Mr. Graham Maynard, wonderfull family history
I am also a Radio Amateur Graham...one of the last to make a CQ DX call (long distance radio calling)
Second World war air figther was wonderfull Graham, you may be very proud, in
your place i will feel pride because of that.
Mosquito, if i am not making confusion, is the one with two motors and 2 vertical
rear stabilizers... pilot go in the middle, between the motors... a beautifull airplane,
could make economy of fuel flying high and with slower speed related others.
I have not so pretty past.... a Religious man, a father of Christian religian arrived
Brazil Northeast, around 1540, and could not resist to the Indians beauty...hehe,
Here i am proving that religious people can be crazy for an indian girl (now Germans
are turning crazy here, returning Germany with our girls), the father had a daugther,
and some more generations passed , and one of the Portuguese Catholic Church father
descendent married one Holland invader...and them one more marriage with an Italian
woman and some more generations...here i am.
My wife was worst, a pirate from Dennmark had one Enginner descendent that arrive Brazil to construct a railroad inside Amazon Jungle.....he saw an Indian very pretty, and
runned to catch her with a rope.... they turn friends, first using energy, and time passing, they get marriage, and this produces my first wife....Red hair.... 180 centimeters Nordic
woman.
The second wife is result of an Spanish man, a revolutionary man that scaped from Spain.
so, i have not so wonderfull past as you, ..... sorry, ...your Majesty, the king of UK.
Very nice History, thank you to share that with us...in special with me.
GEM is the name we call the stones used to jewellery here....so, we go calling GEM, not only because you want that, but also because is a name that is very adequated.
Regards,
Carlos
I am also a Radio Amateur Graham...one of the last to make a CQ DX call (long distance radio calling)
Second World war air figther was wonderfull Graham, you may be very proud, in
your place i will feel pride because of that.
Mosquito, if i am not making confusion, is the one with two motors and 2 vertical
rear stabilizers... pilot go in the middle, between the motors... a beautifull airplane,
could make economy of fuel flying high and with slower speed related others.
I have not so pretty past.... a Religious man, a father of Christian religian arrived
Brazil Northeast, around 1540, and could not resist to the Indians beauty...hehe,
Here i am proving that religious people can be crazy for an indian girl (now Germans
are turning crazy here, returning Germany with our girls), the father had a daugther,
and some more generations passed , and one of the Portuguese Catholic Church father
descendent married one Holland invader...and them one more marriage with an Italian
woman and some more generations...here i am.
My wife was worst, a pirate from Dennmark had one Enginner descendent that arrive Brazil to construct a railroad inside Amazon Jungle.....he saw an Indian very pretty, and
runned to catch her with a rope.... they turn friends, first using energy, and time passing, they get marriage, and this produces my first wife....Red hair.... 180 centimeters Nordic
woman.
The second wife is result of an Spanish man, a revolutionary man that scaped from Spain.
so, i have not so wonderfull past as you, ..... sorry, ...your Majesty, the king of UK.
Very nice History, thank you to share that with us...in special with me.
GEM is the name we call the stones used to jewellery here....so, we go calling GEM, not only because you want that, but also because is a name that is very adequated.
Regards,
Carlos
Graham Maynard said:
I thought you already had a "GEM" amplifier. In fact I am fairly certain, since the whole thread is printed and sitting on my shelf awaiting the time when my test equipment is built (by me).
Should I build this one instead?
Maybe Carlos is the one to answer that question!
Jacco and Stocker, answering you two.
Thank you Jacco, very deep message.
Stocker:
This amplifier can produce a lot of fun to you, but, observing your message;
"Jesus loves you"
I deduce you have something precious, already having something important to believe...those other things, are really a toy for big boys alike us.
You see, even beeing a competent designer, even having fun with his constructions, famous to publish texts in important magazines,...you see the importance Graham give to his family, and how proud and sad he feel about his lost father.
Graham is much more important to me since i discover the good heart he has inside the "crazy scientist envelope"....as important things that happens with him, fast he remember his father and dedicate all good amplifier to his father memories.
I have to increase the size of my "feeling meter" related some persons...as Graham already top the up end limit.
Jesus loving us, we can construct, or not, amplifiers....
Jacco, God is love too...so...let's have fun inside our shacking cars..ahahaha!...may be old car vibrations man?
regards,
Carlos
Thank you Jacco, very deep message.
Stocker:
This amplifier can produce a lot of fun to you, but, observing your message;
"Jesus loves you"
I deduce you have something precious, already having something important to believe...those other things, are really a toy for big boys alike us.
You see, even beeing a competent designer, even having fun with his constructions, famous to publish texts in important magazines,...you see the importance Graham give to his family, and how proud and sad he feel about his lost father.
Graham is much more important to me since i discover the good heart he has inside the "crazy scientist envelope"....as important things that happens with him, fast he remember his father and dedicate all good amplifier to his father memories.
I have to increase the size of my "feeling meter" related some persons...as Graham already top the up end limit.
Jesus loving us, we can construct, or not, amplifiers....
Jacco, God is love too...so...let's have fun inside our shacking cars..ahahaha!...may be old car vibrations man?
regards,
Carlos
Hi Stocker,
The GEM was a long time being developed.
Th class-AABB did not sound right, this is the outcome of dozens of dead ends, and my finished design but for possible adjustable input filter, and temperature controlled line powered ultra low noise AC fan.
I won't be building anything else. It is better than my transformer limited (even though expensive) KT88 chassis.
Cheers ......... Graham.
The GEM was a long time being developed.
Th class-AABB did not sound right, this is the outcome of dozens of dead ends, and my finished design but for possible adjustable input filter, and temperature controlled line powered ultra low noise AC fan.
I won't be building anything else. It is better than my transformer limited (even though expensive) KT88 chassis.
Cheers ......... Graham.
Hi Carlos,
The Mosquito - multipurpose - yes twin engines, Spitfire type, but the plane was faster than a Spitfire - my father said capable of about 450mph ( wooden airframe ) in a dive after munitions released, but not allowed unless for emergency escape purposes - pilot had to push through the throttle stop and then there would be a powerful kick of acceleration, but a report would have to be written giving details. Single tail only though.
My Dad thought the war was awful; he did not like talking about it. His family home in London was not directly hit but suffered damage from a stick of bombs; they had to move.
Of course it is not the amplifiers that are the real loves of our lives, merely aspirations ( our desires for better things ).
Hi stocker,
It already is the final circuit. Now named, as attached.
I could do many things to this circuit, but every option has an associated disadvantage.
At <0.01% this circuit does not have the super-low thd performance that some designers claim, but then nor does it have the NFB loop created output inductivity or poor phase coherence they don't even mention !
At present it has approximately 125W - 4 ohm maximum output, but I recon it could be taken to +/- 45 V rails for 100W - 8 ohm simply by changing the 390 ohm bootstrap feeder to 680 or 820 ohms, and I will try this, but not just at the moment.
I want to think about a novel variable input filter where you can gradually pull down the hf response for less dynamic background/leisure listening, though this would not be just a simple tone control.
I'd be happier with auto-speed silent fan cooling, though no problems so far; its just that an automatic fan would give total peace of mind.
Why not try it for yourself ? Its not complicated !
Give it a new thread ? If it is any good it will make its own way out of here !
Though come to think of it, I wonder when Carlos ( or myself ) last put an amplifier in a case ?
Cheers ....... Graham.
The Mosquito - multipurpose - yes twin engines, Spitfire type, but the plane was faster than a Spitfire - my father said capable of about 450mph ( wooden airframe ) in a dive after munitions released, but not allowed unless for emergency escape purposes - pilot had to push through the throttle stop and then there would be a powerful kick of acceleration, but a report would have to be written giving details. Single tail only though.
My Dad thought the war was awful; he did not like talking about it. His family home in London was not directly hit but suffered damage from a stick of bombs; they had to move.
Of course it is not the amplifiers that are the real loves of our lives, merely aspirations ( our desires for better things ).
Hi stocker,
It already is the final circuit. Now named, as attached.
I could do many things to this circuit, but every option has an associated disadvantage.
At <0.01% this circuit does not have the super-low thd performance that some designers claim, but then nor does it have the NFB loop created output inductivity or poor phase coherence they don't even mention !
At present it has approximately 125W - 4 ohm maximum output, but I recon it could be taken to +/- 45 V rails for 100W - 8 ohm simply by changing the 390 ohm bootstrap feeder to 680 or 820 ohms, and I will try this, but not just at the moment.
I want to think about a novel variable input filter where you can gradually pull down the hf response for less dynamic background/leisure listening, though this would not be just a simple tone control.
I'd be happier with auto-speed silent fan cooling, though no problems so far; its just that an automatic fan would give total peace of mind.
Why not try it for yourself ? Its not complicated !
Give it a new thread ? If it is any good it will make its own way out of here !
Though come to think of it, I wonder when Carlos ( or myself ) last put an amplifier in a case ?
Cheers ....... Graham.
shinOBIWAN, i tried the Krell 100, but could not make it work...do not know
Do not know the mistake i have done.... i checked but could not find the mistake.... i have some time limit to try to fix my own errors of assembling...not more than 5 hours...passing that i accept that i fail and dismount the unit.
If sound bad, with normal VBEs.... i check twice the circuit to see errors in passive... and if no error, i use to give a shot over the board.... my revenge...send it to hell.....BOOOOM!
Will try again, someday, as i could see enormous thread related this circuit, and another very good Engineer, Mr. Jan Dupont appreciate that circuit, and this to me, is a strong sign that the circuit is very good.
I also will produce another leach, because the first one was not good enougth..will try it once again.
regards,
Carlos
Do not know the mistake i have done.... i checked but could not find the mistake.... i have some time limit to try to fix my own errors of assembling...not more than 5 hours...passing that i accept that i fail and dismount the unit.
If sound bad, with normal VBEs.... i check twice the circuit to see errors in passive... and if no error, i use to give a shot over the board.... my revenge...send it to hell.....BOOOOM!
Will try again, someday, as i could see enormous thread related this circuit, and another very good Engineer, Mr. Jan Dupont appreciate that circuit, and this to me, is a strong sign that the circuit is very good.
I also will produce another leach, because the first one was not good enougth..will try it once again.
regards,
Carlos
Well Graham, i have a already ready to fire 54 plus 54 volts supply....10 amps!
So, i will put more transistors in the output...and double extra NPN...will increase to 1K2 the resistor, will change electrolitics to higher voltage and will put power on it.
hehe...wonderfull...and two fans pumping air to that cook machine.
GEM is wonderfull...try it Stocker...easier to construct than you can imagine.
Can call me Charlotte if not satisfied!
regards,
Carlos
So, i will put more transistors in the output...and double extra NPN...will increase to 1K2 the resistor, will change electrolitics to higher voltage and will put power on it.
hehe...wonderfull...and two fans pumping air to that cook machine.
GEM is wonderfull...try it Stocker...easier to construct than you can imagine.
Can call me Charlotte if not satisfied!
regards,
Carlos
Hi CARLOS,
remember me.....
You are one of the most amazing persons on the forum who fascinates me ...your style of writing is too wonderful......continue postings for ever.....
When does the Brazilian Carnival festival starts...[on trucks] could you know the exact date.....
Do you know the Selenium loudspeakers?
At last sorry for little bit of off-topic.
regards,
K a n w a r
remember me.....
You are one of the most amazing persons on the forum who fascinates me ...your style of writing is too wonderful......continue postings for ever.....
When does the Brazilian Carnival festival starts...[on trucks] could you know the exact date.....
Do you know the Selenium loudspeakers?
At last sorry for little bit of off-topic.
regards,
K a n w a r
Hellô Workhorse, you are very kind, and i feel you good people too, already observed
You many times...you are very nice too.
I thank you very much.
Carnival is around february, the firsts days if i am not making mess...but it is in the same period in all Christian countries.
We have a lot of "out of season" Carnival.... in special they use to be jumping from State to State, mainly in Brazilian Northeastern States, going to Bahia, that is the place were that out of season Carnival was invented....normally start at friday nigth and finished around monday 1 O clock morning.
This is organized by State Governments...and there are the "Cold circuits too"...where those trucks visit the German towns we have here, normally in high and cold weather places.... "Winter festival" and things alike...my people is happy, irresponsable happy, having so much problems and smilling all the time...but this is better than find wars to figth and other crazy things.... we are not belicist...for us, brazilians, what matter is make love, eat good food, dance in good parties and never kill no one.... never!
War is not our problem...we are always out of that!....i am afraid if someone invade if we will or not invite them to have lunch with us.
Yes Selenium is already alive, but we have Bravox as the main company to produce speakers here...but very snobish with us, brazilians, you cannot find...all speaker are exported, mainly to United States...we have many other brands...to automobiles competition of sound loudness...but Selenium, Bravox, Arlen, Novik are the main brands here (i am not sure if Arlen and Novik are alive or not)
Selenium produce an armoured tweeter, fluid cooled, silk dome that sounds great.
Now the text i prepare of my last explosions here:
Well boys, i used 54 Volts plus and 54 volts negative into GEM incredible amplifier.
Also i replace the 390 volts resistor that is connected to positive line, the voltage divider to feed bias to all output transistor and trans resistor responsable for bias control, the
Vbe multiplier.
Also i had to increase the 1K resistor that is in the the feedback line, the one that control gain and is connected into feedback diferential transistor.
I had to increase the electrolitic condensers value because of the supply increased value.
Also i installed more transistor in the output, each one of them with 0.33 ohms resistor, the wattage capacity was increased to 420 watts each rail, two fan blowers where attached, one pumping air and the second one exausting.... heatsinks one facing the other,
Insulated by wood and making a tunnel to air flow.
Stand by current was increased to 1 ampere to each 54 volts rails that immediatelly reduced to 51.5 volts each rail.
The extra transistor was adjusted increasing its Vbe till reach 620 milivolts...some nice current to control the amplifier, keeping one guaranteed class A current always flowing
The other transistors are really AB with very bigh bias...the heat did not appear as my
Heatsinks are enormous, fan blower pumping fresh air, natural 25 degrees wind crossing
The room at 4 km per hour speed (around that, i have no anemometer...wind speed meter)
First observation, the gain was reduced, even with the 1K feedback resistor replaced to 2K2....also the high treble turns less beautifull, and i think was the result of increased bias, and also because of transistor slew rate....having to achieve bigger voltage, delayed more time...so, speed to achieve maximum was reduced.... first time to observe the speaker hitting the end...hehe, very nice pop, this is real power...very high power, at least
80 Rms to make this speaker to touch end or compliance movement.
Could not test further, because i touch the Miller Capacitor, very thin leads bent and a short was made between base to colector in my very good 2SC1819.... very hard to find
Transistor this one...and burn a lot of transistors also...one fuse open, the other no..but both rails where damaged... beautifull Sankens gone....
Will prepare a cerimony and will be buried alike heroes in the Cemitery of D’Arlington,
Having 21 shots of cannon 75 milimeters and Marines Military Band playing... a very
Sad moment to me guys...thank you by the messages of support to that pain moment in
My life....no way to have Sanken in this third world land...the best here is 15003 and 15004 or something alike...very slow and treble eater transistors.
Now i am hearing the Symassym, another amplifier designed by Mr. Michael Bittner, a
Class AB unit that sounds great and boomy...because of Tip 3055 in the place of the old
And good Sankens that dead in battle to defend the high fidelity research in South America.
At least, the one is very good even with that loss of brigth.... nice amplifier, but cannot, and could not, beat the GEM...the sound of GEM, was powefull and very clear...you
Feel immediatelly that is in front of the Royalty.
Regards,
Carlos
You many times...you are very nice too.
I thank you very much.
Carnival is around february, the firsts days if i am not making mess...but it is in the same period in all Christian countries.
We have a lot of "out of season" Carnival.... in special they use to be jumping from State to State, mainly in Brazilian Northeastern States, going to Bahia, that is the place were that out of season Carnival was invented....normally start at friday nigth and finished around monday 1 O clock morning.
This is organized by State Governments...and there are the "Cold circuits too"...where those trucks visit the German towns we have here, normally in high and cold weather places.... "Winter festival" and things alike...my people is happy, irresponsable happy, having so much problems and smilling all the time...but this is better than find wars to figth and other crazy things.... we are not belicist...for us, brazilians, what matter is make love, eat good food, dance in good parties and never kill no one.... never!
War is not our problem...we are always out of that!....i am afraid if someone invade if we will or not invite them to have lunch with us.
Yes Selenium is already alive, but we have Bravox as the main company to produce speakers here...but very snobish with us, brazilians, you cannot find...all speaker are exported, mainly to United States...we have many other brands...to automobiles competition of sound loudness...but Selenium, Bravox, Arlen, Novik are the main brands here (i am not sure if Arlen and Novik are alive or not)
Selenium produce an armoured tweeter, fluid cooled, silk dome that sounds great.
Now the text i prepare of my last explosions here:
Well boys, i used 54 Volts plus and 54 volts negative into GEM incredible amplifier.
Also i replace the 390 volts resistor that is connected to positive line, the voltage divider to feed bias to all output transistor and trans resistor responsable for bias control, the
Vbe multiplier.
Also i had to increase the 1K resistor that is in the the feedback line, the one that control gain and is connected into feedback diferential transistor.
I had to increase the electrolitic condensers value because of the supply increased value.
Also i installed more transistor in the output, each one of them with 0.33 ohms resistor, the wattage capacity was increased to 420 watts each rail, two fan blowers where attached, one pumping air and the second one exausting.... heatsinks one facing the other,
Insulated by wood and making a tunnel to air flow.
Stand by current was increased to 1 ampere to each 54 volts rails that immediatelly reduced to 51.5 volts each rail.
The extra transistor was adjusted increasing its Vbe till reach 620 milivolts...some nice current to control the amplifier, keeping one guaranteed class A current always flowing
The other transistors are really AB with very bigh bias...the heat did not appear as my
Heatsinks are enormous, fan blower pumping fresh air, natural 25 degrees wind crossing
The room at 4 km per hour speed (around that, i have no anemometer...wind speed meter)
First observation, the gain was reduced, even with the 1K feedback resistor replaced to 2K2....also the high treble turns less beautifull, and i think was the result of increased bias, and also because of transistor slew rate....having to achieve bigger voltage, delayed more time...so, speed to achieve maximum was reduced.... first time to observe the speaker hitting the end...hehe, very nice pop, this is real power...very high power, at least
80 Rms to make this speaker to touch end or compliance movement.
Could not test further, because i touch the Miller Capacitor, very thin leads bent and a short was made between base to colector in my very good 2SC1819.... very hard to find
Transistor this one...and burn a lot of transistors also...one fuse open, the other no..but both rails where damaged... beautifull Sankens gone....
Will prepare a cerimony and will be buried alike heroes in the Cemitery of D’Arlington,
Having 21 shots of cannon 75 milimeters and Marines Military Band playing... a very
Sad moment to me guys...thank you by the messages of support to that pain moment in
My life....no way to have Sanken in this third world land...the best here is 15003 and 15004 or something alike...very slow and treble eater transistors.
Now i am hearing the Symassym, another amplifier designed by Mr. Michael Bittner, a
Class AB unit that sounds great and boomy...because of Tip 3055 in the place of the old
And good Sankens that dead in battle to defend the high fidelity research in South America.
At least, the one is very good even with that loss of brigth.... nice amplifier, but cannot, and could not, beat the GEM...the sound of GEM, was powefull and very clear...you
Feel immediatelly that is in front of the Royalty.
Regards,
Carlos
Attachments
Fresh brand new dismounted board, "I will be back"
A good friend knowing that i lost my Sankens told me nothing.
10 minutes ago he called me by phone... and say, already gone.
Then i asked him what is gone?
He told me one pair of Sankens gone to my home adress by mail..hehe...in 24 hours more Sanken...and will hear GEM again!
Here is the board dismounted, one of them, will make it again.
This board was made for the second Graham circuit published in this thread, and missed one trimpot to adjust bias.
This board is not for the last GEM version.
Never give up!
I will be back!
regards,
Carlos
A good friend knowing that i lost my Sankens told me nothing.
10 minutes ago he called me by phone... and say, already gone.
Then i asked him what is gone?
He told me one pair of Sankens gone to my home adress by mail..hehe...in 24 hours more Sanken...and will hear GEM again!
Here is the board dismounted, one of them, will make it again.
This board was made for the second Graham circuit published in this thread, and missed one trimpot to adjust bias.
This board is not for the last GEM version.
Never give up!
I will be back!
regards,
Carlos
Attachments
Carlos,
Thanks for the info on the P3A, Leach and Cygnus. I don't think I'll be starting a Leach amp soon as it takes me as long to do the schematic as it does you to build a complete amp, but the GEM looks very tempting.
I think I got your recommendations for the GEM.
Monitor the temperature of the zobel resistor for indication of oscillation. Add a Miller cap if necessary, but because of the class A component, it shouldn't be necessary.
Be careful setting the bias pots because incorrect setting will possibly blow up the amp. I like the idea of putting in safety resistors. Any ideas on the appropriate values? How about a sketch?
I'm not 100% clear on setting the two bias but I would worry about that yet. It will be months before I get to that stage.
Graham,
Thanks for the feedback on my schematic of your amp.
I don't quite understand the implications of the low input impedance. Most amps range form 10k to 100k but the GEM is only about 600 ohms or so. Does this mean you must use a pre-amp? Also, the lack of an input cap means the device connected to the input must be free of DC.
You mention bypass caps, which I assume are the 2 rail filter caps but should the feedback cap C6 be bypassed as well.
Can you give a few details of the PSU? Carlos has sort of hinted at what you have but I'm not clear. With big caps at the amp you don't really too much on the PSU.
What sort of DC offset can I expect?
Thanks
Thanks for the info on the P3A, Leach and Cygnus. I don't think I'll be starting a Leach amp soon as it takes me as long to do the schematic as it does you to build a complete amp, but the GEM looks very tempting.
I think I got your recommendations for the GEM.
Monitor the temperature of the zobel resistor for indication of oscillation. Add a Miller cap if necessary, but because of the class A component, it shouldn't be necessary.
Be careful setting the bias pots because incorrect setting will possibly blow up the amp. I like the idea of putting in safety resistors. Any ideas on the appropriate values? How about a sketch?
I'm not 100% clear on setting the two bias but I would worry about that yet. It will be months before I get to that stage.
Graham,
Thanks for the feedback on my schematic of your amp.
I don't quite understand the implications of the low input impedance. Most amps range form 10k to 100k but the GEM is only about 600 ohms or so. Does this mean you must use a pre-amp? Also, the lack of an input cap means the device connected to the input must be free of DC.
You mention bypass caps, which I assume are the 2 rail filter caps but should the feedback cap C6 be bypassed as well.
Can you give a few details of the PSU? Carlos has sort of hinted at what you have but I'm not clear. With big caps at the amp you don't really too much on the PSU.
What sort of DC offset can I expect?
Thanks
When you need me, just call me Greg, i will be around.
I think explain now, how to adjust this bias, may be lost in your memory, as monthes will pass till you start them, but i will do it.
Those things are good to make immediatelly after explanation, not only to avoid memory problems, but also to fix the information that will turn real practice.... this way will never forget...doing!
I will construct other GEM, as you know i had my problems here...i have burned my circuit because an accident. (Stupid constructor)
When re-constructed, i will put the safety resistor and will adjust it doing.... to limit current into a reasonable level...but this can be calculated too...because will be 2.4 volts flowing into 1K...we have to limit to 0.680 the voltage from base to emitter in the Vbe multiplier.... i will do it and will send you results.
The first idea Graham had, was to adjust 400 miliamperes of current, passing inside the extra NPN transistor.
The first step was reduce the normal transistor bias to zero... joining the Vbe multiplier base to emitter, turning the trimpot to that position, this way no current in the normal output.... and them adjust the other trimpot that increase extra NPN transistor VBE, till the current passing inside colector to emitter, reach 400 miliamperes..... and the last adjustment part was to increase the normal transistors bias to make them conduct something around 100 miliamperes...so, bigger current for the lonely one, the extra transistor, so, it will work in class A.... and low current to others, that will work class AB.
But i made a mess and resulted very good... i made different... i adjusted the normal output transistors to 400 miliamperes, and them i turn the other adjustment (100 ohms trimpot) measuring the voltage from base to emitter in the lonely transistor...when voltage from base to emitter was around 630 to 640 milivolts, i stopped there,...this current will produce good current in Colector to emitter output circuit
So, resulted in a class A amplifier with some class A aid...and even Graham class A has not with too big current..... we can call big biased class AB or underbiased class A...if you prefer bias between AB and A class amplifier.
Graham decided to put 1 ampere flowing in the main transistors and more 100 miliamps to the extra one. (If i remember)
So, things are not well defined in my mind, and Graham must pronunciate about that to define and clarify.
To obtain the current that is circulating you can measure the voltage over emitter resistors.... will be 22 milivolts over 0.22 ohms, resulting in 1A...or ....100 milivolts over 0.1 ohms resistor, resulting also in one ampere.
The extra transistor can be measure the same way....install a resistor in series with the colector and measure the voltage there...lets imagine 40 milivolts for instance,...using ohms law, you have to divide that voltage expressed in Volts (0.040V) divided by the resistance expressed in Ohms (0.1 ohm).. this will result in 400 miliamperes.
To first power on, install 5 ohms resistor, 5 watts in series with positive supply and another one in series with negative supply, this is some protection, because 5 volts will be over that resistor when the current reach 1 ampere...check if both rails have the same voltage over those protective resistors.
They can be used to obtain the current that is circulating, as you can divide the voltage you find over those resistors by its own value to obtain current...let's imagine you found 7 volts:
7 / 5 = 1.4A
In this case, have to reduce current in the main bias trimpot, the one that have the auxiliary transistor.
If something was wrong, and enormous current cross the circuit rails, the voltage over the protection resistor will be enormous..let's imagine that you measured 31 volts over the resistor... this have to be done fast, if not the resistor will melt or explode..too much power over it... the supply switch must be near your hand...or install fuses to burn and open the circuit if something turns bad to you.
31 volts measured over 5 ohms resistor will be 6.2 amperes.
The interesting is that only some volts will be applied to the circuit, this will limit the power circulating... if 6.2 amperes are flowing, and 4 volts are measured (35 the supply voltage less the 31 volts that was developed over the 5 ohms resistor give the result of 4 volts....or the supply lost voltage and over the board only milivolts or you can reach 4 volts there.
Power is voltage multiplied by current...so.... 4 Volts multiplied by 6.2 amperes result in 24.8 watts...no doubts that 100 watts transistor will be alive in that sittuation.... reason why people call that resistor protective resistor to power up.
Well, save this to future references...needing more details i can do it and send direct to your mail adress...just tell me if you need something more, telling me your mail adress to.
If i am explaining something that you already know..something you are tired to know.....very basic informs to you, excuse me, i am sorry, have no intention to disturb you...but will use that to inform some details to the very beginners that use to read our forum to learn some...as i use to do also.
Greg, i am not receiving messages from the forum administration, so, do not know the reason...profile and all options are to send me messages...not receiving, so, needing some, use my direct mail adress:
nanabrother@yahoo.com
regards,
Carlos
I think explain now, how to adjust this bias, may be lost in your memory, as monthes will pass till you start them, but i will do it.
Those things are good to make immediatelly after explanation, not only to avoid memory problems, but also to fix the information that will turn real practice.... this way will never forget...doing!
I will construct other GEM, as you know i had my problems here...i have burned my circuit because an accident. (Stupid constructor)
When re-constructed, i will put the safety resistor and will adjust it doing.... to limit current into a reasonable level...but this can be calculated too...because will be 2.4 volts flowing into 1K...we have to limit to 0.680 the voltage from base to emitter in the Vbe multiplier.... i will do it and will send you results.
The first idea Graham had, was to adjust 400 miliamperes of current, passing inside the extra NPN transistor.
The first step was reduce the normal transistor bias to zero... joining the Vbe multiplier base to emitter, turning the trimpot to that position, this way no current in the normal output.... and them adjust the other trimpot that increase extra NPN transistor VBE, till the current passing inside colector to emitter, reach 400 miliamperes..... and the last adjustment part was to increase the normal transistors bias to make them conduct something around 100 miliamperes...so, bigger current for the lonely one, the extra transistor, so, it will work in class A.... and low current to others, that will work class AB.
But i made a mess and resulted very good... i made different... i adjusted the normal output transistors to 400 miliamperes, and them i turn the other adjustment (100 ohms trimpot) measuring the voltage from base to emitter in the lonely transistor...when voltage from base to emitter was around 630 to 640 milivolts, i stopped there,...this current will produce good current in Colector to emitter output circuit
So, resulted in a class A amplifier with some class A aid...and even Graham class A has not with too big current..... we can call big biased class AB or underbiased class A...if you prefer bias between AB and A class amplifier.
Graham decided to put 1 ampere flowing in the main transistors and more 100 miliamps to the extra one. (If i remember)
So, things are not well defined in my mind, and Graham must pronunciate about that to define and clarify.
To obtain the current that is circulating you can measure the voltage over emitter resistors.... will be 22 milivolts over 0.22 ohms, resulting in 1A...or ....100 milivolts over 0.1 ohms resistor, resulting also in one ampere.
The extra transistor can be measure the same way....install a resistor in series with the colector and measure the voltage there...lets imagine 40 milivolts for instance,...using ohms law, you have to divide that voltage expressed in Volts (0.040V) divided by the resistance expressed in Ohms (0.1 ohm).. this will result in 400 miliamperes.
To first power on, install 5 ohms resistor, 5 watts in series with positive supply and another one in series with negative supply, this is some protection, because 5 volts will be over that resistor when the current reach 1 ampere...check if both rails have the same voltage over those protective resistors.
They can be used to obtain the current that is circulating, as you can divide the voltage you find over those resistors by its own value to obtain current...let's imagine you found 7 volts:
7 / 5 = 1.4A
In this case, have to reduce current in the main bias trimpot, the one that have the auxiliary transistor.
If something was wrong, and enormous current cross the circuit rails, the voltage over the protection resistor will be enormous..let's imagine that you measured 31 volts over the resistor... this have to be done fast, if not the resistor will melt or explode..too much power over it... the supply switch must be near your hand...or install fuses to burn and open the circuit if something turns bad to you.
31 volts measured over 5 ohms resistor will be 6.2 amperes.
The interesting is that only some volts will be applied to the circuit, this will limit the power circulating... if 6.2 amperes are flowing, and 4 volts are measured (35 the supply voltage less the 31 volts that was developed over the 5 ohms resistor give the result of 4 volts....or the supply lost voltage and over the board only milivolts or you can reach 4 volts there.
Power is voltage multiplied by current...so.... 4 Volts multiplied by 6.2 amperes result in 24.8 watts...no doubts that 100 watts transistor will be alive in that sittuation.... reason why people call that resistor protective resistor to power up.
Well, save this to future references...needing more details i can do it and send direct to your mail adress...just tell me if you need something more, telling me your mail adress to.
If i am explaining something that you already know..something you are tired to know.....very basic informs to you, excuse me, i am sorry, have no intention to disturb you...but will use that to inform some details to the very beginners that use to read our forum to learn some...as i use to do also.
Greg, i am not receiving messages from the forum administration, so, do not know the reason...profile and all options are to send me messages...not receiving, so, needing some, use my direct mail adress:
nanabrother@yahoo.com
regards,
Carlos
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