Morgan Jones and cascodes

[Ryssen]

I was reading Morgan Jones book "Valve amplifiers" 1st edition,when i saw this:
"As mentioned before the only really satisfactory valve for use as the lower valve is the Ecc88;any other type will waste HT"

Is this true?

[poobah]

Of ourse it's true...

[Ryssen]

Hi hi..

[Eli Duttman]

Originally posted by Ryssen
I was reading Morgan Jones book "Valve amplifiers" 1st edition,when i saw this:
"As mentioned before the only really satisfactory valve for use as the lower valve is the Ecc88;any other type will waste HT"

Is this true?

Not really. A triode with high gm is required at the bottom of a cascode. The ECC88 is an excellent, but not the only, choice. Rozenblit uses 2x 6s45p to form the cascode 1st gain block in his phono stage. My McIntosh MR71 FM tuner uses a 6DS4 nuvistor at the bottom and a 12AT7 at the top of its cascode TRF front end.

Jones is accurate in pointing out the ECC88's convenience, as 90 V. per section is quite satisfactory.

[JoshK]

Great timing, I read the same thing this morning.

[Geek]

Many others could work well.... 6AQ4 comes to mind

[Brian Beck]

6AQ4 comes to mind

Shhh! Let's keep that little tube a secret.

[SY]

(Perks up)

Oh, yes?

[Geek]

Originally posted by Brian Beck


Shhh! Let's keep that little tube a secret.

D'OH! I did it again!

[Johan Potgieter]

Surely the type of tube will depend on the output amplitude required? E.g. as input stage in a power amplifier usually an output signal of a few volt only is required, so wasted voltage is of little consequence. I am not suggesting all tubes will do; I do not see the ECC83 in that role. But there are also disadvantages in using too high Gm triodes at low currents required for voltage amplifiers; they could operate on a steep slope in their transfer characteristics rendering work points critical. There are other factors beside a low operating Va for the input unit.

Regards.