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In Reply to: RE: Aluminum plate thickness for amp project posted by rogerh113 on June 04, 2015 at 06:30:42
Ran into one other plate related question (so far).....
I need to undermount the 805 tube socket, and am down to 2 options. I can cut a section of Al tube (1/2 dia) and use a through bolt. Option 2 is a ceramic standoff which is threaded on both sides. I am tending toward the Al solution, as I figure the through bolt would be stronger. I can use fibre washers between metal as well as ceramic contacts to eliminate any vibration or rattling. Is there some reason ceramic standoffs would be better??
Regards -- Roger
Follow Ups:
Which sockets are you using? The large EF Johnson sockets were designed to be mounted on top of a plate. The bottom of the socket is machined and registered for this purpose, but the upper surface is glazed and only roughly dimensioned. When I designed my 211 amps, I decided early on not to use the top surface of the sockets for mounting. I wanted to be sure there was no slop that could cause vibration, or worse, an uneven mounting surface that might cause the ceramic to crack. The only way to accomplish that was to machine a circular sub-plate that the sockets could sit on. I've never seen anyone else do this, including commercial manufacturers, but I think it's the only way to do it right.
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Buy Chinese. Bury freedom.
I did something similar with my 845 sockets. I mounted them to thick pieces of Teflon, and attached that assembly to my chassis underside..
That's gonna be one fine looking 211 amp.
Willie
Thanks, that's a really old photo. These were completed, then torn apart again for various changes. Among other things, I'm adding auto bias for the 211s. I have the design worked out, but it was a challenge because they're A2. If all goes well, I'll have everything done by the end of summer.
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Buy Chinese. Bury freedom.
I can no longer see the image in my post above. If I attempt to view it separately, the Asylum server returns a File Not Found error message. This is a frequent occurrence, but only on this site. Anyway, here it is again...EDIT: Isn't it odd, the minute I posted this, the image in the post above reappeared. The same exact thing happened earlier today, so I had deleted the earlier repost. Very strange...
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Buy Chinese. Bury freedom.
Edits: 06/07/15 06/07/15
Not custom or as overbuilt as yours may be, but perhaps okay for common sockets?
I don't use Chinese parts. That aside, the rings you linked don't appear to solve the problem. Unless I missed it, there's nothing to support the sockets from underneath. Again, some people might not consider that important, but it's not how the sockets were designed to be used.
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Buy Chinese. Bury freedom.
Edits: 06/07/15
Fair points TK. I think I understand what you are suggesting now.
regards,
91.
Hello,
The sockets were acquired by the initiator/prior owner of the project, and I don't have a clue as to the style/maker.... I have however attached a couple of pictures that will hopefully tell all!!
The upper surface, to which the 1/2" tube would butt, is indeed glazed. I put my small straight edge flat across the glazed base mounting hole, and it does look as though is pretty much perpendicular to the brass cylinder (excuse me for not knowing the proper terminology). I was planning on using a fibre washer (or felt) between the tube and the ceramic as well as the tube and bottom of plate (good buffer to prevent vibration and provides a bit of friction to keep the Al tube from rotating).
Regards -- Roger
Those are Chinese sockets, so I really don't know how well they'll work. Personally, I would toss 'em and hunt up some real EFJ made-in-USA sockets for a project like this. They're pretty common on eBay.
The other potential issue mounting this style socket with nothing underneath is the fact there are only two through-holes. That raises the possibility the sockets will rock and loosen over time. A company like Front Panel Express can probably cut round mounting plates to support the sockets from underneath. It would be worth sending them a sketch to find out.
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Buy Chinese. Bury freedom.
Hello,
I saw a National Co. socket that would work probably better than the Johnson, since the National is built to be undermounted. Any feedback on the relative quality of the two? Is the National a solid socket choice?
Regards -- Roger
The National socket that seems to offer better mounting has only lug connections, while the Johnson has lug and solder connections. Do solder connections offer better performance, or are the two connection methods pretty much a wash?
Thanks -- Roger
Can you post a picture? I don't recall ever seeing anything on these sockets except solder lugs. They're held in place with #10 screws through the ceramic base.
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Buy Chinese. Bury freedom.
Here is a picture. Looks like he only has one, so not really an option.....
I haven't used that type. I'm sure it's supposed to have solder lugs between the washers, they've just been removed. Incidentally, not all of these are for the same pinout. If you wire them as marked, and it turns out the G and P are swapped, you'll have trouble. Not really a problem as long as you know about it, but I'd prefer to have those markings in the correct locations if possible.
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Buy Chinese. Bury freedom.
Thanks very much for letting me know about the sockets - not good news, but better than after they were already in. I will indeed try and run down a pair of EF Johnson sockets. Of course, if these are Chinese, then the 6l6gc and 12au7 sockets are probably the same..... Is it fair to say that if there are no brand marks on the sockets they are Chinese?? As you might have already guess, I am anything but an expert on this.... I am looking to use good quality parts (within some reasonable budget) and put together a solid project. Lucky I am not in a rush !!!
Thanks and regards - Roger
I'm not sure all the US sockets will show a brand name. However, the pin contacts are formed differently than the ones you have, and no American manufacturer ever gold-plated their sockets. I just ran over to eBay, and all the US-made 211/845 sockets look old and tired at the moment. Be patient and you'll get a good pair, even if you have to buy them one at a time. Vintage octal and 9-pin sockets are easier to find, although they frequently sell for more than I think they're worth. Belton sockets have also been recommended by Jim McShane as a good modern replacement for octals and miniatures.
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Buy Chinese. Bury freedom.
~!
The Mind has No Firewall~ U.S. Army War College.
Just to confirm, are you sure it wasn't done after the fact by someone else? I'm also curious how tubes this large (i.e. slow) would be used in radar. Do you have any more info on the origin or use of those sockets (I didn't see your previous post)?
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Buy Chinese. Bury freedom.
Edits: 06/12/15
Here is the link from AA forum... The British invented RADAR and as you know... the lower the frequency the farther the range... a triode would be more than sufficient, the antennae plays just as big a part as it should match the frequency being beamed, moreover the technology progressed to the cavity magnetron, the beginning of fast food via microwave.
As an aside, {as I have learned} a 6SJ7 may be electrically very similar to a 77 or 6C6... the fact remains, aurally the 6C6 will soundly trounce the 6SJ7... pun intended. As usual, more is going on than just reading by the numbers. Size of the plate for older tubes making a difference?
Perhaps.
The Mind has No Firewall~ U.S. Army War College.
Edits: 06/24/15 06/24/15
Thanks for your help in this. I am fine with patience - for some reason I have a strong aversion to Chinese products, so any inclusion would be from ignorance rather than intent. There are some nice NOS vintage sockets out there, and the prices are higher but not prohibitive. Any particular brands I should look for or avoid. I think I am going to stick to ceramic.
Thanks -- Roger
Some users have reported odd noises or susceptibility to vibration associated with ceramic sockets (octals and miniatures). I can't confirm that, but almost all my vintage sockets are bakelite or similar. The only exceptions are ceramic octals that I use for high voltage applications (more than +750V). Good luck with your project!
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Buy Chinese. Bury freedom.
Either one sounds fine. The ceramic standoffs are likely insulated whereas the through-bolts would be conductive; sounds like you've taken that into account.
I'd use the through-bolt approach mainly for aesthetic reasons - you can get a socket-head capscrew, a countersinked fastener or somethings else that looks good to have a clean appearance on top, whereas the standoff would show a nut and exposed threads. Of course, you could use an acorn nut to dress that up, if that's your style.
Why 1/2" tubing? You shouldn't need very big fasteners for the tube sockets. Even #8 would be overkill, #10 way over, and 1/4-20 crazy over. If your local hardware store has a good fastener section (maybe with those vendor-stocked boxes from Dorman or Hillman, etc.), hunt around, they should have bushings or spacers for standard fastener diameters that should do the trick.
If isolation from vibration is a particular concern, you can get isolating standoffs - they have threaded studs on both ends and a rubber body in the middle. Same problem with nuts on the top surface, and not too sure they are actually necessary or beneficial, but would be the gold standard for vibration isolation.
Hello,
Thanks for the reply. I am thinking 1/2" od tubing mainly because the recess in the ceramic socket for the support is a bit over 1/2", and I figured I would get as large a support footprint as possible to minimize wiggling of the socket. The through screw can be a whole lot smaller than 1/2". I will probably try to keep the screw size as much the same as possible for the entire plate, since it would look the best and even a small diameter screw probably has plenty of strength for the application.
Regards -- Roger
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