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FS-100 Hardware

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Posted on November 3, 2009 at 13:44:26
Triode_Kingdom
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 I'm rebuilding my 211 SETs to bring them up to commercial cosmetic standards. The changes will include a pair of new chassis and lots of one-off trim pieces that I'm milling myself. One goal is to have absolutely no hardware like screw heads showing on either the front panels or top plates. In this regard, the FS-100 OPTs present something of a challenge.

The bolts holding the FS-100s together are a sort of dull, brass-mustard color. This looks really out of place, and I'm wondering if these bolts can be removed for painting. Would there be any danger to the mechanical transformer alignments if these were removed two at a time (diagonals)? Also, is there a way to keep the transformers from scratching the chassis and marring the paint around the mounting feet? Would it be useful to fit something like fishpaper under the feet, or is metal-to-metal contact required in order to secure these heavy transformers? Finally, has anyone here designed trim hardware to cover large transformer feet like these?

Any thoughts or advice will be appreciated.
RE: FS-100 Hardware, posted on November 8, 2009 at 17:23:38
Ed Sawyer
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 First, nice work - really well done machining and design eye. I like the 211 socket solution - well thought out there.

Some thoughts:

1) If I was going to the trouble to machine nice trim rings like that for sockets, I'd certainly step up to Yamamoto teflon socket rather than vintage bakelite/etc. They really are worth the $ and are better in bascially all respects.

2) A doghouse is the only elegant solution here. No offense to Mike but open-frame trannies just don't cut it aesthetically on an amp like this. It's like having steel wheels on a chopped/channeled/frenched hot rod that has had a full shaving of exterior trim and a full wire tuck in the engine bay. Just incongruous. I too love the "no fasteners" look, I've gone that way on a few things I've built, and there's others that ascribe to that philosophy too (Josh @ electronluv springs to mind). About the only way to not do a doghouse would be machine replacement billet end-bells and mount the tranny horizontally perhaps, ala some of the Dared amps. that way only the lams are visible, and those can be made to look ok.

Keep us posted with pics and progress, looks like a well thought out project.

-Ed
RE: FS-100 Hardware, posted on November 11, 2009 at 08:31:54
Triode_Kingdom
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 Honestly, I'm not sold on Yamamoto. They're extremely expensive, and in all the years I've been using Amphenol and Cinch sockets, I've had absolutely zero problems. I machined a mounting foot cover for the transformer a couple days ago, but decided I didn't like the look. I'll probably end up just turning some round, button-top bolts about 3/4" diam. for this. I agree, a drawn cover would be ideal. Maybe the look of the open-frame will grow on me, it does lend a certain nostalgic appearance to the amplifier.
RE: FS-100 Hardware, posted on November 4, 2009 at 08:53:15
Doc B.
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 Yes, you can *carefully* remove the screws. But it will void your warranty. One by one is a good idea. Don't torque the nuts too hard when you put them back in the end bells, just snug.

Mount the transformer on insulators. We use fiber shoulder washers. Run a drain wire from one screw, in contact with the bell end, to your chassis near the safety ground connection. One could attach it at the actual chassis/safety ground interface, but this is not UL approved. This will create isolation from hum pickup due to eddy currents that may be generated by the power supply iron in the chassis and still protect you if there is a short from the HV primary to the transformer case. All of the other transformers and chokes should be isolated this way as well.

Eh?, posted on November 4, 2009 at 08:18:51
Triode_Kingdom
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So, no one has an opinion on this? Mike, what about pulling out the transformer bolts? Sorry if these questions seem like nit-pickin'. I'm going to a lot of trouble to build an exceptionally clean chassis. If I could hide all the transformers under covers, I would. The OPT will have to be above the chassis though; any ideas on sanitizing the look will be appreciated.
RE: Eh?, posted on November 4, 2009 at 13:36:25
Bas Horneman
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So you want it to looks something like this? Made by Stixx.
To infinity and beyond!!!
RE: Eh?, posted on November 4, 2009 at 10:08:06
mqracing
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 Hi TK:

Nice looking shroud\cover for that tube socket. Did you do the machine work or find these available ready made somewhere?

Re: pulling out the transformer bolts. If your careful and don't drop the trans or shake, jar, rattle it too much you should be able to take out the bolts and not disturb the airgap. Lay the trans on it's side... definitely use a nut driver and screwdriver. Twist with the nut driver not the screwdriver. If you have brass hardware you could get it gold plated. When you putting the bolts back in... make sure you use insulating washers. You can tighten them fairly snug. For notes about grounding and etc see Dan's post.


As to how to cover up the transformers or other cosmetics.... I wouldn't put insulation under the tranneys as a pad... one reason is that I don't see that it would look any better than just simply mounting them on top of your chassis as normal.


My sense is that I would maybe look at building a "doghouse" to cover all the transformers ala the Marantz 8B chassis look\style. Or alternately getting deep drawn covers (like the Zero alum deep drawn) and mounting these over the transformers with air as the intervening medium inside the cans.

When I read your question my first thought was I'd rather him call me where I could walk you through verbally... and have the advantage of immediate feedback from you on whether or not I was being helpful.

If you would like feel free to try calling me. Nights up to midnight are generally pretty good for me. my number is 215 two eight eight four eight one six.


Mike



Builder of MagneQuest™ & Peerless™ transformers since 1989
Here's Where It's Going..., posted on November 4, 2009 at 18:32:12
Triode_Kingdom
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 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!
RE: Here's Where It's Going..., posted on November 7, 2009 at 20:01:27
2wo
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 "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..., posted on November 7, 2009 at 22:08:07
Triode_Kingdom
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 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...., posted on November 7, 2009 at 15:20:40
thermionic addictions
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 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..., posted on November 5, 2009 at 15:41:58
Mossback
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 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..., posted on November 5, 2009 at 08:02:23
nullspace
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 That is some really nice work. Do you have a schematic for the amp that you could post? Thanks.

Regards,
John

Schematic, posted on November 5, 2009 at 16:10:21
Triode_Kingdom
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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., posted on November 6, 2009 at 17:31:45
tubejack
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 A post of the PS schematic would be greatly appreciated. Thanks for sharing.

PS Schematics, posted on November 7, 2009 at 21:52:17
Triode_Kingdom
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 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.
FS-100 Bonus Schematic :), posted on November 7, 2009 at 22:38:50
Triode_Kingdom
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 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, posted on November 6, 2009 at 08:07:53
nullspace
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 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..., posted on November 5, 2009 at 02:29:52
mqracing
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 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..., posted on November 5, 2009 at 11:01:18
Triode_Kingdom
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 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..., posted on November 4, 2009 at 22:32:45
keto
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 Wow, that's some amazing work!!!

thumbs up, posted on November 4, 2009 at 19:29:34
gluca
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 great job!

A nice doghouse...., posted on November 4, 2009 at 13:41:21
Bas Horneman
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.
To infinity and beyond!!!

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