Decent preamp

No, I just did a curiosity search on eBay. I've never seen or heard one.

Eico was back in the day of buying Kits to assemble yourself, or buying factory complete assembled units. 

a budget brand, (with features and specs equal to the high priced stuff). It's a lot of preamp for that price, other brands, equal features, will ask far more.

https://www.hifiengine.com/manual_library/eico/st-84.shtml

https://www.audioasylum.com/forums/amp/messages/5646.html

http://www.tronola.com/html/st84_mods.html

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OTHERS....... Eico?????

Quicksilver or c-j.....    can be found for around or slightly more, huge value used of you can buy them right. 

Vincent Audio PHO 701. Excellent $599 unit. Very satisfied with the one I have in my main system. 

If all you need is a selector and volume, check this out:  https://www.aliexpress.com/item/32968579204.html?spm=2114.12010612.8148356.36.422e1340ix3rkL
I bought one from Ray Mottram of tubes4hifi.com under his SP10 model number, but it's the same item.  DO NOT get the remote control version!  The simpler hands-on one is the way to go.  I use with hot rodded Dyna ST70 and it is clean, quiet and liquid sounding with the stock Chinese tubes.

Mark Levinson 326s preamp is worth to look at. Phono option boards is still obtainable.