[andyfromdenver]

*edit: I hope you enjoy the pictures of my wiring job and how to make a quiet unit. The finished unit is super-duper-crazy quiet, no heater hum, low hiss when output level is cranked to an unbearably high clipping level.  I have solved all my issues to implement LED VU meters, scroll to the end for scheme, and please feel free to post any questions here if you desire to make your own retro-future-retro super compression box!*

Hi All!
   There are so many people I want to thank for helping this cool project come to life. All the historical players http://www.uaudio.com/blog/la-2a-analog-obsession/, recproaudio including "gambaholic", JLMAudio, and all the genius solder-slingers here at groupdiy.

I'm doing my take on this classic and can only upload one pic at a time and want to talk A LOT, please enjoy!

Andy

[andyfromdenver]

First,  I have printed and collected all the documents. I have a folder filled with info, schemes, layouts, mods, tube data sheets, transformer data sheets, and conceptual sketches. I do this for most of my projects to keep tabs on mods and layouts and half-baked ideas.

Secondly, this is the robust Hammond chassis, which i bought from a member here. I sized and printed out the templates from recproaudio and made some adjustments for my particular plan, then carefully executed the bulk of the hard drilling, punching, cutting, and filing.

With 120VAC action only, I nixed the AC turret strip, and put the power transformer (PT) as far in the corner as possible.
Also, I am using a 50+50/ 500 can cap cause I have stuff like that and I like to get high on my own supply...

Drill, right angles, step bits, knockout punches, dremmel, files, deburring tool, and meticulous patience.

[andyfromdenver]

This is all the glorious power section.

You can see the HT secondary winding (red wires) runs to the tag strip and the rectifier diodes will go to one of the caps with the first dropping resistor between the cap tabs, then down to the board.

All the PT grounds join to the node which is rock-solid thanks to my dremmel removing the chassis paint, and the IEC has a dedicated chassis ground.

The PT itself is secured to the chassis with non-ferrous nuts and bolts and fiber washers, per Designing Tube Amps...by M.B. and RDH4 Hum Reduction*

The entire power section is operational at this point. I like this approach, and adopted it from building my Hairball 1176 kit.
Any amp I build now usually has a separate and complete power section before I move on.

[andyfromdenver]

This is something I am dubbing as "PCB Heaterz"

I went way overboard and sculpted the heaters. Generally, I did a first pass with some wire, got that shape and used it as a template to knock out a precise, minimal bending heater-unit.

[andyfromdenver]

Process close-up and wire used.
The heat shrink tubing keeps them super tight.

[andyfromdenver]

You can see I have abandonded using the central spigot on my 9 pin tubes and will accomodate for that.

The heaters are wired kind of Merlin Blencowe-y.

Excepting the 6AQ5 pentode, the tubes are Twin Triodes, which means that swapping the 123s with the 678s will permit one to rotate the sockets however the heck you want (while still facilitating a clean layout, of course).

This is how I do tube heaters, ever since I bought Mr. Blencowe's awesome design books.

Next step is to orient the output transformer (OT).

[andyfromdenver]

I'm having a difficult time placing my budget OT (the WSM 15k/600) for least/zero hum coupling with the PT.

I'll share the testing procedure.

In the pic, the secondary links to pins 2&3 and pin 1 grounds to the chassis (to reduce the hash when the OT is on the chassis).
Monitor the noise floor by going in mic level and turning the gain all the way up.

A tounge depressor offers something to hold onto, because handling the OT will generate a lot of hash-y noise.

Before even powering the chassis, you will probably have lots of hum pick-up already, and you can experiment moving the OT around to manipulate the field strength/hum.

[andyfromdenver]

I have joined the power switch wires securely, and they are to be carefully secured in the chassis.
Also, I wrapped off (individually!, then together) the exposed heater line (red and black twisted pair).

The rectifer diodes are not in, and we can now safely power on the PT, by plugging it in.

[andyfromdenver]

Now, you can manipulate your OT position on/in the chassis.
Plug and unplug the PT power to get a sense of the "no power" hum/hash baseline, and the "powered" hum level.

The hum that immediately appears when plugging in the PT is your baseline noise floor hum. It will NEVER improve/reduce from this point.  No amount of awesome crazy wiring and wire routing will make your box quieter from here.  This is the induced hum that your PT will transfer through the 3D-12D (lol) space of life directly to your OT.

However!  It's important to remember the condition we are monitoring in.
Mic level with gain on max, is so incredibly hot, in end use you would never get to this level, but that doesn't mean it's not important to optimize the hum noisefloor.

[andyfromdenver]

As you rotate and twist, you will hear extreme levels of hum (try putting the OT in free air close to the PT and rotating and blowing out your speakers.... )

Is this the best spot?

[andyfromdenver]

It would be nice (and my original intent) to put it inside, but is this acceptable hum-wise? (I am not actually asking anyone, but the answer is, no).

[andyfromdenver]

This position is super duper quiet, butcha see the obvious problem... 

In conclusion, I may go on hold for a minute and spend some of my hard earned DIY $ on a proper mu metal-shielded OT, preferably with a threaded single hole for easy entry and rotational option.

Oh proaudio, how you wag your finger at me and laugh....

My last little option, I did build in just enough room for me to rotate my PT 90 degrees. Maaaaybe I can make this $10 OT work.

[andyfromdenver]

Well, no amount of rotating/yoga/3Dgymnastics lets me place the edcor OT where I want to so......New OT on the way!
In the meantime, here are the major parts I am using:

PT- Allied Electronics 6K88VG (bought from a nice memeber here   )

Input-HA-100X copy https://www.studioelectronics.biz/sunshop/index.php?l=product_detail&p=1210 I got this for $100 on ebay which was weird and a little ordeal.

OT-  I just ordered the Sowter 1290 *yeah!* http://www.sowter.co.uk/specs/1290.html This should hoooopefully satisfy my desire for a superb noise floor.

T4B- from the mighty Kenetek http://www.kenetek.com via his ebay store.  I think I chose the default "middle" speed... cause I am so vanilla.

Trimmer caps- ARCO 465 from Surplus Sales of Nebraska http://www.surplussales.com/Variables/Compression/CompCap1.html I'm excited to include these and learn something from testing.

As of this moment, with no tubes (but I have all of them already 'cept the 12BH7) and no meter *ahem...is my plan slowly revealing itself  * I have spent around $400.
The only passives left to buy are some blingy PEC pots, two 33uf/450v caps, two spst carling switches.
The 7 pin socket was an old cinch socket from the fleamarket. cinch sockets are the f-ing best 

DIY was good to me in 2017, I sold 4 of the 6N1P tube DIs with Flux-Master CJs custom iron, and my homage to a two channel Vox ef86 and top boost amp with glow to the music skull eyes visual feature 
That's been my little fund I have been raiding to do this and buy some books.

tbc! 
keep soldering your dreams...(that makes no sense)
Andy

[andyfromdenver]

Here is a detail of my circuit board.

I don't intend to deviate from any of the critical routing that the designers devised.  This little section, alone, kind of bugged me enough to change it. I believe the important take-aways are having these two caps close and the signal wire running perpendicular across them. beyond that it seemed better to rotate R19 and construct a more direct path.

I've also marked the outer foil on the coupling caps and oriented accordingly, as a sacrificial lamb to the mojo gods 
see: http://www.aikenamps.com/index.php/where-to-connect-the-outside-foil-on-capacitors

I am a little hodge-podgy with my resistors, to utilize stock. I'll use carbon comp for the V1 plate resistors. For R17 (plate resistor for 1/2 12BH7) I thought to use a CC, but it seems 1W is more appropriate (it's hard to read the voltage drop on the scheme) so it's, on-hand, CF. Otherwise, I like metal film resistors and use them as much as possible.

I'm going to have to quadruple check with the schemes and layouts, even more so if I start going off script...

Also, I am going to wire from the '68 scheme as a start and include all extra insulated turrets etc. Then, when it's finished, I'll see if any B+ or bias, needs tweaking.

[andyfromdenver]

INFO POST
I think accomodating pot tabs is classy, and worth the effort 

While I await my OT, I have installed the insulated turrets, and loaded the board.

I have also been reading about the compressor, having never used one before. http://lcweb2.loc.gov/master/mbrs/recording_preservation/manuals/Teletronix%20Model%20LA-2A%20Leveling%20Amplifier.pdf

I hope it's ok to post gdiy links as an awesome-reading jumping-off point.
The wisdom shared is so humbling, inspiring, and helpful.
https://groupdiy.com/index.php?topic=984.0

An article mentioned for those learning about the output circuit:
http://www.tubecad.com/october99/page4.html

I finished reading the "all things LA2A" thread:
https://groupdiy.com/index.php?topic=3278.0
A few take-aways:
many find the gain amt excessive when preceeded by preamps.
solutions include: different ratio input tx,
lower gain preamp tube ex: 12AY7, padding the input.
*edit in now that it's built: OMG the Limiter response control is very interesting and if doing again would just use a regular pot and put a knob on it!*

My plan is to pad the input when neccessary, so as not to alter Colonel Sander's secret recipe of seven herbs and spices...

how to: (looking forward to making a cool barrel-inline-pad)
http://www.uneeda-audio.com/pads/

[Foots]

I am really enjoying this thread!!! Please keep it coming!!!

[andyfromdenver]

Thanks for the nice words, user: Foots (ha!!)

I spotted a discrepancy in the Gambaholic Rev 1&2 '68 Urei layout vs the '68 scheme and the original recpro layout.

R35 (220k screen grid2) is connecting to the filter cap instead of to pin 6 directly.

[andyfromdenver]

I made a big push with wiring the chassis in the past couple of days.

Most of the wiring, except the long runs and circuit board connections, is done.
I haven't added the trimmer caps yet, nor the board since I'm still awaiting the OT. I don't want to add them until all the drilling is done.

You can see how I did the paralleled triodes. The socket spanning wiring is more 3D than this 2D pic shows.

Blue wire=plates
Yellow wire=cathodes
White=signal
Orange=screen
Red=B+
Black=ground

This is the guide, mostly, once I start connecting to the board.

[andyfromdenver]

Mas.

I haven't added all the V1 components, because I need to run the circuit board wires first, and lay them down nicely.

I'll pick this up again once I get the OT in place.

[andyfromdenver]

I made a cardboard front-plate template  so that I can continue on with the wiring without risking scratching up the real front.

I'm going to hand paint (and possibly vintage label maker) the lettering, labeling, and art. More on that later.

I drilled everything on the front (incl. pot lock holes  ["he must be so proud of himself" they'll say]) except for the VU meter.

Why no VU cut-out?
Why???!?! you may ask 

Cause I am going to attempt to *Hacker-Man* in some LED VU meters *the crowd goes wild*!

I am not commiting one way or the other, I am prepared to go traditional VU, too.
Yo no se what the future holds...