• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Top cap tube users: pics of your amps?

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sorry, no pix - but for some EL38s I used British made 6mm black plastic plates with phospor contacts. For running the lead, I was lucky enough that the Dynacos already have nearby slots in the metal work. Suggest some heatshrink tubing / rubber / grommet / strain relief to stop the wire from rubbing and potentially shorting out.

will take some pics soon

For future use I would like to build some top-plate cap adapters with the top-cap running to an octal adapter.
This amp is mine. I didn't build it, but I brought to the operating state :)
No grommet or anything, just a drilled hole; however, the wire has a tough braided cloth like material outside. The top plate is very thick, not much of a chance to cut through the wire.


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Here is the top half of my amp, showing the rubber grommet for the plate leads. I use a silicone insulated wire that is very limp and flexible, stocked in various colors by people who cater to model car enthusiasts. It's durable and stands up well to high temperatures. It also is a nice, snug fit into the tube cap


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Silicon wire, eh? I'm on it!

pchw, where did you get those plate caps? I'm always on the lookout for caps that actually fit. I hate the way many of the ceramic ones "fit" ie, do make a secure electrical connection, but look like they're floating above the tube.

Think I'll start a new thread on this...
Let me know when you find some... Mine are the usual Chinese BS, and they are a bit loosey-goosey on the 1625 tubes shown in the picture. I have some old Millen plate caps floating around somewhere. If I can take the time to find them, I'll see if they fit any tighter. The old style tube caps are pretty scarce and expensive. I can't even find the old bakelite caps any more. If I had a time machine, I'd go back and buy a couple of bushel baskets full, maybe buy some selected stocks while I was at it....
I don't think I'll post a picture of my 813 amplifier in one of its development phases; like most of my stuff it looked a bit of a lash-up.

I used rubber grommets, and as the output valves were running at around 1kV, I used PTFE insulated cable with an additional sleeve. For the umbilicals connecting the HT from the separate power supply, I used PET connectors and TV EHT cable which is cheap and rated at 25kV.



I like using silicone test lead wire - it's flexible but its outer diameter is big enough to be managable and look good. I used larger diameter stuff on the 813 amp. For the grid leads on the 829B amp, I used some teflon coax, since it tended to pick up hum (it's the amp input). You gotta watch the capacitance, though - it's high, so only a few inches can be used.

For passing the lead through the chassis, I like these:

An externally hosted image should be here but it was not working when we last tested it.


Nice thing about them is that they secure the wire so that even if you tug on it from outside, no worries about the solder joints inside.

I've also used various other rubber grommet things, usually with a tie wrap positioned underneath to keep the wire from getting pulled out.

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