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What are OA2 tubes and why are there more gear

using them?

I have a First Sound Presence Deluxe preamplifier which I bought used. This preamp as well as the JOULE ELECTRA use the OA2 tubes. What sort of tubes are these? When where they made and why are they not more prevalent in other preamp except in a handful of them such as the JOULE and the LAMMs, as well as the First Sound gear? What particular sound do these produce that make them appealing or unappealing for designers to incorporate them in their designs? Is there a designation that is different than the 0A2 that I am not aware off?
bemopti123

Showing 2 responses by ed_sawyer

ed_sawyer
588 posts
 
OA2 (actually all the O** series I believe, like OD3, etc.) are cold-cathode voltage regulator tubes. Generally filled with mixes of neon/argon/xenon. They glow pretty colors, which I think is why they are used. Generally they conduct at a certain voltage level and can be run in series for higher voltage regulation. (e.g. OA2 @ 105v x 3 in series = 315v regulated.). They are not really in the audio signal path at all, so tube rolling them probably won't affect sound at all.

Enjoy the glow,

-Ed
ed_sawyer
588 posts
 
The cool glow on O** series tubes is from the gas fill - argon, neon, xenon, etc. Not from any radioactive elements. Though some larger (high voltage transmitting type) tubes do give off Xrays in minor amounts.

-Ed
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