When we come to calculate the gain, we find that the anode characteristic begins to curve as we reach its intersection with the load line. I suspect that it arises from a fundamental misunderstanding of the differences in driving requirements between an audio output stage and an RF transmitter. The low frequency response is set by the reflected impedance at the primary in parallel with the output tube plate impedance then that being in parallel with the primary inductance of the output transformer. If you look carefully at the Oddblocks you will see that the output stage is just like a single ended power stage when viewed from the driver side. It can produce 17 W output in Class AB1 in push—pull configuration.

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But in A1 it works fine. Somehow, the sounds of these breadboarded amps are excellent! Sat Jan 28, 5: I’m making myself a tube-decorated throne. EL84 pentode as driver.

This article needs additional citations for verification. While not necessarily a true “military version” of the tube in fact it is more comparable to the6P14P-EVs are known for their low noise and durability. Originally Posted by jim p. Does an SET amp generally run in class A2? The increased power might pentose helpful in this region. To successfully use it you’d want to triode-strap it.

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In other projects Wikimedia Commons. Sat Dec 29, 3: You have to use triodes for this sort of PI because the plate current has to match the cathode current.

If you look carefully at the Oddblocks you will see that the output stage is just like a single ended power stage when viewed from the driver side. The EL84 was developed to eliminate the need for a driver tube in radios, so it has rather more gain than is usual in a power pentode.

Hi All, I didn’t know whether to get into this discussion or not, but Tue Jan 31, 2: Retrieved 25 May We select R5 at 56KOhm. I got the idea from the Legacy amp of Thorsten as well as another project on the net that uses el84 triode strapped to drive a 2a3.

Also if you lower the reflected impedance you will increase the bass if you connect a 4 ohm speaker ppentode the 8 ohm output the reflected impedance will half so ohms instead of ohms so if bass response was down to Hz it would drop down to 50Hz. The ppentode mode is self inflected feedback because the control grid is not isolated from seeing the output plate as it would be in the pentode mode.

Evaluating Gm from the datasheet, by holding anode voltage constant, and measuring the change in anode current for grid voltage, produces value of I posted earlier what the changes were in the amplifier that I modified to have both pentode and triode mode.


Manufacturers were quick to adopt it in general use, and they are found in many old European valve radios and other audio equipment. Originally Posted by TS Bottom line the greater the primary inductance of the transformer the lower the frequency response so in simple terms a bigger output transformer will give you more bass response.

That’s also why we don’t generally use R-C coupling when you want to drive the grid positive; it charges the coupling capacitor and causes strange things to happen which generally are undesirable. Please help improve this article by adding citations to reliable sources.

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The drivers I use types in many of the amps are nearly a clone little lower ek84 than the 12AX7 which could have been used. It is perfectly valid to treat the anode curve as a straight line, and to project this line onto our load line pentoce order to find the gain.

It could also make a good LTP splitter because its increased power makes possible the driving of K ohm grid resistors in the power stage. I don’t have a clue what these terms mean?