[nlitworld]

Yep, that looks super easy to make a star ground connection like you're describing. Thanks for the tip! Looks like I'll be busting out the soldering iron this weekend. 

[MosDeaf]

After I attached the purple shield wire from the power transformer to chassis that got rid of the last hint of hum/buzz. I did a listen test after attaching the IEC to chassis & leaving the power transformer still in the IEC as initially directed. Well it's initially directed to leave both wires in the IEC but just doing the safety to chassis & not the transformer I could still hear a hum/buzz with ear to the woofer on my test 2-way speakers. After attaching the transformer shield to chassis as well I can put my ear On the woofer & hear nothing. With ear On the tweeter I can still make out what I call tube hash. But I'm talking ear on the tweeter to hear it. My ears are in their 50's though.

A builder/repair tech friend of a friend told me how to test if the heater circuit is grounded or floating.. or if only one of the heater pins is grounded or floating & to give him the B+ voltage. He said if the amp is designed how he's guessing it is he will show me how to do a heater elevation mod. Said it's like making a 2 resistor junction near the B+ with a small terminal strip or whatever I want to use & then run 2 small wires to the 6.3v inputs with a small resistor in series. Said it should drop the noise floor by at least 10db. He says that's a small estimation as it could be much higher depending on the circuit. I'm happy with the amp as it stands though.. but I'll give it a shot.

I think this is a legit good sounding amplifier.. especially for the money. I did try a handful of other . 22uF caps, even tried raising the value with a couple but those old Russian oil caps were pretty good right out of the gate. I'll give them a few hundred hours before considering something different. But I have to mention that they measured kind of high in ESR on my LCR meter vs newer caps. I gave them a chance anyway & thought overall they were good. I have a quad of V-cap ODAM's I haven't tried in that spot yet. I've used them in other builds & they are more transparent & extended at both ends of the FR. More transparent than adding any character or emphasis anywhere to the sound.

I've also built a couple preamps from tubes4hifi that I had to redo the wiring scheme that they give you..in order to make it quieter. Very good preamps.. even the 9pin SP13. A little tricky when it comes to getting dead quiet. Anyway, I hope that these little changes reduce any of the noise you can detect. Good luck.

[nlitworld]

Yep, I'm excited to bust out soldering iron and try these grounding scheme mods. I've heard several people suggest mods to the preamps to improve ground noise, so it doesn't surprise me that amps need the same. My SP9 preamp needs the same.

[MosDeaf]

I finally got a chance to listen to the amp outside of my testing set up. Something seemed a little off with it.. unless it was something else in that system. The el84 didn't sound as good is the easiest way to describe it.

I went & looked at the ANK build of this PCB & they direct builders to hook the OPT's to the speaker jacks.. not the PCB. I'm wondering if me rerouting the output transformers to the PCB has altered the feedback design in a bad way. Some time this weekend I will reverse it then give it a good listen.

[nlitworld]

I was wondering about that. Keep me posted how that works out. 

I did look at my amp again and wondered if twisting the wires to and from opt should have been done. I didn't twist them at all, but I could easily go back in and do the pcb to opt blue,res,brown wires. The opt to speaker connections I cannot as they are crimped and soldered in place.

Aside from that, I'm excited to explore your grounding mods. Need to finish a couple other projects around the house first, but that is definitely on the table.

[MosDeaf]

Yeah I have a handful of different projects & chores to always get done as well. I'll definitely share my thoughts when switching the OPT's back to the speaker jacks. The music was just kind of flat & the bass just sounded wrong with them hooked to the PCB.

[Bill Baker]

Very nice build. Love the paint job.

[nlitworld]

Parts ordered for ground breaker. Will see how it works out next weekend when I tear into it. Also snagged a few other parts for dac coupling cap upgrade as well. Horray for soldering projects.

[nlitworld]

Very nice build. Love the paint job.

Thanks Bill. I like fun painting projects like this, so it's good I get to keep my chops up in spraying.

[nlitworld]

Parts ordered for ground breaker. Will see how it works out next weekend when I tear into it. Also snagged a few other parts for dac coupling cap upgrade as well. Horray for soldering projects.

So groundbreaking and better star grounding certainly did make the noise less, but it's not exactly 0. Probably 80% better than before. Wouldn't be surprised if the NOS Sylvania tubes I have in there are just a touch noisy. One of these days I need to go back and measure voltages just to see if perhaps there's something else causing that last little bit of hum, like a low B+. But all in all, it's definitely better. Thank you for the tips!

[nlitworld]

So I did decide to open amp up and take some measurements of voltages and think I found part of my hum problem. I may have overdone it on the choke and it's pulling my B+ voltages down too far. The schematic wants it roughly 330V, and I was sitting at 299V using the suggested 22uf cap. Also the bias voltage suggested between 10 and 12v and it was sitting about 9.25.

Checking suggested measurements it recommended changing the first filter cap to 24.2ish to get up to correct voltage, but it only pulled it up to 305.5v. It also pulled bias voltage up to 9.5/9.6ish. Moving in the right direction, but calculating change in voltage vs change in cap size, my first power supply cap likely needs 33uf. Ordered another from Elon so we'll give it a go next week. If anyone is interested in a pair of 12uf Obbligato silver caps for cheap, let me know. Barely used... 

Good news is I'm learning a bunch on how tube amps function and power supply filtering. I figure an applied education lesson at $50ish in tinkering is pretty good deal. I'll post results once I swap those caps out.

[MosDeaf]

Good job 👍 Certainly doesn't hurt to start getting a better understanding of the power supplies.. it's such a vital component of these tube amps.

I haven't had much time to play with mine & I was all excited after switching up the Grounding & better audible improvements on my test system. But when I brought the amp into my music system there is still some audible noise floor. It's better, not bad, but I can't help but want silence.. or close to. But I didn't even try switching out the resistor for a choke yet. I was looking at a 2 Henry 350ma choke. Do you recall which size you went with?

Last time I checked my B+ I was closer 337-339vdc. Bias at 11v

[nlitworld]

Choke I used was a Hammond 193P. Circuit diagram calls for 5H 350ma and that 193P was the closest to without undersizing (5H 500ma). I think since that filter is so filtery, it dropped the voltage though. It is YUGE though. You could probably go less than that, but I didn't know enough to make that designation.

And yeah, I don't demand SS amp dead silence. I'm totally understanding of tube amps having something there, but I don't want to hear it 6ft away.

[MosDeaf]

Thanks for re-sharing the choke that you went with. I'll have to search for something closer to spec.. without raising the resistance too high compared to the 10ohm resistor it replaces.

But in actuality, as far as noise goes, I'm not hearing anything unless I stick my head near-ish the speakers

[nlitworld]

Oh yeah. I went with easily available meeting equal or over specs, but I'm sure there's a lundahl or other one that would meet spec without being 11lb behemoth. Most people would consider the ear to speaker performance good enough, but we are not like most people. We want that last 5% of performance squeezed out of everything. I should have that other cap Wednesday most likely, so I'll keep you posted how that goes.

[nlitworld]

Update: no change in voltage by applying a larger first filter cap. I actually had higher voltages running the 2x 12uf caps than I do the 33uf. Back down to 299v B+ and 9.25-9.5v on power tube test points.

It does sem to be a smidge quieter though. Not sure if there's just less AC noise right now or if ambient noise in the house is just higher. Either way I'm keeping the higher 33uf in there for the moment. I think I'm done tinkering... for the moment. It sounds freakin amazing so I need to hyper fixate elsewhere in my system.

[nlitworld]

I adjusted the position of the choke from the second resistor to the first resistor point making it a clcrc filter. I think there was a typo on their circuit board as to where it was intended. Now rather than just the ecf80 tubes getting filtered power, the whole unit is benefitting.  Voltages seem about the same of 305v B+ and same for the bias points. There was a good difference in black background though. My preamp connected still makes a tiny amount of hum with ear to speaker, but with no input connected it is absolutely dead silent. I'm already eyeballing new preamp options, so I'm calling the amp tinkering done. Last night playing some music to test out, it was sounding very very good. 

Thank you guys for following along and all the help with this build. I've learned a lot along the way.