Epiphone Comet EA-32RVT Help

[fenderguy81]

I recently acquired a nice vintage Epiphone Comet EA-32RVT amp that has some issues. It looks like it had the power transformer and choke replaced with Mercury Magnetics GIB-GA17-P and EP-EA32RVT-C respectively. I did the usual servicing of replacing the electrolytic caps, added a grounded 3-prong power cable, cleaned the pots and tube sockets, and also cleaned up some of the power supply wiring that was pretty messy. I am experiencing a loud low hum when the amp is turned on that does not change when the controls are moved. Turning off the reverb with the Footswitch helped some and pulling the 12au7 quiets it down a lot. Any help would be greatly appreciated!

Thanks!

Here's a modified schematic I found on this site that's closer to the amp:

[Latole]

  "I am experiencing a loud low hum when the amp is turned on that does not change when the controls are moved.  "

IMO there are some filtering issue in power supply .
Bad grounding scheme ?
https://el34world.com/charts/grounds.htm


How did the amplifier work before the work was done ?
hum or not ? and what else .

[fenderguy81]

Thank you Latole for the response. I purchased the amp from a family member of the former owner and was told that it had issues but unfortunately they did not know much beyond that. I opened the amp up and saw the rats nest, 2 prong lamp cord, and questionable work (see photo) so I did not have a chance to get a baseline assessment of any prior issues. I added individual chassis grounds for the 2 sets of filter caps so I will try to alter them to more of a star ground like the link you provided. In addition I was thinking about adding 2 100 ohm resistors on pins 4 and 5 to ground on V5 to create an artificial center tap for the heaters since the power transformer does not have a center tap.

Amp as it came to me:

[Latole]

Thanks for the photo.
It's not often I've seen such a poorly done wiring
.
Regarding the heaters, and based on the schematic, we must redo all the wiring by isolating the heater wire that is at ground, twisting the wires  together and put two 100 ohm resistor directly to the transformer.

[fenderguy81]

Thanks for the response Latole! I went ahead and added the 100ohm resistors to ground for the heaters and moved the ground points for the filter caps to something closer to the star ground layout you provided. Unfortunately, the hum is unchanged. Pulling V3 (12au7) makes the hum go away. I tried other 12au7’s and even a 12at7 but it made no difference. I also tried temporarily grounding the grids on V3 hoping to isolate the issue, but it made no difference to the hum. Any suggestions would be appreciated. Thanks again!

[Willabe]

Here read this from fellow member Melin's web site on grounding;

https://www.valvewizard.co.uk/Grounding.html

[BrianS]

You should double check the solder joints on the fiber board...where all the orange drops are.  Some of them look iffy.  It could just be shadows, but might be worth poking and gently tugging at some of the leads.

[fenderguy81]

I redid the grounding scheme for the filter caps and also put the PT high voltage CT on its own isolated ground to the chassis. I actually rechecked the diodes and am seeing ~.2 in both directions opposed to the ~.5 & OL that they initially tested at before initial power up. They are labeled 5J F8, which I’m not too familiar with. I tried looking them up and did see F8 was 800v so I’m assuming they are 5A 800v? Any recommendations for replacements? I was hoping to just use some 1n4007’s but obviously can’t if these are indeed 5A.

The diodes not doing their job rectifying would explain the hum so hopefully they’re the culprit. 🤞

Also regarding the fiber board connections, I’ll go ahead and touch them up when I replace the diodes. Thank you!

[BrianS]

I'd suggest just taking a step back and re-assessing your diagnostic procedures.
-Leave the amp and components as they are-Triple check your grounding connections.  It looks like you have some wires soldered directly to the chassis.  It is very possible that your soldering equipment cannot generate the heat needed to make this joint.  A better course of action would be to mechanically connect a lug to the chassis that you can then solder to.-Before "touching up" the fiber board solder connections, examine them and look for actual failures:  wires or component leads that pull out of the eyelets with little force, "cracked" joints, "frosty" looking joints.   It doesn't make sense to touch up a good joint, as that is an opportunity to make a bad one. 

Ask yourself, if the rectifier is bad, why does my hum go away when I pull V3? 

Good luck!

[mresistor]

If you want/need to use 1KV 5A diodes there are these   and there are others that are suitable.
https://www.digikey.com/en/products/detail/good-ark-semiconductor/BY500-1000/18649444

[mresistor]

In addition to what Brian has suggested which is very good advice and Willabe's Merlin link I see you have the Power Supply filter capacitors grounded in two different locations and they are soldered direct to chassis.  The power supply caps should be grounded to the PS ground point in the star scheme. The preamp power filter capacitors should be grounded near the input jacks hopefully on the other end of the chassis from the power supply.

[fenderguy81]

Thanks for all the advise, it's really appreciated! I went ahead and chopsticked/pulled on the component leads on the fiber board and examined them for any cracks. I cleaned up a lot of the flux on the board and redid some of the eyelet joints that were questionable. Some of the components were tacked soldered together and not in the eyelet. I also lifted the board to make sure there weren't any connections underneath that shouldn't be there.

I checked the grounds and also made sure that my chassis connections were good. I use a higher wattage large chisel tip soldering iron for chassis grounds. I did rough up the chassis a little to make sure the solder had something to "grab" onto and have read that it's better practice than attaching to a chassis lug if you have the right iron. I know Fender used to add ground attachments to transformer lugs, but obviously transformers vibrate and the joints can crack over time. This chassis wasn't as easy as soldering to a Fender, but the connections show <.2 ohms to ground and I applied pressure to make sure they aren't going anywhere. The high PT CT is a bit long, but I already had a good chassis ground at this location from the previous filter cap ground, so I may shorten it and attach it closer to the transformer. The power supply filter cap grounds were moved to the star point on the terminal strip and the preamp ground node was moved to the last ground point on the furthest pot, but I just saw the comment to move it to the input jack so I will move it there.

Just to clarify, is the 5J denoted on the diode referencing 5A? I think I have some 1000v 1A and 3A diodes on hand and read that 1A diodes were suitable for most small amps. I'll have to order the 5A diodes if this amp needs them.

Thanks again!

[Willabe]

Just to clarify, is the 5J denoted on the diode referencing 5A? I think I have some 1000v 1A and 3A diodes on hand and read that 1A diodes were suitable for most small amps. I'll have to order the 5A diodes if this amp needs them.

That amp does not need 5A diodes for the a SS B+ rectifier. Those 2 x EL84's wont draw much current at all, not even 1/10A = 0.100mA at peak output.

You can use 1N4007, 1KV/1A, put 2 in series on each side if you want to.   

[BrianS]

Fiberboard solder joints look way better! 

I disagree with your soldered ground logic.  At the very least, you may want to consider redoing the safety ground using the bolt/lug/nut style of connection.

[fenderguy81]

I put in the 1n4007 diodes, moved the preamp filter cap ground to the input jack ground but am still having a very loud low hum that gets even louder when the reverb is engaged with the foot switch. I also tried a different speaker, but that made no difference. I inspected the old Gibbs reverb tank and thought it might be the culprit at first because it's reading 172 ohms on the output and 166 ohms on the input, but I believe that's normal to see that high of resistance on the input for this type of tank. Perhaps a bad reverb or output transformer?

[Willabe]

Here read this from fellow member Melin's web site on grounding;

https://www.valvewizard.co.uk/Grounding.html

[AlNewman]

Is the red/yellow soldered to chassis the B+ center tap?  That kinda looks like a dodgy connection.  You need a really high power iron to make good chassis connections.  May be better off with a eye connector and star washer.

[fenderguy81]

I moved the chassis ground connections to terminal screws and will try to experiment with the amp later today. I came across this video highlighting the same problem that I am experiencing:

Perhaps not the most ideal fix as it sounds like a complete overhaul of the ground scheme would be best, but this looks like it could be a decent work around?

[fenderguy81]

Well a little progress but still having a lot of hum. I reviewed the grounding pdf that was recommended and am still trying to wrap my head around everything. I tried grounding the reverb tank at various points as shown in the above video without any improvement. I also made new RCA/terminal cables for the reverb pan. I moved the HV CT to the same grounding terminal point as the filter caps/main board, which helped reduce the noise some. I moved the 3-prong power cable ground to a lug underneath the transformer and got rid of all of the chassis soldering points. I also added (2) 100 ohm resistors to create an artificial CT for the heaters and mounted them to the V5 cathode and redid the heater supply with a twisted pair to the back of the chassis. I removed the heater ground from V1 that was tying into the preamp. Finally, I tried lifting the V1 cathode resistor/bypass cap ground and experimented with different ground points as I read the reverb recovery tube ground can sometimes add hum depending on where it is grounded. Here's an updated picture and any recommendations are appreciated.

[AlNewman]

Where is the interstage transformer grounded?
And when you say you moved the HV center tap, you put it at the same spot as the reservoir cap?

[shooter]

still having a lot of hum.

dirty wires and sensitive signals in close proximity tend to do that

[fenderguy81]

Where is the interstage transformer grounded?
And when you say you moved the HV center tap, you put it at the same spot as the reservoir cap?

The transformers are mounted on the underside of the chassis (see above photo) with the exception of the choke mounted by the power transformer.

The HV center tap (red/yellow wire) was soldered directly to the chassis, but is now attached to the same node as the power supply filter caps (black wire), main board ground (brown wire), and what I believe is a dropping resistor (130 ohm).

re: Shooter
Would cleaning the dirty wires with iso alcohol help? Also, are there any obvious signal wires that you would recommend moving? I know these older 60s era Gibson/Epiphone amps are known for having a subpar layout and can be quite noisy.

[SEL49]

Where is the interstage transformer grounded?

The IT is not grounded. The CT connects to the wiper of the tremolo intensity pot.

[shooter]

dirty wires

 
not the behind your ears kinda dirt, Power supply wires, large signal wires, crossing low signal wires
where they "must" cross, they should be elevated above as much as possible
those old sockets have been known to be noisy also, with a gloved hand (because tubes get hot) push on each tube as you hear the hum, does wiggling the tube cause the hum to "change"?

[AlNewman]

The IT is not grounded. The CT connects to the wiper of the tremolo intensity pot.

Ahh, you're right.  I don't actually see the wire from the IT to the pot, but I do see the cap off of the intensity.

Also, I'm not sure i would connect the screen and rectifier filters together.  The reservoir and CT should have their own dedicated ground, theoretically anyways.  I think that's noted in Merlin's grounding link Willabe shared.

[Willabe]

Also, I'm not sure i would connect the screen and rectifier filters together.  The reservoir and CT should have their own dedicated ground, theoretically anyways.

Very close. Yes, tied to each other but not directly grounded to the chassis.

You run the B+ CT directly to the 1st filter caps, node A, ground lead. Nothing else gets grounded to those 2 wires. Then you run a single wire from those 2 wires over to the screen filter cap, node B, ground lead.

You can't leave this single wire out.

It's what isolates this noisy connection from the rest of the amp. This is the noisiest connection in the amp.

You want the PT's B+ CT and 1st filter cap's charging current pulses loop to be able to go round and round by themselves. The loop goes from the PT B+ through the rectifier, charges the filter cap, goes out the caps ground lead, back through the PT's B+ CT through the PT's B+ wind, back out the B+ to the rectifier, and round and round it goes.

These pulses are the ripple, which is highest/the least smoothed in the B+ string, at the 1st filter cap. Again, this is the noisiest connection in the amp. So you want to isolate it, that's why you wire like Merlin shows, Kevin O'Connor says the same, so does R.G. Keen, etc.

And you want that 1st Filter cap/CT kept off the chassis. You don't want those pulses radiating out through the chassis.

Study this Merlin page on grounding until you see it.

https://www.valvewizard.co.uk/Grounding.html

[AlNewman]

Yes, but there is also lots of examples of amps, quiet mass produced amps, which use a multiple star system grounded to chassis. 

I've worked on a lot of old, old stuff, which most of the designers of the 50's and 60's copied to produce guitar amps.  Everything is chassis return, all PTP wiring, and is grounded as soon as physically possible.  They aren't high gain circuits, but they're high interference circuits.  In fact, they're built to pick up and filter interference. 

They all look like a rat's nest, but most are built in a way that the grounding follows the chassis back to the rectifier. Most produce very little hum, and the well built ones produce next to none.

[Willabe]

Yes, but there is also lots of examples of amps, quiet mass produced amps, which use a multiple star system grounded to chassis.

I'm not talking about the whole amps grounding. Just the 1 filter cap and the PT's CT grounding.

I'm replying to what you said here;

Also, I'm not sure i would connect the screen and rectifier filters together.  The reservoir and CT should have their own dedicated ground, theoretically anyways. I think that's noted in Merlin's grounding link Willabe shared.

[Willabe]

Yes, but there is also lots of examples of amps, quiet mass produced amps, which use a multiple star system grounded to chassis. 

They all look like a rat's nest, but most are built in a way that the grounding follows the chassis back to the rectifier. Most produce very little hum, and the well built ones produce next to none.

3 things from the R.G. Keen post on The Amp Garage on grounding;

"It is possible to get away with many things that are not technically correct."

"There are an infinity of ways to ground an amp. Only a few of those can be demonstrated beforehand to be quiet. Others may be quiet, and can be found by trial and error. Others are quiet by accidental cancellation, and remain quiet - until something changes."

"Because of cancellation, it is possible to have uncountably many of the infinite number of possible grounding schemes be as quiet as pure star grounding. But it is in general not possible to predict ahead of time which of these non-star-grounded setups will be this quiet. Star grounding is a PITA, lots of wires and lots of thinking (which always hurts!) so humans want to find an easier way. They do something else, don't like the result, then tinker with minor ground wire changes until they stumble on something that's less noisy, and think they have found a new universal truth. They then tend to publish this on the internet and call it the "One True Grounding Way" because after all, they found it worked.  :lol:"

This is why I stick with Merlin's and Kevin O'Connor's wired multiple star ground, where the individual stars are daisy chained/bussed together, with only 1 chassis grounds as possible. And why I don't like to use multi cap cans, because of grounding. Or some use a power amp ground and a preamp ground.

Here the full post's from R.G. Keen, he explains it extremely well. Had to repost it in 4 posts.

https://ampgarage.com/forum/viewtopic.php?t=27991

"The baffling things about grounding in general is that exactly where the currents flow matters because all wires (and chassis metal, and...) are actually low-value resistors, and the common (mis-)conception is that there is zero voltage between all ground points.

Where big currents flow, the voltages generated across ground wires make a big difference. Here are some highly important examples:
1. The "ground" wire from the PT center tap must go directly to the first filter cap, no where else. This wire conducts big pulses of current from the first filter cap, so the wire resistance makes the voltage along the wire vary. If you connect this somewhere to chassis, the amount of hum you get will vary depending on where it's connected.
2. The output stage conducts heavy (for tubes) currents from output tube conduction on alternate half-cycles from the tube "ground" to the negative terminal of the first filter cap(s). This wire should not be shared by any of the preamp circuitry, or it will appear as a small distortion signal on each section it shares a ground with. Screen filter cap should be tied to the first filter cap negative for the same reason.
3. Succeeding decoupling/filtering caps for preamp sections may be individually grounded to the first filter cap negative, or connected into one or more local star points, and these points connected to first filter cap negative.

It's likely that 2 and 3 are where the grounding scheme you mention get that."

    gui_tarzan wrote:
    "I believe every amp I've worked on, save the old Gibsons with floating grounds, has the PT center tap going to a chassis ground along with the first B+ cap's ground. Am I reading what you said wrong?"

"No, you're not.

It is possible to get away with many things that are not technically correct.

If the amps had the CT and the first filter cap grounded to the chassis at one and only one point, they're probably OK. Something like 10x or more times the DC output current of the first filter cap goes into the (+) terminal every half-cycle peak. And the same current is pulled out of the (-) terminal, and must flow back through the CT lead to the PT.

If those points (CT and first filter - ) are separated along a wire, the wire has a voltage across it of V = I * R. I is large(-ish in tube amps) and R is small, but there is a voltage. If you connect the ground of the preamp section on the PT end of a wire, the preamp "ground" sees a moving voltage equal to the charging current times the resistance in the wire."

And 1 more from R.G. Keen in the next reply.

[Willabe]

R.G. Keen on The Amp Garage;

"This voltage is 120-cycle and a "buzz", being pulses at 2x the power line frequency. It's not generally possible to get rid of unless you move the preamp ground reference back to the first filter cap negative. If you ground the preamps at some remote point on the chassis and the CT and first filter cap are connected together at one point on the chassis, it may be quiet, as little current is flowing through the (unknown) resistance of the chassis, and what is flowing is from the preamp itself, not charging current of the power supply.

So you have to ask yourself - do you feel lucky today? :lol:

There are an infinity of ways to ground an amp. Only a few of those can be demonstrated beforehand to be quiet. Others may be quiet, and can be found by trial and error. Others are quiet by accidental cancellation, and remain quiet - until something changes.

As I said, it's all about exactly what conductor the current flows through. That makes it HARD to deal with for voltage-trained people. Like us."

dinkotom wrote: "So this simply means that, in the end,everythíng is basically grounded at the first cap?"

"Yes, and no. That particular limit is called "star grounding".

Pure star grounding has every single component that connects to "ground" have its own wire to the star-ground point. Star grounding can be shown to have the least possible interaction between "ground" points in the circuit, because the voltage across the wire/resistors from components to the One True Ground cannot possibly cause a voltage in other sections of the circuit.

 Pure star grounding causes massive numbers of ground wires, and is very unwieldy to wire. So practical - and lazy! - humans looked for other ways.


There is another process at work in determining how much voltage appears across ground wire/resistors - cancellation. In a circuit where each stage inverts the signal, the current from one section is in opposition to the current in the next/previous stage (neglecting phase funnies for the moment). So some portion of the ups and downs cancel. At least, they are the same signal, but added in different proportions. So this cannot introduce distortion or crosstalk, only a change in effective gain by partial cancellation or local feedback.

 The partial cancellation idea leads to local star grounds. A few stages with the same signal waveform in them can be gathered into a local ground point with no crosstalk, only a minor gain change. Then these local star points can be connected to the One True Ground star point with little or no loss of signal integrity compared to pure star grounding. This cuts down massively on the number of ground wires.


This works beautifully well. I star grounded a tube amp built on a PCB, and it was noticeably quieter than the same circuit built on wires and tagboards.


Because of cancellation, it is possible to have uncountably many of the infinite number of possible grounding schemes be as quiet as pure star grounding. But it is in general not possible to predict ahead of time which of these non-star-grounded setups will be this quiet. Star grounding is a PITA, lots of wires and lots of thinking (which always hurts!) so humans want to find an easier way. They do something else, don't like the result, then tinker with minor ground wire changes until they stumble on something that's less noisy, and think they have found a new universal truth. They then tend to publish this on the internet and call it the "One True Grounding Way" because after all, they found it worked. 


As I said, good grounding involves knowing what currents flow in what wires and then making sure that the currents flowing through these resistors (all wires are resistors!) do not induce unwanted voltages in other parts of the circuit, especially and most critically the input of the whole amplifier.

[Willabe]

And, R.G. Keen;

"Teemuk brought out the next lecture early: speaker return grounding. He says:

Additionally, some of these high currents are also directed to the loudspeaker. For same reasons loudspeaker's ground return currents should not share conductors with other ground returns.

 And this is correct. The highest currents in a tube amp are the heater wiring and the speaker output. The heaters are set up to be push-pull and center tapped, with no center tap ground current, so this is pretty quiet if done properly. The speakers are not.

 The speaker output in a tube amp is usually transformer isolated. The speaker output is push-pull, and has no particular need to be connected to ground at all - until you introduce feedback from the speaker output to an earlier part of the circuit. Most amps do some of this, with feedback usually going to the phase inverter.

 This forces the speaker output to share a ground with the tube circuits, otherwise there can't be any feedback signal. So one end (or a tap!) of the speaker winding has to be grounded. This is often done without any thought by simply screwing down the output speaker bushing to the chassis, "grounding" the common side.

 But look at where the current goes. If the speaker output winding is tied to the output jack, all is (probably) well, because the return current from the speaker jack common side is sucked right into the speaker winding. Things get ugly if the speaker winding common is just attached to the chassis somewhere else. Now the amperes-big speaker currents have to flow through the chassis resistance to the speaker winding return, causing a voltage across the chassis. If the input jack happens to stand in the way somewhere along that path, the input "ground" is now wobbled around by the speaker return current-voltage. You have unintended feedback from speaker output to input, and a good chance of oscillation.

 The right way to do this is to ensure that speaker return currents only flow directly to the speaker winding by taking the speaker winding common directly to the output jack on a "ground" wire that is not the chassis and not shared with any other ground. Now the winding currents have to flow back on their own resistor/wire. The speaker jack can then be grounded and the speaker "hot" output can be taken back to the PI for feedback without the speaker return current/voltage being involved. The theoretically correct way to do this is to isolate the speaker output jack from chassis, and run a speaker jack ground wire back to one of the One True Ground or to the stage that is using speaker-voltage feedback.

 The chassis is a substantial hunk of metal, and it's natural for humans to decide that it's all ground, so tie everything to it. That works OK sometimes, miserably poorly other times, and the differences lie in what currents flow in the chassis. If the currents are all small, chances are that the chassis resistance is low enough to make only insignificant voltages; or if the currents flow at right angles to one another, the voltages are lower. But with enough gain, as in the metal-head's cry for "MORE GAIN!!" you can make anything oscillate."

[Willabe]

Finish, R.G. Keen;

"The theoretically correct thing to do is to isolate input and output jacks from chassis, and have one and only one wire connect the chassis to ground so it can act as an RF shield. Done this way, the chassis simply cannot be carrying any currents, so current-generated voltages across the chassis don't exist. In practice what happens is that amp builders use the chassis, and then go looking for places on the chassis to connect certain ground points that are quieter somehow, so they look for cancellation quiet places on this two-dimensional mess of voltages on the chassis. It's not that you can't find such cancellation points, but they're very, very hard to predict.

 And then there's the difference between power line, audio, and radio frequency signals. Radio frequency signals can be take to be "any frequency where the field effects cause by high frequency overwhelm the pure Ohm's law effects of current flow".  At DC and up to above audio, the field effects are negligible, so you want wires for ground currents. At RF, you need transmission lines and that means planes. Field effects make return currents flow independently under the conductor that carries the signal current, so using the chassis as a big, clumsy ground plane is needed for shielding.

 That's why if you isolate your input jacks from chassis, you ought to use a good RF capacitor from the input jack ground bushing to the chassis right there at the jack. This connects incoming RF from the input cord/antenna to the chassis/shield and keeps the RF from flowing down the wires to be amplified."

[fenderguy81]

Re: Willabe
Thank you for all the information on grounding theory. I played around with the CT and first filter cap grounding trying to follow the diagram from Merlin, but was still unable to get rid of the hum. I then went to remove the reverb connections and noticed how loose the terminal felt. It came right out! I am contemplating removing and trying to fix the connection or just replace it with a new transformer.

Re: Shooter
Additionally, I worked on some of the lead dress--trying to elevate the signal wires and have them cross at 90 degrees. Thank you for clarifying the "dirty" wires as I thought you may have meant corrosive/leaking DC. I've seen some techs soak old cloth covered wires and conductive boards in iso alcohol with good results so that's where my mind initially went.

[AlNewman]

@Willabe Thanks for taking the time to post all of that, it was a good read. 

I do like chassis returns, mainly because most of what I do is with tag strips and point to point, but also because it seems bus wires create the most probability for a ground loop error between stages.  I look at the chassis as one big wire, although I still create grounds from the most noisy to least noisy.  I'll run wires from my pots to filter grounds, depending on which stage the pot is referenced to. 

Basically I'll create a star at every filter cap, as well as one at the input, and tie everything in accordingly.  The heaters have their own reference, close to the PT, and the OT has it's own reference, also close to the PT/power section.  CT and reservoir, also close to the PT.  It's a matter of designing the layout to allow everything to flow from most sensitive to least sensitive.  It seems the major hums and feedback come from one section not lining up with the proper flow.

[Willabe]

I do like chassis returns, mainly because most of what I do is with tag strips and point to point, but also because it seems bus wires create the most probability for a ground loop error between stages.  I look at the chassis as one big wire, although I still create grounds from the most noisy to least noisy.  I'll run wires from my pots to filter grounds, depending on which stage the pot is referenced to.

You've got it backwards.

R.G. Keen, Merlin, Kevin O'Connor, Randell Aiken and others, all teach against random chassis grounding. And instead teach wired daisy chained multi star grounding. 

How can you say you have read what I posted from R.G. Keen on grounding and then say you "look at the chassis as one big wire"?   

Keen very clearly explained why not to use the chassis as a ground wire.

That was a huge part of what he was saying. You can not predict or control where the current goes through the chassis. But you can control where a wire goes. So we want to get rid of as many chassis grounds as possible.

Yes every B+ filter cap ground lead gets all the grounds from the circuit it feeds. Simple. That forms a ground star, from that B+ node, that then gets daisy chained, just a single wire for the buss, to the next ground star and so on.

There's no "most probability for a ground loop error between stages" doing this. It's simple.

Through the 15 years I've been here and I've read almost every post here during that time, there has been soooooo many grounding problems. And most took a lot of time trying to untangle what the builder had done. 

You should re-read that from R.G. again.

You can lead a horse to water........ 

[AlNewman]

I guess I just see a lot of technology from the 30's, 40's and 50's which are quiet and work fine with chassis return.  How quiet?  Some have a slight hum for sure, but nothing more than a healthy tube guitar amp.
I don't believe it's in the same vein as winning a lottery as stated in your copy/paste, because it seems like every manufacturer did it for decades with acceptable, and sometimes great success, based on a proper design and layout.
There may be different ways to apply the same technology, and depending on implementation, perhaps more successful, but there comes a point when you're just splitting hairs.
There's more than one way to skin a cat.

[Willabe]

I guess I just see a lot of technology from the 30's, 40's and 50's which are quiet and work fine with chassis return.  How quiet?  Some have a slight hum for sure, but nothing more than a healthy tube guitar amp.
I don't believe it's in the same vein as winning a lottery as stated in your copy/paste, because it seems like every manufacturer did it for decades with acceptable, and sometimes great success, based on a proper design and layout.
There may be different ways to apply the same technology, and depending on implementation, perhaps more successful, but there comes a point when you're just splitting hairs.
There's more than one way to skin a cat.

Yeah, well, I think I'm going to listen to the men I listed, and what I've seen here for the past 15 years and not what you think.

Your ignoring everything Keen said. Your not even open to considering or thinking about what he wrote. This is not about more than one way of doing things. And it's not splitting hairs at all.

It's about knowing before you build the amp it will not have any humm from grounding. You can not say that or know that for sure when you use random chassis grounding. 

You point to old amp builds that are quiet that use random chassis grounding, but have no idea how long it took them to work and re-work the grounds until they got enough of the buzz/humm out of the proto type before they could send it into production.

Keen and Merlin, K. O'Connor, Randell Aiken are talking about using a proven, a head of the time, grounding scheme that will work in any amp. 

How quiet?  Some have a slight hum for sure, but nothing more than a healthy tube guitar amp.

And just how much humm does a healthy guitar amp have? Shouldn't have any. Maybe you just got used to hearing the humm from old amps and think it's ok. So you have a skewed base line as to how much humm is ok.

The multi stared grounding is dead quite. Quieter than any production amp I've ever heard.

...because it seems like every manufacturer did it for decades with acceptable, and sometimes great success, based on a proper design and layout.

Sure they did. And at the time, some were fairly acceptable to pretty good, but not great, and others were pretty bad. But they did it to keep the production costs down and to get the product out the door. And they got away with some humm, but they didn't care, they only had to be quite enough to make the sale. And random chassis grounding is not proper design and good layout, again it was about money/time. But why copy flaws in design when we have a better understanding now and how to apply it simply? And they are/were flaws.

3 things from the R.G. Keen post on The Amp Garage on grounding;

"It is possible to get away with many things that are not technically correct."

"There are an infinity of ways to ground an amp. Only a few of those can be demonstrated beforehand to be quiet. Others may be quiet, and can be found by trial and error. Others are quiet by accidental cancellation, and remain quiet - until something changes."

"Because of cancellation, it is possible to have uncountably many of the infinite number of possible grounding schemes be as quiet as pure star grounding. But it is in general not possible to predict ahead of time which of these non-star-grounded setups will be this quiet. Star grounding is a PITA, lots of wires and lots of thinking (which always hurts!) so humans want to find an easier way. They do something else, don't like the result, then tinker with minor ground wire changes until they stumble on something that's less noisy, and think they have found a new universal truth. They then tend to publish this on the internet and call it the "One True Grounding Way" because after all, they found it worked.  :lol:"

[AlNewman]

so humans want to find an easier way. They do something else, don't like the result, then tinker with minor ground wire changes until they stumble on something that's less noisy, and think they have found a new universal truth. They then tend to publish this on the internet and call it the "One True Grounding Way" because after all, they found it worked.  :lol:"

I agree.

[Willabe]

so humans want to find an easier way. They do something else, don't like the result, then tinker with minor ground wire changes until they stumble on something that's less noisy, and think they have found a new universal truth. They then tend to publish this on the internet and call it the "One True Grounding Way" because after all, they found it worked.  :lol:"

I agree.

What is your problem? Your being a smart ass and I don't appreciate it.

You can't disprove what Keen wrote so now your taking that quote above completely out of context and you know it. That's a form of false editing which you also know. Your leaving out the rest of why he wrote that. Which included several major points.

Your wrong on this defending of mass production methods from the early 40's/50's and so now your being a smart ass and falsely editing the post to make it look like I'm pushing some new flash in the pan thinking. That's being completely deceptive and misleading about this.

And multi star bussed grounds are not new, they've been around for a long time. K. O'Connor has it in his 1st TUT book, that's got to be 15 years old by now, he calls it Galactic Grounding, and it was around before then. I just looked, I bought O'Connor's TUT 1 in '96, so 28 years ago. Merlin calls it Multiple star grounding in his book and that's been out a long time too. 

I'm sure it was know before these guys started using it. So this has been around and on the internet for a long time. 

You mentioned me about the 1st filter cap and the PT's CT grounding in reply #24. So I replied because you used my name. Then you had to contest what I said.

Then I posted something from R. G. Keen, I thought maybe you'd accept some theory on grounding from him. He is extremely highly respected for tube amps and electronics, and you then had to contest what Keen was saying by posting how you ground your builds that is completely opposite of what Keen had wrote and explained why.

You could have just said thanks for posting that on grounding or said nothing at all and leave it at that if you didn't agree. But no, you had to tell us how you use grounding from the 40's/50's and it's just as good. Which goes completely against what Keen had written. Nothing learned since the 40's/50's on better grounding. 

Nothing there to learn from you, but lots to think about and learn from R.G. Keen. That's why I posted that from Keen.

Too many times here trying to fix some guys build from humm because of random chassis grounding.     But you say it's great! 

I have tried to reason with you by pointing to Keen's logic, but you just ignore Keen's reasoning and explanation for it.

You can build your amps anyway you want, but you are not wiser than those men, Keen, Merlin, O'Connor, Aiken. In fact, they have probably already forgotten more about tube amps then you will ever know. 

Don't you think they've had their hands on the same type of old gear that you have? And probably a lot more than you since they do this for a living? And yet they reject random grounding for being too noisy and use a different system.

It's a pretty big statement when guys at this level of knowledge and experience agree and use the same type of grounding. But in your wisdom, you disagree with them. 

You would do well for yourself to consider what they have to say and not reject it.

I have tried to be fair about this, but from now on when I post something stay away from contesting it. I don't need or want your help, opinion or correction. So knock it off! 

And R.G. Keen wrote that quote at the top, not me. 

[AlNewman]

I don't believe I was contesting you, or RJ Keen, or Merlin, or Aiken.

I think if you were to read over my statements in this thread, they are mainly made respectfully with an open mind, based on my experience and opinion.  Nothing in any of the data you have shared has specified something right or wrong.  I use Merlin's, and Aiken's very generous sharing of information all the time.  I haven't seen RJ Keen's opinions as of yet, and I read through your posts, which I thanked you for sharing.  I can see he has very insightful and beneficial ideas on the topic, but as he pointed out, there are a million ways to get to the same result, (there is no right or wrong)

I see when I look at the information you shared, that there are no rules, only guidelines.  You and I interpret things differently.

[SEL49]

Hoffman's grounding scheme works very well for me. I do two things slightly different. I don't solder the pot buss to the back of the pots, and I install a dedicated chassis ground lug near the input jack (rather than relying on the jack's ground lug to provide the preamp ground). Yes, the preamp circuit relies on the chassis for a path back to the PT center tap. The dirty power amp grounds are contained in a tight area near the PT. The power amp grounds and CT are connected together and also connected to chassis near the PT. No power amp current flows in the chassis.

Here's Hoffman's ground scheme and also some commentary about his scheme...

     https://el34world.com/charts/grounds.htm