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Simple Simple SE questions

Throwing Fuel on the fire here.......there is a companion book from Morgan Jones called "building valve amplifiers"........it's only money..you can get more of it....

I recommend studying Rozenblatt's book before diving in to "the book of Morgan"........I think I studied Morgan's books for several months when I couldn't get to sleep......it's really a handbook of tube design.

Parts are starting to show up! I started soldering the resistors today. Coupling caps and tube sockets should here in the next few days 🤞

Little update- tubes showed up today! Sockets too.

Not only that, Edcor emailed me to let me know they shipped out the power transformers I ordered! Their website said I shouldn’t expect them to ship til April so that’s quite a surprise.

Now I need get it together and pull the trigger on some of the last parts:
IEC socket with fuse holder and fuse
switches- one for the rectifier (I think) and one for power
hook up wire
cat 5 wire for the binding posts as suggested
Volume control
and maybe a motor run capacitor (still haven’t decided)

I have binding posts and rca jacks left over from a different project
Still waiting on my IXYS from china

I think that will do it for parts. I should really get a move on designing the top plate now that I know the power transformers are on their way!
I would keep an eye out on Mouser/digi-key for the IXYS 10M45........no idea if there is a problem with Chinese fakes of that.....but there are loads of other Chinese Fake semi-conductors around....with most found on Ebay or Aliexpress.

The cat5 wires are for the RCA's to the board; the speaker binding posts will get transformer output wires connected directly to them. Twisted pair CAT5 wires work well; if you want more shielding there are small coax wire types available. You want to keep the input wires from the RCA's away from the mains wires and heater wires as these are AC and they can induce 60hz hum on the input wires.....and if you use the cat5 wire keep it tightly twisted. You should be fine..but sometimes you will need to chase down hum.....and it can be a PITA.

I suggest doing a star ground scheme....there are a few ways to avoid ground loops (which make hum) and star grounding is simple and effective. Keep in mind that you have two grounds....signal ground (like speaker negative, RCA negative, etc) and chassis/safety ground. Pick a fastener on the top deck (like a transformer hold down screw..any screw really) and terminate a green wire safety ground from IEC inlet to this fastener. This is the most important connection in the amp......it keeps everyone alive if high voltage gets on the conductive chassis.

I develop medical devices for a living and there are lots of requirements for this ground......but here's the basics......use a ring lug on the end of the wire (not a spade or a faston) and build the following sandwich on the threaded stud/fastener sticking through the top plate....star lock washer then ring lug then another star lock washer then nut. The star lock washers Bite into the aluminum deck and the ring lug and the nut to get a low resistance ground connection. You will then ground the signal ground from the board to this stud/screw as well using another ring lug and star washer...so your signal ground/chassis-safety ground (and any other grounds that you need) all terminate at this point. If you add another ground use a ring lug and star lockwasher....just like adding beef patties and lettuce to a double/triple burger. :p Ring lugs are used so that if the nut loosens the ground leads won't fall off the stud.

You want the signal and chassis grounds to meet only at this connection.......that means your negative speaker binding posts and RCA terminals need to be insulated from the chassis if you are mounting them to the top plate or other chassis metal, otherwise you will have multiple ground points and ground loops. If you install the binding posts though exotic hardwood ;) they're already insulated. If you use a metal bottom cover tie this to the star ground point with another green wire with rings lugs on both ends and star lock washers. I usually use one of the threaded fasteners holding the feet on the bottom cover for this connection. All of your exposed metal chassis surfaces should be tied to the star ground point and if you check resistance between them with your meter you should see less than 1 ohm of resistance. If the metal is painted or anodized sand a bare spot around the studs where the lockwashers bite into the metal.

You will likely need some 600V rated wire for a few things like a motor run cap or any other caps that you may want to run off-board. You can use 600V rated wire for mains stuff from the IEC inlet to the board, it just has thicker insulation than regular 300V rated wire...again make sure that the voltage rating is inked on whatever wire you are using if it involves mains wiring or other high voltage wiring.

You only need a mains power switch...if you want to switch between 5AR4 and SS diodes make sure that feature isn't easily reachable.....you only want to switch that when the amp is powered down and the caps are discharged (give it a minute or two before powering back up).....bad things can happen otherwise. This may already have been mentioned before...when using SS rectification your B+ voltage will be a bit higher than when using a tube rectifier, as the tubes drop more volts (higher forward diode drop).
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You can see my star ground here.....near the motor run cap.......(and embarrassingly.....a loose short ground wire hanging out in the breeze!!) :oops:

...and note the ground strap tying the top and bottom panels together....and the RCA input leads are routed away from the rat's nest of other wires; they are an example of small coax wires. Start with Cat5 wires, they work well too.


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I would keep an eye out on Mouser/digi-key for the IXYS 10M45........no idea if there is a problem with Chinese fakes of that.....but there are loads of other Chinese Fake semi-conductors around....with most found on Ebay or Aliexpress.
I have heard several stories about fake 10M45S chips from Ali, Ebay, and other indirect sources. They seem to be rather common in Europe. Digikey shows a tentative ship date of Feb 2. Mouser is showing 2023.

The DN2540 can be made to work, but it requires a resistor change and is operated at or above its ratings in an SSE. It's OK in most TSEs and TSE-IIs.

I ordered some other in stock depletion mode mosfets from Digikey to test in the SSE, but for some unknown reason the USPS routed the package to NYC where the tracking has gone cold. Our mail comes from Pittsburgh. For several days the tracking said, "Departed USPS Regional Facility NEW YORK NY DISTRIBUTION CENTER" or "In Transit to Next Facility." There have been no scans since 1-17. I will test them in an SSE if I ever get them.
Don't stress the grounding.....you won't burn the house down....

Ground one signal ground from the board to a ground stud, then ground the IEC power inlet to that same stud. That way the exposed metal is grounded to your house mains ground. If something shorts to the top plate it will blow a fuse.

The ground loop issue is about noise....usually 60Hz hum getting into the signal path. The star ground scheme minimizes that issue. If your amp is noisy you will be asking and we'll guide you through making sure you don't have any ground loops. It's easy enough to remedy by moving wires and a few other things if required.
Aluminum! It's really easy to work.....I've used router bits on it....you can hole saw the tube socket holes or however you want to machine them. 1/8" thick is handy since regular kerf table saw blades are 1/8"......3/16" is also readily available, .093 same as thin kerf rip blades. I would use 1/8" thick since the transformers are heavy. 5000 or 6000 series are both fine. I cut the aluminum plate on my table saw with a freud non-ferrous blade...works like butter. You can use a high tooth count cross-cut blade as well.

If you have a local metal supply house check there.....or you can buy it at McMaster-Carr. My local metal place has remnants.

The trickiest part of machining the top cover is getting the tube socket holes and board mounting holes in the right places. George should have a PDF of the board layout somewhere.....my method is this...I call it the "paper doll" method:

Print the board layout at 100% scale on a regular piece of copy paper (keep in mind that your print out may be off by a little since you are using a printer and not a plotter)..... measure a couple things on the actual board (like length and width) and confirm that the print is accurate.........if not scale 102% or 99% or whatever.

I use 3M artist's spray mount (temporary adhesive in a rattle-can) to stick the pattern to the aluminum top plate, then machine, then remove what's left of the paper. I clean residual glue off with Brake cleaner; acetone or paint thinner may work as well. Print a couple of copies once you get the scaling correct..you may need them.

It can be tricky to get all 4 tube socket holes concentric with each other and the 4 mounting holes.......if you make the tube socket holes oversized the eccentricity won't show as much and you'll have your ventilation holes as well. I have a full size milling machine in my garage with large end mills so I can get pretty accurate locations, and if I wasn't such a hack machinist I wouldn't need the paper patterns.

Clamp the sheet well in your drill press, and hole saw away. You could experiment with a forstner bit or a spade bit on some scrap aluminum, they may give you a better finish on the hole...I have no idea....just throwing out ideas.

Another method that just popped into my head is this:

Use the paper pattern to make plywood router template, then bore the tube socket holes slightly undersized, then use the router template with a router or laminate trimmer to get nice clean edges on the holes.

I brought up the table saw blade kerf stuff above in case you want to kerf/dado the wood chassis and slide the top panel in place (instead of top mount).
I use aluminum.
As I live in a quite small city house I don't have space for many tools, much less a drill press or such.
I actually went with SendCutSend for my plates. Price of admission was quite cheap.

I just did measurements of the board critical dimensions & the transformer mounting holes (Edcor publishes them) & did it up in an open source CAD program.

Upload the dxf & about a week later I got a beautiful piece of laser cut & finished 5052 aluminum.
I can share my dxf if you wish, but remember that the outer dimensions & the transformer & cap holes are specific to the pieces I bought.
McMaster (and likely Digikey and Mouser) sells standoffs to "hang" the board under the top plate.

I used female-female standoffs so there are no nuts required. A screw from the top holds the standoff to the top plate and a screw from the bottom holds the board to the standoff. You'll need to determine the correct length to get the tube socket heights where you want them.