Low voltage Valves/Tubes

[blubman]

I'm looking for some low voltage thermionic valves, I'm 99% sure they exist, as after a long google trawl, i did once find some! I think they were called "missile tubes" due to their axial form, but I may be making that up! It does unfortunately seem like the trail has gone cold... Does anyone have any idea where I might be able to source some.

The reason being that I want to make some sort of guitar preamp/overdrive box for a school A2 level, but of course high voltage would never be let anywhere near a school. Whimps!

I do have extensive experience with valves, so anything that I can get to amplify a AC signal, and that goes non-linear easily would be great. I have tried using your standard ECC83 in a starved plate setting, it sounded horrible!

Thanks in advance!

Ben

[frequencycentral]

http://www.diystompboxes.com/smfforum/index.php?topic=70524.0

http://www.diystompboxes.com/smfforum/index.php?topic=70533.0l

http://www.diystompboxes.com/smfforum/index.php?topic=63479.0

[blubman]

Thanks, it helps a lot!

[brett]

Hi

I have tried using your standard ECC83 in a starved plate setting, it sounded horrible!

As I see it, the two main issues with 12AX7, 12AT7, 12AU7s at low voltage are their low transconductance* and low gain.
Of these, the 12AU7 has by far the highest transconductance.  So much so that it is even used as a power valve in the excellent "Firefly" amp.

Unfortunately, gain is low.  But that can be ok if you feed the tube with a decent boosted signal, coz there's not much headroom either when using a 12V supply.

The 12U7 behaves in quite a similar way to the 12AU7 in many 12V situations.  It was specifically designed for use at 12V.  Unfortunately, it is somewhat harder to find.
cheers
Brett
* one potential solution is to feed the valve output into the very high into the very high input impedance of a JFET buffer.  I tried this a couple of times with moderate success, but eventually went to simply using 12U7s and 12AU7s.

[blubman]

Thanks again! very helpful

[blubman]

OK, the next question is how do i find these! Iv found an out of stock source of 12u7's so far, at thetubestore.com, but I live in the UK, and although id be quite happy to source them from america, it would help greatly if they were in the UK.

[sweetwilly]

ebay is always good.  there's some really good sellers in Germany so you don't have to pay the import and customs fees you'd pay getting them from the US or Canada.