Can the 7AK7 computer tube work as audio output tube ?

[aldovan]

Friends

The forgeten 7AK7 pentode tube can work as audio output tube, with the correct bias ?

Thanks,

Aldovan

[davorin]

I made small Push-Pull guitar amplifier with pair 7AK7 in output: Ua=300V, Ug2=300V(Rg2=470 Ohms for each tube), Ug1=-25V (Set Ia0 to 2x25mA) and Raa=10 KOhms. Output power is >10W, and sound is close to amp with pair of 6V6 tubes.

[smoking-amp]

Putting something like +12 Volts on g3 will square up the curves to be conventional pentode curves. Haven't tried this on the 7AK7, but on 6LE8 and other dual control tubes. Adjust the g3 voltage for minimum g2 current, but don't go too high on the g3 voltage or it will get hot instead.

[aldovan]

Originally Posted by smoking-amp

Putting something like +12 Volts on g3 will square up the curves to be conventional pentode curves. Haven't tried this on the 7AK7, but on 6LE8 and other dual control tubes. Adjust the g3 voltage for minimum g2 current, but don't go too high on the g3 voltage or it will get hot instead.

And if I use in triode output SE mode ? The connections are the normally used in a pentode ?

Thanks,

ALdovan

[davorin]

Here is first version (with 1 pair of 7AK7), and last version (wit 2 pairs of 7AK7).
I was rewired (for test) all versions in triode mode (G2 to Anode) with better sound, but only 40% of power. Also trayed "realy" triode mode (G2 and G3 to Anode), but did not hear difference.

[davorin]

Last version is very good gutar amp with ~28W at clipping!

[aldovan]

Originally Posted by davorin

Last version is very good gutar amp with ~28W at clipping!

Very fine !!!
This tubes are Sylvania ?
You make test with various brands ?

Thanks,

Aldovan

[davorin]

Yes, I was traying with SYLVANIA, RCA, PHILCO and WESTINGHOUSE brands, but all are very closed. PHILCO is mehanically like RCA, and WESTINGHOUSE is like SYLVANIA, and I think there is only 2 manufacturers (RCA and SYLV.). 7AK7 is special "VERY LONG LIFE" tube, with very strong construction and glass, and all good caracterics bether than curent production of tubes. In future, I am planing to made single-end triode conected amplifires for home audio with 3-4 paralel conected tubes (8-10W per chanel).

[aldovan]

Originally Posted by davorin

Yes, I was traying with SYLVANIA, RCA, PHILCO and WESTINGHOUSE brands, but all are very closed. PHILCO is mehanically like RCA, and WESTINGHOUSE is like SYLVANIA, and I think there is only 2 manufacturers (RCA and SYLV.). 7AK7 is special "VERY LONG LIFE" tube, with very strong construction and glass, and all good caracterics bether than curent production of tubes. In future, I am planing to made single-end triode conected amplifires for home audio with 3-4 paralel conected tubes (8-10W per chanel).

I see the Raytheon and Tungsol, too.
The Sylvania "Gold Brand" is a fine option...
I will to buy a SE triode amplifier, because the power do not is problem for me, I use in HIFI with high SPL speakers...
Know this article ? http://www.audioxpress.com/magsdirx/...millet2903.pdf
Pete Millett use a small positive bias in the G3...

Aldovan

[smoking-amp]

The positive voltage on g3 is for pentode (or UL) mode to square up the curve set. (g3 winding pitch is too dense in these dual control tubes and so repels a significant portion of the electron stream back to g2 if g3 is at the conventional 0 V. Causing excessive g2 current. Putting some positive voltage on g3 allows most of the electron stream to continue on to the plate for normal pentode operation.) It won't make much difference for triode mode except to shift the g1 bias slightly.