Recommend me a tube...

[Gordy]

A friend likes my 6H30 / transformer output headphone amp and has asked me to build something similar for him. However he wants the tube on display, and wants ‘a big looking tube’. He means something that looks like a 2A3 for example.

So is there a triode (or triode strapped pentode) that has the following:

Mu about 12 – 18
Internal impedance Rp of less than 2000 Ohms
Indirectly heated cathode
Physically bigger than a 6H30 (i.e. bigger than a typical 9 pin tube)
Any type of base / socket is OK

What would you recommend?

[azazello]

Hi !
6S41S /6C41C Russian/!! Ri = apr. 300 ohm/!!/, mu = 16-19!!
http://scottbecker.net/tube/sheets/018/6/6S41S.pdf
Very good vision!

[SY]

Wimps, all of you. Use a 6528.

[45]

C3m.
It's quite bigger than the 6N30.
Typically a triode connected C3m has (at 150V/ 20ma): mu = 19, Rp = 2.4 Kohm, Gm = 8 mA/V.
It's a low noise device with mesh plate!
Also is a SQ tube. It is guaranteed 10000 h if run within specs, just as the 6N30P-DR
Cheers,
45

[speleo]

How about 6AS7? Looks similar to 2A3 and no OPT needed, see this project for example:
HeadWize - Project: A Single-Ended OTL Amplifier for Dynamic Headphones by Aren van Waarde

I haven't heard that headphone amp but I did build the 6SN7/6BL7 by Eric Barbour some years ago (also on Headwize) and I really liked it. A good preamp with enough power for my 150ohm Sennheiser headphones.

speleo

[Tom Bavis]

The only "affordable" G-style tube that comes to mind is the Russian 6F6G. This is a little higher Rp and a little lower mu (triode connected) than you're looking for... and then there are the Chinese 6L6s that look like mini 6550s. In GT style, 6AH4 and 6CK4 are possibilities, as is 6EM7 and the like if you need a gain stage. Of course, I'm thinking in terms of what's in MY basement...

[azazello]

Originally Posted by speleo

How about 6AS7? Looks similar to 2A3 and no OPT needed, see this project for example:
HeadWize - Project: A Single-Ended OTL Amplifier for Dynamic Headphones by Aren van Waarde

I haven't heard that headphone amp but I did build the 6SN7/6BL7 by Eric Barbour some years ago (also on Headwize) and I really liked it. A good preamp with enough power for my 150ohm Sennheiser headphones.

speleo

I have the same OTL 6AS7 /6H13C Russian/ and Sen. 580 - 300 ohm, I think this is the best tube cathode follower
for OTL! Ri is aprox. 300-400 ohm. I advise You this link!

[Gordy]

Well guys, you have provided me with a nice list of alternatives. Thank you for that, and I will investigate them all.


Can anyone think of any further recommendations that I should also consider?

[belkovod]

E55l -10W
It's quite bigger than the 6N30.
Typically a triode connected E55L has (at 125v/ 55ma): mu = 30, Rp = 650 ohm, - best tube for headphone amp.

[bequerel]

Originally Posted by 45

C3m.
It's quite bigger than the 6N30.
Typically a triode connected C3m has (at 150V/ 20ma): mu = 19, Rp = 2.4 Kohm, Gm = 8 mA/V.
It's a low noise device with mesh plate!
Also is a SQ tube. It is guaranteed 10000 h if run within specs, just as the 6N30P-DR
Cheers,
45

Second that!
Remove the cover carefully to display the mesh grid. (I was corrected when I called it "mesh plate" in another post.) You will need to put a small marking on the glass to keep track of the orientation when the cover is removed. These tubes are also used in AYONs statement preamps.
I bought most of my C3ms from Frag Jan zuerst --- Ask Jan First a few years back. Also bought the rare 6.3V version, C30, before the prices took off.