problems with 805 tubes

[pjpoes]

I have had the worst luck with 805 tubes. The first pair I got were direct from china, and one was blown. The second pair I got cost me 80 dollars, came from a US Tube distributor, but were also the Chinese Sheguang tubes, and the metal "hats" fell off. The Epoxy, or whatever it used to attach them, came undone from the heat. I then ordered a second pair from China, the new version with Ceramic Insulators. I plug them in, it blows a fuse, one of the 805's is bad. I can't seem to get a decent set of 805's at a reasonable price. I could pay 350-400 dollars for the Valve art 805's, which are Chinese, but I guess of higher quality. I could look for a set of NOS RCA's or GE's, or whatever, but I seem them so rarely, and they also go for quite a bit. Anyone got any ideas here. I would not have thought that the 805 tube was such a pain in the butt.

One I dea I had was to take a pair of the good 805's and use a conductive epoxy to resecure the hats. It should work, and at least I know the tubes are good. I wish I could have some with the thermal isolator like the new ones I ordered.

[bear]

You probably can't use conductive or any other sort of epoxy on the plate caps.

Most epoxies can't handle the envelope temperature.

You need either "lamp cement" which is what is normally used on vacuum tubes or some other sort of high temperature "adhesive". Both can be had, although you'll have to do some research to make that happen.

I don't happen to have either myself... fyi.

I'd contact the seller, and see if they'll make good on the bad tube(s).

_-_- bear


PS. you do know the 805 is a zero bias class B tube?
For SE operation, an 845 or 211 is likely preferable.

[SY]

Try Electrotemp Cement No. 8 from Sauereisen.

[pjpoes]

thanks, I'm really getting sick of these tubes. I mean, when working they sound great, but they don't last, and I have currently 6 tubes and 2 good ones. None of them are matched, not that its all that important, but the two good ones don't even look alike. Anyway, thanks, I will look for that cement.

[nhuwar]

SY do you know of any place that sells that cement. I have tryed to use Sauereisen in the past but could not find a reseller. Sauereisen has a very high minimium order if you order directly from the company.

Nick

[SY]

Have you called them to ask about distributors? I haven't bought any in years.

edit: It looks like McMaster-Carr has some similar stuff listed under "refractory cement."

[nhuwar]

Ya I've tried the stuff from crack master it's not bad. I called Sauereisen and ask about reseller and they wouldn't say, they wanted me to deal directly with them.


Nick

[Bas Horneman]

Use nailpolish

[nhuwar]

Nail polish No way it will get brittle way to fast from the heat



Nick

[Bas Horneman]

Nail polish No way it will get brittle way to fast from the heat

Maybe on the top of an 805 tube it will.

But not on the base of a rectifier tube or 300B....works like a charm. Got the tip from: Tube Lore by Ludwell Sibley"


"Loose Bases.

To re-cement the tube, use clear nail polish - paint a ring around the base, let the polish soak into the old cement, recoat, and let dry overnight. Polystyrene "coil dope" works as well, and can be used to refill the nail-polish bottle.

Solvent (acetone, etc.) are ineffective in softening the old base cement - the cement was baked hard in manufacture, and "nothing" dissolves it.
"