Results 1 to 27 of 27

Thread: Grid stoppers?

  1. #1
    Senior Member
    Join Date
    Nov 2007
    Location
    Columbia, SC
    Posts
    410

    Grid stoppers?

    Ive typically seen grid stoppers after a volume control or before the power tubes, etc. However, in what is pretty much a Fender clone, there is a 470k resistor after the first stage coupling cap before the volume control. Is this effectively a grid stopper too?

  2. #2
    Senior Member Enzo's Avatar
    Join Date
    May 2006
    Location
    Lansing, Michigan, USA
    Posts
    28,460
    It is a voltage divider - the resistor and volume pot are in series.

  3. #3
    Senior Member
    Join Date
    Dec 2007
    Posts
    118
    It does indeed form a potential divider, but it also creates a high frequency roll off due to the miller effect. It also behaves as a grid stopper, as I believe it will limit grid current as well if that stage hits saturation. So yes, it is a grid stopper.

  4. #4
    Lifetime Member
    Join Date
    May 2006
    Posts
    4,162
    The purpose of grid stoppers is to stop parasitic oscillation by causing a high frequency rolloff with the grid-cathode and grid-plate capacitance.

    Note that I said grid-plate instead of Miller capacitance, as the stopper is effective in source-follower setups where there is no voltage gain to enhance grid-plate capacitance.

    A grid stopper must be mounted as close to the grid's socket pin as the body and leads will allow, or it's just wishful thinking. The self-inductance of the wire lead will remove any benefits of the stopper and may make oscillation worse if the lead is not as short as is physically possible.

    There are other uses for series grid resistors, including low pass filtering and limiting grid current during positive grid drive, but these may or may not also act as a grid stopper depending on how they are mounted.

  5. #5
    Senior Member
    Join Date
    Dec 2007
    Posts
    118
    Or dynamic input capacitance in other words. RG is right in that you should mount it on or as close to the socket as possible, but this is most important for the input stage, because the main purpose of this resistor is to roll off RF frequencies, and the resistor is useless if you nave a wire after the resistor.

    In other stages it is used most commonly to roll off high end, but there are less noisy ways to do this.

  6. #6
    Supporting Member tubeswell's Avatar
    Join Date
    Feb 2007
    Location
    Wellington NZ
    Posts
    4,075
    Grid stoppers are especially useful at the grid pin of the 1st gain stage for preventing unwanted oscillation. Also useful if you are using shielded signal cable to your grid pins.

  7. #7
    Senior Member
    Join Date
    Nov 2007
    Location
    Columbia, SC
    Posts
    410
    In my case, does the series 470kR increase the gain a bit? The volume pot is 1M, but it seems this resistor would make the signal further away from ground

  8. #8
    Supporting Member tubeswell's Avatar
    Join Date
    Feb 2007
    Location
    Wellington NZ
    Posts
    4,075
    Any resistor in the signal path will attentuate the signal in some way. With a voltage divdier you use Kirchoff's Law to figure out what the attentuation level is on the node between the 470K and the Vol Pot. (it will vary depending on how the pot is set). That is the signal going into the grid of the next stage.

  9. #9
    Senior Member Enzo's Avatar
    Join Date
    May 2006
    Location
    Lansing, Michigan, USA
    Posts
    28,460
    The original question was what is the resistor after the plate coupling cap going down to the volume control. It doesn't get wired to a grid at all, unless we consider the volume all the way up as wired to the grid. I don't know how we would mount this resistor "as close to the socket as possible." How is this a grid stopper?

  10. #10
    Lifetime Member
    Join Date
    May 2006
    Posts
    4,162
    Quote Originally Posted by Joey Voltage View Post
    It also behaves as a grid stopper, as I believe it will limit grid current as well if that stage hits saturation. So yes, it is a grid stopper.
    I'm sorry, I think this is not yet clear. These two sentences seem to say that
    (a) you believe it will limit grid current if the stage hits saturation so therefore (b) is is a grid stopper, having met condition (a).
    That is incorrect. Whether it is or is not effective as a grid stopper depends on where it is mounted physically, not whether it will limit grid current. A grid stopper might limit grid current, but that is an aside and accidental; properly designed, it will stop oscillations whether or not there is any grid current to limit.

    As an aside, "saturation" as most semiconductor people understand it is not what you limit grid current for. Saturation is when the plate can no longer respond to the grid voltage increasing with an increase in plate current. While there is a saturation in tubes, it does not occur when the grid starts drawing current, limited or not. In both triodes and pentodes, you can cause higher and higher plate currents to flow by continuing to raise the grid above the cathode. This is the basis of Class AB2 operation in push-pull amplifiers.

    I believe you meant to say "when the grid is raised above the cathode potential and starts conducting current" instead of saturation. Depending on the value of any grid stopper, the grid current might be limited by the stopper, but may also be limited by biasing resistors or the driving impedance of the previous stage; or a real current limiting resistor, put there only for that.

    Quote Originally Posted by Joey Voltage View Post
    Or dynamic input capacitance in other words.
    Can you explain that? It seems like a non sequiteur.

    Quote Originally Posted by Joey Voltage View Post
    RG is right in that you should mount it on or as close to the socket as possible, but this is most important for the input stage, because the main purpose of this resistor is to roll off RF frequencies, and the resistor is useless if you nave a wire after the resistor.
    I believe that "and" is the correct conjunction, not "but", or simply a full stop. Usefulness in some stages or importance to immunity from RF intereference is not a negation or an exception to the primary use of the stopper, or its positioning.

    Quote Originally Posted by Joey Voltage View Post
    In other stages it is used most commonly to roll off high end, but there are less noisy ways to do this.
    A resistor in series with a grid may do any or all of:
    1) preventing the entry of RF into the grid
    2) limiting grid current in extreme operation
    3) rolling off high frequencies
    However, since these are different effects, the correct value of resistor for one use may not be the right one for another use. For instance, it is common to use high value resistors for audio treble rolloff. This may make the stage MORE sensitive to RF interference by making the impedance at the grid higher. If the resistor is also fairly remote (i.e. an inch or so) from the socket lug, this may even tune in radio sources. Limiting grid current is itself a complex subject; the right value to limit grid current is not necessarily the right value for either grid stopping or treble rolloff.

  11. #11
    Supporting Member tubeswell's Avatar
    Join Date
    Feb 2007
    Location
    Wellington NZ
    Posts
    4,075
    Quote Originally Posted by Enzo View Post
    The original question was what is the resistor after the plate coupling cap going down to the volume control. It doesn't get wired to a grid at all, unless we consider the volume all the way up as wired to the grid. I don't know how we would mount this resistor "as close to the socket as possible." How is this a grid stopper?
    That's right - my understanding of a grid stopper is a (smallish ~up to about 68k) resistor in series with the grid pin (preferably right at the grin pin - for the reasons RG describes), whereas if it is connected to another resistor to ground before the grid pin, it is not a grid stopper but rather is part of a voltage divider (but even with the volume all the way 'up', to use your words in your example Enzo - it is still a voltage divider is it not?, because the pot is still there albeit that it becomes a larger resistor connected to the ground when it is turned 'up').

  12. #12
    Senior Member Enzo's Avatar
    Join Date
    May 2006
    Location
    Lansing, Michigan, USA
    Posts
    28,460
    It was always a voltage divider, regardless of whatever else it might or might not be doing. Many parts are doing more than one job, it all depends on what you are discussing. I understand grid stoppers, I am still not convinced that this is an example of one.

  13. #13
    Senior Member
    Join Date
    Dec 2007
    Posts
    118
    Maybe I was speaking in absolutes, and for that I stand corrected, but If you are calling a resistor that is in series with a tubes input grid a grid stopper only if it successfully performs the task of RF suppression, then most of the 68K resistors in series with the input tube grids of countless fenders, and marshalls are not grid stoppers, purely because the long (mostly unshielded) wire runs from this resistor to the grid, prevents this resistor from doing this task correctly. It then, under Mr. Keen's definition, just becomes a resistor in series with the input tube grid, because it fails to perform this task correctly. That is if we define this resistor purely by successful function. I do not know, I think many of us still label those 68K resistors on older marshalls grid stoppers, whether they perform or not. I see it more as an concise identifier, rather than a product of successful function. Same goes for the the series resistors often seen at the input grid of PA tubes. I Won't, excuse me, will not (sorry RG), call them grid stoppers anymore, because they don not perform this task in a lot of amps either, especially if PCB's are involved.

  14. #14
    Old Timer
    Join Date
    Apr 2008
    Location
    Oceanside, NY
    Posts
    1,649
    A grid stopper doesn't HAVE to be a resistor. A ferrite bead right at the tube socket will accomplish the same thing (i.e. RF suppression) without adding any series resistance at all.
    John R. Frondelli
    dBm Pro Audio Services, New York, NY

    "Mediocre is the new 'Good' "

  15. #15
    Lifetime Member
    Join Date
    May 2006
    Posts
    4,162
    Quote Originally Posted by Joey Voltage View Post
    Maybe I was speaking in absolutes, and for that I stand corrected,
    'S'OK. we all start somewhere.
    Quote Originally Posted by Joey Voltage View Post
    but If you are calling a resistor that is in series with a tubes input grid a grid stopper only if it successfully performs the task of RF suppression, then most of the 68K resistors in series with the input tube grids of countless fenders, and marshalls are not grid stoppers, purely because the long (mostly unshielded) wire runs from this resistor to the grid, prevents this resistor from doing this task correctly. It then, under Mr. Keen's definition, just becomes a resistor in series with the input tube grid, because it fails to perform this task correctly. That is if we define this resistor purely by successful function.
    I think you're missing the point again, if more slightly. It's not successful performance of the function (although that would be very nice if we go to the trouble to put it in) that makes something a grid stopper; rather is is the possibility that it can do that function. A resistor a long way away from the grid it's "stopping" is simply going to be ineffective for that function. Is it a grid stopper? It can't possibly be in fact, so why muddy the waters by labeling it as such?

    And let's get off this "Mr. Keen's definition" stuff. If you put a part in an amp which cannot possibly do the function you ascribe to it, but insist on calling it by a label it cannot possibly live up to, then you can't very well be surprised when someone else thinks it deserves a different label. Well, OK, we do have the example of our dearly departed president, William Jefferson Clinton, who told us that "... it depends on what your definition of "is" is."

    Calling it an elephant doesn't give it a trunk, but you might like it better.

    Quote Originally Posted by Joey Voltage View Post
    I do not know,
    OK. Sometimes I'm confused too.

    Quote Originally Posted by Joey Voltage View Post
    I think many of us still label those 68K resistors on older marshalls grid stoppers, whether they perform or not. I see it more as an concise identifier, rather than a product of successful function. Same goes for the the series resistors often seen at the input grid of PA tubes.
    Using that line of reasoning, I and a number of my friends have decided that those 100K resistors on the plates of preamp tubes are "dingleberries", which we see as a more concise identifier than "plate resistor". We call the resistors from grid to ground "Mersienne Primes". Concise, easy to remember.

    Quote Originally Posted by Joey Voltage View Post
    I Won't, excuse me, will not (sorry RG), call them grid stoppers anymore, because they don not perform this task in a lot of amps either, especially if PCB's are involved.
    Actually, you can - and will, if I know human nature - call them whatever you like. But be clear that calling a resistor a "voltage-controlled hyperlink" doesn't make the circuit operate differently.

  16. #16
    Senior Member Enzo's Avatar
    Join Date
    May 2006
    Location
    Lansing, Michigan, USA
    Posts
    28,460
    And speaking empirically, I have learned that calling an amp a "son of a bitch" doesn't seem to make it work any better either.

  17. #17
    Senior Member
    Join Date
    Dec 2007
    Posts
    118
    Quote Originally Posted by R.G. View Post
    I think you're missing the point again, if more slightly. It's not successful performance of the function (although that would be very nice if we go to the trouble to put it in) that makes something a grid stopper; rather is is the possibility that it can do that function.
    I understand your point


    Quote Originally Posted by R.G. View Post
    resistor a long way away from the grid it's "stopping" is simply going to be ineffective for that function. Is it a grid stopper? It can't possibly be in fact, so why muddy the waters by labeling it as such?
    This reasoning seems very retrospective. You don't know that this resistor is going to be ineffective just by looking at it in a schematic. It is the assembly that dictates this, not necessarily the original intention behind the resistor.


    Quote Originally Posted by R.G. View Post
    let's get off this "Mr. Keen's definition" stuff. If you put a part in an amp which cannot possibly do the function you ascribe to it, but insist on calling it by a label it cannot possibly live up to, then you can't very well be surprised when someone else thinks it deserves a different label.
    Lets go back to my Fender, and Marshall examples. When looking at the schemes of any of these amplifiers, most have little squiggly lines in series with the input tube grid with 68K written above them, or somewhere near them, correct? Most of us refer to these as grid stoppers. Why? They certainly have the potential to be, sure. It's not because I like the way "grid stopper" sounds any better. conventional/traditional labeling, sure (concise identifier was maybe a poor choice of words). It is the presumed intention of why it's there. We simply don't know whether or not this resistor is going to meet the proximity criteria to function properly as a grid stopper in any given design until the manufacturer has produced it. In my marshall/fender example, the physical layout of the component and long wire leads prevent it from suppressing RF, Therefore in the "Working Product" it is NOT a grid stopper, but the intent was there, and we couldn't possibly have known about inadequate layout just by glancing at a scheme, so why mess with the traditional labeling? Most people here know what you are talking about when you call these particular resistors in these particular amps, grid stoppers, whether or not the layout makes it impossible for them to function as such.



    Quote Originally Posted by R.G. View Post
    that line of reasoning, I and a number of my friends have decided that those 100K resistors on the plates of preamp tubes are "dingleberries", we see as a more concise identifier than "plate resistor".
    Thats good stuff, you should update your website with this information. What do you call 220K plate resistors? I think you are going a bit to extremes. Calling a 68K resistor in series with the grid of an input tube, a "grid stopper," because it was most likely intended to be (but didn't quite translate in the layout), and calling plate resistors "dingleberries", are not even in the same ball park.


    Quote Originally Posted by R.G. View Post
    , you can - and will, if I know human nature - call them whatever you like. But be clear that calling a resistor a "voltage-controlled hyperlink" doesn't make the circuit operate differently.
    Speaking of conjunctions, you can leave "but" out of the second sentence

    Quote Originally Posted by R.G. View Post
    is is the possibility that it can do that function.
    I didn't know that two verbs occur successively like that in the english language. You my friend are in desperate need of a subject. Hey! you started it.

    As for "Dynamic input capacitance", I have seen that term used in more than one publication. I can see if I can dig it up one of the sources if you are really curious in where I got that term.

  18. #18
    Senior Member Enzo's Avatar
    Join Date
    May 2006
    Location
    Lansing, Michigan, USA
    Posts
    28,460
    little squiggly lines in series with the input tube grid with 68K written above them, or somewhere near them, correct? Most of us refer to these as grid stoppers. Why?
    Because we are continuing the common mis-use of the term. Some person refers to them that way mistakenly, other person hears that and assumes it is proper so he then uses the term that way.

    It is the presumed intention of why it's there.
    I have to honestly state that I disagree. When I see the two 68k resistors at the input, I see them mainly as part of a pad. The two resistors plus the grounding contact on the jack makes them a series resistance on one jack and a 2 to 1 voltage divider on the second jack - the classic Fender 6db pad. This view is bolstered by the knowledge that they are usually mounted on the jacks, not at the tube socket, or in some cases on the eyelet board instead of at the tube socket.

    Most people here know what you are talking about when you call these particular resistors in these particular amps, grid stoppers
    Most people here know what you are talking about when any number of misnomers are used. That is no defense of a bad habit.

    Calling a 68K resistor in series with the grid of an input tube, a "grid stopper," because it was most likely intended to be
    And there you go, it has come back around. I don't accept your premise. I don't accept that was in fact the intended purpose when the amp was designed.

    I don't buy that all the engineers at Marshall and Fender and a whole list of other places are so inept that they have heard of grid stoppers and tried to stick them in their amps, but "didn't quite translate in the layout." I would give them the benefit of the doubt and assume that if they felt the need of a grid stopper, they are most likely knowledgable enough to implement it correctly. Note that on the Fender amps, the grid stopper for the power tubes is in fact mounted right at the socket. So inadequate layout? Phooey. They know what they are doing. The chosen layout makes the resistor ineffective as a grid stopper because that was never its intent.

    When faced with your wiggly lines on the schematic, you can either choose to think that amp design engineers tried and tried and tried in model after model after model over years and years and years to implement grid stoppers in a totally ineffective manner, OR you could realize you are misusing the term.

  19. #19
    Lifetime Member
    Join Date
    May 2006
    Posts
    4,162
    Quote Originally Posted by Joey Voltage View Post
    This reasoning seems very retrospective. You don't know that this resistor is going to be ineffective just by looking at it in a schematic. It is the assembly that dictates this, not necessarily the original intention behind the resistor.
    It's not really retrospective reasoning. It is simply a recognition that schematics are an abstraction, and do not necessarily contain all of the information needed to make an electronic device work. Well drawn schematics intended for manufacturing reference will be annotated with physical details, including things like grid- and gate-stoppers being close to the device. Circuit reference diagrams often omit that data, since a repair tech is expected to replace bad parts, not redesign the amp.

    Quote Originally Posted by Joey Voltage View Post
    Lets go back to my Fender, and Marshall examples. When looking at the schemes of any of these amplifiers, most have little squiggly lines in series with the input tube grid with 68K written above them, or somewhere near them, correct? Most of us refer to these as grid stoppers. Why?
    Because most of us use it incorrectly, not understanding that there is a physical component to how grid stoppers work, and simply labeling any series resistor as one. Sure it sounds cool, like the person really understands tube amps, but it betrays a lack of in-depth information.

    The Sorcerer's Apprentice strikes a chord in all of us because we all would like to appear to have all the knowledge, whether we do or not. But as the SA found out, a little knowledge is a dangerous thing.
    Quote Originally Posted by Joey Voltage View Post
    They certainly have the potential to be, sure. It's not because I like the way "grid stopper" sounds any better. conventional/traditional labeling, sure (concise identifier was maybe a poor choice of words). It is the presumed intention of why it's there. We simply don't know whether or not this resistor is going to meet the proximity criteria to function properly as a grid stopper in any given design until the manufacturer has produced it. In my marshall/fender example, the physical layout of the component and long wire leads prevent it from suppressing RF, Therefore in the "Working Product" it is NOT a grid stopper, but the intent was there, and we couldn't possibly have known about inadequate layout just by glancing at a scheme, so why mess with the traditional labeling? Most people here know what you are talking about when you call these particular resistors in these particular amps, grid stoppers, whether or not the layout makes it impossible for them to function as such.
    I'm not sure why you're pushing this issue. Presumed intention and traditional labeling have nothing whatsoever to do with what the parts do. As we'll get to in the next ply of this exchange, you can call it anything you like. But if the label does not reflect what it actually does, you may as well call it anything.
    Quote Originally Posted by Joey Voltage View Post
    Thats good stuff, you should update your website with this information. What do you call 220K plate resistors? I think you are going a bit to extremes.
    Of course I'm going to extremes. I'm using hyperbole to try to illustrate the silliness of insisting on calling something by a misleading name. I'm hoping that humor reaches you if reason can't.
    Quote Originally Posted by Joey Voltage View Post
    Calling a 68K resistor in series with the grid of an input tube, a "grid stopper," because it was most likely intended to be (but didn't quite translate in the layout), and calling plate resistors "dingleberries", are not even in the same ball park.
    You've inadvertently picked out the worst possible example to support your case. The 68k resistors at the front end of an amp do have a clearly defined role, that of padding the inputs to be high/low gain.

    What you're missing here is that Enzo and I are not just being difficult. We are trying to help you learn something that no one has taken the time to tell you yet. And you're vigorously defending your right not to learn.
    Quote Originally Posted by Joey Voltage View Post
    As for "Dynamic input capacitance", I have seen that term used in more than one publication. I can see if I can dig it up one of the sources if you are really curious in where I got that term.
    I'd appreciate it. The term is no mystery, as I suspect that it's another term for Miller capacitance, but I would like to go learn what was really meant by it instead of using it as a red herring.

    But just out of casual interest, what did *you* mean by it?

  20. #20
    Senior Member
    Join Date
    Dec 2007
    Posts
    118
    Quote Originally Posted by Enzo View Post
    I have to honestly state that I disagree. When I see the two 68k resistors at the input, I see them mainly as part of a pad. The two resistors plus the grounding contact on the jack makes them a series resistance on one jack and a 2 to 1 voltage divider on the second jack - the classic Fender 6db pad. This view is bolstered by the knowledge that they are usually mounted on the jacks, not at the tube socket, or in some cases on the eyelet board instead of at the tube socket.And there you go, it has come back around. I don't accept your premise. I don't accept that was in fact the intended purpose when the amp was designed.I don't buy that all the engineers at Marshall and Fender and a whole list of other places are so inept that they have heard of grid stoppers and tried to stick them in their amps, but "didn't quite translate in the layout." I would give them the benefit of the doubt and assume that if they felt the need of a grid stopper, they are most likely knowledgable enough to implement it correctly. Note that on the Fender amps, the grid stopper for the power tubes is in fact mounted right at the socket. So inadequate layout? Phooey. They know what they are doing. The chosen layout makes the resistor ineffective as a grid stopper because that was never its intent.When faced with your wiggly lines on the schematic, you can either choose to think that amp design engineers tried and tried and tried in model after model after model over years and years and years to implement grid stoppers in a totally ineffective manner, OR you could realize you are misusing the term.
    Enzo,

    Here's another example for you. Please, if you can, expalin it to me. Most marshall 2203/4 amplifiers have high/low sensitivity jacks. In these amps, the 6db pad using the classic 68K method was ditched in favor of bypassing an entire gainstage by means of the low input jack. The high sensitivity input now has a single 68K resistor in series with the grid of the input stage. In practice (having owned one), marshall mounted this 68K resistor on the PCB between copper traces from input jack, and long unshielded wire to the grid of the input stage. It cant possibly be a grid stopper, because it doesn't have the potential to perform this function, but it cant be part of a 2:1 voltage divider either because there is no other resistor to perform this function with. This was 1986, so the engineers at marshall, as you said are not inept, and knew what they were doing right?. So why is it there? What is the intention in this case? What function does it serve? simply just roll off at a frequency most people can't hear? If it doesn't serve a useful perpose, why is it there? otherwise, to me at least, it is just one more part in the BOM that doesn't need to be there. I'm not trying to be a pain, I really just want to know.

  21. #21
    Noodle of Reality Steve Conner's Avatar
    Join Date
    May 2006
    Location
    Glasgow, Scotland
    Posts
    7,251
    What is this, Guitar Amp Philosophy 101?

    The 68k resistor can be part of an input pad.

    It can be a RF input filter. 68k of series resistance, in conjunction with the ~100pF Miller capacitance of a 12AX7 grid, will form a ~20kHz low-pass filter that keeps LW and MW radio out of the amp. I made an amp with no 68k input resistor, and it picked up Radio Moscow after dark, and adding the resistor stopped that.

    But is it a "grid stopper" in the traditional ham radio sense, which implies that it stops parasitic oscillations in the tube stage whose grid it's attached to?

    On power tubes, maybe, and that's why you find it right at the tube socket, because it wouldn't work if it were placed further away. But preamp tubes are probably stable without it: the tendency to parasitics, all other things being equal, is a function of internal lead length and transconductance.

    The resistor will still suppress external RF no matter where it is in the input wiring, as long as it's inside a screened chassis, because the screening of the chassis implies that any RF present must have got in through the input jack.

    And by that token, the same 68k resistor(s) can be both a RF input filter and a 6dB pad.
    "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

  22. #22
    Senior Member
    Join Date
    Dec 2007
    Posts
    118
    Quote Originally Posted by R.G. View Post
    I'd appreciate it. The term is no mystery, as I suspect that it's another term for Miller capacitance, but I would like to go learn what was really meant by it instead of using it as a red herring.

    But just out of casual interest, what did *you* mean by it?
    R.G.,

    I haven't been able to track down my resources for that term yet but IIRC the term was used to describe the capacitance that results when tubes internal grid-to-plate, and grid-to-cathode capacitances are conjoined with the miller capacitance (effect). I suppose, and this pure speculation, the term "dynamic" is used to describe the variance in the grid-to-plate capacitance due to variance in stage gain. It makes the most sense to me at least.

  23. #23
    Member
    Join Date
    Sep 2007
    Posts
    101
    Great info here. I do know that in several cases I've just willy-nilly mounted/moved a resistor that, in the schematic, appeared to be a grid stopper (like the 68k at the input) and didn't even think to test it to see if it adversely affected tone...I just assumed I had made it 'better' by putting it 'where it was supposed to be in the first place'. Woopsie.

    It's no wonder my homebrews start out so pretty but end up so ugly inside...I keep going back in.

  24. #24
    Old Timer
    Join Date
    May 2006
    Location
    Cheshire, UK
    Posts
    1,584
    Keep up the good work chaps. This is more fun than a Saturday night punch up at Wetherspoons.

    I'm not sure what to call the squiggly dangleberries at the input of my amp now. When I first built the amp I mistakenly put the input tube right next to the input jacks and wired the 68ks directly to the grids hoping for some RF attenuation and stopping action. I hadn't seen inside a Fender or Marshall at that time so I didn't know how it was supposed to be done.

    Dave H.

  25. #25
    Senior Member Enzo's Avatar
    Join Date
    May 2006
    Location
    Lansing, Michigan, USA
    Posts
    28,460
    I see nothing wrong with mounting the tube near the jacks and running the resistors directly. When I build little Champ-like amps, that is how I do it. Fender wouldn't do it that way because it would interfere with the eyelet board where the parts live and the tube would be in the way near the jacks.

  26. #26
    Senior Member
    Join Date
    Dec 2007
    Posts
    118
    Thats kinda how I do it too, except I use a piece of co-ax from the input jack to the resistor/socket. I usually will have the preamp tubes near the front of the amp anyway.

  27. #27
    Senior Member booj's Avatar
    Join Date
    Jun 2008
    Posts
    629
    Ok, so I should put grid resistors close to the output tube socket. That's very helpful!
    Now what about those darn screen resistors? Oops! That's a different subjct!

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Grid current limiting
    By tubeswell in forum Theory & Design
    Replies: 13
    Last Post: 09-03-2008, 09:31 AM
  2. Effects return to PI grid #2
    By Guitarist in forum Mods & Tweaks
    Replies: 5
    Last Post: 04-14-2008, 09:03 AM
  3. grid current draw
    By JC@ in forum Theory & Design
    Replies: 7
    Last Post: 09-30-2007, 09:12 PM
  4. 500 ohm grid stoppers for 6V6?
    By Neal in forum Maintenance, Troubleshooting & Repair
    Replies: 1
    Last Post: 05-08-2007, 02:15 PM
  5. Grid stopper value?
    By daz in forum Theory & Design
    Replies: 3
    Last Post: 02-06-2007, 02:06 AM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •