They really are a shit of a valve. I never have much luck with them 
Also the Amperex SQ 7119 is worth a look.
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I have just seen a pair of Nos/Nib Bendix 6900 tubes on eBay for $1100.
There are soooooooo many reasons my preamps changed from 5687 to 6111wa back in '95 and these are just 2 of them
(The others all involve other odds sounds that 5687s exhibit which you don’t want in a preamp)
Best of luck 
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Just the joy of soldering/desoldering when they do go pear shaped…
Weren’t these developed in the early days of guided munitions - specifically the hairy-arsed lunacy of steerable nuclear artillery shells?
Think Musical Fidelity use the 6112 in some kit.
Indeed a pain, however I have always used 8 pin transistor bases to avoid such problems.
The new amps use some lovely ptfe ones with gold pins from Germany
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Now that sounds cute AF 
It’s the difference between mass market and hand-knitted
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I think the AN dac zero uses 6111wa but soldered to the board, so when you get a noisy one, approx 1 in 5, it’s a total pain.
The 6111wa is like a mini ecc82 but with a cleaner sound. There are a few other interesting ones, 6112 is good, and I have some 5744 for an as yet unbuilt Phono amp
Nice overview here;
http://monster.partyhat.co/article/subminiature-tubes/
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A brave man uses nuvistors. Reminds me, I have a stag of 6CW4 somewhere.
Must also be a deaf man if the MF amplifiers I’ve heard are much to go by.
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My old AN DAC 1.1x sig had a 6111wa, came with a spare valve as well.
And a soldering iron?
No they had a base so just plugged in, the wires are very thin so was a bit of a pain to get lined up though.
Here’s the inside of @sjs pre after the courier managed to throw it and rip the transformer off its mount and dislodge one of the sub valves
U need to rut about looking for them
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That pic shows what is left after the base has been ripped off 
Doesn’t show the base 
Here are the ones in the new preamp
And here are a couple from an old amp as they should look 
No but it did come back nicely foo’d up. Was a right fucking mug for selling that and the 300b amp
e1259d6df32004d3ae37aaf7d03e6051591d6725_1_690x460 by The Biglebowski, on Flickr
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Back to the op, I ended up using mostly Sylvania and Philips 5687 in the preamps that went out the door as they were the most reliable in terms of low noise. I have a stack of RCA left as it was difficult to find sufficiently quiet for preamps, but they were fine as power amp driver valves.
Does that mean you have a stack of noisy RCA left? 