300B sockets (different question)

[Alex M]

I am just finishing putting together the chassis for a couple of push-pull 300B amplifiers, and have a couple of questions about the UX4 sockets I have. I don't know what the origin of these sockets is (I bought them through Hi-Fi Collective in the UK, if that's any help), but they are made of a shiny white ceramic material and have a copper rivet through the base to secure each of the four connections. I am mounting these to the underside of the top plate, and have made a 35mm diameter hole for the base of the valve.

I have two questions:

- Is there a standard diameter for the base of a 300B? I can't see this measurement on the datasheets I have found so far (I am intending to use JJ valves, by the way). Is 35mm likely to be a large enough cutout?

- Has anyone used sockets like these with the copper rivets showing on top? They will be 3-4mm below the level of the top plate if I mount the sockets flush, and inset from the edge of the cutout by about the same distance. Should I worry about arcing from the 400 volts on the anode?

Thanks,

Alex

[Andrewbee]

Your description fits the cheap Chinese sockets to a "T". My advice is get proper sockets.

If it looks like this it is the cheap one.

http://i18.ebayimg.com/01/i/000/a9/99/da29_2.JPG

Get the (good) sockets and then cut the holes for them.

[Alex M]

Originally Posted by Andrewbee

If it looks like this it is the cheap one.

http://i18.ebayimg.com/01/i/000/a9/99/da29_2.JPG

Yup, those are the ones. Perhaps I had better look around for some better sockets, then!

I have already cut the holes, unfortunately, which puts certain constraints on the replacements.

Alex

[Eli Duttman]

Alex,

Only the anode connection may be vulnerable to arcing. Reduce the vulnerability by covering that rivet with several thin coats of corona dope. Allow plenty of time for drying, between coats.

[Tom Bavis]

Look for EF Johnson parts. They're the same size. If these rivets are exposed, 400V is accessible to touch from the top - I'd want additional insulation...

[tomchr]

Couldn't one just use some ordinary enamel rather than the corona dope? 300B's "only" run at 400 V after all.

~Tom

[Eli Duttman]

Originally Posted by tomchr

Couldn't one just use some ordinary enamel rather than the corona dope? 300B's "only" run at 400 V after all.

~Tom

Built up layers of nail polish might very well do. Corona dope is 100% certain to work.

[astouffer]

Some 5 minute epoxy should do the trick.

[DynacoDave]

I am about to start a st70 scratch rebuild. I have nos Amphenol with the molded in plate that I intended to use. Other than the connectors wearing out, older Amphenol sockets I have in other amps/radios still look fine. I am haveing second thoughts about using them, because the ceramics would look better, but some of the ceramic sockets I have seen don't fit up well, so I am not so sure of these. Regards, Dave

[Alex M]

Originally Posted by Tom Bavis

Look for EF Johnson parts. They're the same size. If these rivets are exposed, 400V is accessible to touch from the top - I'd want additional insulation...

Are these the ones you recommend? If so, they look similar enough to the Chinese ones for it to be hardly worth changing...

Alex