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Why do we use the some old "boring" types of tubes?

Posted by Rob Mercure (A) on August 23, 2006 at 04:27:10

In Reply to: With TV damper diode tubes cheap and plentiful, why bother with . . . posted by Ray Moth on August 23, 2006 at 03:49:00:

Ray,

Why are folks stuck on 12A_7s and 6SN7s, 2A3 and EL34s (etc, etc,) when there are scads of NOS "horrible" and vertical output tubes and signal level tubes available for pennies? The same answer - inertia and consumer distrust of the unfamiliar! I purposely design around my multiple "life time supply" of old radio and TV tubes and have rarely been disappointed or frustrated (arranging for the "low" voltage screen supply for some of the HOs in an existing amp can be a challenge) - there are scads of good bottles going unused. Almost every type tube 'cept DHTs is out there including some nice power triodes used for vertical outputs.
I agree about the dampers and there are some dual diode dampers with separate cathodes that are unused from the 1950s. But there are some "conventional" rectifiers that remain unused. The 3DG4 is much more rugged than the 5U4GB and selling at AES for only $1 each right now. Add a single resistor (0.45 ohm/10W) and you can wire a 5V rectifier socket to utilize this tube - they only draw 0.8 A more than a 5U4 and most power trannies have that much reserve! Or the 5BC3 which requires a "noval" socket.
Dampers are easy to add to a design with SS rectification by installing one "downstream" of the silicon if you want "sag" and the heaters are easily run from the line voltage if you use a 25V heater "cognate" (315 ohms in series with a 25W4 heater - but high wattage - better to series 4 and make a bridge).
Et cetera, et cetera - go for it brother! Use what's available and of higher quality and cheaper price than current production and get away from the minutia of comparing the construction of one common "boring" valve to another that's almost identical("90%" of the sound of a device is circuit topology [but, then again, "95%" of all statistics are made up on the spot ]). And don't neglect the "odd" voltage heaters - there are lots of RCA black plate 20EZ7s unused (a 12AX7 with a 20V heater).

Remember, other than DC/switching, audio is the least demanding application for tubes!

Rob

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