Output transformer for EL84 PP

[Chris Hornbeck]

Your higher Gm valve will make the design easier. You may wish to remove the positive feedback between first and second stages, and it will be possible to remove the capacitor coupling between them. If you're really enamored of the common cathode current supply, you may want to increase the value of the bypass capacitor - maybe 1000 or 2000 uF. Capacitors have gotten very affordable since this was designed.


This biasing scheme is also critically dependent on matched valves. Including individual small (10 Ohm or so) cathode resistors will allow you to monitor valve idling currents. Channel pairs need to be within 5 or 10% for best output transformer performance.


All good fortune,
Chris

 

[El Sid]

Your higher Gm valve will make the design easier. You may wish to remove the positive feedback between first and second stages, and it will be possible to remove the capacitor coupling between them. If you're really enamored of the common cathode current supply, you may want to increase the value of the bypass capacitor - maybe 1000 or 2000 uF. Capacitors have gotten very affordable since this was designed.


This biasing scheme is also critically dependent on matched valves. Including individual small (10 Ohm or so) cathode resistors will allow you to monitor valve idling currents. Channel pairs need to be within 5 or 10% for best output transformer performance.


All good fortune,
Chris

Thanks Chris - I chose the E88CC partly for that reason (and its good linearity). As the amp stands now, it has a pretty conventional DC-coupled pre/splitter stage, but I am intrigued by this design. The amp is as much a test bed for different ideas as anything else, so I may give that a go.

The thread for my amp is here: EL84 PP design

 

[huggygood]

someone have an idea about this manufacting ?
Mullard 5-10 Mono magnetic kit – Primary Windings

 

[mooreamps]

Have a look at the frequency response. Maybe ok for guitar. jeff

Only for guitar amp. Last P/P amp I built , I used the Hammond .
Tube Output (10 - 280 Watts) Easy Wire Secondary (1608A-1650A Series) - Hammond Mfg.

 

[kodabmx]

It says it's rated at 10W/20Hz - Hardly a guitar OPT, and not even a bass OPT. They are British made and seem to be of good quality... I would try them if I lived in the UK and needed the iron for a peewee amp.