like signal generator and oscilloscope to tackle a problem like this.
First task is to make sure the poweramp section is working OK. Disconnect R47 and apply 1 volt RMS sine, square or triangle wave signal to pin 2 of IC 8. Do you get a nice replica of that across the dummy load, or does it sound OK with a sacrificial speaker system. If yes then wait until it farts out and then test, or punch it really hard a few times to see if that causes bangs or pops in the sound (bang it with a rubber hammer if you have delicate hands), and so on and so forth.......
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Thanks!
But I think it can be hard to measure anything when that "Something" turns in. Before and after it happens the amp behave normal. It seems like the Brutal Thing suddenly hits, the amp gets silent (Locked, blocked, schocked, shivering? :smiley:), and then sounds again, now with some of the speakers fried and hot. So the question is, is it DC or oscillation? It seems like it happens when the volume is slightly raised when he plays a solo with a dist or drive box. But this is not quite clear, so I have to ask him more about this.
First I will check the solder joints though.
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Actually Lennart, the banging with hammer is probably not such a good idea if you are not experienced. Better to bang around on the circuit boards and wiring connections with the tip of a wooden drumstick, wooden kitchen spoon handle or some other NON CONDUCTING object until you find a spot that is sensitive - crackly, poppy or buzzy - whatever.
This behaviour of suddenly working, or suddenly cutting out when extra loud inputs are applied is very typical of either a dry solder joint, bad IC to socket connection or a faulty switch or potentiometer. It could also be many other things unfortunately.
Those things (dry joints etc) also typically cause "when it warms up it gets faulty" stuff to happen. Unfortunately transistors, op amps and, well ... just about everything else, can exhibit those behaviours as well.
Your conclusion that, ultimately, it is DC or supersonic oscillation that is doing the frypan tick on the speakers seems fair. But what is causing the supersonic oscillation is the big problem. DC is a lot simpler to detect and you appear to have eliminated it.
Best of luck and all the best.
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Iīll be back...
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OK, I found something. When banging around I noticed that the screw and nut that holds one of the driver transistors to, what I assume is the metal cooling plate, is loose. I tried to fasten it but the thread of the screw is totally worn. So the transistor has no contact with the metal part. Comments on that? And how the **** can such a thing happen? Nobody seems to have worked with amp. The guy in the factory was too strong?
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I'm servicing one of these amps right now; it's not exactly a simple circuit, and there are some pretty dangerous voltages inside. The intermittent nature of the problem, coupled with the lack of suitable test gear...
In addition to taking a long time, shotgunning parts won't tell you that you've fixed the fault until the amp stops blowing speakers. Let's say that you replace a bunch of parts, reflow some solder joints, etc, and presume you've fixed it. Then you hook the amp up and it melts some more speakers. Blowing a bunch of speakers is a pretty expensive way of telling you that the amp isn't fixed yet.
You're going to need to:
A) find the problem
B) find out what caused the problem
C) fix the problem
D) make sure that whatever caused the problem won't happen again
I wouldn't feel comfortable connecting this amp to 200+ dollars worth of speakers unless I was SURE that it wouldn't burn them.
Dunno. Weird problem; I can only speculate from here.
I hate to be the one to suggest this, but perhaps you should take the amp to a professional...
Weird question: How is the health of the filament supply? Does it act up at all? Specifically when the amp has been on for a while....
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Do you have any pic's of the board with the loose screw and transistor?
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Replace with new transistor, bolt, screw and most importantly if there is a plastic washer or mica washer under the transistor replace that as well. Smear a very thin coating of thermal paste on both sides of the washer. Clean all surfaces thoroughly first, no abrasives though. That may not be the whole problem but it is definitely a very bad thing. There may also be little plastic washers on the bolt holes of the transistor. It is essential that you replace these exactly as they are now. The plastic washers will hopefully prevent a major explosion when you switch it back on.
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Do you have any pic's of the board with the loose screw and transistor?
http://www.flickr.com/photos/99357732@N02/9358928095/ (http://www.flickr.com/photos/99357732@N02/9358928095/)
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I hate to be the one to suggest this, but perhaps you should take the amp to a professional...
+10000
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I hate to be the one to suggest this, but perhaps you should take the amp to a professional...
+10000
Yeah, off coarse...But the story goes like this. Last year I took care of a bandmates Music Man. Set bias, replaced tubes and electrolytes, and the guy was happy. And then he told the owner of the actuel amp of this and gave him my phone number. He called me and asked if I am willing to look at his amp, and I...why not, at least I can look and see if Iīll find something. I asked him the question why not take it to a proffesional, and the answer was that nobody in town was ready to deal with such an old amp. I donīt know if he tried. Itīs not a very big town, and probably he has to search for someone in another part of the country. The guy is nice but I donīt know him really. He seems a bit strange to me, a young man and
donīt even own a computer or a cell phone, which is extremely rare in this country.
For me itīs a opportunity to learn, and I think itīs fun. I have an education as a TV and amp repairman since younger days, but have never worked in the field, so much of it is forgotten.
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[
For me itīs a opportunity to learn, and I think itīs fun. I have an education as a TV and amp repairman since younger days, but have never worked in the field, so much of it is forgotten.
I understand now , but this kind of amp , solid state with printed circuit is very difficult to work on . Hard way to learn . Vintage tubes amps are most easy .
The problem the amp have ( burninf speaker and now oscillation ) need a very skill repairman or a very very lucky beginner.
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A question. Iīm a bit puzzled about one thing I havenīt thought about before.
There are cables attached to the metal frames of all four speakers, connecting them all together. And when measuring with the multimeter, it proves that these cables are connected to the minus poles of the speakers. Why? It means that all minus poles are one electrical point (language?) What does that mean in a series/parallell winding?
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An oscilloscop I can borrow, but donīt have a dummy load. How to make one? Order big resistors from somewhere?
I use two of these wired in parallel inside of a two banger metal wall junction box that you can buy at Home Depot, Lowe's, etc.:
http://www.mouser.com/ProductDetail/Arcol/HS100-16R-1/?qs=%2fha2pyFadujijxGS6LgfEhSF8Qrp0NAdKBcMwSytpfojd1fucZuuog%3d%3d
(http://www.mouser.com/ProductDetail/Arcol/HS100-16R-1/?qs=%2fha2pyFadujijxGS6LgfEhSF8Qrp0NAdKBcMwSytpfojd1fucZuuog%3d%3d)
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And when measuring with the multimeter, it proves that these cables are connected to the minus poles of the speakers. Why? It means that all minus poles are one electrical point (language?)
1. The speaker coils may have burnt and shorted to the metal structures inside, what do the positive poles of speakers measure to these mystery cables.
2. It means they are not wired series - parallel. Either it is an all parallel wiring, in which case the impedance is one quarter the impedance of an individual (1) speaker,
OR
3. It's very wrong indeed. Do all the speaker + connections go together (measure 0.0 ohms), or not?
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A question. Iīm a bit puzzled about one thing I havenīt thought about before.
There are cables attached to the metal frames of all four speakers, connecting them all together. And when measuring with the multimeter, it proves that these cables are connected to the minus poles of the speakers. Why? It means that all minus poles are one electrical point (language?) What does that mean in a series/parallell winding?
This mean speakers are not well connected . On side of the output transformer ( is going to speakers negative side ) is at ground on the amp . And If all the speakers negative pole are attached to the metal frame of each speaker , there is something wrong there.
You see what I mean when I ask ; "did you know what is serie parallel ? "
There are many other thing you don't see or heard in your amp can help us.
Send picture.
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No, I was wrong... I had diconnected the fried speakers. The two remaining are in parallell, 4 Ohm. The one end of the "extra cables" goes to minus of one of the speakers and then to its own metal frame, and then only to the others metal frames.
Well, I made a dummy load consisting of two water boilers and an iron. Parallell with that a small car speaker connected in series with a bunch of power resistors.
I played at full power and nothing unnormal happened. The dummy load got warm. Even loosened the screw to the drive transistor. I got very hot, but nothing more.
So after all, could it be the that the speakers canīt take the power? :w2:
Last step: I will play it through a 2X12 cabinet.
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If you do a sketch of speaker connection you see how they work . But you probably do that before .
IMO if somebody replace burn speakers and put some new ones that burn too ; Sketch is a must to realy understand AND see if the wiring are OK. That's the way I work.
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I made a sketch and also followd a wire diagram from Music Man, so thatīs not the problem. And also measured the resistans to 8 Ohm.
So I suspect the speakers inability to cope with the power. That subject was up in the beginning of the thread. I asked the man more about the speakers history. When he took over the amp the speakers were already replaced. The guy who sold the amp to him is a friend of his did not have the problem with fried speakers, so the question is, does he play louder than him?
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I made a sketch and also followd a wire diagram from Music Man, so thatīs not the problem. And also measured the resistans to 8 Ohm.
I made a sketch too wit your last information and I see speaker wiring is wrong :dontknow:
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What??
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What??
That 's what I write earlier this morning .
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That post did a long detour in cyberspace. :icon_biggrin:
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I made a sketch and also followd a wire diagram from Music Man, so thatīs not the problem. And also measured the resistans to 8 Ohm.
I made a sketch too wit your last information and I see speaker wiring is wrong :dontknow:
Sorry I MIGHT BE WRONG :BangHead:
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Today Iīve palyed it with the 2x12 cabinet. Itīs made for a 100W amp. Covered the cabinet with blankets and cloths and played with post and pre on 10 for one hour. No problems. What do you think guys, too low speaker power handling?
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I would have expected a DC resistance to be between 6 and 7.
OK, yuo got me. It was 7. But nominal 8...
I am wondering if the speakers that were put in were used.
Yes. Two of them fried. The ghost may have been used up.
The ghost? What does it mean?
Regarding the 2x12 cabinet, what is the cabinet's nominal ohm rating, and what ohm output did you run on the amp?
8 Ohm and 8 Ohm... :smiley:
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Have you fixed that loose transistor?
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Regarding used speakers,
No, sorry, I misunderstood you. They were new.
Just out of curiosity, did the speakers that fried, were they hooked in series? If so, this could explain why you had three seconds of silence, (The second speaker now overloaded,)
Yes, in series. One is now open circuit, the other 0,2 Ohm.
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Lennart , if you have no output for any time period then it returns something is overheating in the circuit weather its caused by oscillation I couldn't tell you neither can anyone else here without it sitting on our bench. My suggestion is start at the input and work to the output of this amp , everyone on here is here to help you , a little less attitude my serve you well friend.
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Have you fixed that loose transistor?
It is a must as soon as possible.
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Yes off coarse. New screw and nut.
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To make it easier for the guy when he borrows my speaker cab, I converted his combo to a top :icon_biggrin:
The "cabinet" is a Lab L5 without amp. Speakers are CTS from -79.
http://www.flickr.com/photos/99357732@N02/9403922474/ (http://www.flickr.com/photos/99357732@N02/9403922474/)
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I keep checking back to see how this ends.
It's like a good mystery. :laugh:
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:guitar1
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Yeeeaaahh!!
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Howdy!
The guy has now played the amp with other speakers cabinets without frying them. But now there is another problem, maybe connected to the other one. Ghost notes, you know. These notes are low and follow the actuel pitch. When a note is played and slowly disappears, the ghost note is more and more evident. That is, it doesnīt fade out in the same amount as the original note. Regardless what speaker is used.
Would you say filter caps?