How to test a Bi-Directional Triode Thyristor

[Planobilly]

Out until tonight.

 

[Salvador]

I apologize before that I will not be able to be helpful here with my post but I just wanted to say a few things, first of all , looks like the triac isn't much of a " regulated psu" after all than a mere safety thing implemented in such a rather puzzling way but maybe it's really useful and has good protection I think Planobilly will see after he solves this mystery.
second of all personally I find the schematic rather hard to read maybe the copy is bad quality but without extreme magnification the traces seem to connectet everywere , although I've seen worse so maybe isn't that bad except for the labeling , I struggled with Onkyo integra myself until i finished it and now it works , although it had a more classic approach when the outputs were blown it simply disconnected the speaker out and when powering up i was able to measure and see the faults easier due to the DC voltage being at the output and also input stages so I frankly knew then were to look for faults.

They do call the transformer a "magnetic field coil". Maybe there is something special about it and the unlabeled pins.

Big Guy said

Well I think it's bla bla radio GA GA , the HI FI high end stuff has many unorthodox names simply for appearance and or any other magic that folks who buy them believe in or like.
For example what Carver meant with magnetic field amplifier as he calls some of his models like the one in question ?

 

[meBigGuy]

I guess you did not read the Carver white paper I linked to.
Too bad.

 

[Planobilly]

Update
After replacing almost everything around the triac and taking a good look at all the transistors without any change I jumped the triac. I lowered the input voltage to around 50V with my variac. One of the filter caps smoked so I removed the secondary connection and am checking the transformer which I think is most likely ok. Nothing got hot except the cap at 50V. I also had a light bulb in the circuit which came on and went off when the cap failed.

I need to order a couple of filter caps and there are a couple of diodes that I want to change. The idea is to find the fault in the amp and then go back to the input of the power supply to resolve the gate issue.

This is for sure not a easy amp to troubleshoot.

This is a link to the patent for the power supply. I really did not understand much of it...https://www.google.com/patents/US4218660

No matter, I am not designing the amp...so I guess I replace parts till get it right...lol

Onward through the frog...or fog or something like that..lol

Cheers,

Billy

 

[Tom.G]

This is a link to the patent for the power supply. I really did not understand much of it...https://www.google.com/patents/US4218660

That patent describes high frequency switching to the power xformer primary. For that to happen, the Triac (TR401) would have to be a Gate Turn Off (GTO) device. That makes sense when you notice that the polarity of D402 and D403 supply Positive and Negative voltage to TR401.

https://en.wikipedia.org/wiki/Gate_turn-off_thyristor

(Sounds like more confusion for this project!)

 

[Salvador]

I read the patent too and quite frankly I don't get were is the big fuss. Carver explains quite reasonably that bigh power HI FI home amps are heavy because of big heatsinks and big transformer.Ok that's true.He also says that heat in heatsinks is a waste product which again is true.
Ok I get his point of jerking the transformer primary to higher and lower power with respect to the input signal waveform with the help of a circuit that " reads" the input and then controls the primary current accordingly by the means of that triac.
But here's the point I don't get , his main points are the size and weight of such amps. with this circuit he hasn't got rid of much the weight only maybe of some of the waste heat in the heatsinks since they now have lower currents at lower signals levels and higher when they are needed. Ok that goes for smaller heatsinks , but the mains transformer being a iron core mains frequency transformer still needs to be as big as the max possible or predicted load of the amplifier will be , in other words it has to be as heavy and big as to be able to supply the amp when it's driven at it's max or near that.
since when a triac is fully open it becomes just a wire and so it simply let's through the whole mains sinus which is no more than 60hz

So where's the gain in that ?

 

[meBigGuy]

Gate Turn Off (GTO) device.

There is a link to the triac spec sheet in the OP.

 

[jim hardy]

Sorry for my gaffes above. I've often said it - I'm a plodder.

There is a link to the triac spec sheet in the OP.

and a link to a Carver brag-sheet in one of meBigGuy's posts.
In that document Mr Carver himself describes the power supply , albeit briefly.
It's just a phase control like a lamp dimmer but instead of a knob it uses that D401/PC401 to control firing angle.
Observe PC401 is under control of the opamp just above.
That opamp's inputs include power supply voltages, and via the heavy dark line a measure of the output.
So i'll correct my last sketch

Good work PlanoBill

 

[Salvador]

Oh trust me Jim , I have added less to this thread than you could ever and I hope Planobilly isn't angry at me for that , I do wanted to say some stuff , I just read the white paper which Big guy desperately wanted me to read.
Much of it is talk-talk although true but still smart advertising then some of it's actual physics and electronics , the thing that still haunts me is were he talks about that a unregulated transformer passes current through only at the peaks of a sinus , isn't that BS? a transformer has the same sinus at it's secondary output the current may lag voltage but it can't simply be there when the voltage has risen to it's max.And with all the benefits at lower power levels and etc I still asked the question which big guy largely ignored dismissing me as a fool , is at full power when the psu is under it's heaviest load , what can the TRIAC help there but to be fully open and acting simply as a wire , so at full power the transformer in this design still becomes the very " dumb" unregulated transformer Carver himself talks about in the paper.So as any transformer it's power rating must be sufficient to deliver the load without dropping much voltage.
I wonder what does the TRIAC and all the fancy name calling (magnetic field etc) help in this case? My guess is nothing.

Also he talks about that a transformer " resists" the ac sine wave 4/5th's of it's time , that would probably be most of the rise and fall time of each cycle , but then how does his TRIAC solve this problem , the TRIAC turns on near the peak of each cycle ad that means that the rise that the transformer primary sees is even steeper almost vertical , ok I see that uses only the most powerful parts of each half cycle , but without that triac those parts are still there with the rest of the rise and fall of the half wave so at near max power again what reduces the very size vs power here ?the frequency is the same.
a genuine question of mine not a show off as some may think.
I also apologize for messing up tis thread but this question seemed very interesting to me.

 

[jim hardy]

the thing that still haunts me is were he talks about that a unregulated transformer passes current through only at the peaks of a sinus , isn't that BS?

no, it's not BS...

Think about a transformer and simple bridge rectifier with capacitor filter

Current flows only during that portion of the cycle where voltage from the transformer exceeds voltage on the filter capacitor. Rest of the cycle the diode is reverse biased. That is the narrow shaded area under the sinewave peak in Carver's drawing.

Here's an example
http://arduino.stackexchange.com/questions/873/reading-a-varying-voltage-into-arduino

That sharp pointy waveform has a high RMS heating value for its average value so it requires big wire
which requires a big core to surround it
I suspect he uses a much smaller transformer than would be required for 1000 watts continuous, and his smart amplifier overloads it only for brief intervals.. hence thermal sensing on the transformer.
But that's only a suspicion - I've never seen the inside of a Carver.

read up on "Crest Factor"

old jim

 

[Salvador]

ok right, stupid me , thanks for pointing that out.I was thinking all the time of a transformer with no bridge rectifier and filter caps at the secondary but those added they do change the picture , hence everything having capacitors also talks about power factor.

according to this graph then we could just use a simply TRIAC for every mains transformer operated psu in it's primary even without the input signal control over it , simply cut off the very starts of rise and fall on each cycle since they would rarely ever go to the cap bank , unless it's being driven so hard the caps are empty almost all the time but that would be beyond hard clipping and distortion anyway.
and so get away with smaller transformers for the same power output ,
why don't others do that ? especially considering the tiny price a thyristor has compared to copper and iron.

 

[jim hardy]

See ? You knew already... Much of learning is discovering what we know.

 

[Planobilly]

Hi guys,

First, I am not put off in the least about what anyone said. A lively bunch of guys are always going to express different thoughts about any subject.

I also did not understand the Bob Carver statements about a transformer resisting the sine wave 4/5 th's of the sine wave. I see Jim is explaining that as I write.

The Carver amp design may in fact be very good, well until one has to repair it...lol Heavy iron may cost lots of money and well, be heavy but it is a hell of a lot less trouble to understand and work on.

One thing is for sure, this project and reading everything everyone has said has forced me to learn a bunch of new stuff!

Cheers,

Billy

 

[Salvador]

now that I'm coming to terms with this approach i would say it's not as complicated as an smps and not as easy as a simple iron with wire outputs , somewhere inbetween.I guess I was a bit out of my manners when I replied to " me big guy" because when I did that I wasn't fully aware of how this thing actually works until Jim pointed out the fact I had forgotten that once you put a rectifier with a cap bank at the load of any transformer it then charges the top of the AC cycle because the rest is already there in the capacitor and this creates uneven load for the AC sine wave.
hence the PFC in the smps units and other stuff.

So Planobilly this is what Carver meant when he was writing about the 4/5ths of a cycle getting through , although I would say the white paper could have been more directly about physics than comparisons and half of it simply about manufacturers that " cheat" and the ones who don't but I guess it's business you have to say some nice words about yourself first.

 

[Tom.G]

There is a link to the triac spec sheet in the OP.

Yup, I missed that. So the patent

This is a link to the patent for the power supply. ...https://www.google.com/patents/US4218660

with its high frequency switching is not applicable here.

 

[Planobilly]

Hi Salvador,

I sort of read around the sales pitch part of the white paper. All this seems straight forward now that Jim posted the graph. Thanks Jim !

Bob Carver seem to be saying "I can build you a amp for $1500 that is just as good as one costing $10,000 and in a blind taste test you can not tell the difference"

I will be glad when the parts get here so I can finish this project.

Cheers,

Billy

 

[Planobilly]

Hi Tom,

I sort of assumed the patent was not directly related to this amp. I did not read all of it. It was more general background information for me into what direction Bob Carver was going toward.

Repairing this amp has taken on a life of it's own and has caused me to consider a good many new things. I guess if one is going to take a dip in the deep end of the pool this amp is as good as any..lol I am sure to many of you this amp design is easy to understand but I have a ways to go to be able to really understand it.

Now if I can just get Jim to show me how to draw on a schematic and get it in a post !

Cheers,

Billy

 

[jim hardy]

Now if I can just get Jim to show me how to draw on a schematic and get it in a post !

click "copy image"
open MSPAINT
click PASTE
click the pencil icon, select a color, draw

click "save as" and give it a name ,
i always save in jpg format because it makes a smaller file than png

Back at pf click UPLOAD IMAGE and start guessing where Windows hid your drawing. I made a folder named "for pf" on desktop where i put mine.

Find Microsoft's "snip" feature, it let's you select and copy part of any image.

 

[meBigGuy]

Just want to share an insight (from the white paper) about why this is a "magnetic" power supply, and can have a significantly smaller transformer and output caps compared to conventional supplies.
(also, it is a class G amplifier, which vastly reduces output stage dissipation)

When the triac switches off, it opens the primary (like an ignition coil) and causes most of the transformers magnetic field energy to dump into the output capacitors.

 

[meBigGuy]

@Planobilly
I really wish you could have made the simple measurements I suggested. That would have helped locate the issue. Who knows how much has been damaged now.

BTW, starting with low line voltage is a good way to destroy things.

Eventually you will need to make the measurements I suggested unless you get real lucky.

 

[jim hardy]

meBigGuy is thinking straight.

I too would like to see 'scope traces at top of R403-C405 to see of the cap is getting charged
and gate of triac to see if any of the charge on C405 makes it on over to gate

 

[Salvador]

I wanted to say that actually I'm quite happy that I jumped into this thread, at first I was much like big guy already said kind of stupid towards the whole concept , went on with what I think it does instead of looking at what it really does.
I must admit I'm taken by surprise.
But happily I now know better.I must say of all the HI FI bla bla bla stuff which is there like 80% of the time and except the sales things of the Carver , this power supply idea is rather simple but very cool , he really manages to squeeze a mains transformer to it's max with not that many extra parts.Quite interesting.
Basically Jim's post about the tops of the rectifier cycle and another place at the internet gave me some clues as one other folk had mentioned about the ignition coil thing besides big guy at one other place.

 

[jim hardy]

as one other folk had mentioned about the ignition coil thing besides big guy at one other place.

i'm still chewing on that one



Thyristor stops conducting when current through it is zero.
At the instant of zero current there should be zero energy in the transformer, energy being ½LI² with I=0 .
So which is true - intuition or math ?
Actually the the thyristor ceases conducting when current through it drops to its "holding current" value , near zero but not quite.
from its datasheet at http://www.datasheet.hk/view_online.php?id=1927120&file=0465\sm16gz41_6629879.pdf

So i am relieved - the "ignition coil" effect is small but very real and there. Math and intuition agree.

meBigGuy is right the filter caps enable graceful turnoff by capturing the stored energy.
R310-C404 help too.

Hang in there Salvador - we all continually add to our understanding one tiny piece at a time. I had missed the significance of C405.

my two cents.

old jim.

 

[Salvador]

well correct me if I'm wrong but I guess I'm starting to get there myself , the whole " secret" is in how and when you turn on or off the sine wave.
if I'm correct the magnetic field strength is larger when the rise or fall of a waveform is steeper or closer to vertical and also when the point at either turn on or off is at a higher potential , in other words if you switch the sine wave to the transformer primary while it's at about few volts above zero the field begins weak and then builds up with the sine wave but that happens evenly and quite slowly the same with turn off , but if you turn on the TRIAC when the sine wave is already at say near maximum , it has high potential at that point so the primary current starts quite quickly and the rise is fast so the field in the transformer starts much stronger than when it would begin together with the sine wave.

this is why they call it an " ignition coil" and ignition coil wo5rks much like an smps only the switching is the other way around , but in both cases you rapidly and suddenly apply a full steady DC potential to where no current and voltage was before and that gives you a rapid change in flux and if the energy source is strong enough a lot of power with it.
the sine wave starts much slower and ends the same way so it doesn't create the fast change in flux and at lower than peak voltages were the caps are already full it simply goes in and back away without much use except for winding loss and stray fields.

this is how I have came to see this if there is something wrong I would appreciate if someone corrected me , thanks.

 

[Planobilly]

As soon as the parts arrive and get installed I will make the measurements you guy ask for. I have replaced or tested everything from the mains to the transformer. The only exception are the two diodes D402 and D403 which were 1n4002 which got replaced with 1n4004's. 1n4002's are on order. The fuse in the transformer is working because voltage got to the three main bridge rectifiers when I jumped the triac.

Edit: also I do not understand the data sheet regarding the triac. What is the max voltage that can be applied at the gate?

 

[jim hardy]

Edit: also I do not understand the data sheet regarding the triac. What is the max voltage that can be applied at the gate?

It's sort of like a zener diode , at some unspecified forward voltage it'll start accepting gate current
They're telling you that unspecified forward voltage will be not more than 3 volts
http://www.datasheet.hk/view_online.php?id=1927120&file=0465\sm16gz41_6629879.pdf

and triac will "fire", ie commence conduction, at gate current ≤ 50 milliamps.
A line or two later they tell you the unspecified gate voltage will be not less than 0.2 volts, so we should see gate pulses between 0.2 and 3 volt .
Up in Maximum Ratings they tell you that if you want to use the triac ever again, don't force enough current into the gate to exceed ten volts between gate and T1.

 

[jim hardy]

if I'm correct the magnetic field strength is larger when the rise or fall of a waveform is steeper or closer to vertical and also when the point at either turn on or off is at a higher potential , in other words if you switch the sine wave to the transformer primary while it's at about few volts above zero the field begins weak and then builds up with the sine wave but that happens evenly and quite slowly the same with turn off , but if you turn on the TRIAC when the sine wave is already at say near maximum , it has high potential at that point so the primary current starts quite quickly and the rise is fast so the field in the transformer starts much stronger than when it would begin together with the sine wave.

There's a long long thread "how power transfers across an ideal transformer"...

Go back to your basics
B=μNI/L_{ength of magnetic path}
The only term that's a function of time is current I .
So magnetic flux is in proportion to current.
The derivative relation between flux and voltage makes it counter-intuitive until you have accustomed your brain to work that differential .

So break up your run-on sentence into bite sized thoughts,
one step at a time,
one thought per line
and your thinking will get better.

AC circuit theory is usually taught without emphasizing that sinewaves are a mathematical oddity -
they and their derivatives look just alike.

 

[jim hardy]

The fuse in the transformer is working because voltage got to the three main bridge rectifiers when I jumped the triac.

That fuse is for gate drive current, not power

with it unplugged - got no ohms between p5 and p6 ?

on another track.......

The PCB track where D402's anode lands - any components nearby where a previous troubleshooter might have accidentally shorted something?

Seems to me this area would require caution when poking around.. check for smoke residue

 

[Planobilly]

Hi Jim,

I built this circuit and why I was asking about the max gate voltage. The lamp was 72 watts, as I did not have a 100 watt bulb. Close SW1 and the lamp lights as would be expected.

I also replaced the 100 ohm resistor with a 1000 ohm resistor. The voltage was 115 VAC 60hz. I did not have a heat sink attached to the triac so I did not leave it on for too long.

So, with this circuit, based on a 72 watt lamp ( lamp resistance of 15 ohms apx. Z=?) and a 1000 ohm resistor and 115 VAC 60hz what is the gate voltage?
I am still stuck on stupid trying to understand the triac...lol

To answer your question about D402 and the area near it...no sign of any shorts. I replaced all the resistors, the two diodes, and the four transistors connected to D402. I have tested the bridge rectifier and the optocoupler which I think are OK.

Cheers,

Billy

Update: after replacing the filter cap I smoked and disconnecting the 100V secondary the triac is working and sending current to the transformer. That is the good news.

Now I need to find the fault in the 100V part of the amp and when I do I think everything will go back to normal. This amp is a PITB to work on...lol...Don't try this at home...lol

 

[jim hardy]

what is the gate voltage?
I am still stuck on stupid trying to understand the triac...lol

The gate voltage in your TEST circuit will be a squarish-looking wave at line frequency
with flat tops between 0.2 and 3 volts
and maybe a spike at front edge that reaches 3 volts.
So a DMM set to AC should read between ~0.15 and ~2 volts.

The gate voltage in your amplifier will be a short pulse once per line half-cycle, again between 0.2 and 3 volts.
It's narrow because its source is C405.
So it has not enough area to cause a DMM to show much of anything. You'll have to measure it with a 'scope.

That's my thinking.Think of the Triac as a snap action switch , initially open,
that snaps closed when gate current reaches a few milliamps
at which point all 3 terminals become very nearly shorted to one another
and remain so until current falls to zero with next sinewave zero crossing , at which time it snaps back open.

That's your simple mental model.

Your "new" SCR manual describes in detail how the gate strikes conduction in a small region and it spreads out from there as current rises , That's why they need di/dt protection. And why it has a finite turn-off time.

A useful device to have in your "bag of tricks" - can be a power control device, also a memory device.

old jim

 

[Planobilly]

OK...Thanks Jim, I think I understand now. Looking forward to reading the SCR manual. Books are generally slow to arrive so it may be a bit before it gets here.

As a side bar I was able to sell two of the Fender Hot Rod DeVille amps so I got more money to feed my amp addiction...lol All these electronic toys seem to be multiplying like rabbits. I need a smaller house and a bigger shop but don't let my wife know I said that...lol

It's back to the farm early in the morning. I have work to do on the back hoe and the potting machine. It helps if one is not put off by the smell of cow manure and diesel fuel !...lol

Cheers,

Billy

 

[jim hardy]

I have work to do on the back hoe and the potting machine.

agreed on shop ...

I have to put torque converter back in neighbor's backhoe. Never a shortage of things to fix, is there ?
Ah well this is after all the age of technology and it should be enjoyed..

IMHO high school should teach more physics and appliance repair .

 

[Salvador]

hopefully we will one day get to the age were technology repairs itself much like robots build cars in an automated conveyor line these days. And then we will be finally able to proceed to the next step which would either be finding out aliens and fighting with them (Star Wars) or the rebellion of the machine and civilization would be taken over by robots (I like Stanley Kubrick's Space Odyssey)

as for the thread topic , I didn't understand from your last response to my post Jim , so was I right in the understanding of this psu design or not or half way there ?
Now it seems logical that opening a primary loop while the sine wave through it is still near its peak causes a larger B field to develop in the core than if the sine wave goes down to zero the usual way it does.Although I guess one would have to calculate the field strength in the switch opening case VS the one you would get if the current runs the way it normally does.
Although Carver talks about getting as much out of the mains through a given size xformer as he can so since the secondary has cap bank to feed this sudden current on/off switching may do the trick.

 

[jim hardy]

so was I right in the understanding of this psu design or not or half way there ?

I apologize Salvador... Iwas having so much trouble parsing out that long long long sentence into individual thought steps that i gave up.

if I'm correct the magnetic field strength is larger when the rise or fall of a waveform is steeper or closer to vertical and also when the point at either turn on or off is at a higher potential , in other words if you switch the sine wave to the transformer primary while it's at about few volts above zero the field begins weak and then builds up with the sine wave but that happens evenly and quite slowly the same with turn off , but if you turn on the TRIAC when the sine wave is already at say near maximum , it has high potential at that point so the primary current starts quite quickly and the rise is fast so the field in the transformer starts much stronger than when it would begin together with the sine wave.

that doesn't sound right to me.
One step at a time. Transformers first.

Here's steady state flux and voltage.

if you energize a transformer by closing the switch(or Triac) at the voltage peak , you start with flux at zero and voltage at peak, which is normal and it's a gentle start for the transformer. That's why they sell solid state relays that switch at peak instead of zero crossing for use with inductive loads.

If you energize a transformer at the voltage zero crossing, you stare art with flux and voltage both at zero which is not normal and some period of adjustment will be required for the flux-voltage relation to establish normalcy.

from http://www.allaboutcircuits.com/textbook/alternating-current/chpt-9/practical-considerations-transformers/

since the transformer core will probably saturate there'll be a current inrush

That inrush can persist for several cycles
from a decent article here http://www.globalspec.com/reference/74817/203279/10-3-transformer-protection

you need to think derivative. For that it's helpful to use non-sine wave.

so closing the triac near peak is easier on the transformer's iron.
But it gives a current surge into the filter capacitors.

You might peruse that ideal transformer thread.

 

[Salvador]

Hmm I will have to read up some more on this but it sounds weird the fact that at zero crossing or starting from zero the flux is higher than when the primary is connected at near peak of half wave.
I was thinking like this , when you are near or at zero the AC value is basically zero for a very short moment of time there is no voltage , that I think we can agree upon.
This is what I can't understand , how can it be when you basically connect almost no voltage to an inductive load there develops a bigger than usual flux and inrush current respectively ?
I've always though it's about how fast the change happens from zero to max that determines many things including core saturation inrush current and flux.
in an smps for example each time a semiconductor connects the primary to the DC load the primary starts off from usually no voltage to suddenly up to max supply voltage and this creates a large flux in the core.
if each of the cycles would be made longer than necessary the core would probably saturate and the current inrush would get even bigger but I can't see how can one saturate a mains iron core with a since wave starting at zero.

Ok I will go read some on my own too otherwise I am turning this into a theory discussion

 

[dlgoff]

I need a smaller house and a bigger shop ...

My whole house is becoming a shop.

 

[meBigGuy]

At any point in time the triac can turn on and the transformer field (current) builds up. When the triac opens, the field collapses causing a voltage surge in the secondary which is captured by the filter capacitors.

 

[jim hardy]

..

When the triac opens, the field collapses causing a voltage surge in the secondary which is captured by the filter capacitors.

That's how a flyback converter works

but to pick nits, the triac won't open until current through it falls to zero (well actually to less than its holding current, 50ma for this one) .

caution - that's the current zero crossing which is not exactly at the voltage zero crossing.

 

[Planobilly]

If all this, let's call it "Carver Power Amp idea" is really such a good idea, could this type of power supply be used in guitar amps? If so, why is it not being done?
I have never met a guitar player who is happy about how heavy his amp is. This is really true with 100 watt plus guitar amps. Ever load a 100 Watt Fender Twin Reverb into the club? Is there anything special about tube amps that would make this system not workable?

Cheers,

Billy

 

[NascentOxygen]

When the triac switches off, it opens the primary (like an ignition coil) and causes most of the transformers magnetic field energy to dump into the output capacitors.

I don't think so!

 

[meBigGuy]

I don't think so!

I'm glad for you, but that's the way it works. Did you read the white paper? I know it's a bit short on hard technical details (to say the least), but that's essentially what it is saying.

BTW, the waveform in Jim's post is Voltage. A standard transformer conducts into the filter caps at the voltage peaks.

I don't know how he is shutting it off at peak current so it can dump into the caps. Let's focus on that for a bit. After-all, such a thing is certainly possible. That is, the " field collapse dump" idea can work, so why wouldn't the circuit do what he says it does.

 

[Salvador]

I think Planobilly the tube amps don't have much use for this type of psu because their load is rather different from a semiconductor amps load. most of the load in tube amps is actually constant because it goes to the heating of the filament which is constant and rather huge especially for big tubes.
I don't know specific numbers but I assume the amps musical output takes up to no more than 1/3 of the other " waste" loads that are supplied all the time , most of which goes to heating filaments then some goes to cathode idle current etc.
for a tube amp I think a well made very "silent" smps would be the weight reducer but you would still need an iron output transformer so half the weight still would be there.
unless someone maybe has an idea about a class D tube amp :d I don't know if that's even possible.But surely would be a bad idea.

 

[Svein]

unless someone maybe has an idea about a class D tube amp

Using tubes as switching devices was tried in the earliest computers. It was not a success.

 

[Planobilly]

Hi Salvador,
I guess guitars players will be out of luck for a while. Perhaps someone in the future will find a way to make light weight transistor guitar amps that will meet the needs of guitar players. For bass guitar, transistor amps are very common and Harke is now making amps with switching power supplies.

Back to the Carver. There is a long conversation at http://www.diyaudio.com/forums/everything-else/69614-carver-magnetic-field-power-amp-whazzit.html
It was long and not easy to read but it did give me a better idea about Carver amps in general. The main guy that was posting said his shop was the factory Canadian warranty station and seemed to be up to speed on Carver. He at one point or the other described the issues I am having dealing with the repair of this amp.

Based on what I have learned so far, I will muddle through this and fix the bloody thing but I don't think I will be in a big hurry to to work on any other Carver amps.
People who are liking this kind of amp also seem to be liking electrostatic speakers which I would not want for free. Each to his own I guess. Of all the Carver amps the M1.ot I have is not well liked as Carvers go. For sure this will be a "fix it and sell it" project.

The biggest issue with working on this amp is how to find the fault It looks like there is no easy answer to that question. To add insult to injury, very small issues with the amp can cause big damage. It appears that one needs to be very up to speed on this amp to work on it. Way passed my skill set at this time but not the first project I have taken on that was over my head! Most likely will not be the last..lol

Thanks for all the education you guys are giving me.

Cheers,

Billy

 

[jim hardy]

I don't know how he is shutting it off at peak current so it can dump into the caps. Let's focus on that for a bit. After-all, such a thing is certainly possible. That is, the " field collapse dump" idea can work, so why wouldn't the circuit do what he says it does.

Had Mr Carver's figure looked like this

i would agree with his explanation.

As to inductive "kick"
The triac will turn off only when current through it has decreased to less than its "holding current " of a few tens of millimaps.
So i expect a small but finite "kick" effect. Perhaps it's enough to power the amp at comfortable listening level of a watt or two..
120 volts X 50ma is after all 6 watts...

Mosfet SMPS's do switch off at substantial current but i think Carver's power supply is more akin to a lamp dimmer .

old jim

 

[jim hardy]

@Planobilly

how's it going?

I didn't get very far in that long conversation.

Where are you at with the amp now ?

Have you figured out how to check the transformer ? Easy if you can disconnect the secondaries...

old jim

 

[Planobilly]

Hi Jim,

The transformer is ok. The fault is in the 100V part of the amp. I disconnected the 100V secondary from the transformer and the triac is working now. I am still looking for parts to show up. Perhaps this week.

Knowing what I know now I understand a little better how to go about troubleshooting this amp. There is no easy way! Check every transistor. Check every opamp. Check every diode, Replace all the electrolytic caps as there are all old. Jeezzs...Oh well, such is life.

At least not having the parts has given me the time to finish a few other projects. I have a Gibson ES 335 that I have been putting off replacing tone caps on. I got it done but it is like building a ship in a bottle! Much teeth nashing and a few rude words in Italian...lol

Cheers,
Billy

 

[jim hardy]

The transformer is ok. The fault is in the 100V part of the amp. I disconnected the 100V secondary from the transformer and the triac is working now.

What Good News !If you're able to get full line voltage across transformer primary, 120V,
that puts to rest one of the (unlikely) suggestions from that diyaudioblog , namely that the transformer is some kind of saturable reactor- because it doesn't saturate and there's not a DC control winding on it .

This part of 100V supply is easy 'nuff

any idea how 100V gets to those opamps that control the photodiode?
If + and - 100 are unbalanced they'll do something to the bottom opamp via R308(or is it 306?) and 309...

i don't have a grip on it yet.
Remember "Deer Hunter" ? It's challenge - nail that trouble in one shot.

I do not understand the significance of that heavy black line that goes so many places.

None of my business i know, but it's sure an interesting circuit.

old jim

 

[dlgoff]

There is no easy way! Check every transistor. Check every opamp. Check every diode, Replace all the electrolytic caps ...

Welcome to the shotgun approach to troubleshooting.

 

[Tom.G]

I do not understand the significance of that heavy black line that goes so many places.

It is circuit common, or Ground in the vernacular. (notice it connects to the low side of the audio input connectors in the upper left of the schematic and the CT of the pwr xformer secondary.)