12AX7 testing

[Chuck H]

I like the sound of the JJ's long plates too, but not as much as the Sovtek LPS...

What I'm about to say amounts to nothing more than my opinion, but take from it what you wish.

Lately I'm using Sovtek LPS tubes for everything except for V1 in high gainers. My usual 12AX7 tube is the RCA gray plate. The RCA sounds as good as the Sovtek but is usually non microphonic. Where the Sovtek is almost always a little too microphonic for V1. So I use the Sovtek WA short plate tube for V1. Not as dynamic as I'd prefere. The WA sounds good but lacks some top end clarity, but when I'm cranking an amp it all evens out and the WA is dead quiet. So my tube line up for the amps I use and sell is usually a Sovtek WA followed by all Sovtek LPS. Unless NOS tubes are requested and then I like the RCA's and Mullards.

The only way to know if you like a tube is to try it. I've tried a lot of tubes and IMHE there is no point at all in buying preselected/rebranded tubes from Ruby, Groove or Mesa. I've always done just as well or better buying the original MFG labled product.

JM2C

Chuck

[Kage]

So what would be the difference between the LP and LPS? I know one has a "spiral filiment" but I have no idea what that means/does.

Further discovery indicates that the EH's I'm liking so much are a shorter plate version of the LP/S, not just the same tube with a different label.

[tubby]

spiral filament just means that the heater wires in the tube are twisted pretty much in the same way as it is done with heater wiring inside the amp chassis in order to minimize stray-pick up from the heaters (if operated with AC). this supposed to be quieter, could be also just a marketing thing....

Someone ever A/B tested spiral and normal filaments?

[guitician]

A spiral filament will have less Cathode-to-Filament capacitance than a straight wire type. Depending on the application, you will notice a difference. The spiral is like a spring, not like two wires twisted together, as are normally run to heater connections.

[rockon1]

I have 3 JJs on hand, 81, 82, and 83s, all with different run times on them, and they're flash is all the same, and they all vibrate when I tap them with my finger while holding them. Looking at the getter, it only supported by one piece of very thin metal, so that's probably what's vibrating. I have some other tubes, an old RCA and a Chinese 12AX7, that are both constructed the same way and both vibrate like the JJs. Conversely, I have an old Mullard 84 and GE AU7 that have their getters suspended differently and don't vibrate.

Ah but how the "getter" is supported is relatively meaningless. Its done its job already. Its only function was to hold the material to make the actual "getter" which is generally called the flashing-the silver coating inside that absorbs unwanted gases. Bob