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Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
aonomus -
What you are looking for are medium-power transmitting triodes. Generally, when you find a "pile of tubes" at surplus stores, thrift shops, etc they are radio and television receiving tubes. You'll have better chances of finding transmitting tubes at "hamfests" and amatuer radio get-togethers, or eBay.
If you can find them in good condition, there are many different types of triodes that work well for small to medium sized VTTCs. Some of the more common military and commercial types are: 211 (VT-4C), 805, 806, 810, 811A, 812, 250 (TL or TH), 304 (TL or TH), T40, 572, T200, T300, 833 (A or C), along with many more less commonly seen types.
Also usable are "industrial" triodes used in RF induction heaters.
If you find any candidates, first turn the tube sideways and very gently tap it while looking for any tiny wire fragments (pieces of broken filament or grid).
Check that the mirror-like "getter" deposit on the inside of the tube is bright silver colored, without any fading around the edges or "rainbow" appearance.
Check for filament continuity. Be aware that some tubes (like 304 series) have multiple filament segments, and should show continuity between three of the base pins.
Good triodes are getting harder to find, as tube collectors like them for their "vintage" appearance, and the tube-audio guys are willing to pay astronomical prices for good functional tubes.
Registered Member #1497
Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801
Any specific number of pins I should be looking for?
Essentially the store (which I'm going to tomorrow, and I don't get to go to often) has these cardboard boxes of tubes on the floor filled with tons of old ones, $1 a piece... so hence the semi-vauge question.
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Suitible tubes for a VTTC?
