Bottlehead Forum
Bottlehead Kits => S.E.X. Kit => Topic started by: RW on June 07, 2015, 12:48:56 PM
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Hey Bottleheads,
I have a small issue with some noise, hopefully someone could help. Here are the symptoms, and some things I've tried.
-all testing was done with out anything hooked up to the rca jacks
-I tried plugging into a line conditioner, and multiple circuits in my apartment
-tried adding 100 ohm resistors in C1 & C2, to C3
-I didn't hear anything with my less sensitive headphones (he500 and Q701) but the buzz/hum is audible in my more sensitive headphones (denon d5k, Focal Classic, B&W p7)
-with the volume all the way off/down there is a hum, constant in both channels
-when I raise the volume pot upto and over 75% a second hum is superimposed over the first hum, if I listen carefully, I can hear that there is definitely 2 different tones of noise. Not sure if it's both from the same source or not.
Any help would be much appreciated, thanks :)
-r
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Plug in a source. Any open input will pick up noise. Also how are the outputs wired ?
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Still hear it with a source plugged in. That's why I disconnected it, to see if it was the issue.
As for output, I'm using headphones out of the TRS jack. I also have the C4s and impedance switches. You can hear the noise thru any combination of the switches, and using the volume control.
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Set the impedance switches for lo and unbalanced. This will give the best signal-to-noise regardless of headphone impedance. You can also install 120Ω resistors in series with the headphone output, which will most likely solve your problem.
It sounds like this is very low level stuff. Does it actually interfere with the music?
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@Full
If I use sensitive headphones it definitely is audible over music. The 120 ohm resistors; do I need one for L,R, and ground? And should I remove the other resistors that are on the headphone jack? Do I need to add resistors to the speaker terminals also? Will this increase the output impedance?
@grainger
Will a single rca cable to from one input to the other be good enough, or should I just connect a jumper under the plate? What should I look at after I short them?
Thanks
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Before rushing out to modify this amp, I would start by reheating all the solder joints. This is free, fairly quick, and may drop the noise floor of your amplifier.
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@PB
I'll reflow and report back
@grainger
Sounds good. I'll post back tomorrow after I resolder
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Well, reflowing joints ended up being a little more difficult than I thought. The sex is 50% apart, I'm just going to redo the entire kit with extra caution and report back.
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Hey Bottleheads,
So, it's been quite some time since I posted in this thread last. I rewired the entire kit. I reflowed every joint. I double and triple checked everything. Needless to say, it didn't help at all. I still have a hum in the kit. I don't know what else to look for. I invested a lot of time and money, and I haven't made any progress. I'm at the point where I may just shelf this kit and cut my losses. If anyone has any input that may lead to a solution, I would greatly appreciate it. I listed a few things that Ive tried below
-I tried different tubes
-I tried multiple circuits in my apartment
-I tried plugging into an isolation transformer
-I removed the wiring for the speakers
-I tried a different attenuator
-different components of the same value.
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sorry to hear your issues. the sex should be dead quiet (mine is), so there should be a solution. can you post pictures of the underside? the guys here in the forum often spot something that could potentially help solve the problem. also please describe the noise that your hear. Is it low fequency 60 or 120 Hz like or high pitch? Also post the voltage readings as per check out process.
Good luck and don't despair!
Michael
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I am seeing that you did not try the suggestion of 120 ohms resistors in series. Also, what output impedance configuration are you using?
Try rewiring the output transformer to the 4 ohm output configuration and using the 120 ohm resistors in series with the headphone jack.
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@Zimmer I will get pics up. It's going to take me a day or two to get the voltages. I didn't note them a second time. The hum is low. 60hz, and it's it's constant
@Doc I haven't installed the resistors. Do I need them just for the L&R or should I use one for the ground as well? Will 1/4 watt do, or do I need bigger? I have the impedance switches installed. The tone is constant through all of the positions, except when I put the switches on HI the tone gets a tad louder.
Thanks
-r
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The 120R resistors just go in the L&R hot legs.
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Its very hard to tell what levels of hum you are hearing, but it does sound like there is something wrong. 4 & 8 ohm impedance has a lower noise floor, but if your not hearing any difference that implys the noise isn't coming through the audio path and being amplified, it really does sound like just a bad connection somewhere or a grounding issue. As suggested, post some pics of the wiring in case we can spot something that doesn't look right. Don't give up, it will be something simple..
Also try the 120r resistors on the headphone socket as Doc suggested, any 1/4w will be fine.
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My 120 ohm resistors won't be here for a few days, but I did find four 60ohm resistors. I took two put them in series, hooked them up to the L&R (in series), and the hum is still present :( I will try again when the 120s come in, but my hopes aren't high. Is there anything else I should start looking into? Any help would be much appreciated.
@Mc
The noise changes if I switch back n forth between high and low on the impedance switches. Anything specific I should take photos or should I just post a bunch at different angles. There's a lot to photograph under the hood
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Here are some of the photos of the build. Some of the components were changed out, but they're all equal values to the stock components that came with the kit, they're just matched closer. I'm still experiencing the same issue that the stock components had.
I did a continuity test on the grounds, I'm not sure if safety ground, and signal ground are supposed to be common, but they are. If any more photos are needed, I'll be happy to post them. Thanks!
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Hi,
The top plate looks painted or powder coated. Some components require a good connection to it to be properly grounded. Have you made sure that the paint was scratched off in the relevant places?
Kind regards
Michael
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I did grind off the powder at all ground points. I did a continuity test between all grounds and they all check out. All 3 of my BH kits have the same finish, this is the only one with the hum.
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If you don't build it with the stock parts first, troubleshooting stuff like this becomes incredibly difficult.
My advise would be to put the stock parts (caps, wire, resistors and all!) into the amp, then let us know what you hear.
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It was stock originally. All my measurements were the same now as they were when I first had the issue. The parts that are in now are the same value of all of the stock parts, except the 10000uf cap, it's now 35v. My issue is still the same as it was when I first reported it and was told to resolder everything. I'll put the stock stuff back in again. If that's what it's gonna take to get this issue fixed, consider it done. I don't understand why it would be any different though.
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To go back over this, just to be sure I understand what is going on -
You are experiencing hum when using very sensitive headphones but not with less sensitive ones. The lowest impedance tap sounds the least hummy. That is all to be expected. 120 ohms in series did not reduce the hum further. That is not expected.
Could it be that the 120 ohm resistors were possibly not installed the way we intended? I say this because they were first suggested by PJ when I required the S.E.X. amp to be usable with sensitive headphones, specifically to lower the noise floor even more than the lowest impedance tap alone will. So the hum should be more quiet with the 120 ohm resistors in series with the outputs than without them in there. So just to verify, is each 120 ohm resistor in the hot (positive) leg of each channel? Basically one would break the connection of each red wire that goes from the impedance board POS pad to the headphone jack and solder a 120 ohm resistor into each break.
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I took the resistors out last night to start putting all of the stock parts back in. The 120 ohm resistors were right at the headphone jack, one was on the right lead, one on the left lead, nothing was on the neutral.
I didnt notice the hum until I put on a more sensitive headphone, now i know it's there, I can hear it on all of them.
I should have it finished and back to stock after work tonight. I Just have to finish wiring the RCAs and the pot. I'll take some measurements, take some photos, and report back.
Just for clarification, would you like for me to install the 120 ohm resistors again?
Thank you for your time and efforts, I certainly appreciate it :)
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Also while your in there snap a pic of the wiring around the volume pot, i noticed you changed the audio path wiring, its important to have the shielding properly terminated as per the stock layout.
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I am going to ask in this case that the community refrain from additional commentary for a bit so we (Bottlehead staff) can work through this methodically. Three or four different people suggesting three or four different things at once may serve to confuse things.
When you get it back together - with the 120 ohm resistors installed as you will need them for sensitive headphones - if you could check the following it would give us a good point at which to start with the redone circuit-
Is the hum constant regardless of volume control setting?
Is the hum a soft 60Hz, or is it buzzy?
Does it start the instant you turn on the power, or does it come on as the tubes warm up?
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I added the shield ground to a terminal block. It followed the schematic, the stock terminal was too packed to fit it in so I added the screw strip and soldered everything there. I pulled it out last night to go completely stock again
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Yes, for us to be able to offer useful suggestions regarding stock noise performance your taking the layout back to the stock configuration will indeed be necessary. Rerouting or adding connections in the ground potential circuits seems like it wouldn't do any harm, but grounds are often not absolutely at zero potential and they can become a conduit for interference. The reason we are such sticklers about following the assembly instructions closely is that we have wrestled with these issues in many designs and the final layout we publish is the only one that we can post performance figures for with confidence.
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No problem Doc, I totally understand. It's 90% back to stock. Once I get home from work, the other 10% will be finished. The only thing that I'm not wiring in is the speaker terminals. I just have to finish the input wiring to the pot. Once im done, I will post now photos. I'll also reinstall the 2 120 ohm resistors (2 60 ohm resistors in series) on the headphone jack.
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I finished getting everything back to stock and took measurements again. Every thing is within the 15% tollerance. The hum is still audible.
**note**
I couldn't find the solen 1.5uf caps. The ones installed are also 1.5uf at 630v
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OK, so now that we are back to stock and voltages check out, let's see if we can qualify the hum level a bit.
Is it just a soft deep hum - 60Hz - or is there a buzzy 120Hz component to it? If it is buzzy there might be a ground connection that is not quite 100%.
Is it present with less sensitive headphones with the 120 ohm resistors in place? Or is it just noticeable with sensitive headphones?
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Soft 60hz hum for the most part. My least sensitive headphones (akg q701), with the impedance switches on low, I can barely hear it, but it's there. My 470 ohm r70x (highest impedance I own), I hear it on all switch positions. Everything I own in between I hear it on all switch positions as well.
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OK, now put the 100 ohm resistors from C1 to C3 and from C2 to C3 back in, and see if that helps.
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100 ohm resistors are in. It helped a little, but not a lot, it's still audible.
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Just out of curiosity, can you measure the AC voltage from ground (on the headphone jack is fine) to the red and white wires that go to the headphone jack? You'll likely need the mV scale to get a useful reading when taking this measurement.
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My headphone jack isn't secure to th chassis right now because of disassembly.
If I put my neg probe on lug 13, I get around 350mv on the red and white.
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My headphone jack isn't secure to th chassis right now because of disassembly.
If I put my neg probe on lug 13, I get around 350mv on the red and white.
Hmm, are you sure it's not 0.3mV? 350mV would show as about 0.4V on a higher scale.
350mV is way, way higher than normal. The immediate thing that comes to mind to cause this would be poorly connected power supply caps.
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I'll measure again. I'll be home in 30 min. Does it matter if I use safety, or signal ground when I take this measurement?
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Signal ground is better.
300mV of signal on sensitive headphones would be audible from about 3 feet away, so do have a careful look at the units.
-PB
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I just measured the headphone jack again. It's definitely 350 mv AC on my meter. I get .3 mv DC. Unfortunately my other meter doesn't read that low, so I can't confirm it.
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This may sound like a silly question, but I'll ask anyway. Am I supposed to have continuity between all of the conductors on the output of the impedance switches, to the headphone jack? If I test the Jack and have one probe on black, I'll get continuity when I hit red or white. It doesn't matter what color I keep the probe on, the other two will beep when touched. Same with the impedance switches. If I keep one probe on the positive terminal of the impedance switch, I can hit the other 3 outputs and it will show continuity. But, headphones work fine. I'm looking at the schematic and I don't see where the two should cross (or four in this case)
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I just measured the headphone jack again. It's definitely 350 mv AC on my meter. I get .3 mv DC. Unfortunately my other meter doesn't read that low, so I can't confirm it.
Can you post a photo of your meter grabbing this reading? It doesn't seem like a reliable measurement, as your sensitive headphones wouldn't handle that much voltage.
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This may sound like a silly question, but I'll ask anyway. Am I supposed to have continuity between all of the conductors on the output of the impedance switches, to the headphone jack?
Yes, the output transformer secondaries will show continuity.
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I'll post a pic of the measurement when I get home from work. ~7pm Est
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Here are a few pics. Using terminal 13 for ground. There's an AC, and a DC measurement for each lead.
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I think there is something in the way the measurement is being done that is throwing off the result, simply because 300mV of hum on the output would make the amp un-listenable. Your description is of hum that is there enough to bother you, but not something that completely overwhelms the music, so I will assume that the hum you are hearing is a couple orders of magnitude lower than 300mV.
What we often find when trying to do AC measurements that that the test leads themselves can pick up stray hum. What I would suggest is to make that AC measurement again, with the red and black test leads twisted together (this helps to reject interference) and with the black test lead clipped to the negative terminal of the headphone jack, right next to the red test lead clipped to one of the positive headphone jack terminals.
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There is no ground wire from the headphone socket to 23U so the secondary's are floating. See top paragraph of page 29 in the manual.
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@Mc
Good call! Thanks for spotting that! I don't know how I missed it, I went thru this manual a bunch. That solved the voltage on the jack leads. Unfortunately, the hum is still there.
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Can you do as Doc asked and remeasure the AC voltages using the headphone socket ground.
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I did, there's no voltage. Even if I use lug 13, it still reads 0v
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Hey Guys/Gals
So I need a little advice. What would be the best way to break this kit down in sections to isolate this hum? I've read just about every post in this forum, and the one solution that I haven't tried, which seemed to work for another member, was to rebuild the heater supply with a few 4700uf caps and a few resistors. I'm ordering parts to bread board it up, but I want to minimize the disassembly of the amp as much as possible, and I don't want to work on sections that are working fine? If I can't solve this hum, I'm just gonna drop the extra scratch and ship it over to the service dept to take a look at it.
Thanks :)
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The first thing that you absolutely need to do is to get a better multimeter. The reading of 300mV of noise indicates that your meter can't resolve low AC voltages, so even if you could break the circuit down to isolate the noise, you can't measure it. If at all possible, take that one back to Radio Shack (FYI - the last six meters that I bought at RS were all defective)
Try the $25-ish multimeter from Harbor Freight, or borrow a different meter from a friend, then recheck the noise at the speaker posts/headphone jack. A very loud amount of noise in your application might be something like 10-30mV.
-PB
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Is the $25 HF meter going to be able to do what we need it to? If so, I'll have it tomorrow after work. Do I need something more accurate? Ill buy the $200 millivolt meter from MCM if need be. I also have an oscilloscope at my disposal right now. I'm not a pro with it but I can make it work. If there's something specific I need to do with it, just let me know and I'll do my best to make it happen.
As always, I appreciate your help
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I'm totally OK with helping you out while you use the scope, but the meter is a lot easier. I don't believe you'll need anything more accurate than that meter. I'll pick that particular one up on my way to work tomorrow and double check for you, just in case. The $200 meter is overkill, as in that case you'd want to move to your scope to have a look.
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Awesome, thanks PB! Let me know what to get, and I'll scoop it up.
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I tested our stock SEX (no C4S, no impedance switch kit) with the $25 HFT meter, it shows 0mV of noise on the 2V scale on the speaker taps on the 8 Ohm setting. It does seem to be able to resolve low AC voltages pretty well, so I'd say it's up for the task.
-PB
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Ok cool. I'm on my way to grab it now. Just an FYI, i don't have the speaker terminals wired in, this shouldn't make a difference, correct?
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I took measurements on each leg of the headphone jack. No matter the impedance switch position, they all read .004AC
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What noise figure do you get on the other side of that resistor on the headphone jack? (crank the volume pot all the way down too)
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Same, .004 on all switch positions. Volume pot was off on all measurements, including the originals.
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Try twisting the black and red test leads together. That will cut down their tendency to pick up outside interference that might be adding to the waveform coming out of the jack, and possibly give you a lower and more accurate reading.
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Same, .004 on all switch positions.
All output transformer measurements?
I'd get out the scope at this point and post up a photo of what you see on the display.
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@Doc
The meter leads have been twisted since the first time you mentioned it.
@PB
What points on the transformer would you like me to measure? What would be the ideal setup on the scope to take these measurements? How many V/Div would you like me to setup for? I'll take the measurements after work today.
@Grainger
The big reduction of the measurement came from a ground that I missed. Even though the measurement was reduced, it seems that the hum was barely reduced if any. I have my soldering iron (that wasn't powered on), and my oscope, both plugged into a rotel rlc900 line conditioner. I can unplug everything and go straight to the wall if need be. When I first experienced the hum, I tried multiple outlets in my house, in two different line conditioners, I've also tried plugging into an isolation transformer, the hum was present no matter what.
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I may have had my phone in my pocket, I don't remember 100%, for the most part it's basic test bench gear, or projects that I'm working on, but only the amp, scope, and soldering iron were plugged into the line conditioner at the time I took the measurements last night
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The first two images are measurements taken before the resistors at the headphone jack, images 3 and 4 were after the resistor. I also would like to note that my scope was confirmed with a BK function generator. If any of my measurements or procedures need to be modified for more accurate measurements, please let me know.
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That looks familiar, if i'm not mistaken that 60hz base frequency is each half of the B+ voltage doubler circuit conducting. Also from memory ~3mv was the natural noise floor of my amp so you may just be at the limit of the amp which is fine for speakers and less sensitive headphones.
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835 microvolts of noise is a completely reasonable noise floor for this amplifier. Just for fun, take the probes off your amplifier, connect them together, then look at what' left on the scope ;)
If you want to drag it down even more, put a 10 Ohm resistor between tip and ground and one between ring and ground in addition to your current resistor modification.
These must be some very sensitive headphons!
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I don't know the sensitivity of them off the top of my head, but just now, off of the Hi setting on the switch, I hear it in my HE500, AT R70X, Denon D5000, Denon MM400, HD598, B&W P7s, HD650s, and focal classics. The only ones where it was barely noticeable was on the Q701s, and Mad Dogs.
@PB
I only have one probe right now, I can get another one tomorrow. I'm going to order the 10R right now. What about the upgraded transformers, would they improve it? I also saw a modified power supply from a few months back, I think it's on page 7, titled Sex buzzing. I'm going to mock that up to try, I guess. It's just a shame that I went through a lot with this device, I hear people saying that they have black backgrounds, or they're using them with Grados, and so on. I'd do pretty much anything to get it silent. I even found a pair of mullard 6DN7s for it that weren't too cheap, hoping something positive would come from it :(
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If you can hear it with HD650's on 4 or 8 ohms there is certainly something wrong, it should be dead silent with those. I also own the HE500's which aren't especially sensitive either and should be silent on 4 ohms, the Grados however, they can hear a fly fart in the next room.
Point is, something still isn't right, but dont lose heart as the problem can be cured, we just need to find it first. Without reading back through the pages, have you tried another set of tubes?
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I have at least 4 pair. Rca that came with it, RCA coin base, Mullard, and GE's. I hear it on all of them. One of the coin base valves are a little noisy, I have another on the way. I'll buy anything I need to nail this issue down. I don't even know where to start to figure it out. I'll buy or borrow any tool needed. I've bought multiple valves, better pot, better caps, resistors, and diodes. It's just a little disheartening after all of the time and effort.
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There is so much HF stuff on that waveform that it's very hard to tell what the actual 60/120Hz amplitude is. That 800uV average might be even lower with the fuzzy stuff cleaned off the test signal.
At this point it seem we might be at a the limit of what can be determined via the forum, as it seems like the amp is operating fine after all of this in terms of measurements. We don't have a way to tell if you are far more sensitive to hum than the typical person who builds this amp, if there is some other environmental interference issue that is unique to your environment, or if there is still something in the amp that is creating this issue (which doesn't seem likely after the fairly exhaustive testing you have done).
I think we are pretty much at a point where you need either another stock S.E.X. amp on your bench to compare to or to have someone else check the amp over to see if it is performing to spec.
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@PB
I have a second probe. What would be the ideal setup for this? Just connect the ground clips and the hooks? AC or DC coupling? Do I have to invert anything or do any math functions with the scope?
What would I gain from upgraded transformers or chokes from MQ? Would they help with the noise?
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@PB
I have a second probe. What would be the ideal setup for this?
No need for a second probe. Take the prove you used for the photos, and clip the ground clip to the tip, then see what's left on your scope.
What would I gain from upgraded transformers or chokes from MQ? Would they help with the noise?
You would lose the ability to switch between all the different impedances.
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@Doc
that kind of stinks. Its definitely not me. I don't have the golden ear or anything special. It's clear as day on 80% of my headphones at the 4 ohm settings. I don't think I'll get a chance to compare and measure against another sex. I've read pretty much every page in this forum, I have some breadboarding to do. If all else fails, and I have no other avenues, I'll send it over to your team to look at, measure, and compare. I'll pay whatever charges there is. If your team says it is what it is, then I know I've tried everything I could.
@PB
here is a pic of the ground connected to the probe tip
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The noise floor of your scope/probe setup is just barely below what you're measuring. On your scope, is there an option to shelve off the high frequency hash? (I think there is, I have an Owon scope that is similar to yours)
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Do you know what this setting may be called? I'll look for it. the manual that came with the scope is hardly a detailed manual.
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It might be called something like HF reject.
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I'm sorry that I don't understand exactly what you think stinks. My point is simply that without hearing the amp ourselves we are limited in our ability to help by referring to the measurements that have been posted. If the amp was on my bench I could listen for myself with a familiar set of headphones, compare the noise floor to that of another S.E.X. amp as a point of reference, and possibly come up with some more ideas. As it is we are doing our best to help with something we can't experience first hand. Do try what PB is suggesting as that might give a cleaner picture of the noise floor in the hum frequency range.
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@PB
The only setting that I was able to find was bandwidth limiting, which only limits to 20Mhz. I couldn't find anything in the manual, or the google regarding HF reject, or reduction. The photo shows the measurement of the probe with the ground clip connected to the lead, and the BW limiting engaged.
@Doc
what I meant by this kinda stinks, is that I/we worked a lot on this issue and that I may be stuck with this hum. It wasn't meant to be in any way offensive. As I mentioned above, If all else fails, I would be more than happy to send you the amp and pay all fees associated with the service. Your team, and this forum have been very helpful to me in all of my BH builds, and I appreciate everyone and all of their efforts. I apologize if my statement came off in a negitive way
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This is a long shot, but easy to check:
In the very first post, RW said "-tried adding 100 ohm resistors in C1 & C2, to C3". The purpose of this is to keep the DC heater supply centered at ground potential. It assumes that C3 is grounded to the chassis, by way of the adjacent power transformer mounting screw, through the end bell, to the mounting screw nearest the power inlet, and from there to the safety ground adjacent to the power inlet. You can check the resistance from C3 to the chassis, which should be essentially zero. While you are there, power transformer terminal 10 (the heater winding center tap) is grounded to terminal 3, bolted to the chassis. Check that one as well, it should also be zero resistance (within the ability of your meter of course).
It's possible these checks were made; I did not review the entire thread today to check.
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Hey PJ,
This may be the issue, or at least part of it. That terminal isn't grounded properly. I don't have any continuity from ground to the #3 lug. The only thing I can see that would be in the way is the fiber washers on either side of the plate, possibly? Because my plate is powder coated, I have the powder ground down to bare metal in all of the terminal, tube socket, and all screw locations. Should I remove the plastic washers and replace them with something else? Or, should I run a jumper from 3L to chassis ground?
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It grounds through the power transformer cover, which may also have powder coating on both sides?
If so, you can crank down on that mounting hardware and that may help your cause.
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The bottom of the cover is ground down, but not the top. Should I pop it off and grind the top?
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The most reliable thing IMHO would be delete the wire from terminal 3 to power transformer terminal 10, add a wire from power transformer terminal 10 to C3, and another wire from there to the safety ground adjacent to the power inlet.
Explanation: the ground through the power transformer end plate was not an intended design feature - nothing is connected to C3 in the stock configuration. If it were there would be a star washer between the C3 mounting screw head and the top of the end plate. To my mind that route is circuitous as well as sensitive to paint, thus unreliable. So I suggest (above) doing it with wire and solder.
Historical note: The SEX amp was originally designed to be a speaker amp. Before release it was decided to incorporate a headphone option (this was some 12 years ago) and we discovered it needed some work on hum. We added a power supply filter section for the driver stage, beefed up the main PSU capacitors, added a DC heater supply, and implemented the IHF standard 120 ohm source impedance resistors (since removed for unrelated reasons). IIRC we took the hum on low-impedance phones down around 20dB. This was our first foray into headphones.
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Hey PJ,
So I just got done rewiring. It definitely helped a bunch. I didn't have time to test with all of my headphones, valves, or take measurements to see where I'm at, yet. My Q701s which are my least sensitive, I can only hear the hum on the HI setting. My HD650s I can hear it on ML, MH, and Hi. The real sensitive headphones I can hear it on Low, but barely. It's still prominent on all other settings. It made an improvement, from initial testing. I'm still waiting on the 10r resistors to add to the headphone jack. I'll do some more in depth testing tomorrow after work, and report back.
Thanks Paul!
Btw, I totally dig the history of BH. I've read a bunch of old articles and interviews from magazines, And while doing research, I still find BH posts on message boards and forums from the early 2000's. It's pretty nifty to see how BH has evolved over time!
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Yup, I was the first commercial sponsor/forum host of Audio Asylum, in 1997 IIRC. And on the Joelist for a few years before that. There's archives of both around, I think. That was baby boomer joelist which you found by searching with Alta Vista. Google search #1 for Joe List is now a gen X comedian. Time flies.
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Hey PJ,
So I just got done rewiring. It definitely helped a bunch. ...
That's great - it means that at least some of the hum was coming from the heater power. You are probably down around 0.3mVrms of hum now, which is normal - the amp is operating as designed.
There are more things that could be done, of course. However, when searching for noise solutions you must be aware of the iceberg effect - whenever you remove a cause of noise, you expose the next-most-significant one. (I spent a career in aircraft noise control...) There are no tested approved mods to further reduce the hum, so any such attempt becomes a research project, with likely more failures than successes - that's how research works. Sometimes it's a grand adventure, sometimes it's just frustrating and annoying.