[JoshK]

Thanks for the props, guys.  I am a bit proud, like a proud new papa.  I'm ultimately glad I took the time to learn a few skills--patinization, box joints, some circuit tricks--along the way.  They will be worthwhile down the road. 

I am really certain the remaining hum is a confluence of a couple things left to do with the AC heaters.  I just followed Pete's circuit pretty much verbatim, except a few equivalent part substitutions and different grounding scheme.  Pete uses a copper clad PCB board for a ground plane, I used two 12gauge wires to star ground to locally.  I basically wanted to see if I could learn a few things from an experienced builder, so I didn't want to override his styling much.  Although you could argue the ground plane exemption was a big override.

Pete shows that he does not use centered heaters.  He also doesn't lift the heater above ground potential either.  So I thought I'd follow suit and then change things later on as neccessary.   I reasoned that if I built the circuit as is, I'd hear it as he did.  Then I could opt to change things at my discretion but at least I'd have heard it as intended.

I am reasonably confident that its the AC heaters.  When I first fired it up, I had forgotten to ground the heaters, as I was debating if I wanted to do it Pete's way or center the heaters and lift above ground.  I had forgotten that I didn't do anything and the heaters were left floating.  That produced a loud hum.  I went back in and grounded the heaters and that dropped the hum to a low level they are now.  That tells me that the tubes are a bit sensitive to grounding.

I used a seperate filament transformer, as the rating of my power transformer was a little too marginal.  Pete uses a huge James PTx.  I used a large surplus Chicago PTx.  Its big but still gets pretty warm.  So I used a Raytheon military surplus potted filament transformer.  It is not center tapped so I will use resistors to ground.  This also provides a convenient place to experiment with raising the heaters above ground. 

There are two other reasons I can think of to further reduce noise, but I am reasonably confident that it is the above issue.   I tightly twisted my heater wires and routed them up in the corner of the chassis as suggested in Morgan Jones's Building Valve Amplifiers. 

I've been a big too busy in the last week plus to experiment with the amp and the bit of free time I've had I've been listening to it.  The hum isn't heard at the seat so it doesn't bother me that bad. 

I will take some up the skirt shots when I unplug the amp for fixing.  I made use of 3 dimensions, but my wiring isn't the neatest I've seen. 

[JoshK]

I was curious just how long did it really take me.  Since this thread is a sort of diary, I can easily check.

Post #169 on Mar 7, 08 was where I had decided on the E-linear design and ordered parts. 

Post #384 on Jan 24, 09 was when I declared victory (less subsequent tinkering which is likely ongoing). 

Roughly 10 1/2 months.  Given my snail's pace at projects, I am reasonably pleased.

[BillB]

I have a little hum in my new pre as well, it is pretty low level but one of those things you want to get rid of nonetheless.

I am wondering if an unregulated DC would be > an AC circuit as it would be relatively easy and I modeled one on PSUD with some hefty caps and it produced a decently low ripple 6.4vdc signal off the 6v filament tap on the Hammond transformer I am using on mine.

Going regulated would require another transformer and there is simply no room for that in my tiny chassis.

I am sure we will really see the difference between your 10 month job and my 2 nights work. I am glad I did it though, I think the next one will be much better laid out.

[DaveC113]

Josh, that looks great. Its very satisfying to hear it work after months of parts collection, research and building. 

I had some hum, it mostly (%99) went away after strapping the topsheet of the amp to the chassis of my preamp... The ground scheme for the simple se is very uh... simple, but I plan on changing it (removing the cfb option), and running the speaker ground directly to a star ground location at some point in the future. I'll use the old cfb switch to switch in a cathode resistor to adjust for el34 or kt88s.   

[Freo-1]

Great job, Josh 

An inspiration to all who partake in the world of DIY audio!

[TomS]

Josh,

Congrats - that is really a lovely piece!  10 1/2 months doesn't sound bad to me at all given the amount of wood and metal work, as well as parts gathering you must have endured.  That should sound terrific on the new speakers too.

Tom

[JoshK]

::Update::

I decided to see if I could hunt down the hum.  I wanted to do it semi-scientifically, doing only one step at a time.  I snipped the local unbalanced grounding to star ground and grounded the heaters via a psuedo center tap using a pair of 100 ohm resistors to ground.  Well that dropped hum to the point where you have to put your ear in the speaker to hear the 60hz hum. 

Not having build tube amps before, I imagine that is about the lowest one can get it with ac heaters.  The truth test will be whether it is still low (enough) with 96db speakers.

How many others are using all AC heaters?  What level of hum do you get?

The list of tricks is not exhausted but I was pretty happy to get the hum that low with one simple trick.  I didn't actually think that alone would do it but I was surprised.

[bricktop]

Hey Josh,

I haven't had any problem with hum with AC heaters, at least with power amps (as long as the heater center taps are tied to a fixed potential).   More hum reduction can be had with regulation as well.  I made a small (~5W) SE amp with a 6080 B+ regulator that was super quiet (all AC heaters).  This adds a bit complexity though and needs more power. 

- Micah

[JoshK]

Some more pics to complete the profiles...

Backside


Up the skirt


Was working on the Aikido preamp this evening. I'm getting closer to done.


Backside


Up the skirt...not quite done

[lonewolfny42]

Nice Josh....nice !!

So...your almost there...

[JoshK]

Nice Josh....nice !!

Thanks.

So...your almost there...

With the Aikido preamp, yes.  I tend to work on many projects in tandem.  I am nearing completion of my speaker baffles, finished my TVC preamp and made progress on the Aikido. Earlier in the week I designed my bass bins. 

I am just not that linear when it comes to projects. 

[slbender]

Hi Josh,

Yes, your Uber Amp and Pre are really looking good.  I just managed to squeeze all the parts that are physically needed into my metal chassis, using a new layout of my Uber SET Amp, and that also includes a new 25% bigger HV. power transformer.  The prior ones may end up in a pair of mono-block versions.  Next I drill for some power resistors and than I will finally start wiring up things.
 
What is the size of those Aikido Circuit boards?  There is also a miniature tube version PCB too right?  Are those the same size?  How to order them, and price?

tnx,

-Steven

Nice Josh....nice !!

Thanks.

So...your almost there...

With the Aikido preamp, yes.  I tend to work on many projects in tandem.  I am nearing completion of my speaker baffles, finished my TVC preamp and made progress on the Aikido. Earlier in the week I designed my bass bins. 

I am just not that linear when it comes to projects. 

[JoshK]

Steve,

Everything you need to know is in the Glassware store.  Quick answers, yes it comes in noval and octal configurations.  This is octal.  The newer noval boards can be setup for 5687 or 6922 pinouts. 

JRB just released an all-in-one Aikido just this weekend.  It has heater and B+ power supplies included for those who didn't feel comfortable making their own power supply circuit.

His boards are super nice too, not the standard fare you get on diyaudio group buys. 

[JoshK]

I just got some Russian 6Ж52П, by all accounts they are a Russian D3A.

6J52P data

D3A data

Confirmed pinout is the same.  Data is close enough.  I will have to give these a try in my elinear amp. 

I got them off ebay.  They are a bit cheaper than current sources for D3As, but not greatly so.  Still, thought it would be worth a shot for some choice. 

[JoshK]

Today I had an oh sh** moment.   I turned on the amp and the damper diodes flashed and then nothing.  Turned the amp off, then I tried to turn it back on again and nothing.   

I was thinking that the damper diodes might have arced over (one or the other) but they are pretty hardy.  Their PIV is super high, much higher than a typical tube rectifier. 

When I woke up from a nap I decided to test out the DDs to see if they were shot.  I realized my tester won't test novar tubes (nine pin but big, unlike small nine pines like 12ax7).   Duh, my amp has a thermal breaker. 

Blonde moment.  Reset the breaker and replugged in the DDs and the amp fired up.  But I took the opportunity to add a thermistor like Pete Millett's original schematic.  No more booooinnngg when turn the amp on.

I also biased up the filaments to ~88v (based on resistors I had on hand).  This lowered the hum very slightly but not a lot.  Still I hear hum about the same level with ear against the transformer as I do with ear against the cone of my speaker.   You can't hear it at 3 feet away but it still annoys me.

I am starting to suspect the mains.  My UcD amp transformers buzz too, all my OneAC transformers buzzed and the Felicias buzzed. 

[JoshK]

Maybe I should rename this thread to "confessions of a solder-slinger".   

I fired up my Aikido the other day and tested the voltages.  As mentioned earlier my PSU was running at ~400V which is too high, but I plugged in 6SN7GTBs as they can handle the higher voltages and all my caps can too and just gave it a go.

Well I got no sound out of it.  I looked at all the wiring and nothing was obviously wrong, so I put it away until I could test it out.  Well this weekend I started to test it out and determined that the ladder stepped attenuator was the culprit. 

This is one of those asian cheapies.  I had bought one and then was given two more for free from Ken because one of them didn't work.  I must have accidentally installed the bad one.       I guess you should always check out the components before you install them.

P.S.  I think that the KT88 e-linear amp should be called the SEEL (single ended e-linear). 

[JoshK]

Lately I have been having a lot of grief over a big tweak.  A tweak known as mortgage refi.

Rates are very very low.  Better yet, I heard of a program in my area where you could get obscenely low rates on 30 year fixed mortgages (4.25%).  I had to give it a try.  Sure enough I got approved in short order (through HSBC) and locked in the 4.25% rate for 60 days while I went through closing.   No points, closing costs <$1,000.  Wow! 

Then the grief...  freaking appraisor is not the sharpest knife in the drawer.  Economy is soft, housing is down, that is a given, but there is no freaking way that vinyl sided boxes in the ghetto should be worth the same as a victorian row house on the cliff with manhattan views.   

DIY has taken a back seat until this tweak is resolved.

[mgalusha]

Maybe I should rename this thread to "confessions of a solder-slinger".   

I know the feeling. I recently spent a couple of weeks trying to figure out why a preamp was making horrible noises at any volume position other than fully closed. Went through everything, could not figure out it. Finally all that was left was the volume pot, which of course measured OK and was a $$ TKD. Out of desperation I replaced it with a $3.99 Alps from Radio Shack just to see if it helped. Noise was gone and the preamp behaved perfectly. Weird as measuring the TKD showed nothing amiss but swapping in the cheap one fixed it. Really strange.

Good luck on the refi, they always seem to be more painful than they should be.

[jeffdavison]

tel me about it....

mine is getting hung up over a $300 check my wife wrote to me for our health insurance premium, The lender wanted records and stubs to make sure I wasn't "padding" my bank account...   nucking futs!!!

Jeff

Lately I have been having a lot of grief over a big tweak.  A tweak known as mortgage refi.

Rates are very very low.  Better yet, I heard of a program in my area where you could get obscenely low rates on 30 year fixed mortgages (4.25%).  I had to give it a try.  Sure enough I got approved in short order (through HSBC) and locked in the 4.25% rate for 60 days while I went through closing.   No points, closing costs <$1,000.  Wow! 

Then the grief...  freaking appraisor is not the sharpest knife in the drawer.  Economy is soft, housing is down, that is a given, but there is no freaking way that vinyl sided boxes in the ghetto should be worth the same as a victorian row house on the cliff with manhattan views.   

DIY has taken a back seat until this tweak is resolved.