Triode mode: 5K:8 transformer, 330 ohm cathode res., 300V/41mA operating point.
0.8W, 1.7% THD.
Finito .
Try pentode mode, with 10K:8 OPT.
4.7W/10% THD.
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Euro21, in addition of triode mode and pentode mode. Will there be any advantage in both power/distortion by running this directly heated pentode in Ultralinear mode over pure pentode mode?
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Just curious, why do you want to use a pentode for this? No real performance advantage over triode and higher parts count.
Whichever direction you go, the figure of merit is the transconductance. Output impedance is roughly the reciprocal of transconductance, so high gm = low source Z. That's why some of us have bitten the bullet and gone to MOSFET source followers to drive output stages.
Whichever direction you go, the figure of merit is the transconductance. Output impedance is roughly the reciprocal of transconductance, so high gm = low source Z. That's why some of us have bitten the bullet and gone to MOSFET source followers to drive output stages.
It's a "wide band amplifier". It needs lots of current. Low-Mu means high current.
Power pentodes tend to even lower Mus. A few High-Gain pentodes run Mu of 40 or 60.
I'm seeing higher numbers for Mu of 6AK5. As Alllensoncanon says it varies with operating point.
How did you pick "-2V" so quickly??
You like the sound of it?
Let's think. A 2A3 may need as much as 60V grid drive. A driver with Mu of 20-30 will give gain of 15-20. 60V/20 means you may need 4 Volts of signal to the driver grid. That's a lot for many Hi-Fi sources. And does not seem to fit a "-2V bias" condition.
You have two prime paths:
1) List your Resources, and your Requirements, and *design* something to get from one to the other.
2) The '45 and 2A3 have been around for over eighty years. Didn't ANYone ever use them? And write-down that they did? I think so. There must be heaps of happy '45/2A3 plans out there. I thinks soundhappy(?) has a thread where every other image is a magazine article about DHT power amps. Elsewhere on the Web I keep running into SE '45 plans, and probably 2A3 also. Stealing a known-good plan is the low-pain low-risk way to build an amplifier.
2A3 normally -45 grid bias
Mu 30 -35 CCS on 6AK5 triode strapped x2 gain 60-70 v
WE408 6AK5 EF95 Data Sheet
EF95 Datasheet PDF ( Pinout ) - VHF Pentode
Mu 30 -35 CCS on 6AK5 triode strapped x2 gain 60-70 v
WE408 6AK5 EF95 Data Sheet
EF95 Datasheet PDF ( Pinout ) - VHF Pentode
dissimilar cascode history with 6AK5 as triode + 6J4
A while ago I got the idea I thought was just fishing for a crazy idea...making a cascode with two triode-wired pentodes.
I recently read that the first Wallman (published as Valley & Wallman) cascode, was actually made with 6AK5 as triode plus 6J4 (high gm). Of course it was for small signal RF so the warning earlier in this thread about small signal capability for UHF tubes restrains my excitement...but tells me it wasn't such a wacko idea.
I may be getting some used 6AG5-6J4-12AT7 sets from a neighbor, but when I have them I'll believe it.
A while ago I got the idea I thought was just fishing for a crazy idea...making a cascode with two triode-wired pentodes.
I recently read that the first Wallman (published as Valley & Wallman) cascode, was actually made with 6AK5 as triode plus 6J4 (high gm). Of course it was for small signal RF so the warning earlier in this thread about small signal capability for UHF tubes restrains my excitement...but tells me it wasn't such a wacko idea.
I may be getting some used 6AG5-6J4-12AT7 sets from a neighbor, but when I have them I'll believe it.
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