Connecting HV to tube

Rebuilding my machine post old tube demise, install analogue mA meter (digital only previously), change out cooling plumbing, mods here and there.

Could you advise on connecting hot end of the new tube ? Tube in question is EFR F4 (100W, 1400mm). Tube came with pigtails attached, no connectors or screw terminals like on RECI.
The materials i have is used ceramic block off of old tube, where wire was just twisted and inserted, no RTV or siliconing was done (block is clean, no sparking in there). I have some 7x14mm silicone rubber hose i used to re-plumb my machine, use it as an insulation for the splice ?
I cant get a hold of RTV quickly here, online only. Why not construction silicone ?

Should i just twist/solder, insert into the block and ziptie to the tube (as it was before, sans soldering)? Is soldering HV line a good idea ?

Hi there,

Can I ask where you bought the tube, the tube from EFR would come with full fitting instructions.

On the high Voltage end there should be a red rubber cover,
this just pulls off and under there should be a screw connection to attach the HV wire too, usually using a split connector.
I use their X series now, but had F4 before and this is the same connection.

I buy direct from EFR in china, they are very good. I have a contact if you need Support, but if you didn’t buy direct your first port of call should be the people you bought it from and ask them for the instructions.

I would not splice the HV cable together to lengthen it, just replace with a piece long enough, solder the HV cable together to lengthen it if you have to… Do not solder direct onto the tube the heat could crack the glass.

If you have pigtails already attached, I’d use those…

I buy these connectors from Amazon and have used them pretty exclusively.

Just ensure they hv wire is the correct size…

The last tube I used, was simply remove the hv connector from where it was connected previously.

I have mine going to a resistor stack that gives me a hv reading… So it was simple to just change out connectors an plug it in…

Upper one goes to the tubes anode. You could easily put one of these as a safe way to connect the two… I doubt a foot of length makes any difference at these voltages…

I usually solder connections, but I keep these mechanical, screwed to the end… no solder.

Keep in mind you are dealing with very high voltage and a pinhole somewhere will allow it to reach out and touch you or the machines case… it will take the path of least inductance to ground.

Thanks for making it public… :pray:

Good luck… any issues sing out…


New EFR tube is from 2019, sat in the corner boxed since then. No idea how F4s changed since then.

I need to connect as is, as no fresh connector. Just checked the connector that came from old tube - its siliconed in place and i cannot remove it to reuse. Old tube was CDWG 80w deal, same configuration - prewired pigtails on both ends.

Checked old connector i kept from blown power supply (blew one flyback and arced internally, ZYE MYJG100W) - that one is siliconed in place as well, cannot reuse. My only option at the moment is twist the wire up and shove it into ceramic insulator as it was done on previous tube (no silicone or soldering on that one).

Do motor parts stores usually keep RTV in stock (liquid silicone gaskets ?) ? Might pop in to get some. Any brands to mention ?

Some pics below…

As it was wired before:

New tube’s hot end, no cap:

New tube’s business end:

New tube’s label:

What i have to work with (note wire with connector is siliconed, i cannot just remove it to replace on tube’s pigtail…):

I’m off to local car parts dealers to see what they have silicone wise…

#Edit 1# Well, builder merchants came up empty, local car part place came up with this… Also expensive…

Just put another connector on the splice end that you have on the other end…

When you get voltages in the thousands, most silicone isn’t rated for these voltages even though it’s one of the best insulators.

You should really use a silicone based on voltages and if you can’t do that, use another screw on connector… you know that’s insulation…

Hopefully your lps is grounded to the frame so any arcing will be contained within the machine.

Having said what I had to say, I doubt the Chinese manufacturers paid extra for silicone sealant for these…

Keep the connections short so the exposed wire is inserted the furthest distance away from the open end… do you best to fill it, and if possible reposition it back to where it was… I put some on the end of the splice and if possible into the splice. When you insert it it seems to distribute it pretty well…

I just started using the hv connectors like on the end of yours…

Always be cautious about splices… they seem to be the most likely places that fail…

Good luck


Well, here goes.

My attempt at ball soldering. Not as easy as it seemed. had to hold the twist vertically, otherwise the ball would sag one way and just drip off (70/30 solder, 350c).

Then filled the piece of 7x14mm silicone rubber hose with above mentioned RTV and shoved the soldered joint in till in the middle of the tube(excess squeeze out at the end). Been curing since 2am last night. Haven’t fired it up yet.

Wiring and plumbing done, lets see what happens. New LPS and new tube.

Well, it lives. Tested and cutting better than when it was new. All that remains is to replace god awful k40 1st mirror mount, all the optics to new and properly align…