Repairing EL34 valve

[PJL]

I am looking at an intermittent heater in an EL34 xf1 that is crystal clear and has perfect gettering implying it has never been used. I have sucked the solder out of pins 2 & 7 and the wires seem to be well short of the top so likely never soldered.

How do I fix it? I could try grinding a small hole in the side of the pin to gain access to the wire?

[vidjoman]

I had a similar experience with a 6V6 some years ago. With the pin clear of solder, as it seems you now have, inject some liquid flux inside then heat the pin and apply new solder, not lead free, into the pin and it should work.

[Craig Sawyers]

A week or so ago I tested a bunch of valves for a friend on my AVOIII, among which were several EL34's. Most were fine, except one. That showed heater continuity, but simply would not glow.

A weird fault. Didn't have time to get to the bottom of it.

Craig

[GrimJosef]

Air in the valve can do that. A surprisingly small amount of air, i.e. not enough to whiten the getter, will conduct enough heat away from the heater to stop it getting hot enough to glow brightly.

[PJL]

I can get continuity by gently poking a wire down the pin 7 hole, the wires in both 2&7 seem to be 5mm short of the top of the pin so I have ordered some liquid flux. Seems like a manufacturing issue.

[GrimJosef]

I wonder if the wires inside any of the other pins are also too short to make a reliable contact ?

Cheers,

GJ

[cathoderay57]

I successfully repaired an intermittent heater on a KT66 using the technique you identified in Post #1. That is the most reliable fix, but be careful not to grind too much meat off the pin, otherwise you might weaken it sufficiently to snap off when inserting or removing the valve. I used a needle file to take off the minimum amount, and scraped the exposed wire inside to make sure it got tinned properly. Before doing that it's worth trying to insert a short length of tinned wire into the end of the pin. The trouble with this is that if the wire from the valve stem is oxidised the new wire won't solder to it easily and the fault will probably recur. Jerry

[Silicon]

The wires coming out of the glass bulb may have been cut to the correct length but may have bent when the Octal valve base was attached.

They would then be effectively too short to reach the ends of the hollow valve base pins.

[G6Tanuki]

You could always use a Dremel or similar to cut round the circumference of the base to remove it. I have done this in the past, then carefully slit and broken away the remaining cylindrical part of the base attached to the valve, before fitting a base salvaged from a scrap valve.

[In that case it was to repair a Mazda Octal valve whose central locating spigot had been snapped off by a hamfisted previous keeper and the detached bit lost].

[GrimJosef]

I've also replaced octal bases successfully, but it does require care as the relatively fragile glass pump-out tube is inside the base and may be bonded to it by the base adhesive. My experience of removing the older type of base fitted to valves whose wires pass through a 'pinch' has been good. But removing the newer bases fitted to valves with flat glass bottoms, like the EL34, is very much more challenging (the bases are very well stuck on !) and I'd really only try that if there was no alternative open to me.

Cheers,

GJ