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Here's Where It's Going...

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In Reply to: RE: Eh? posted by mqracing on November 04, 2009 at 10:08:06

Thanks for everyone's input on this. The photo below is just a quick partial assembly so you can see what the amplifier deck looks like. This will be mounted on 1/4" side rails. The power supply deck will be mounted behind this, recessed between the rails and covered with a perforated cage. The top of the cage will be at roughly the same height as the FS-100.

I did consider a rectangular cover for the FS-100, but I think it would really dwarf the 211. As it is, the FS-100 is huge, and the only thing that saves the look is that it's black. I want to black out the lam bolts too, but I'm starting to think it's not such a good idea to remove them, even one at a time. Maybe I can figure a satisfactory way to paint them in place. Mike, these FS-100s are about six or seven years old. Would you happen to remember what the lam bolts are made of, and on the chance that they're actually brass or brass plated, whether they're coated with anything?
After reading the replies here about mounting the OPT, I've pretty well decided to mill aluminum trim pieces to hold the feet to the chassis. I can install 1/4"-20 studs in the trim, so each piece will serve as both cover and holddown. I can't think of anything else that won't look like "hardware." Even smooth, stainless carriage bolts have a look I don't care for when they're on the top of a chassis. Again, my goal is to have *no* hardware visible from the front, top or sides of the amplifiers.
Yes, I milled the trim rings for the tubes myself, as well as the mounting system for the 211. It's not entirely visible in the photo, but the 211 mounting system consists of two machined plates and four standoffs underneath, and the trim ring on top. The ceramic socket is supported only by its bottom surface, which is how all these sockets were intended to be mounted.
Keep those suggestions coming!

Edits: 11/04/09

Follow Ups:

RE: Here's Where It's Going... - 2wo 20:01:27 11/07/09 (1)
"I've pretty well decided to mill aluminum trim pieces to hold the feet to the chassis. I can install 1/4"-20 studs in the trim, so each piece will serve as both cover and holddown"

How about if this piece extended up to cover the screws ( recesses milled out). What I am thinking is a solid piece that surrounds the bulge in the cover out to the edge of the lam stack, A inverted U with the 2 mounting studs at the feet . Similar to the way your octal socket cover…John

But it’s the sense of satisfaction I get, by getting it to do anything at all…
- RE: Here's Where It's Going... - Triode_Kingdom 22:08:07 11/07/09 (0)
  I'll consider that if the individual pieces I'm milling now don't look right after they're mounted. This is a tricky area in terms of esthetics. I'm finding that I can't get a good mental picture of the outcome, even when the holddowns are already designed on paper. Thanks for the idea!
Not fair, not fair, not fair.... - thermionic addictions 15:20:40 11/07/09 (0)
why can't I have a milling machine? If it is OK with you I am going to go sit in the corner and pout for awhile :))

All kidding aside, nice work, I am very jealous of your abilities.

Cal
RE: Here's Where It's Going... - Mossback 15:41:58 11/05/09 (0)
Mill two rectangular parts that would bolt on in place of the existing covers. Not symmetrical, one would be the “top” the other a base. The top would use hidden bolts or threaded stock fastened from the bottom. This would require you to rotate the OPT 90deg. It would then sit on its side. The top would have 45deg bevels all four sides.
I’ve started the same idea on my Foreplay III PS Trans that has been in work for a few years now.
Paint the lams, the aluminum rectangular parts could be bead blasted or powder coated.
RE: Here's Where It's Going... - nullspace 08:02:23 11/05/09 (5)
That is some really nice work. Do you have a schematic for the amp that you could post? Thanks.

Regards,
John
- Schematic - Triode_Kingdom 16:10:21 11/05/09 (4)
  Here is the basic amplifier schematic. This circuit can drive the 211 into Class A2, and in that mode, it exploits the full 30W capability of the FS-100s. Distortion is very low, even drawing grid current, and this design sounds every bit as open and detailed as my earlier single-tube prototypes. I'll also post the PS schematics if you want, but they are similarly complex due to the multiple voltages required by the amplifier. It's not a project for newer builders.
  - RE: Schematic - yes, pls post the PS schematic. - tubejack 17:31:45 11/06/09 (2)
    A post of the PS schematic would be greatly appreciated. Thanks for sharing.
    - PS Schematics - Triode_Kingdom 21:52:17 11/07/09 (1)
      Here are the schematics. I've included a brief commentary for each, and I'll be glad to answer any questions.
      The original HV supply is shown below. A Hammond 20H choke is located in the negative leg of the supply to stay within its maximum voltage rating. The 5R4GYB is used primarily to delay B+ until the 211 heater is on. It also drops the voltage about 50V, which avoids overstressing the FS-100s. The next version will relocate the 5R4GYB (but not the choke) to the positive leg and will eliminate two diodes from the bridge. In other words, it will be a hybrid SS/tube bridge rectifier. Although I haven't had problems with diode hash, a hybrid supply should be virtually noise-free.
      
      The LV supply uses a trick that I developed specifically for this amplifier. A single transformer drives a capacitor-input filter and a choke-input filter simultaneously. As you can see from the schematic, it only takes a single diode to isolate the higher voltage of the cap-input section from the choke. Unlike supplies that use series resistances to create multiple output voltages, both of the primary sections of this supply (+510V and +360V) can deliver significant current with minimal voltage sag.
      
      The bias supply is straightforward. The -80V output provides the relatively large current needed for the 6BL7 cathode follower; the other output varies grid bias on the cathode follower as a means to adjust the 211's anode current. Note that this is a shunt adjustment. If the adjustment pot becomes dirty or otherwise fails, full negative bias is delivered to the cathode follower.
      
      Finally, here's a rather shoddy photo of the power supply deck in its "trial fit" stage. The deck is approximately 12" x 8". I designed this before I had access to a mill, and it was cut by Front Panel Express from 0.150" aluminum. They did an excellent job. This holds everything shown in the power supply schematics except the 5R4GYB and bias adjustment.
      
      Edits: 11/08/09
      - FS-100 Bonus Schematic :) - Triode_Kingdom 22:38:50 11/07/09 (0)
        
        In Reply to: RE: PS Schematics posted by Triode_Kingdom on November 07, 2009 at 21:52:17
        
        Just thought I'd throw this out for good measure. It shows how a 3P3T non-shorting rotary switch can be wired to select the FS-100 output impedance. This is the best I could come up with - if someone here has devised a simpler switching scheme, please post it!
  - RE: Schematic - nullspace 08:07:53 11/06/09 (0)
    Thanks for posting that. I had looked around on TubeDIY for info, but the links to the schematic were broken. That looks pretty sweet; I'd like to do an 809 A2 amp at some point in time.
    
    500Vdc or thereabouts is my limit. I'm pretty awestruck by the huge amps seen around here and on the GM70 boatanchors mailing list, but I wouldn't be comfortable working around that much voltage.
    
    Regards,
    John
RE: Here's Where It's Going... - mqracing 02:29:52 11/05/09 (1)
Wow... superb work there. I like the extra thick chassis. And all of your machine work looks first class. Your going to have a really cool amp when your done.

Since you are doing the machine work on the alum... for picking up the outputs why not machine some small risers out of alum to put in btwn the tranneys and the top plate... maybe round off your corners to visually match your other doodads (said with envy)... sort of like the wood pieces you have shown in your photo but machined from a matching alum stock...

the brass bolts are solid brass... with no finish... so they will oxidize and get darker over the years... but actually with the black covers and black lams... at least in your photo they don't stand out at all to my eyes.

Kudos... great work...

MSL

Builder of MagneQuest™ & Peerless™ transformers since 1989
- RE: Here's Where It's Going... - Triode_Kingdom 11:01:18 11/05/09 (0)
  Thanks MIke, I think I know how to handle this now. It's OK for the transformers to be in contact with the chassis if I use trim/holddown parts on the feet. The trim will cover the contact area, so any scratches or impressions in the paint won't show. All I need to do is make sure the trim itself can't mar the paint. BTW, you've given me another idea for the design, but I'll need to mill the parts and trial mount the trim to see if I like the look. I'll post a photo if it's a go.
  
  Being as they're uncoated, the lam bolts should be pretty simple. Surface prep will be straightforward, and epoxy-based black paint should last the life of the transformers (or at least the life of the paint that's already on the endbells). Incidentally, the brass screw heads look dull in the photos, but they really stand out in person. If there was other gold or brass hardware, it might not be a problem. They just look odd to me with everything else being black or silver and with no other hardware showing.
  
  I think this will work out well. I can go ahead and cut the chassis now for the OPTs, then mount them temporarily with through bolts. When other issues are further along, I can replace the bolts with trim pieces. Wow, it'll be a real relief when all of these mechanical and cosmetic design decisions are done. I'd much rather spend my time listening to this superb iron you make!
RE: Here's Where It's Going... - keto 22:32:45 11/04/09 (0)
Wow, that's some amazing work!!!
thumbs up - gluca 19:29:34 11/04/09 (0)
great job!

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