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Thread: Cathode follower without elevated heater voltage

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    Okay, so it turns out the problem is not fixed. But I can turn the amp up way, way louder before it occurs than before. So I'm thinking it's a lead dress/grounding issue. I think I need to look at where all the ground points are, and create a more optimal ground scheme.

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  2. #142
    Bent Member Chuck H's Avatar
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    Quote Originally Posted by Dark Mavis View Post
    Okay, so it turns out the problem is not fixed. But I can turn the amp up way, way louder before it occurs than before. So I'm thinking it's a lead dress/grounding issue. I think I need to look at where all the ground points are, and create a more optimal ground scheme.
    There are a lot of threads here that are basically grounding tutorials. That's how I learned how to do it. And in all immodesty I've never had a problem with the ground scheme in any of my builds***. We're here as always if you have questions.

    *** There are always exceptions when it comes to reverb circuits I've had to rework grounds on a couple of those.

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    "In fact when I run into problems working on electronic circuirts, there are so many times that when I finally track it down, the source of the problem is located between my soldering iron and my seat." SoulFetish

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

  3. #143
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    Quote Originally Posted by Chuck H View Post
    There are a lot of threads here that are basically grounding tutorials. That's how I learned how to do it. And in all immodesty I've never had a problem with the ground scheme in any of my builds***. We're here as always if you have questions.

    *** There are always exceptions when it comes to reverb circuits I've had to rework grounds on a couple of those.
    Have you ever started reading about something and wished you hadn't started? There seems to be an awful lot of people confidently saying that the things that other people are confidently saying, are incorrect. I guess if it really mattered, there would only be the right way, and then all the ways that don't work at all. But when the very first two articles you read, completely contradict each other on several things, you know you're headed down the rabbit hole. I read an article abut it on Randall Aiken's page, then an equally long article elsewhere that basically said the reverse.
    So what I'm gonna do is just this: https://el34world.com/charts/grounds.htm Cus this one has a picture. I'm gonna put a terminal lug by the input jack for a ground though, even though they're not isolated jacks. Occasionally I get static that a tap on the jack plug can get rid of, so I don't trust the contact those sockets are making. I guess a ground loop won't be an issue if the wire is short. I know all my power tube cathodes are grounded to the chassis at each tube's socket. I don't think the pots are grounded at all, beyond their physical connection to the chassis, and all the filter caps except the last one, share the same ground.
    What about the filter cap that's connected to the driver tube plates (and to the reverb transformer)? Should that one be grounded at the input jack end, or by the power trans?
    I got a bunch of lock washers and nylock nuts, and I'm going to clean up the chassis and make all new ground points. Might as well try to clean up the tube sockets while I'm at it and see if I can get rid of the snap, crackle and pop. I have no tools for this though. I think I'll just spray contact cleaner on a tube's pins and push it in and out a few times, then maybe rinse with isopropyl.
    I'll also take the opportunity to replace all the plate resistors, and restore the values of those 470k ones to 220 or maybe 100.
    More contact cleaner in the pots, too, when I have them out. With them in place, I dunno if I was getting it on the actual track.
    What about the filament's false center tap dealie? Right now, each is grounded where the resistors are bolted into place. Where should I ground those?

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  4. #144
    Bent Member Chuck H's Avatar
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    Quote Originally Posted by Dark Mavis View Post
    What about the filter cap that's connected to the driver tube plates (and to the reverb transformer)? Should that one be grounded at the input jack end, or by the power trans?
    Ah! The reverb grounds. The reverb power supply is often the same as that for the screens in most classic designs. It seems your amp isn't like that. Here's what I do for amps like yours that have a "s" ton of circuitry going on. It's technically wrong but fundamentally right and it makes building easier and helps keep things tidy in the chassis. I use three star ground points. One by the input for the preamp, one at the power supply end and one at the mid point for, ah, well, anything that's NOT the preamp or power amp/power supply. Lemme splain it.

    The preamp grounds would be anything that pertains to the dry signal chain and the power supply filter cap grounds that power those circuits only. That's easy. The power amp and power supply is the power tube plate, screen grid and cathode circuits and the power supply filters cap grounds for those circuits. That's easy too. So where does the PI belong? Is it preamp or power amp? Well it's mostly preamp, but sorta power amp idn'it. And in your case the reverb shares a power supply with it. It seems Dan thinks a little like I do here because the reverb isn't exactly part of the preamp, it's an effect. Then there's the presence control and any post PI master volume circuits.?. They're really part of the power amp circuit even though the controls are on the front panel. So I use a third ground point sorta near the power amp end that's for the reverb power transformer and driver tube cathode grounds (not the reverb signal grounds, I'll get to that), the PI grounds, any tremolo circuit, the presence control and any associated filters for those circuits. Now, the reverb signal ground would include the grid leak resistor for the driver tube because that's actually still part of the preamp. As is the reverb tank output and recovery tube. So ground those with the preamp. There's a chance your reverb drive power filter is different from your reverb recovery filter. Use your best judgement here and remember that you want to ground power supply filters with their circuits. And...

    Daisy chains are often bad. Those places on the board where one eyelet is a ground point for three different things and then one lead goes to ground. When you do this ALL those grounds share the resistance of the wire. Wait? WHAT! The resistance of wire? Yes, hypothetical you. Wire has a tiny resistance and in something that is very high gain, like a guitar amp, it can matter a little. Get a bunch of peripheral circuits together with other leads flying all over the place and it can matter more. Worse is when you have more than one of these multi ground points and then sorta tack a wire between them (often under the board because it looks neat) and then use one lead to the ground point for the whole array. Do not do this. Now you CAN get away with clumping some grounds together on the same eyelet IF you know how. You can share a ground eyelet with a single lead for individual circuits. Say, a tone stack with an associated volume control where the signal leaves one tube plate and terminates at another tubes grid. The tone stack, volume control and any associated voltage divider or bleed cap grounds can share an eyelet. You might even get away with having the sending triodes cathode grounded there or any grid to ground resistor for the following tubes grid. DO NOT clump or daisy chain grounds of like phase from different preamp circuits and have them share a lead to the ground point. If that's confusing you're not alone. When in doubt just run an individual lead to the ground point.

    As to pot cases I am out on a limb compared to most vintage amp specialists here because there is no guru mojo or lore associated with my logic on the matter. So here you go. Don't bother grounding the pot cases and don't use the pot cases as a ground point. There. I said it. The pot cases are not connected to any of the lugs and the resistive elements inside are ALREADY IN THE CHASSIS LIKE EVERY OTHER RESISTOR. No one is taking steps to add a grounded case to the rest of the resistors in the amp, so why the pots? Nope. If a pot lug is schematically grounded then run a lead to the circuit ground. Tack soldering a long copper wire across the backs of the pots and using it as a ground buss is a fundamentally crappy idea. Pot to chassis contact can corrode. You could end up with your whole preamp grounded up chassis by the damn power switch. There's a tendency to use the buss inappropriately and share grounds that should be otherwise be separate (like the presence ground, which is a power amp ground, and the preamp grounds). You should literally ignore any advice that suggests the pot cases should be grounded together with a buss wire. Like the Hoffman drawing. With all the pots soldered together AND the ground bar at the filter caps there is a ground point IN the chassis near the power amp end and multiple ground points along the front of the chassis. Including the unisolated input jack. There should be ONE ground point for the preamp and it should be nearer the input end of the chassis.

    When running a lot of individual leads ground points can get crowded fast. I use these little five lug terminal strips that I use to get at Radio Shack, but now have to buy on line. The center lug on these is grounded via being bolted to the chassis and I just solder a solid copper wire across the lug rivets so I have five fat lugs I can solder grounds to.

    Sometimes you don't get a choice on where to ground something. As with non isolated jacks of any kind. In this case the - jack terminal is grounded at the chassis. You still want to run an individual ground lead to the ground point, but only use that - jack terminal as a ground lug for cable shields and resistors that connect the jacks + terminal directly to ground.

    Shielded leads should only be grounded at one end.

    Reverb cables often break this rule and reverbs often hum like they don't know the words. With the exception of the input grid the reverb drive circuit and all the shaking springs is a FUNCTION circuit and not part of the signal chain or preamp. The reverb recovery circuit IS in the signal chain and is the tanks output transducer and the tube stage that amplifies it up to a useful level. Old school reverb circuits tend to clump grounds together for all this and they often (though not always) hum. When I repair I do the best I can with what's in the amp. When I build I always get a tank with an isolated output jack and I even isolate the RCA jack on the amp chassis so I can choose my ground points for the recovery circuit which IS part of the preamp.

    The green lead on the power cord gets securely bolted to the chassis near where the cord enters the amp. This is a safety ground and not a circuit ground. The Hoffman layout is wrong on this matter. It's not a problem if you want to do it this way, just know that it's a different function. A safety measure. So be certain it's secure.

    Ok, I dissed the Hoffman drawing three times here. It's not "bad" and it's how most vintage amps were/are done and it "works". It can be improved upon in practice unless you're cloning a design.

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    "In fact when I run into problems working on electronic circuirts, there are so many times that when I finally track it down, the source of the problem is located between my soldering iron and my seat." SoulFetish

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

  5. #145
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    Quote Originally Posted by Chuck H View Post
    Ah! The reverb grounds. The reverb power supply is often the same as that for the screens in most classic designs. It seems your amp isn't like that. Here's what I do for amps like yours that have a "s" ton of circuitry going on. It's technically wrong but fundamentally right and it makes building easier and helps keep things tidy in the chassis. I use three star ground points. One by the input for the preamp, one at the power supply end and one at the mid point for, ah, well, anything that's NOT the preamp or power amp/power supply. Lemme splain it.

    The preamp grounds would be anything that pertains to the dry signal chain and the power supply filter cap grounds that power those circuits only. That's easy. The power amp and power supply is the power tube plate, screen grid and cathode circuits and the power supply filters cap grounds for those circuits. That's easy too. So where does the PI belong? Is it preamp or power amp? Well it's mostly preamp, but sorta power amp idn'it. And in your case the reverb shares a power supply with it. It seems Dan thinks a little like I do here because the reverb isn't exactly part of the preamp, it's an effect. Then there's the presence control and any post PI master volume circuits.?. They're really part of the power amp circuit even though the controls are on the front panel. So I use a third ground point sorta near the power amp end that's for the reverb power transformer and driver tube cathode grounds (not the reverb signal grounds, I'll get to that), the PI grounds, any tremolo circuit, the presence control and any associated filters for those circuits. Now, the reverb signal ground would include the grid leak resistor for the driver tube because that's actually still part of the preamp. As is the reverb tank output and recovery tube. So ground those with the preamp. There's a chance your reverb drive power filter is different from your reverb recovery filter. Use your best judgement here and remember that you want to ground power supply filters with their circuits. And...

    Daisy chains are often bad. Those places on the board where one eyelet is a ground point for three different things and then one lead goes to ground. When you do this ALL those grounds share the resistance of the wire. Wait? WHAT! The resistance of wire? Yes, hypothetical you. Wire has a tiny resistance and in something that is very high gain, like a guitar amp, it can matter a little. Get a bunch of peripheral circuits together with other leads flying all over the place and it can matter more. Worse is when you have more than one of these multi ground points and then sorta tack a wire between them (often under the board because it looks neat) and then use one lead to the ground point for the whole array. Do not do this. Now you CAN get away with clumping some grounds together on the same eyelet IF you know how. You can share a ground eyelet with a single lead for individual circuits. Say, a tone stack with an associated volume control where the signal leaves one tube plate and terminates at another tubes grid. The tone stack, volume control and any associated voltage divider or bleed cap grounds can share an eyelet. You might even get away with having the sending triodes cathode grounded there or any grid to ground resistor for the following tubes grid. DO NOT clump or daisy chain grounds of like phase from different preamp circuits and have them share a lead to the ground point. If that's confusing you're not alone. When in doubt just run an individual lead to the ground point.

    As to pot cases I am out on a limb compared to most vintage amp specialists here because there is no guru mojo or lore associated with my logic on the matter. So here you go. Don't bother grounding the pot cases and don't use the pot cases as a ground point. There. I said it. The pot cases are not connected to any of the lugs and the resistive elements inside are ALREADY IN THE CHASSIS LIKE EVERY OTHER RESISTOR. No one is taking steps to add a grounded case to the rest of the resistors in the amp, so why the pots? Nope. If a pot lug is schematically grounded then run a lead to the circuit ground. Tack soldering a long copper wire across the backs of the pots and using it as a ground buss is a fundamentally crappy idea. Pot to chassis contact can corrode. You could end up with your whole preamp grounded up chassis by the damn power switch. There's a tendency to use the buss inappropriately and share grounds that should be otherwise be separate (like the presence ground, which is a power amp ground, and the preamp grounds). You should literally ignore any advice that suggests the pot cases should be grounded together with a buss wire. Like the Hoffman drawing. With all the pots soldered together AND the ground bar at the filter caps there is a ground point IN the chassis near the power amp end and multiple ground points along the front of the chassis. Including the unisolated input jack. There should be ONE ground point for the preamp and it should be nearer the input end of the chassis.

    When running a lot of individual leads ground points can get crowded fast. I use these little five lug terminal strips that I use to get at Radio Shack, but now have to buy on line. The center lug on these is grounded via being bolted to the chassis and I just solder a solid copper wire across the lug rivets so I have five fat lugs I can solder grounds to.

    Sometimes you don't get a choice on where to ground something. As with non isolated jacks of any kind. In this case the - jack terminal is grounded at the chassis. You still want to run an individual ground lead to the ground point, but only use that - jack terminal as a ground lug for cable shields and resistors that connect the jacks + terminal directly to ground.

    Shielded leads should only be grounded at one end.

    Reverb cables often break this rule and reverbs often hum like they don't know the words. With the exception of the input grid the reverb drive circuit and all the shaking springs is a FUNCTION circuit and not part of the signal chain or preamp. The reverb recovery circuit IS in the signal chain and is the tanks output transducer and the tube stage that amplifies it up to a useful level. Old school reverb circuits tend to clump grounds together for all this and they often (though not always) hum. When I repair I do the best I can with what's in the amp. When I build I always get a tank with an isolated output jack and I even isolate the RCA jack on the amp chassis so I can choose my ground points for the recovery circuit which IS part of the preamp.

    The green lead on the power cord gets securely bolted to the chassis near where the cord enters the amp. This is a safety ground and not a circuit ground. The Hoffman layout is wrong on this matter. It's not a problem if you want to do it this way, just know that it's a different function. A safety measure. So be certain it's secure.

    Ok, I dissed the Hoffman drawing three times here. It's not "bad" and it's how most vintage amps were/are done and it "works". It can be improved upon in practice unless you're cloning a design.
    Then I think, what I need to do first is mark the current ground points (Not things like shielded wire grounds) on a photo or layout drawing of the amp, and label them. And then mark each ground on the schematic with the letter/number of the ground it's connected to. I think that will help me visualise what's going where, and it will also make it easier for someone to communicate where I went wrong, if I do.
    I already have one ground point by the input jacks, one by the mains transformer, and one or two in the middle of the amp. Space is the problem. I don't really have room for terminal strips, so it's gotta be those little solder tags. I've never liked the idea of using a bunch of those with a single bolt. It seems like too many physical connections where corrosion could get in-between. I guess if I tin the whole tags and bolt them down securely enough, it will be fine. It's better than what's in there now. One ground point is just a bunch of tags bolted to the circuit board, so the electrical connection to ground is only through the head of the bolt. I dunno how critical this stuff is, but that doesn't seem ideal to me

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  6. #146
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    So here's what's in the amp. The points marked #1, #2 and #3 are the existing grounds. #1 and #3 are tricky to get to without moving other stuff. #1 is under a transformer, and #3 is under the circuit board. So I'm gonna move them to A, B, and C. All the filter caps except the one over by the input jacks are grounded at #1
    Now I'm gonna mark all the grounds on the schematic

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    Here's what's in the amp. There's a lot of stuff connected to the middle ground point, that probably shouldn't be. And I think the last 2 filter caps should be grounded at G1. The next one - the one providing B+3 - I assume that one should be on the middle ground, along with the driver tube cathodes and some other stuff. The power tube cathodes are each grounded at that tube's base, so I guess they should all be taken over to G3, as should the ground from the false center taps on the filament strings? The negative feedback from the speaker is grounded at the middle point. The ground from the reverb trans is grounded by being connected to the reverb jack.
    There's also that 47k resistor to ground, that exists on the original schematic, but is not in the amp. The schematic seems to be from a slightly different model to the circuit board drawings in the manual. I dunno what effect its ommission would have, but it's a resistor to ground from the signal path, so I guess it's there to reduce output. Could too much gain be the cause of the amp's instability? Bear in mind, that since the re-wire, the amp can go way louder without breaking up than before.
    Also: I recorded a demo of the original problem. I'll post that here when I upload it. Basically, the amp plays normally until you turn it up to a point where maybe hitting the strings harder, or hitting a chord instead of a single string, causes it to make a loud machine gun sort of sound.
    Also: I noticed the mains transformer isn't bolted down tightly. I'm guessing that's why the amp is humming more.

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  8. #148
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    Quote Originally Posted by Chuck H View Post
    Then there's the presence control and any post PI master volume circuits.?
    Presence control is just adjustable negative feedback, right?

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  9. #149
    Bent Member Chuck H's Avatar
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    Quote Originally Posted by Dark Mavis View Post
    Presence control is just adjustable negative feedback, right?
    Exactly. So it's a combination PI tail and power amp circuit. I usually ground it, and the PI tail at your G2.

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    "In fact when I run into problems working on electronic circuirts, there are so many times that when I finally track it down, the source of the problem is located between my soldering iron and my seat." SoulFetish

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

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    Quote Originally Posted by Dark Mavis View Post
    Presence control is just adjustable negative feedback, right?
    Yes but frequency-dependent. It allows reducing NFB at higher frequencies and thus acts as an active treble control.

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  11. #151
    Bent Member Chuck H's Avatar
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    Quote Originally Posted by Helmholtz View Post
    Yes but frequency-dependent. It allows reducing NFB at higher frequencies and thus acts as an active treble control.
    I believe he already understood that aspect. Mark (I think that's his name ) catches onto this stuff easily and a lot faster than I think is typical. I do like that you point out the specifics though because it makes these threads more informative for more viewers. Since I idealize this forum as an information resource I think it's a good thing.

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    "In fact when I run into problems working on electronic circuirts, there are so many times that when I finally track it down, the source of the problem is located between my soldering iron and my seat." SoulFetish

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    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

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    Since I idealize this forum as an information resource I think it's a good thing.
    Same with me.

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    Quote Originally Posted by Chuck H View Post
    I believe he already understood that aspect. Mark (I think that's his name ) catches onto this stuff easily and a lot faster than I think is typical. I do like that you point out the specifics though because it makes these threads more informative for more viewers. Since I idealize this forum as an information resource I think it's a good thing.
    Nah, I never use my name on the internet. But I was in a band with a guy called Marc Davis, and I figured Dark Mavis would be a cool name for a character in an urban legend. Once I got all the grounds moved, I'll give the amp a quick try, to see if that has somehow cured the problem - I already recorded a demo of the original problem, so I'll be sure to include that - then I guess it's on to measuring the stuff I never got round to measuring.
    I think I also need to double check the shematic I drew. Right now it's a combination of the schematic I got with the amp, and what's actually in the amp. There may still be discrepancies. For example: That 47k resistor to ground right after the effects loop, isn't in the amp. Though, I might have missed it if it's on the Jack socket. It's the first place I'd look right now, but I've slept since.
    What other stuff should I measure? I don't recall if I measured any voltages on the power tubes, and I know I never measured any currents, cus I assumed I'd have to break a connection to do that...or maybe do math. Both of which I'll need a rainy day for.

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    There's also that 47k resistor to ground, that exists on the original schematic,
    V5 grid needs a ground reference under all circumstances, so a resistor to ground makes sense. Not all effects provide such DC path to ground.

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  15. #155
    Bent Member Chuck H's Avatar
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    Quote Originally Posted by Helmholtz View Post
    V5 grid needs a ground reference under all circumstances, so a resistor to ground makes sense. Not all effects provide such DC path to ground.
    This^^^^^^^^^^^^^^^^^^^^^^^^^^

    Though you mentioned that resistor before I hadn't looked into it. I'm surprised at the 47k value though. On the return jack for the effects loop recovery you typically want a somewhat higher impedance. When the loop is not in use (and assuming the switching jack is working correctly) that 47k would be parallel to a 6.8k and the reverb circuit load. But if you were to plug a cord into the return jack and leave it unterminated or if it's plugged into a device without a reference to 0VDC the recovery triode could actually become damaged. I'd hang a 1M resistor there rather than a 47k. Really. I think it's schematic error or Dan was off his meds that day.

    And can I call you Mark anyway

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    "In fact when I run into problems working on electronic circuirts, there are so many times that when I finally track it down, the source of the problem is located between my soldering iron and my seat." SoulFetish

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    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

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    Lifetime Member Enzo's Avatar
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    There seems to be an awful lot of people confidently saying that the things that other people are confidently saying, are incorrect.
    I think someone achieves a successful design, and assume that must be the right way. Reality is there are many "right" ways.

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    Quote Originally Posted by Chuck H View Post
    This^^^^^^^^^^^^^^^^^^^^^^^^^^

    Though you mentioned that resistor before I hadn't looked into it. I'm surprised at the 47k value though. On the return jack for the effects loop recovery you typically want a somewhat higher impedance. When the loop is not in use (and assuming the switching jack is working correctly) that 47k would be parallel to a 6.8k and the reverb circuit load. But if you were to plug a cord into the return jack and leave it unterminated or if it's plugged into a device without a reference to 0VDC the recovery triode could actually become damaged. I'd hang a 1M resistor there rather than a 47k. Really. I think it's schematic error or Dan was off his meds that day.

    And can I call you Mark anyway
    I'll check again. Maybe I didn't check on the jack itself, since I was trying to determine which of the star grounds everything was connected to.
    Ah. Yeah, it was on the jack.
    Yeah, y'all can can me whatever you want

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    Master Destroyer nosaj's Avatar
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    Quote Originally Posted by Dark Mavis View Post
    Yeah, y'all can can me whatever you want
    just don't call him late for dinner........


    nosaj

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    Quick question: Since I'm limited to using those little solder tags for grounds, and space is limited, I'm thinking of just bolting down 2 or 3 of them and connecting them together with a ring of wire that can act like a mini circular bus bar. It will give me the room I need to connect all the grounds, and will minimize the number of mechanical contacts acting as electrical contacts. But...is there any reason not to do this? I never see it done else where, but I can't think of a single reason not to, except...maybe ground loops? But they'd be tiny. Smaller than the holes drilled in the chassis anyways for the tube sockets. It just seems like too simple a solution, to not have a downside. Or maybe I can cram enough tags onto one bolt, if I keep them flat and let them overlap. I'm just thinking of if I have to go back in there and desolder or resolder a wire.

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    Bent Member Chuck H's Avatar
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    All practical considerations. And the method you propose isn't a problem. The short length and low resistance of that piece of bus wire will be inconsequential. You don't need a ring or a closed loop for any reason (and that actually DOES make a ground loop, but such a short path that it wouldn't manifest). You could just have a three inch piece of buss wire from each ground point off of one tag. When you're done soldering you just bend it over out of the way. But I like your idea of having several tags on one bolt too. If you turn them in a spiral and can tag a little solder between them to avoid so many possible oxide points. It might make for a neater appearance. But either way will work. And I've seen the inside of that thing so I don't think you're trying to make it look fancy now.

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    "In fact when I run into problems working on electronic circuirts, there are so many times that when I finally track it down, the source of the problem is located between my soldering iron and my seat." SoulFetish

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    Quote Originally Posted by Dark Mavis View Post
    Quick question: Since I'm limited to using those little solder tags for grounds, and space is limited, I'm thinking of just bolting down 2 or 3 of them and connecting them together with a ring of wire that can act like a mini circular bus bar.
    I used to use these. Stack two together and you have a 10 point star. They can be bent up a little to clear the chassis or use a nut as a spacer.

    Click image for larger version. 

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    Quote Originally Posted by Dave H View Post
    I used to use these. Stack two together and you have a 10 point star. They can be bent up a little to clear the chassis or use a nut as a spacer.

    Click image for larger version. 

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    I was looking for something like that on Ebay, but didn't know what to call it. I might make something similar. I wanna do it tomorrow so I can't order anything. I could just cut something out of sheet steel and tin it, I guess.

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    Actually...COULD the grounding be the cause of the issue I described? Filter caps supplying the first preamp tubes are grounded at the same point as those providing the plates of the output tubes, and the B+ to the output trans primary. Could that cause a situation where, above a certain volume, there's a kind of feedback, where some of the signal at the output part of the amp, finds its way back into the earlier stages, and the amp runs away? And might that manifest as just higher than expected hum at lower volumes? I don't know much about this stuff, but that kinda feels like something that could happen

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  24. #164
    Bent Member Chuck H's Avatar
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    Improper grounding has been known to cause instability. Or, maybe more accurate, correcting improper grounding has been observed to cure instability. Not exactly the same thing I guess because it's always possible that something other than grounding is inadvertently corrected in the process. But that's just my experience. Others here do have more conviction about it.

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    "In fact when I run into problems working on electronic circuirts, there are so many times that when I finally track it down, the source of the problem is located between my soldering iron and my seat." SoulFetish

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

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    Quote Originally Posted by Chuck H View Post
    Improper grounding has been known to cause instability. Or, maybe more accurate, correcting improper grounding has been observed to cure instability. Not exactly the same thing I guess because it's always possible that something other than grounding is inadvertently corrected in the process. But that's just my experience. Others here do have more conviction about it.
    Well, I'll find out tomorrow. Either way, I'll post a video, cus I've recorded a demo of the problem. If the problem persists, it's back to diagnosing. After that, I got a 1978 Orange that's basically just a pile of parts

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  26. #166
    Bent Member Chuck H's Avatar
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    Quote Originally Posted by Dark Mavis View Post
    After that, I got a 1978 Orange that's basically just a pile of parts
    Sounds like fun. And it might have been a simpler start this Torres amp

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    "In fact when I run into problems working on electronic circuirts, there are so many times that when I finally track it down, the source of the problem is located between my soldering iron and my seat." SoulFetish

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

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    Quote Originally Posted by Chuck H View Post
    Sounds like fun. And it might have been a simpler start this Torres amp
    Much simpler. Electronically all it needs is a touch of assembly. It's just a mess. It's more a restoration than a repair, so...tough decisions to make. Like whether to re-cover. The cab has a burn mark on top that's been used as an ashtray for years. I'm thinking I may be able to turn the cab upside down, leaving just the screw holes from the sleds, rather than a giant burn. Or...I can re-cover it. The torres was uncovered when I got it, and covering that was pretty easy. There's also a hole in the faceplate. There's no way I can re-fill it and cover it up cus...Orange! I'd have to re-paint the whole plate, and I know nothing at all about silk screening or whatever they did. Guess I'll have to put a switch or pot in that hole and then decide what purpose to give it. Guess I'll just clean the grime off and then decide. That's gonna have to be a different thread.
    There's also a hole in the grille cloth, and one of the speakers is not original. The hole was always there, and one of the speakers was always dead. Don't tell anyone, but I may have moved the dead speaker to be under the hole, and then stabbed a guitar headstock through there. I'm too cheap to destroy functioning equipment, except a few Marlin sidewinders. But they had a habit of destroying themselves if you were ever foolish enough to try to use the whammy bar.
    Though...I wonder what caused the hole. There's no serial number on the cab, so I can't check its history, and I don't think it's from the same period as the head. Even when I got it...in like 1996, it looked like it had been gigged hard for years. The head still has its inspection tag and serial number, so maybe I can at least find out if it was bought new by someone famous

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  28. #168
    Bent Member Chuck H's Avatar
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    I had a Marshall head like that. Not a super collectible model. A 50W JMP master volume with the big, square illuminated switches. Before it got all grimy, torn and scratched up someone had covered it in white Tolex, hacked a hole in the side for a fan, hacked some holes in the face plate and chassis for another big, square switch (that was there, but not connected to anything?) and a couple of mini toggles. There was a band name spray painted in stencil on the back, but I can't remember now what it was. The name in the amp chassis, and on the inside of the cabinet and on the outside of the chassis written with a black Magic Marker was "Jay Rosignolo". Many years ago I managed to find a few pictures of the guy on line. I know it was him because you could see the white Marshall in the background of one of the shots. This was after I'd already parted the amp out. The transformers are in an amp built and owned by our own big_teee. He got them in trade for some really great strat pickups he makes that I loaded in my main squeeze. But after seeing the pictures of Jay it was clear that this guy LOVED to gig and play rock and roll. And that amp was clearly used hard and long. I had pangs of regret for hacking it further and then parting it out. If I had my druthers I might have cleaned it a little, snuffed it up electronically and just given it back to him (if I could find him?). The way it looked in the photo's I can't imagine anything other than hard and unfortunate circumstances separated him from his passion and I'll bet he would have been stoked to see that old turd Marshall. Oh well. No backsies sometimes.

    EDIT: Well it's a snow day here on Whidbey, sooo...

    I looked up Jay again and it turns out he died a couple of years ago. I don't know the circumstances because I didn't have the heart to dig into it. But a friend of his has managed to post up a couple of his demos on the web. Not a real good player as it turns out, but not bad. It hardly matters because all the photos I've seen are of him with a guitar or on a stage. He was what I call "the real deal". He just loved to play his guitar. Gotta respect that. As it happens it seems to me he probably got rid of the amp because it was obsolete for the direction he was going in with his playing. You can see in the (very grainy) photos below, the old white Marshall in the first photo and him later in life with his multi channel Marshall uber gainer. So now I don't feel so bad about the amp. But of course it's sad anytime a true believer leaves our ranks.

    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Last edited by Chuck H; 01-15-2020 at 02:09 AM.
    "In fact when I run into problems working on electronic circuirts, there are so many times that when I finally track it down, the source of the problem is located between my soldering iron and my seat." SoulFetish

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

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    Quote Originally Posted by Chuck H View Post
    I had a Marshall head like that. Not a super collectible model. A 50W JMP master volume with the big, square illuminated switches. Before it got all grimy, torn and scratched up someone had covered it in white Tolex, hacked a hole in the side for a fan, hacked some holes in the face plate and chassis for another big, square switch (that was there, but not connected to anything?) and a couple of mini toggles. There was a band name spray painted in stencil on the back, but I can't remember now what it was. The name in the amp chassis, and on the inside of the cabinet and on the outside of the chassis written with a black Magic Marker was "Jay Rosignolo". Many years ago I managed to find a few pictures of the guy on line. I know it was him because you could see the white Marshall in the background of one of the shots. This was after I'd already parted the amp out. The transformers are in an amp built and owned by our own big_teee. He got them in trade for some really great strat pickups he makes that I loaded in my main squeeze. But after seeing the pictures of Jay it was clear that this guy LOVED to gig and play rock and roll. And that amp was clearly used hard and long. I had pangs of regret for hacking it further and then parting it out. If I had my druthers I might have cleaned it a little, snuffed it up electronically and just given it back to him (if I could find him?). The way it looked in the photo's I can't imagine anything other than hard and unfortunate circumstances separated him from his passion and I'll bet he would have been stoked to see that old turd Marshall. Oh well. No backsies sometimes.
    It's always fascinating to think about the history of amps and guitars and where they've been and what they've seen.

    Here's Jay tearing it up on SoundCloud:

    https://m.soundcloud.com/jay-rosigno...t-it-rip-0-8-1

    I wonder if that's his white Marshall you can hear?

    If you Google him, it's there in one photo.

    Edit: simultaneous postage! RIP Jay

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  30. #170
    Bent Member Chuck H's Avatar
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    Quote Originally Posted by minim View Post
    Edit: simultaneous postage! RIP Jay
    Yep. R.I.P. to Jay. Clearly "Da Man" among his fans and friends because his vestiges are still traceable on line

    Something about the amp... It had the (I'm certain) original "mustard caps" in it. Now, mustard caps are "vintage", but the master volume models are not. So this must have been a very early master model. I did own one other JMP master volume amp and it had the box caps in it.

    My thinking now is that it's eloquent that a guy making outstanding pickups is using the transformers (PT, OT and choke) from this amp in a vintage clone to better refine his own art and so Jay's amp just keeps giving to the cause And I'm hopeful (and intending to be helpful) that Mark's amp (He said I could call him Mark ), the Orange will enjoy greater respect and continue to find useful avenues in the cause.

    And my apologies to Mark is he finds this off topic aside on his thread a problem.

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    "In fact when I run into problems working on electronic circuirts, there are so many times that when I finally track it down, the source of the problem is located between my soldering iron and my seat." SoulFetish

    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

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    Quote Originally Posted by Chuck H View Post
    This^^^^^^^^^^^^^^^^^^^^^^^^^^

    Though you mentioned that resistor before I hadn't looked into it. I'm surprised at the 47k value though. On the return jack for the effects loop recovery you typically want a somewhat higher impedance. When the loop is not in use (and assuming the switching jack is working correctly) that 47k would be parallel to a 6.8k and the reverb circuit load. But if you were to plug a cord into the return jack and leave it unterminated or if it's plugged into a device without a reference to 0VDC the recovery triode could actually become damaged. I'd hang a 1M resistor there rather than a 47k. Really. I think it's schematic error or Dan was off his meds that day.

    And can I call you Mark anyway
    Is 3.3 meg okay? The only 1 meg resistors I could find were 5 watts. Ran out of daylight today. Or rather I used it for other things. But I Can still upload the demo of the problem. I'll just make it private or unlisted

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    Quote Originally Posted by Chuck H View Post
    And my apologies to Mark is he finds this off topic aside on his thread a problem.
    Not a problem. I ran out of solder anyways. Got caught thinking I had plenty, and there's nowhere to buy it here. I have to wait for EBAY.

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  33. #173
    Lifetime Member Enzo's Avatar
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    SOlder shows up in many places. Often hardware stores have some - being careful to get electrical solder, not plumbing solder. Hobby/craft stores sometimes have it as well. And I bet a lot of electronic repair places would give/sell you a small amount. Places that repair TVs, amps, whatever. I would certainly give a guy a foot or two of solder off my roll.

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    Education is what you're left with after you have forgotten what you have learned.

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    Quote Originally Posted by Enzo View Post
    SOlder shows up in many places. Often hardware stores have some - being careful to get electrical solder, not plumbing solder. Hobby/craft stores sometimes have it as well. And I bet a lot of electronic repair places would give/sell you a small amount. Places that repair TVs, amps, whatever. I would certainly give a guy a foot or two of solder off my roll.
    The nearest place is a Screwfix a few miles away and I don't drive. But I was in the area yesterday, so I picked some up...at a horrible price. Then, I got home and the stuff I ordered off EBAY had arrived...a few days early. That seems to happen a lot

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    Click image for larger version. 

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    This is where I'm at right now. I'm a bit unsure about everything between the relay and the driver. I'm thinking of just using G2 for everything after that first triode of V4. Also: I ran a wire from the sleeve of the output jack to G2, even though it's not an isolated jack. I'm thinking of doing the same with the reverb jack. Not sure if it's necessary or even a good idea or not.
    The mains transformer was really loose. I guess I never got round to tightening it down. I think that's where a lot of the extra hum came from. Just gotta cram everything back into place now, to find out

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