How to test a Bi-Directional Triode Thyristor

[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.)

 

[jim hardy]

Thanks Tom -
i may have missed a tie point. That makes sense now.

 

[jim hardy]

While 100V secondary lifted: 100 volt filter caps both good ? 100V Bridge ? Winding not grounded ?

 

[Planobilly]

Hi Jim,
In reading the many things that have been said both here and on other forums, it is clear that there are many opinions as to how this amp works. I am most likely the least qualified to make any determination on my own. I also do not understand the heavy black lines. It is also hard to read this schematic for many reasons. The symbol for the triac did not look like anything I had seen before, nor have I find found one just like it elsewhere. Perhaps it is normal and just not known to me.

I will have to do some digging to find out where and how the 100V supply gets to things.I have all the electrolytics removed from the amp at the moment. When I get the parts and things back to normal I will continue the troubleshooting.

As far as the transformer goes there are only three wires going in and six wires coming out. Two each on the secondary for the three voltages and two wires on the primary from the mains, one going through the triac. Also one wire from the thermal safety device. I have not removed the transformer so I guess something could be in a place I can not see but I don't think so. I do not think there is anything special about this transformer as far as I can see at the moment. Someone would need to put me up to speed on how DC could be used to control a transformer in the first place. At the end of the day, three AC voltages come out of the secondary 30V, 60V, and 100V and go to the three bridge rectifiers providing positive and negative supply voltages.

I got the idea from some post that the triac (or what ever was controlling the triac) was not only controlling the timing of the AC but was controlling the voltage to the transformer. I have no idea how that could be possible. Perhaps when I get the book you recommended I will have a better idea of what a triac can be used for. Where ever I got the idea I remember that person saying the voltage to the primary was about 40V. I did not measure the voltage to the primary. I measured the voltage on the secondary after I removed the 100V connection from the transformer to the rectifier. At that time I was not comfortable letting things being powered up and only made a few quick measurements.

And Don...I had given the shotgun approach some thought...but more along the lines of using my 12 gauge on the amp...lol

Cheers,

Billy

 

[Planobilly]

Thanks Tom...good eye!

 

[Planobilly]

While 100V secondary lifted: 100 volt filter caps both good ? 100V Bridge ? Winding not grounded ?

I removed and am replacing all the filter caps Jim. Also 100V windings are good.

 

[jim hardy]

The symbol for the triac did not look like anything I had seen before, nor have I find found one just like it elsewhere. Perhaps it is normal and just not known to me.

Meh,
i'd call it an Andy Warhol Edit oops make that Salvador Dali - triac.

 

[jim hardy]

Someone would need to put me up to speed on how DC could be used to control a transformer in the first place.

When you're ready to go there start a search on Magnetic Amplifier. Dont worry this isn't one.

I got the idea from some post that the triac (or what ever was controlling the triac) was not only controlling the timing of the AC but was controlling the voltage to the transformer. I have no idea how that could be possible.

When you chop out part of the wave you are controlling the voltage.
Shaded are is where conduction is going on

actually, conduction into the caps stops when they've charged , before zero crossing.
Mr Carver's artist was not an electronics guy.
Point is, when there's no conduction, before triac gets fired, there's no voltage applied to the transformer.
That is called "Phase Control ". Your SCR manual has a chapter on it.

Remember "average value" is the area under the curve ?
Firing triac earlier or later in the cycle varies the shaded area. So the average value of voltage is controlled.
This is just a lamp dimmer with electronically adjusted knob, the knob being current through the optocoupler.

Remember - Triac is a just a snap action switch , a very fast one like only a few microseconds to turn on .
Gate current turns it on.
Remove gate current and it stays turned on until current through it falls to almost zero. That happens at or near sinewave zero crossing.

 

[Planobilly]

Thanks Jim,

I went to bed last night thinking about this. I then remembered what the phase angle could be so I now see how the voltage is reduced.

Thanks,

Billy

 

[jim hardy]

I went to bed last night thinking about this.

Our mind settles a lot of things in our sleep. And in the shower, for me ...

Congratulations - we learn fastest by simultaneous doing & studying, don't we ?

 

[Tom.G]

Meh,
i'd call it an Andy Warhol triac.

Salvador Dali maybe? (https://www.google.com/?gws_rd=ssl#q=famous+painting+melting+clock)

Actually it seems to be a slightly elongated line drawing version of the very early symbol for a TRIAC.

 

[jim hardy]

Salvador Dali maybe? (https://www.google.com/?gws_rd=ssl#q=famous+painting+melting+clock)

Actually it seems to be a slightly elongated line drawing version of the very early symbol for a TRIAC.

you are EXACTLY right...
I'll never forget old what's his name ..

Thank you, i'll go fix that.

 

[Planobilly]

You know you are dealing with a strange amp when Salvador Dali's name gets mixed up in the conversation...lol

 

[jim hardy]

TomG cleaned up the schematic.
He sent me a copy
But i don't know how to post it, it's a 3.2meg jpg.
Photobucket didn't work , shrunk it down to illegible.

old jim

 

[Planobilly]

Hi Jim,

Perhaps there is no way to post such a large file here on the forum.

I also received a schematic from Mesa Boogie for the Nomad 45 guitar amp via email that I do not know how to post here. Actually there is no new information on the schematic except for a mod to the amp which we really don't need.

Still do not have the parts yet for the Carver or the Mesa. I guess if one had a 10,000 sq foot room filled with parts there would always be something missing...LOL

I did not grow up in this internet world so I am always having issues trying to post stuff. We all need a couple of nine year old kids to show us the way..!..LOL

Cheers,

Billy

 

[NascentOxygen]

Jim, can your large image be cropped somewhat, and then uploaded? I think the upload limit is around 3 MB

 

[dlgoff]

Jim, can your large image be cropped somewhat, and then uploaded? I think the upload limit is around 3 MB

Dang. I just logged into catch up on this thread and was going to suggest just that. You're putting out some fairly strong bran waves I guess.

 

[Tom.G]

TomG cleaned up the schematic.
He sent me a copy
But i don't know how to post it, it's a 3.2meg jpg.
Photobucket didn't work , shrunk it down to illegible.

old jim

It's a PDF, using ZIP compression internally. I didn't use JPG because that loses details during compression.

I'll try some tight cropping and see what happens.

 

[jim hardy]

Here it is cropped and resized to 50%
still about two screens wide
further reduction is too small to see

and it gets autoshrunk (by forum software i guess) to one screen wide , which is a good thing, keeps it from wrecking the thread - see feedback forums thread on that subject.Image removed to save disk space

 

[jim hardy]

It's a PDF, using ZIP compression internally. I didn't use JPG because that loses details during compression.

Yes i was able to "copy image" and paste into paint, save as jpg... Sorry for the mis-information.

 

[NascentOxygen]

It might be better to leave it as a thumbnail, not display it inside the post, then readers (those who want to see the detail) can open the image in a separate browser tab and magnify it to heart's content.