DIY Audio Home

Push-pull EL802 spud amplifier

I've been playing with a push-pull "spud" amp using EL802 tubes.  EL802's are high Gm pentodes.  For this experiment I have them connected as triodes.

Here's a schematic (click for full size):

I used some output transformers pulled from an old console, which I think are 8k:4.  The input transformers are a pair of Sescom MI-19's a found cheap on E-bay.  The breadboard looks like this...

It actually sounds very good, and measures well also.

Here are some numbers:

B+ = 300V

Vplate-cathode = 287V

Vcathode = 3.27V

Rcathode = 72 ohms

Icathode = 45mA

Ptube = 7W

Ig2 = 4.2mA

Pg2 = 1.2W

Pplate = 5.8W


1W THD < 0.18%, as low as 0.05%

6.78W @ 5% THD


The downside is that the EL802 has quite high input miller capacitance.  Driven with a 600 ohms source it's -3dB at 20kHz.  Driven with a 50 ohm source it goes out past 50kHz.