Guitar Research T60R Zener Diode values

[hatcherd]

A customer brought me a Guitar Research T60R Tube (1 12AX7) that the zerner diodes are fried. Does anybody know what value these zeners might be or does anybody know where you can get schematics for these amps? In addition, what would have caused the zeners to blow? Nothing else around them is bad, so it seems.

[teemuk]

It's an OEM product of Chinese Mega Amplifier.
::::: Welcome to Mega Amps :::::
Try emailing them.

[hatcherd]

Guitar Research Zeners

I have - no repsonse. There is also another company that sells Mega amplifiers called Guitar Jones, Inc, but calling that number from the website leads you to a medical clinic!

Thanks, I will keep trying.

[Enzo]

OK then, what do the zeners do in the thing? Are they voltage regulators for the +/-15v supplies or something - assuming it has them? I mean besides this one tube, are there op amps and such?

[hatcherd]

Guitar Research Zeners

I am not sure if they are regulators for the +-15V but there are op amps. So they probably are the voltage regulators for the op amps - is that your guess?

The real question is this: After we figure out what zener's I need, what do you think caused them to crash and burn?

[Enzo]

If there are two, then that points to power supply. Is there a dropping resistor from the non-grounded end of each to a higher voltage supply? And you got op amps? OK, so measure continuity or follow traces from the op amp power pins to these diodes.

if these zeners run the op amps, we usually expect them to be 15v, maybe 12 in some cases. Very rarely 5v.

If there are op amps, there pretty much has to be regulated power supply for them. if not zeners, then likely three- terminal regulator ICs. You got any 7815/7915 or similar on there?

Are we sure both failed? Run the unit a little bit, then stick your finger on the top of each IC. Any getting hot? Pull it and see if your voltages return. The zeners might be fine and the circuit is loaded by a shorted IC. Also a filter cap could be loading things down.

[doctorvalve]

mega t60r zeners

A customer brought me a Guitar Research T60R Tube (1 12AX7) that the zerner diodes are fried. Does anybody know what value these zeners might be or does anybody know where you can get schematics for these amps? In addition, what would have caused the zeners to blow? Nothing else around them is bad, so it seems.

i have unfortunatly, one of these on the bench right now, but a different problem . i measured the voltage on the zeners ,they are 15 volt types. if you come across a schematic post the link, regards,doctorvalve.

[KennyDee]

If this helps with finding the cause of the problems, I'm glad to have helped.....

A Zener diode is a diode which allows current to flow in the forward direction in the same manner as an ideal diode, but will also permit it to flow in the reverse direction when the voltage is above a certain value known as the breakdown voltage, "zener knee voltage" or "zener voltage" or "avalanche point".

The device was named after Clarence Zener, who discovered this electrical property. Many diodes described as "zener" diodes rely instead on avalanche breakdown as the mechanism. Both types are used. Common applications include providing a reference voltage for voltage regulators, or to protect other semiconductor devices from momentary voltage pulses.

Operation

A conventional solid-state diode will allow significant current if it is reverse-biased above its reverse breakdown voltage. When the reverse bias breakdown voltage is exceeded, a conventional diode is subject to high current due to avalanche breakdown. Unless this current is limited by circuitry, the diode will be permanently damaged due to overheating. A zener diode exhibits almost the same properties, except the device is specially designed so as to have a reduced breakdown voltage, the so-called zener voltage. By contrast with the conventional device, a reverse-biased zener diode will exhibit a controlled breakdown and allow the current to keep the voltage across the zener diode close to the zener breakdown voltage. For example, a diode with a zener breakdown voltage of 3.2 V will exhibit a voltage drop of very nearly 3.2 V across a wide range of reverse currents. The zener diode is therefore ideal for applications such as the generation of a reference voltage (e.g. for an amplifier stage), or as a voltage stabilizer for low-current applications.[1]

Another mechanism that produces a similar effect is the avalanche effect as in the avalanche diode.[1] The two types of diode are in fact constructed the same way and both effects are present in diodes of this type. In silicon diodes up to about 5.6 volts, the zener effect is the predominant effect and shows a marked negative temperature coefficient. Above 5.6 volts, the avalanche effect becomes predominant and exhibits a positive temperature coefficient.[2]
TC depending on zener voltage

In a 5.6 V diode, the two effects occur together and their temperature coefficients nearly cancel each other out, thus the 5.6 V diode is useful in temperature-critical applications. An alternative which is used for voltage references that need to be highly stable over long periods of time is to use a Z-diode with a TC of +2 mV/°C (breakdown voltage 6.2-6.3 V) connected in series with a forward-biased silicon diode (or a transistor B-E junction) manufactured on the same chip.[3] The forward biased diode has a TC of -2 mV/°C, causing the TCs to cancel out.

Modern manufacturing techniques have produced devices with voltages lower than 5.6 V with negligible temperature coefficients[citation needed], but as higher voltage devices are encountered, the temperature coefficient rises dramatically. A 75 V diode has 10 times the coefficient of a 12 V diode.

Zener and avalanche diodes, regardless of breakdown voltage, are usually marketed under the umbrella term of "zener diode".
Construction

The zener diode's operation depends on the heavy doping of its p-n junction. The depletion region formed in the diode is very thin (<1 µm) and the electric field is consequently very high (about 500 kV/m) even for a small reverse bias voltage of about 5 V, allowing electrons to tunnel from the valence band of the p-type material to the conduction band of the n-type material.

In the atomic scale, this tunneling corresponds to the transport of valence band electrons into the empty conduction band states; as a result of the reduced barrier between these bands and high electric fields that are induced due to the relatively high levels of dopings on both sides.[2] The breakdown voltage can be controlled quite accurately in the doping process. While tolerances within 0.05% are available, the most widely used tolerances are 5% and 10%. Breakdown voltage for commonly available zener diodes can vary widely from 1.2 volts to 200 volts.
Surface Zeners

The emitter-base junction of a bipolar NPN transistor behaves as a zener diode, with breakdown voltage at about 6.8 V for common bipolar processes and about 10 V for lightly doped base regions in BiCMOS processes. Older processes with poor control of doping characteristics had the variation of Zener voltage up to +-1 V, newer processes using ion implantation can achieve no more than +-0.25 V. The NPN transistor structure can be employed as a surface zener diode, with collector and emitter connected together as its cathode and base region as anode. In this approach the base doping profile usually narrows towards the surface, creating a region with intensified electric field where the avalanche breakdown occurs. The hot carriers produced by acceleration in the intense field sometime shoot into the oxide layer above the junction and become trapped there. The accumulation of trapped charges can then cause Zener walkout, a corresponding change of the Zener voltage of the junction. The same effect can be achieved by radiation damage.

The emitter-base zener diodes can handle only smaller currents as the energy is dissipated in the base depletion region which is very small. Higher amount of dissipated energy (higher current for longer time, or a short very high current spike) will cause thermal damage to the junction and/or its contacts. Partial damage of the junction can shift its Zener voltage. Total destruction of the Zener junction by overheating it and causing migration of metallization across the junction ("spiking") can be used intentionally as a Zener zap antifuse.[4]
Subsurface Zeners

A subsurface Zener diode, also called buried Zener, is a device similar to the surface Zener, but with the avalanche region located deeper in the structure, typically several micrometers below the oxide. The hot carriers then lose energy by collisions with the semiconductor lattice before reaching the oxide layer and cannot be trapped there. The Zener walkout phenomenon therefore does not occur here, and the buried Zeners have voltage constant over their entire lifetime. Most buried Zeners have breakdown voltage of 5-7 volts. Several different junction structures are used.[5]
Uses
Zener diode shown with typical packages. Reverse current -i_Z is shown.

Zener diodes are widely used as voltage references and as shunt regulators to regulate the voltage across small circuits. When connected in parallel with a variable voltage source so that it is reverse biased, a zener diode conducts when the voltage reaches the diode's reverse breakdown voltage. From that point on, the relatively low impedance of the diode keeps the voltage across the diode at that value.[6]
Zener diode voltage regulator.svg

In this circuit, a typical voltage reference or regulator, an input voltage, UIN, is regulated down to a stable output voltage UOUT. The breakdown voltage of diode D is stable over a wide current range and holds UOUT relatively constant even though the input voltage may fluctuate over a fairly wide range. Because of the low impedance of the diode when operated like this, resistor R is used to limit current through the circuit.

In the case of this simple reference, the current flowing in the diode is determined using Ohm's law and the known voltage drop across the resistor R;

IDiode = (UIN - UOUT) / RΩ

The value of R must satisfy two conditions :

R must be small enough that the current through D keeps D in reverse breakdown. The value of this current is given in the data sheet for D. For example, the common BZX79C5V6[7] device, a 5.6 V 0.5 W zener diode, has a recommended reverse current of 5 mA. If insufficient current exists through D, then UOUT will be unregulated, and less than the nominal breakdown voltage (this differs to voltage regulator tubes where the output voltage will be higher than nominal and could rise as high as UIN). When calculating R, allowance must be made for any current through the external load, not shown in this diagram, connected across UOUT.
R must be large enough that the current through D does not destroy the device. If the current through D is ID, its breakdown voltage VB and its maximum power dissipation PMAX, then I_D V_B < P_{\mathrm{MAX}}.

A load may be placed across the diode in this reference circuit, and as long as the zener stays in reverse breakdown, the diode will provide a stable voltage source to the load. Zener diodes in this configuration are often used as stable references for more advanced voltage regulator circuits.

Shunt regulators are simple, but the requirements that the ballast resistor be small enough to avoid excessive voltage drop during worst-case operation (low input voltage concurrent with high load current) tends to leave a lot of current flowing in the diode much of the time, making for a fairly wasteful regulator with high quiescent power dissipation, only suitable for smaller loads.

These devices are also encountered, typically in series with a base-emitter junction, in transistor stages where selective choice of a device centered around the avalanche or zener point can be used to introduce compensating temperature co-efficient balancing of the transistor PN junction. An example of this kind of use would be a DC error amplifier used in a regulated power supply circuit feedback loop system.

Zener diodes are also used in surge protectors to limit transient voltage spikes.

Another notable application of the zener diode is the use of noise caused by its avalanche breakdown in a random number generator.

Hope this helps in some small way!!!

KenDee

[gbono]

If this helps with finding the cause of the problems, I'm glad to have helped.....

A Zener diode is a diode which allows current to flow in the forward direction in the same manner as an ideal diode, but will also permit it to flow in the reverse direction when the voltage is above a certain value known as the breakdown voltage, "zener knee voltage" or "zener voltage" or "avalanche point".

The device was named after Clarence Zener, who discovered this electrical property. Many diodes described as "zener" diodes rely instead on avalanche breakdown as the mechanism. Both types are used. Common applications include providing a reference voltage for voltage regulators, or to protect other semiconductor devices from momentary voltage pulses.

Operation

A conventional solid-state diode will allow significant current if it is reverse-biased above its reverse breakdown voltage. When the reverse bias breakdown voltage is exceeded, a conventional diode is subject to high current due to avalanche breakdown. Unless this current is limited by circuitry, the diode will be permanently damaged due to overheating. A zener diode exhibits almost the same properties, except the device is specially designed so as to have a reduced breakdown voltage, the so-called zener voltage. By contrast with the conventional device, a reverse-biased zener diode will exhibit a controlled breakdown and allow the current to keep the voltage across the zener diode close to the zener breakdown voltage. For example, a diode with a zener breakdown voltage of 3.2 V will exhibit a voltage drop of very nearly 3.2 V across a wide range of reverse currents. The zener diode is therefore ideal for applications such as the generation of a reference voltage (e.g. for an amplifier stage), or as a voltage stabilizer for low-current applications.[1]

Another mechanism that produces a similar effect is the avalanche effect as in the avalanche diode.[1] The two types of diode are in fact constructed the same way and both effects are present in diodes of this type. In silicon diodes up to about 5.6 volts, the zener effect is the predominant effect and shows a marked negative temperature coefficient. Above 5.6 volts, the avalanche effect becomes predominant and exhibits a positive temperature coefficient.[2]
TC depending on zener voltage

In a 5.6 V diode, the two effects occur together and their temperature coefficients nearly cancel each other out, thus the 5.6 V diode is useful in temperature-critical applications. An alternative which is used for voltage references that need to be highly stable over long periods of time is to use a Z-diode with a TC of +2 mV/°C (breakdown voltage 6.2-6.3 V) connected in series with a forward-biased silicon diode (or a transistor B-E junction) manufactured on the same chip.[3] The forward biased diode has a TC of -2 mV/°C, causing the TCs to cancel out.

Modern manufacturing techniques have produced devices with voltages lower than 5.6 V with negligible temperature coefficients[citation needed], but as higher voltage devices are encountered, the temperature coefficient rises dramatically. A 75 V diode has 10 times the coefficient of a 12 V diode.

Zener and avalanche diodes, regardless of breakdown voltage, are usually marketed under the umbrella term of "zener diode".
Construction

The zener diode's operation depends on the heavy doping of its p-n junction. The depletion region formed in the diode is very thin (<1 µm) and the electric field is consequently very high (about 500 kV/m) even for a small reverse bias voltage of about 5 V, allowing electrons to tunnel from the valence band of the p-type material to the conduction band of the n-type material.

In the atomic scale, this tunneling corresponds to the transport of valence band electrons into the empty conduction band states; as a result of the reduced barrier between these bands and high electric fields that are induced due to the relatively high levels of dopings on both sides.[2] The breakdown voltage can be controlled quite accurately in the doping process. While tolerances within 0.05% are available, the most widely used tolerances are 5% and 10%. Breakdown voltage for commonly available zener diodes can vary widely from 1.2 volts to 200 volts.
Surface Zeners

The emitter-base junction of a bipolar NPN transistor behaves as a zener diode, with breakdown voltage at about 6.8 V for common bipolar processes and about 10 V for lightly doped base regions in BiCMOS processes. Older processes with poor control of doping characteristics had the variation of Zener voltage up to +-1 V, newer processes using ion implantation can achieve no more than +-0.25 V. The NPN transistor structure can be employed as a surface zener diode, with collector and emitter connected together as its cathode and base region as anode. In this approach the base doping profile usually narrows towards the surface, creating a region with intensified electric field where the avalanche breakdown occurs. The hot carriers produced by acceleration in the intense field sometime shoot into the oxide layer above the junction and become trapped there. The accumulation of trapped charges can then cause Zener walkout, a corresponding change of the Zener voltage of the junction. The same effect can be achieved by radiation damage.

The emitter-base zener diodes can handle only smaller currents as the energy is dissipated in the base depletion region which is very small. Higher amount of dissipated energy (higher current for longer time, or a short very high current spike) will cause thermal damage to the junction and/or its contacts. Partial damage of the junction can shift its Zener voltage. Total destruction of the Zener junction by overheating it and causing migration of metallization across the junction ("spiking") can be used intentionally as a Zener zap antifuse.[4]
Subsurface Zeners

A subsurface Zener diode, also called buried Zener, is a device similar to the surface Zener, but with the avalanche region located deeper in the structure, typically several micrometers below the oxide. The hot carriers then lose energy by collisions with the semiconductor lattice before reaching the oxide layer and cannot be trapped there. The Zener walkout phenomenon therefore does not occur here, and the buried Zeners have voltage constant over their entire lifetime. Most buried Zeners have breakdown voltage of 5-7 volts. Several different junction structures are used.[5]
Uses
Zener diode shown with typical packages. Reverse current -i_Z is shown.

Zener diodes are widely used as voltage references and as shunt regulators to regulate the voltage across small circuits. When connected in parallel with a variable voltage source so that it is reverse biased, a zener diode conducts when the voltage reaches the diode's reverse breakdown voltage. From that point on, the relatively low impedance of the diode keeps the voltage across the diode at that value.[6]
Zener diode voltage regulator.svg

In this circuit, a typical voltage reference or regulator, an input voltage, UIN, is regulated down to a stable output voltage UOUT. The breakdown voltage of diode D is stable over a wide current range and holds UOUT relatively constant even though the input voltage may fluctuate over a fairly wide range. Because of the low impedance of the diode when operated like this, resistor R is used to limit current through the circuit.

In the case of this simple reference, the current flowing in the diode is determined using Ohm's law and the known voltage drop across the resistor R;

IDiode = (UIN - UOUT) / RΩ

The value of R must satisfy two conditions :

R must be small enough that the current through D keeps D in reverse breakdown. The value of this current is given in the data sheet for D. For example, the common BZX79C5V6[7] device, a 5.6 V 0.5 W zener diode, has a recommended reverse current of 5 mA. If insufficient current exists through D, then UOUT will be unregulated, and less than the nominal breakdown voltage (this differs to voltage regulator tubes where the output voltage will be higher than nominal and could rise as high as UIN). When calculating R, allowance must be made for any current through the external load, not shown in this diagram, connected across UOUT.
R must be large enough that the current through D does not destroy the device. If the current through D is ID, its breakdown voltage VB and its maximum power dissipation PMAX, then I_D V_B < P_{\mathrm{MAX}}.

A load may be placed across the diode in this reference circuit, and as long as the zener stays in reverse breakdown, the diode will provide a stable voltage source to the load. Zener diodes in this configuration are often used as stable references for more advanced voltage regulator circuits.

Shunt regulators are simple, but the requirements that the ballast resistor be small enough to avoid excessive voltage drop during worst-case operation (low input voltage concurrent with high load current) tends to leave a lot of current flowing in the diode much of the time, making for a fairly wasteful regulator with high quiescent power dissipation, only suitable for smaller loads.

These devices are also encountered, typically in series with a base-emitter junction, in transistor stages where selective choice of a device centered around the avalanche or zener point can be used to introduce compensating temperature co-efficient balancing of the transistor PN junction. An example of this kind of use would be a DC error amplifier used in a regulated power supply circuit feedback loop system.

Zener diodes are also used in surge protectors to limit transient voltage spikes.

Another notable application of the zener diode is the use of noise caused by its avalanche breakdown in a random number generator.

Hope this helps in some small way!!!

KenDee

Our next lecture will be on Gunn domains in Gallium Arsenide Hetrojuntion Bipolar Transistors

[Jazz P Bass]

Copy & paste from Wiki.
Cute.

[KennyDee]

Well,

I'm just trying to be helpful....and who says it better then Wiki....I mean I looked it all over before pasting it and it looked right.....Just trying to be helpful being the new kid on the block.....

Oh, and Wiki encourages their material to be copied and pasted.....so, did I do something that's discouraged?

And when will I be getting the stones tossed at me,----> now or later??? Or both???

KennyDee

[Enzo]

Oh don't worry about it, welcome to the forum.

[Jazz P Bass]

Yeah, I was just spoofing ya.
Welcome aboard.

[KennyDee]

Yeah, I was just spoofing ya.
Welcome aboard.

Thank you for the warm spoof and I was a little worried when the one and only reply to My research on the subject matter brought (ahheeemmm) "a spoof"....

But I do feel closer to the group now and look forward to future informational swaps (and a few spoofs from time to time I suppose) along with some fellowship and a good chat with everyone.....

I look forward to many future conversations!!!

KennyDee

[witchburner]

First off, sorry about posting in a 'dead' thread.
(new member)
But an amp that me and my buddy use to practice and just jam out. Kind of broke.. haha.

And it was the same amp that was posted about in this thread.. ( guitar research amp t60r tube) That's why I'm posting here I guess.

I haven't found anything online so I was wondering if anyone knew about it
Plus I'm kind of new to the whole "DIY" fixing your stuff. But I'm too broke to pay any one else to fix my amp for me anyways haha.

So this happened I opened it up and the only thing that looks wonky to me is these guys, the rest looks fine,
i've cloned some pedals and fixed me and my friends guitars so i have somewhat of an idea what things SHOULDN'T look like, and welp.

The resistors to me seem like, brown (?) / white / Yellow (?) / silver
And i look it up and it shows me some 190k Ohm 10% values is this the correct one?? I've tried looking for schematics and I haven't found a single thing,
And apparently no local stores carry resistors anymore so online is the way to go I guess.

Could anyone lend me a hand on this, thanks

Anyways.