Structo wrote:I wonder if you could find a high heat grommet to fit in the tube holes in the chassis?
So that they fit the tube rather tightly.
That would help hold the tube in the socket and cushion the tube from vibrations as well.
Excellent thought! There is an old post where I saw this once but I never was able to verify what kind of grommet he used.
I did get better with each tube and I think it will work well. However, this mounting technique will require some sort of tube keeper to really produce a gig friendly amp. The IC sockets don't really grip the tube carrier and it's real easy to pull the tube out with just the slightest touch.
enjoy,
rj
I don't know what sockets you are using but the ones I have been ordering grip very well. I'll see if I can dig up the mouser part number. I can actually lift the chassis off the ground by just grabing the tubes themselves and they stay snug. I see that you are using machined pins and that is good . The other style spring clips sockets pretty much suck. I have literally shipped amps all over the world using these sockets and never had one arrive with a tube loose or fallen out.
UR12 wrote:...The other style spring clips sockets pretty much suck. I have literally shipped amps all over the world using these sockets and never had one arrive with a tube loose or fallen out.
This pretty much gets right to the point. I used the the spring clip sockets on the two boards in question and I wasn't too pleased with either of them. It sounds like I need to change to the machined sockets for the board as well. Thanks for the help on this.
Now if could just find those high temperature grommets. Teflon seems like a good candidate, but I can't nail down the operating temperature of the tubes yet. I see some 9 pin Teflon tube sockets that are rated for use from 180 to 250 degrees, but the spec didn't say whether that was C or F. I found one materials list that showed Teflon was good for 550F, which sounds like it would be more that adequate. I just need to find more data on the tube temperatures.
thanks again for the help,
rj
I found this after I posted the note above - McMaster Carr has these... High-temperature flexible grommets are silicone with a temperature range of -60° to +500° F. I guess I just need to sort out what size is right.
I also found a spec sheet that gave a maximum bulb temperature of 220C which works out to 428F if I did my math correctly.
Good stuff, RJ. I ended up going in the opposite direction by removing the bypass cap from the 2nd gain stage, raising the cathode resistors to 2.7k on the first 2 gain stages, and raising the cathode follower resistor from 68k to 100k to ease the compression a bit.
Still need to get it on the scope (the amp is on loan at the moment). It seems the 2nd stage cathode resistor change is more effective than the first stage resistor change; may change that 1st stage back to stock.
Great sounding amp, and I'm looking forward to hearing others reports as they build 'em...
Everyone who has seen and heard the amp has been amused by it's small size, the tiny tubes and the big sound they make, and how sweet it sounds
rbryerton wrote:Good stuff, RJ. I ended up going in the opposite direction by removing the bypass cap from the 2nd gain stage, raising the cathode resistors to 2.7k on the first 2 gain stages, and raising the cathode follower resistor from 68k to 100k to ease the compression a bit.
Great technical info for us Rob. I do feel that the Rockets strongest point is the clean tone. These little tubes really deliver the chime.
It's interesting that the gain on the 6112 tube is 30% less than the 12AX7 and yet there is more than enough gain to really rock these amps.
There are several more kits out there and we should be getting some additional reports coming in soon. I know that two of them were successfully finished with good results...
Been lurking awhile - but may have something to offer here. On another forum I have read reports of someone using 1-inch or so piece of aquarium tube slit on one side as both a tube stabilizer and microphonics muffler of sorts. Should mention that the tube this technique were applied to (6418) are pretty low output and as such do not produce much heat. Might want to check out the heat situation first probably.
From what the poster said the 6418 sub-minis are super microphonic (they are DHT and ring if you even touch the table that the unit is on) and the aquarium tube really quiets them. Might be worth a try. -- Thanks to all for this great thread!!
Just back from a visit to Ft. Collins... not so far away from you there.
Anyway, I think the aquarium tube idea is new t me and would probably work. I haven't found the 6112's to be especially bad with microphonics but the idea is valid anyway. Maybe similar effect as to the silicone o'rings that some folks sell as tube dampers.
I found this at Mcmaster. Not sure what the dim's should be, but they have quite a few sizes to choose from. It's a lot cheaper than those grommets.
I think this would work better, since you could pull the tubing off and remove the tube/socket from the top side of the chassis - although the holes may have to be increased in size for the socket to fit through.
BTW RJ, what do you do for a living?
You do not have the required permissions to view the files attached to this post.
I am using a mixed pair of 10's for most of my off site gig work... one alnico and one ceramic.
My favorites are the vintage 30's that I used in my videos and I have those in the shop in an open back cabinet. They are in an old Randall combo cabinet and I choose to leave them there as a shop cabinet and never move them. They sound awesome but I haven't gotten enough fan support yet to have anybody offer to carry them for me.
